Annual Report Editors: B. Blümich, M. Küppers Cover: K. Kupferschläger RHEINISCH-WESTFÄLISCHE TECHNISCHE HOCHSCHULE AACHEN

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1 RHEINISCH-WESTFÄLISCHE TECHNISCHE HOCHSCHULE AACHEN INSTITUT FÜR TECHNISCHE UND MAKROMOLEKULARE CHEMIE LEHRSTUHL FÜR MAKROMOLEKULARE CHEMIE ZENTRUM FÜR MAGNETISCHE RESONANZ Annual Report 2009 Editors: B. Blümich, M. Küppers Cover: K. Kupferschläger

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3 Contents 1 Review of NMR of Materials and Processes Magnetic Resonance Center MARC Overview of Research Activities Theses, Disertations, and Visitors Chair of Macromolecular Chemistry Staff Directions Overview of the Scientific Work Materials Science Chemical Engineering Hardware and Methods Individual Reports 18 Andrea Amar Nadia Amor Lisandro Buljubasich Ernesto P. Danieli Qingxia Gong Agnes Haber Sabina Haber-Pohlmeier Maxime Van Landeghem Jörg Mauler Maria Alexandra Olaru Eva Paciok Markus Raue Oscar Elías Sucre Ning Sun Lavinia Uţiu Publications Papers Talks Posters

4 1 1 Review of NMR of Materials and Processes Nuclear Magnetic Resonance (NMR) is a physical phenomenon with an abundance of applications in Science, Engineering, Medicine, and Art. The magnetic nuclei, often the abundant 1 H nuclei of hydrogen atoms or the rare 13 C nuclei are interrogated with radio-frequency waves when aligned by a magnetic field. The most popular uses are Magnetic Resonance Imaging (MRI) in Medicine and NMR spectroscopy in Chemistry. There are many other uses of NMR, and their number grows with time, as the instrumentation and the measurement methods are being refined. This remarkable development is observed since the first NMR measurements of condensed matter in The members of the Chair of Macromolecular Chemistry (MC II) at the Institute of Technical and Macromolecular Chemistry (ITMC) of RWTH Aachen University actively contribute to this development by specializing on the development and use of NMR to analyze polymer and other materials as well as chemical processes. The Magnetic resonance Center MARC (Fig. 1.1 of ITMC is one of a few laboratories well equipped for a broad range of NMR investigations in this area. The NMR machines serve high-resolution NMR spectroscopy to analyze the structure and dynamics of molecules in solution and in the solid state, NMR imaging to study the structure of objects from soft matter and the function of heterogeneous chemical processes, and mobile low-field NMR for nondestructive testing and chemical analyses at the site of interest. The unique equipment and expertise is applied in a broad range of interdisciplinary research projects within ITMC, RWTH Aachen University, international cooperative projects, and industrial collaborations. 1.2 Magnetic Resonance Center is a resource of large-scale NMR instrumentation that provides a highly effective platform for interdisciplinary research utilizing NMR with applications in Chemistry, Materials Science, Chemical Engineering, Bomedicine, Geophysics, and Quality Control (Fig. 1.1). Founded in 1994, the instrumental capabilities have continuously been improved and extended. Today is equipped with up-to-date instrumentation for imaging, spectroscopy and relaxometry at field strengths covering 10 MHz, 20 MHz, 40 MHz, 200 MHz, 300 MHz, 400 MHz, 500 MHz, 600 MHz and 700 MHz. The combination of instruments and the expertise in MARC are unique in Germany and among a few of their kind worldwide. The center is internationally known for

5 2 1 Review of 2009 Figure 1.1 : Magnets in the three laboratories of the Magnetic Resonance Center MARC at ITMC. Left: The main laboratory for imaging, solid-state NMR spectroscopy, and routine liquid-state NMR spectroscopy. Middle: The 700 MHz NMR magnet for use with spectroscopy and imaging in the annex. Right: Compact 30 MHz magnet for medium-resolution 1 H NMR spectroscopy suitable for use in the fume hood of the chemistry laboratory which has been developed in the low-field annex of MARC also known as the "MOUSEoleum". its leading role in the development of low-field and mobile NMR instrumentation and applications. Solid-state NMR with applications to Materials Science is in the hands of Dr. Alina Adams. Imaging and flow NMR for Chemical Engineering are directed by Dr. Federico Casanova, who also leads the activities in mobile NMR. NMR with hyperpolarized gases as well as ultra-low field NMR are directed by Prof. Dr. Stephan Appelt who has a joint assignment at the Research Center in Jülich and RWTH Aachen University. Liquid-state NMR research and analysis are in the hands of Dr. Jürgen Klankermayer from Prof. Leitner s team with assistance by Mrs. Ines Bachmann-Remy. Dr. Markus Küppers manages the administrative affairs in Macromolecular Chemistry and maintains the proper functioning of the high-field NMR instruments at in addition to conducting research in flow imaging, while Prof. Blümich is the acting Chair of. 1.3 Overview of Research Activities 2009 The research activities of the Blümich group cover three fields (Tab ). These are 1) Material Science with the focus on polymer materials, 2) Chemical and Biomedical Engineering, and 3) Mobile NMR. The materials science activities mainly use solid-state NMR as a research tool both, at high and at low field for a variety of topics in polymer science such as the characterization of polymer morphology and polymer aging. Many high-field activities use magic-angle spinning, multi-quantum NMR and measurements of spin-diffusion to charactize the morphology of natural and synthetic polymer materials. Mobile NMR is used mainly for depth profiling of layered objects, but also for studies of polymer aging and objects of cultural heritage. A central characteristic of the work in chemical and biomedical engineering is the transport of matter. Examples are component flow in micromixers, flow of a complex fluid like blood

6 1.3 Overview of Research Activities Table 1.1: Research activities in the Blümich group at ITMC of RWTH Aachen University Activity Materials Science Chemical and Bio- Mobile NMR medical Engineering Staff Scientists Dr. Alina Adams Dr. Federico Casanova Dr. Federico Casanova Dr. Markus Küppers Prof. Stephan Appelt rubber catalysts, porous media magnets for relaxometry, polymers micro-reactors imaging, composites mixing spectroscopy Topics biological tissue reaction unilatteral NMR processing separation, extraction hyperpolarisation cultural heritage rheology ultra low fields Methods }{{} liquid state NMR, solid state NMR, Fourier NMR, Laplace NMR, spectroscopy, imaging, depth profiling, relaxometry, diffusometry, flow NMR in a rheometer, and moisture transport in soil. The Work on soil moisture is pursued as one of the tasks in a transregional collaborative research center TR32. A considerable part of the work in this area concerns methodical developments, for example, ultra-fast velocity vectorfield imaging and quantitative Laplace exchange NMR. For many years, mobile NMR was synomymous to stray-field NMR with small sensors like the NMR-MOUSE. This changed in 2009, when the first Halbach magnets built from permanent blocks could be shimmed to high homogeneity, so that proton NMR spectra can now be measured with small magnets and high-quality images be acquired with larger, desk-top magnets. Today portable magnets are availble for relaxometry, imaging and spectroscopy, both with the closed Halbach geometry and open as stray-field sensors. The use of such low-field NMR magnets suffers from a lack of sensitvity compared to high-field NMR, but advances in hyperpolarization technologies are expected to provide remedies for different types of molecules and applications. Moreover, NMR at ultra-low field turns out to provide a wealth of chemical information in addition to high sensitivity when combined with hyperpolarization. Important publications of the group were by Danieli et al on a "Mobile sensor for high resolution NMR spectroscopy and imaging" (J. Magn. Reson. 198 (2009) 80-87) which was one of the most frequently cited papers of the Journal of Magnetic Resonance, the feature article "NMR at low magnetic fields" by Blümich (Chem. Phys. Let. 477 (2009) ) which made the title page of Chemical Physics Letters, and the paper entitled "Der mobile Kernspin-Scanner", in the November issue of Spektrum der Wissenschaften. All this work benefits from the expert support, creativity, and dedication by Klaus Kupferschläger and Dipl.-Ing. Michael Adams in the mechanical and electronics workshops, by our accountant team Claudia Kohnen, Marion Sieprath, Nadine Baumann Margret Rosen who returned to the Institute after a long leave of absense, and of Gerlind Breuer and Ingrid Schmitz

7 4 1 Review of 2009 who handle the daily operations in the secretariat. Last but not least, it is the academic staff and the students whose dedicated work defines the profile of the group and the contents of this booklet. 1.4 Theses, Disertations, and Visitors Table 1.2: Bachelor / Diploma theses and dissertations completed in 2009 Name Thesis Maria Baias Science and History Explored by Nuclear Magnetic Resonance Dr. rer. nat Claudiu Melian-Flamand Advanced NMR Analysis of Polymers and Biomolecules Dr. rer. nat Eva Paciok Ultrafast NMR imaging to map velocity distributions in Dipl.-Chem. microstructures devices Jochen Vieß Zerstörungsfreie Identifikation verdorbener Lebensmittel B. Sc. mittels mobiler NMR The bachelor / diploma and doctoral theses completed in 2009 are listed in Tab The research results were published in 17refereed papers and presented at several conferences in lectures and as posters (see end of this booklet). Among the visitors received in the group were Prof. Roberto Simonutti from the University of Milano-Bicocca, Italy, Dr. Leif Schröder from the University of California at Berkeley, USA, Dr. Gonzalo Alvarez, Ciudad Universitaria, Cordoba, Argentina, and Dr. Marcus Greferath, University College Dublin, Ireland. Dr. Ernesto Danieli arrived in the group as a Humboldt postdoctoral fellow to work on portable NMR devices, and Dr. Juan Perlo received the Friedrich-Wilhelm Award of RWTH Aachen University for his outstanding thesis. Funding of the group derives largely from outstanding support by the Deutsche Forschungsgemeinschaft (DFG) in terms of personal projects by the staff members of the group and and TR32. Further funding is received from the European Community within the CHARISMA project, which concerns art diagnostics, and from industrial cooperations as well as from research foundations of industry like AIF. Aachen, April 2010 Bernhard Blümich

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9 6 2 Chair of Macromolecular Chemistry 2 Chair of Macromolecular Chemistry 2.1 Staff Function Name (0) ext Head of the institute Prof. Dr. Bernhard Blümich / 21 Staff scientists Dr. Alina Adams Dr. Federico Casanova Dr. Markus Küppers Postdoctoral Scientists Dr. Andrea Amar Dr. Ernesto Danieli Dr. Sabina Haber-Pohlmeier Dr. Juan Perlo Dr. Rudra Choudhury Ph. D. Students Dipl. - Phys. Nadia Amor M. Sc. Santosh Ayalur Karunakaran Dipl. - Phys. Lisandro Buljubasich Dipl. - Chem. Sven Englert Dipl. - Chem. Qinxia Gong M. Sc. Agenes Haber Dipl. - Math. Ute Kremer Dipl. - Chem. João Martins Dr. med. Dipl. - Phys. Jörg Mauler M. Sc. Alexandra Olaru Dipl. - Chem. Eva Paciok M. Sc. Oscar Elías Sucre M. Sc. Markus Raue Dipl. - Chem. Silke Reuter M. Sc. Ning Sun 26447

10 2.1 Staff 7 Function Name (0) ext M. Sc. Lavinia Uţiu M. Sc. Maxime van Landeghem External Ph.D. Students Dipl. - Phys. Daniel Kalthoff Dipl. - Chem. Petra Kudla M. Sc. Robert Ferencz Diploma Students B. Sc. Rance Kwamen Cand. - Chem. Simon Küster Administrators Gerlind Breuer Ingrid Schmitz Technical staff Dipl. - Ing. Michael Adams Ines Bachmann - Remy Klaus Kupferschläger Financial resources Claudia Kohnen Marion Sieprath Nadine Baumann 26464

11 8 2 Chair of Macromolecular Chemistry Figure 2.1 : Foto of the work group. Names listed from left to right. First row: F. Casanova, R. Kwamen, L. Wentau, Y. Zhang, Prof. Blümich, A. Olaru, A. Adams, M. Küppers, S. Haber-Pohlmeier Second row: K. Kupferschläger, E. Danieli, O. Sucre, M. Adams, J. Mauler, I. Schmitz, D. Oligschläger Thrid row: Q. Gong, L. Uţiu, E. Paciok, N. Amor,A. Haber 2.2 Directions Address Prof. Dr. Bernhard Blümich Institut für Technische und Makromolekulare Chemie (ITMC) Lehrstuhl für Makromolekulare Chemie Sammelbau Chemie, Raum 38 B 121 RWTH Aachen Worringer Weg 1 D Aachen Germany Phone: (0) e - mail: mc.rwth - aachen.de Fax: (0) WWW:

12 2.2 Directions 9 Airports Köln / Bonn, Germany Düsseldorf, Germany Frankfurt a. Main, Germany Brussels, Belgium 85 km to Aachen via A4, 2 h by train 90 km to Aachen via A44, 2 h by train 300 km to Aachen via A3/A4, 90 min by ICE train 143 km to Aachen via E314, 3 h by Thalys train Arrival by train Take a train to Aachen and leave at the stations "Aachen - West" or "Aachen - HBF". Exiting the "Aachen - West" train station, you will find a bus stop on your left. Take line 33 (dest. "Uniklinik" or "Vaals (NL)") or line 3A (dest. Uniklinik) and leave at the bus stop "Wendlingweg" right in front of the institute. At daytime, there is a bus every 8 minutes. Not all trains stop at "Aachen- West". If you have to get off at "Aachen-Hbf" (main station), you will find bus stops in front of the station. Go across the street and take line 3B to "Uniklinik". Leave the bus at "Uniklinik". Facing the Uniklinik, a factory-like hospital, turn to the right and walk about 200 m straight. Follow the sign Chemische Institute. At daytime, there is a bus every 15 minutes. Arrival by car Arriving from Cologne (Köln) by car, take freeway A4 or coming from Düsseldorf, take A44. At "Aachener Kreuz" take A4 towards Antwerpen/Heerlen. Leave the freeway at the exit "Aachen- Laurensberg" (last but one exit before the border to The Netherlands (see Fig. 2.2). Verry soon after the exit, bear right towards Aachen. Bear right after ca. 1 km and follow the sign "Uniklink" with a red cross. Stay on that highway in the right lane and bear to the right. Follow the signs to "Uniklinik" (about 2 km after the intersection and through a tunnel). After the tunnel bear right and follow the street to pass underneath a brige. You now drive along "Pauwelsstr." (see Fig. 2.2). After about 150 m, there are parking lots on the left. Enter the one with the sign "Chemie". The institute is in "Sammelbau Chemie" across across the street. It is easily recognized by the octogonal green glass towers, which accomodate stair cases. Figure 2.3 shows an aerial view of the building and the surrounding terrain.

13 10 2 Chair of Macromolecular Chemistry The City of Aachen Figure 2.2 : Maps

14 2.3 Overview of the Scientific Work 11 Figure 2.3 : Picture of "Sammelbau Chemie". 2.3 Overview of the Scientific Work Materials Science The use of NMR in materials science deals with a variety of topics. For application of any (polymeric) material, the molecular structure as well as the interactions of the components in a composite are of interest. This topics are investigated mainly by high-field solid-state NMR spectroscopy. Polymer morphology in terms of chain mobility, influences of processing conditions, as well as correlations of morphology with the macroscopic, i.e. mechanical and thermal, properties are investigated by high-field and low-field NMR techniques. Low-field NMR is especially practical for large samples and for investigations outside the laboratory at the production site. Altogether, solid-state NMR of materials has attracted attention in a variety of branches in science and industry, mainly in chemistry, physics, and biology, but also in chemical engineering, pharmaceutics, mineralogy, geology, and in the food industry. The big advantage of solid-state NMR compared to other analytical techniques is the high flexibility of the method. Therefore, for a certain material, the NMR methodology can be tailored to obtain the information in demand, such as the chemical structure, the molecular orientation and the mobility of different parts of molecules. Furthermore, as NMR probes the local environment of the nuclei, its application is not restricted to crystalline materials so that solid-state NMR is especially useful for analyzing amorphous materials. The spectroscopic characterization describes the local surrounding of each nucleus, and correlation spectra indicate close contacts and help to identify the structure. Of highest importance in solid-state NMR is the access to homo- (like spins, e. g. 1 H - 1 H) and heteronuclear (unlike spins, e. g. 1 H - 13 C) dipolar couplings between

15 12 2 Chair of Macromolecular Chemistry nuclei through space. On one hand these correlations reveal close contacts and distances between functional groups or individual atoms. On the other hand they are sensitive to motions of the whole molecule or of certain functional groups. With the latter, information about segmental chain mobility and molecular dynamics can be obtained. Furthermore, dipolar couplings are responsible for the process of spin-diffusion which provides information about domain sizes in block copolymers and semi-crystalline polymers and about polymer morphology. NMR-relaxation measurements are powerful techniques for investigating and understanding materials. A very attractive aspect of relaxation measurements is the fact that different dynamic time scales are interrogated by changing the magnetic measuring field. Thusly, correlations of measured values and material properties can be established. Furthermore, the comparison of results from experiments carried out at high fields and at low fields typical for desktop spectrometers is not straightforward. The widespread topics of materials science covered in our group are divided arbitrarily into polymers and polymer networks and cementious based materials. Polymers and Polymer Networks Today, the use of polymers advances from basic construction materials to smart functional materials that allow the development of high-end applications. Modern polymers offer numerous opportunities for breakthrough technologies and innovative products. One can hardly think of any high-technology equipment, from spacecraft to medical tools or implants, without noting the involvement of polymers. Our research efforts are directed toward understanding the link between observed macroscopic behavior and the microscopic, molecular properties of these materials by using solid state NMR techniques. These methods are well suited to obtain structural, dynamical, and morphological details. The effects of processing and of external impacts on the microscopic properties of the polymer can be characterized as well as the polymer chain interaction with internal and external interfaces. One topic of the current research interest is represented by polyolefins. They are an important class of polymer materials with a broad range of applications such as, for example, for pipe systems for water and gas transport. In a common effort togheter with two other leading polymer institutes, DKI and SKZ, we want to establish the use of the NMR-MOUSE for truly non-destructive investigation of the morphological changes induced by the aging in the polyethylene pipes and to develop a better way for lifetime prediction of such materials. N. Sun togheter with A. Adams performed different types of 1 H and 13 C experiments under static and MAS conditions as well as 1 H low field NMR relaxometry in order to investigate from one side how the extrusion process is affecting the morphology along the pipe wall and from the other side which are the morphological changes induced by short time aging. A good agreement was obtained between low and high field NMR. Polyester amides represent an important class of polymer materials which combine the degradability of the polyesters and the enhanced mechanical properties of amides. Despite of intense

16 2.3 Overview of the Scientific Work 13 work on developing different types of polyester amides less is known about their morphology which at the end will determine not only the mechanical properties but also their degradation behaviour. The work started by P. Lohakare togheter with A. Adams concerning the effect of the amide content on the morphology of these materials was published on the Macromolecular Chemistry and Physics. This research direction was further on continued by A. Adams who performed various 13 C NMR measurements for getting a better insight into the microstructure and chain dynamics of these materials. A poster based on some of these results was presented during the Alpine Conference on Solid State NMR. Cementious based materials Nowadays a lot of research is done for the improvement of the thermal insulation of buildings from one side and for the reduction of the thickness of the concrete elements which in turn allows the reduction of cement consumption as a direct result the reduction of CO 2 emission, from the other side. To achieve these goals, new high performance cementious based materials are produced. M. Van Landeghem used a combination of T 1 - T 2 correlation maps and T 2 - T 2 exchange maps to obtain more information about the pore size distribution and the way the pores are connected on a model system with two relaxation sites for water molecules. The measurements were done in a truly non-destructive way with the help of a NMR-MOUSE system. He was showing that the values of the relaxation times of the two water sites are affected by the exchange of the water between the pores. A quantification of the exchange rate was done by solving the differential equations describing the two site exchange process. Polymer cement dispersions (P/C), pastes of polymer dispersed in a cement concrete matrix, are one of the most promising materials in current day construction engineering as they offer improved durability and greater versatility. The time-dependence of the mechanical and chemical resistance of P/C, as well as the sensitivity to hydration, have been attributed to the effect that the addition of polymer has on the macrostructure. By using a combination of NMR solidstate and imaging methods, A. Olaru togheter with A. Adams were able for the first time to investigate the physical and chemical changes that occur in poly(vinyl alcohol) and poly(vinyl acetate)/cement dispersions upon hydration. The effect of the temperature was as well investigated. The obtained results were presented to various international conferences as posters and invited lecture. Chemical Engineering MRI techniques are widely applied to monitor a variety of chemical processes. To establish NMR in a technical environment requires methodical integration of suitable contrast parameters

17 14 2 Chair of Macromolecular Chemistry such as relaxation, diffusion, velocity, and chemical shift with the imaging technique. Moreover, accurate correlation of these parameters with material properties for achieving quantitative assessment of objects and processes with spatial resolution has to be achieved. To maximize the performance of NMR methods more and more elaborated pulse sequences specially optimized for each particular application are presented every year. The conditions at RWTH Aachen with its traditionally strong background in engineering provide excellent opportunities for finding suitable problems and applications for the versatile NMR toolbox. The dynamics of reacting and mixing processes involving mass transfer within a continuous phase or across an interface in multiphase systems is strongly regulated by diffusion and convective flow. Modeling and predicting such processes requires not only knowledge of inter-diffusion coefficients of the different chemical species, but also exact information about the velocity distribution in each phase. Our group has been active in this field since 1999, when we engaged on a large collaborative research center created with the aim of model and understand transport in multiphase systems. It is supported by a number of other cooperative projects and by strategies pushing the limits of the NMR method and hardware to facilitate, enable, and expand the role of MRI as an accepted and important tool for process monitoring and quality control. During the last year Dr. A. Amar worked on the implementation and optimization of a new pulse sequence that allowed us to acquire 2D velocity vector maps during a single excitation train. The new sequence called FLIESSEN (Flow Imaging Employing a Single Shot ENcoding) samples in a time of the order of a second the full information required to reconstruct 2D velocity vector maps of selectively excited chemical compounds involved in the mass transfer experiment. This sequence has been tested and compared against standard methods showing that high robustness and reproducibility can be achieved in extremely short measurement times. Particular interest focuses on the study of flow in microstructured devices. In this case specialized, high-sensitivity rf probes are needed to image liquids flowing through microchanels. In a recent work E. Paciok applied the FLIESSEN sequence to a phantom-setup that bears all the characteristics of a microdevice. She showed that FLIESSEN has a remarkable resilience to magnetic field inhomogeneities and that its implemented flow compensation allows flow mapping over a wide velocity-range. As a result, we continued our work on an actual micromixer. For this purpose, due to higher demands in terms of resolution and S/N, a segmented acquisition scheme for FLIESSEN was developed. In her work she systematically evaluated the trade-off between resolution and speed offered by different pulse sequences. The use of surface coils certainly led to the sensitivity improvement required for in-situ monitoring of reacting and mixing processes inside micromixers. Another focus in the flow and MRI studies have been the research on hollow fiber membranes by L. Utiu. With the MRI technique it was now possible to follow the complete process of the cake layer formation on the outside of an fiber membrane. In a second set of measurements the dependence of the flow speed was now observable far a large range of the inner part of the membrane.

18 2.3 Overview of the Scientific Work 15 Parameter weighted or chemically selective MRI techniques are of great assistance to study reacting systems. L. Buljubasich investigated heterogeneously catalyzed reactions taking place in the presence of finely dispersed catalysts (metals such as Ni, Pt, Pd, Cu, etc) localized in porous materials with large internal surface. The motivation in this study was to identify potential NMR parameters suitable to monitor the reaction speed and the conversion rate on-line. Similar lethods have been applied by Markus Raue to characterize new hydrogel types synthesized on the base of acrylic acid and maleic acid with its anhydride for a higher charge density and on the base of vinylphosphonic acid fora higher ionic strength which influence the mechanical properties and the swelling behaviour. The new types of hydrogels should be established as sensors, actuators and switchable porous media. The mobility of sodium ions and exchange reaction between different ions is investigated with NMR by 23 Na and 27 Al imaging, self-diffusion coefficient and their relaxation times T 1 and T 2 for a better understanding. Polarized Xenon is a remarkable tracer for the study of the diversity of materials. The NMR proportion of Xenon atoms diffusing into the material can describe the accessible cavities and channels and provide information on their size, shape, and chemical nature. To improve the poor fraction of polarized Xeonon in the thermal equilibrium one has to use the optical pumping method. One of the leading scientists in this field is Prof. S. Appelt. Together with him N. Amor performed a series of measurements focussing on the enrichment of Xenon in blood by the use of a xenonizer. Hardware and Methods Nuclear Magnetic Resonance is a powerful non-invasive technique widely used to assess material structure in medicine, biology, and material science. This methodology has been developed to work in the homogeneous fields generated by strong magnets. However, such large and static devices are inconvenient for in situ studies of large objects. In addition to conventional NMR, where the sample is adapted to fit into the NMR probe, there is mobile NMR, which uses magnet geometries made from permanent magnets specially adapted to the object under study. A powerful realization of mobile NMR is single-sided or inside-out NMR. The inside-out concept was born in the oil industry, where the entire spectrometer is lowered into the well to characterize the underground formation. The same principle, based on projecting both static (B 0 ) and rf fields (B 1 ) outside the sensor, was exploited more than one decade ago in our group when developing the NMR-MOUSE (MObile Universal Surface Explorer), a hand-held single-sided NMR sensor that quickly showed excellent versatility in addressing a large number of applications inaccessible to closed magnet geometries. The NMR-MOUSE was initially intended to scan the surface of large objects by laterally repositioning the device to measure signal amplitudes, relaxation times T 1 and T 2, and self-diffusion coefficients in a volume crudely defined by the highly inhomogeneous B 0 and B 1 fields. However, with the aim of extending the methodology for material characterization, our group has become one of the leaders worldwide that advances the portable NMR technology. Besides finding powerful solutions to measure ex situ

19 16 2 Chair of Macromolecular Chemistry 3D images, flow, diffusion, multiple-quantum coherences, and even highly resolved spectra, significant advances were achieved in learning to taylor magnets that generate specific magnetic field profiles. Different versions of the NMR-MOUSE are used nowadays in a number of research areas like, art conservation, geophysics, medicine, and industry. A large version that measures up to 25 mm inside the sample has been used by A. Haber to analyze and characterize the layer structures of wall paintings. Depth profile measurements were performed on wall paintings that were recently excavated in the Papyrus Villa in Herculaneum, where it proved in many cases to be suitable to determine the composition and moisture of the layer structure in these objects. J. Mauler used similar sensors to test new skin moisturizing solutions produced by the cosmetics industry. The goal here is to measure the speed of ingress, the penetration depth, and the residence time of cream in the different skin layers. Creams penetrate the skin but are usually stopped by the stratum corneoum. In order to localize the penetration depth with high resolution while maintaining low measurement time, a new pulse sequence was developed for the Profile NMR-MOUSE. By Fourier transforming the spin-echo a frequency band with 100 khz width is evaluated in one shot. Another application with high potential of the NMR-MOUSE is its use to characterize building materials. The sensor can be brought to the construction site to measure moisture content and water migration in a non-destructive way. M. Van Landeghem measured powerful T 1 - T 2 relaxation correlation maps and T 2 - T 2 exchange NMR maps, to evaluate the exchange of water between the pores. An important application field is the one related to the characterization of water dynamic in porous structure of natural soil. S. Haber-Pohlmeier studied with different NMR tools the ability of soil to retain and transport water which is mainly controlled by pore-size distribution. NMR has shown to be a powerful method to determine pore size distributions by measuring the relaxation time of the water molecules filling the pores, for which different measurement methods can be used. The aim of her study was to investigate the multi modal nature of the relaxation distribution functions observed in relaxation experiments of macroscopic samples at low field and to find an answer to the question whether or not they are caused by macroscopic structures like fractures or by the inherent microscopic heterogeneity. While these experiments have been done in the lab, O. Sucre has developed a slim-logging tool that can be lowered in previously bored holes to measure the same properties in situ. It is fitted with a radiofrequency coil to sense a NMR signal from a slice 9 mm away from the sensor external surface. The sensor has been used in imbibition and drainage experiments by shifting it through a plastic pipe embedded in a soil column. The approach taken to shim the magnetic field of open magnets has been successfully applied to achieve high homogeneity in closed magnets like those based on the Halbach geometry. Dr. E. Danieli has shown that including a suitable arrangement of small and mobile magnet blocks, the inhomogeneities caused by imperfection in the magnetic material as well as by inac-

20 2.3 Overview of the Scientific Work 17 curately positioning individual pieces during construction can be corrected. The possibility to achieve homogeneous fields is obviously desired to incorporate spectroscopy as a routine analytical method also in mobile applications, but it is also of great importance to reduce the size of portable magnets required to implement imaging techniques. Danieli designed a new and more efficient main magnet array, which besides generating a stronger magnetic field in a larger volume compared with previously reported ones, allows a more compact arrangement of the pieces by including the movable pieces required to generate the different spherical harmonic terms needed to correct for the field imperfection in the main magnet. This strategy allowed us to obtain not only the desired homogeneity but also a higher magnetic field strength, since all the magnets contribute to the magnetic field in the same direction. Due to the higher performance of this new approach high homogeneity could be achieved in a 40 mm diameter cylindrical volume. The magnet is equipped with a solenoidal radio-frequency coil to excite the homogeneous volume and with a three-axes actively shielded gradient coil system which allows fast switching times without introducing Eddy currents, to furnish the sensor with imaging capabilities. The system was tested to image rubber gasket. From the images the material properties can be obtained and the geometric structure can be determined with micrometer precision, both in a non-invasive way in accordance with most quality standards.

21 18 3 Individual Reports 3 Individual Reports Testing the ultra-fast sequence FLIESSEN performance on closed systems Dr. Andrea Amar PostDoc supported by DFG During the last period, our entire work was focused on the development, performance and application of the ultra fast sequence FLIESSEN (FLow Imaging Employing a Single-Shot ENcoding) to measure velocity maps in closed systems. Fast velocity distributions could be measured in seconds, benefiting from the long T 2 of the sample. Although some applications were shown before, a detailed study of the performance in known systems as well as comparison with the so-called standard techniques is still required. In order to measure velocity maps, usually a velocity encoding module is combined with an imaging sequence. The most common and robust sequence is the Spin Echo (SE) preceded by a bipolar pair of gradient pulses to encode velocity. Even though high velocities can be measure with this technique, it is very time consuming, and for dynamic systems it is not suitable. The most common solution to spare time in the imaging module, is to employ multi-echo sequences like RARE, to speed up the acquisition of the k-space. This approach is definitely faster than the SE, but have some limitations for its application: (a) The first and most obvious requirement is that the velocity must not change during the acquisition, that means that the velocity should remain constant during the whole imaging module, limiting either the maximum velocities that can be measured or the spatial resolution; (b) the phase shift imposed at the beginning by the gradient pulses must be preserved during the whole echo train. That means that a proper phase cycling of 4 scans has to be done, leading to a longer experimental time. The sequence FLIESSEN has the advantage of refreshing the phase shift for every echo, so only requires that the velocity does not change during the echo-time. Since there is no phase to be preserved from echo to echo (it is given before the acquisition but removed before the next refocusing π-pulse), no special phase cycling is required, therefore (if the S/N is good enough) only one scan can be used.

22 19 Table 3.3: Experimental time for the acquisition of two 2D velocity maps. The times are calculated using TR=5 sec. Since the SE and the RARE require three independent velocity encodings, the total number of experiments is three times the number of scans. Spin Echo RARE FLIESSEN ns=1 ns=4 ns=1 3 experiments 12 experiments 1 experiment 8 min 72 sec 1.7 sec In Table 3.3 comparison between the experimental times of the three techniques are shown. For the SE and RARE sequences, three independent encodings are required to generate a vector map (velocity in two directions plus the reference map), but with FLIESSEN only one is needed, since the encoding velocity direction can be switched from echo to echo. As an example, Figure 3.4 shows the velocity maps obtained with all three sequences for a couette cell. These maps correspond to a maximum velocity of 70 mm/s and a spatial resolution of200 µm 200 µm. Can be observed that the one corresponded to the RARE sequence is already distorted. In the FLIESSEN case, maps up to 150 mm/s were acquired without distortions. Spin Echo RARE FLIESSEN +v max v x y x -v max +v max v y -v max Figure 3.4 : Two dimensional velocity maps for a 5 mm (7 mm) inner (outer) diameter couette cell with a spatial resolution of 200 µm 200 µm and maximum velocities of 70 mm/s acquired with a Spin Echo (left), RARE (middle) and FLIESSEN (right) sequence. The experimental times correspond to the ones in Table 3.3.

23 20 3 Individual Reports HP 129 Xe NMR and MRI of a Xenonizer Setup Dipl. - Phys. Nadia Amor Ph. D. student supported by DFG In order to further develop the new technology of the so-called xenonizers 1 for effective and bubble-free dissolution of HP 129 Xe into various liquids including porcine blood, a homebuilt setup was constructed and investigated in cooperation with the Institute for Applied Medical Engineering of RWTH Aachen University. The complete system consisting of hyperpolarizer (built at Research Center Jülich), Xenonizer, and spectrometer is depicted in Figure 3.5. Figure 3.5 : Complete Xenonizer Setup with the fiber module inside the rf resonator. As model substances, water as well as isotonic saline solution with the same ph as blood were employed for first spectroscopic and imaging experiments before referring to porcine whole blood, plasma and erythrozyte (RBCs, Red Blood Cells) samples. Different materials of the hollow fibers within the xenonizer were investigated: OXYPLUS (PMP, OD: 380 µm, ID: 200 µm, outer skin: <1 µm); OXYPHAN (PP, OD: 380 µm, ID: 200 µm, pore size: 0.2 µm); CELGARD (PP, OD: 380 µm, ID: 240 µm, pore size: aver µm, porosity: 40%); Silclear (silicone, OD: 635 µm, ID: 305 µm). Preliminary results showed a (1.7 ± 0.2)-fold better xenonization through the OXYPHAN fibers in comparison to OXYPLUS. While CELGARD yields similar results, hardly any dissolved HP 129 Xe could be detected using 16 silicone tubes in a first trial setup. Therefore, the number of tubings will be increased for future experiments in order to make use of this very pressure-resistant material. 1 D. Baumer et al. Angew. Chem. Int. Ed,45: , 2006; P. Blümler et al. Patent EP A2, 2008

24 21 (a) HP 129 Xe gas (b) dissolved HP 129 Xe (c) gaseous (colored) and dissolved (green) 129 Xe Figure 3.6 : HP 129 Xe 2D projection image of the xenonizer overlayed on a gray-scaled 1 H image. (a,b) GE images. (c) CSI. The fluid flow was stopped to avoid artifacts; gas flow was set to 170 ml/min. For spatial resolution of the xenonizer function, various MR images were acquired employing 2D gradient echo (GE) as well as chemical shift imaging (CSI) sequences. Eventhough CSI is fairly time-consuming, the advantage of the wide chemical shift distribution of xenon can be made use of in order to distinguish areas of different substances within one image data set. The results of the measurements in the transverse plane (s. Fig. 3.6) clearly show the distribution of HP 129 Xe gas in the empty (a) as well as in the water-filled xenonizer (b,c). Especially the successful CSI images are important for future blood MRI experiments since a dinstincion of plasma (194 ppm) and RBCs (range ppm) is required. For further functional analysis, images were also acquired in axial direction (s. Fig. 3.7). Eventhough different imaging methods were employed, all images consistently show that the dissolution of HP 129 Xe mainly occurs in the front region of the xenonizer (top region of the figures) proving the high gas exchange effiency of the hollow fibers. Furthermore, the results suggest that even more compact setups will be sufficent for equivalent gas and fluid volumes. (d) dissolved HP 129 Xe (e) gaseous (grey) and dissolved (colored) 129 Xe (f) gaseous (grey) and dissolved (colored) 129 Xe Figure 3.7 : MR projection images of the xenonizer. (a) Water-dissolved HP 129 Xe GE (Overlayed on 1 H image ) (b) GE of the xenonier filled with saline solution: gas (grey) ; fluid (colored). (c) CSI of the xenonier filled with saline solution.

25 22 3 Individual Reports In summary, the experiments performed on the xenonizer setup improved its effiency and yield valuable information for medical engineerging research and a wide variety of future medical applications. Hydrogen Peroxide Catalyzed Decomposition Monitored via NMR Imaging Dipl. - Phys. Lisandro Buljubasich Ph. D. student supported by DFG; in colaboration with Prof. S. Stapf In an NMR imaging experiment, the image brightness is a direct measure of the NMR signal intensity obtained under the particular pulse sequence used in the image acquisition. This brightness does not only reflect spin density, but is weighted by the chemical constitution, the hardness or softness of the material, the diffusion coefficient and the translational motion or motion on a much faster time scale, depending on the design of the sequence. The contrast of an image reflects the heterogeneity of the sample with respect to the chemical and physical properties mentioned. This is because these properties reflect on NMR parameters such as NMR signal amplitude, frequency, T 1 and T 2 relaxation times and line shape. Therefore, the NMR sequence 7 6 x mm y [mm] x [mm] Figure 3.8 : 2D x y image of a Pd pellet submerged in water, with slice selection in z direction. The F OV in read as well as phase direction is 7 mm, and the slice thickness is 500 µm. The experiment was performed acquiring 32 points in read direction, with 32 steps in phase direction, NS = 1024 and t R =125 ms. On the right-hand side a picture of the pellet is shown, with a cut to observe the Pd layer. 0

26 23 can be designed accordingly to obtain the desired contrast. The wide range of contrasts that can be imposed on a spin-density image is a unique power of NMR imaging. The wide variation of T 2 in an H 2 O 2 decomposition appears to be an ideal factor to use as a contrast in NMRI. Monitoring the image intensity as the reaction advances would allow to have a global idea about the reaction stage, simultaneously in different parts within the catalyst particle. In this contribution we show as an example how a reaction can be followed in a spherical-like porous medium particle (BASF, R0-20/72 PDE) with an outer shell containing 0.72 wt-% Pd as catalyst metal by NMRI. In Fig. 3.8 a 2D x y image of a 4 mm diameter Pd pellet submerged in water, with slice selection in z direction, as well as a picture showing where the Pd layer is located. In order to set the optimal parameters for the experiments, and thus obtaining the maximum contrast between initial and final states of the reaction, several preliminary studies were performed (not shown here) involving T 1 and T 2 maps for pellets with and without metal layer previously saturated either in water and H 2 O 2 (initial and final state of the reaction). We present here results obtained by monitoring the pixel intensity inside the pellet during the decomposition of 5 % initial H 2 O 2 concentration, for several hours. In this case, t R was set to be 7 x y [mm] C 1 C 2 C 3 C x [mm] Intensity [arb. u.] 4x10 4 3x10 4 2x10 4 R 2 R 1 R Intensity [arb. u.] T 2-outside [ms] x x x x x10 3 T 2 outside the pellet t r [h] R 2 R 1 R 3 R 4 1x t r [h] R t r [h] Figure 3.9 : Results of monitoring an H 2 O 2 decomposition in the presence of the Pd pellet. The 2D image represents 1 of the 1400 images acquired during the experiment. The circles were included to separate the pellet into different regions (see the text). The top-right plot shows the evolution of T 2 of the liquid outside the pellet. The plots in the bottom show the time evolution of the mean pixel intensity, averaged out in every region (left) and the same curves shifted to coincide in the origin, to allow clearer comparisons.

27 24 3 Individual Reports 125 ms and t E =1.85 ms. Figure 3.9 shows a 2D image with 4 concentric circumferences, separating the image into excluding regions. The circumferences were labelled as C i with i = 1,.., 4. The size of the circles were chosen in order to identify the pixels with approximately the same intensity (thus, relaxation times). The regions were labelled as R i with i = 1,.., 4, and can be described as, R 1 includes all the pixels placed inside the C 1. R i includes all the pixels placed between C i and C i 1, for i = 2, 3. R 4 includes all the pixels which intersect the circumference C 4. The experiment consisted of a series of 1400 images, with a CPMG experiment performed every 30 images, in order to follow the T 2 evolution of the liquid outside the pellet. The corresponding plot is shown in Fig. 3.9, where it is possible to observe that the 50 hours of reaction represent a large fraction of the total time needed to fully decompose the H 2 O 2. Portable MRI system for in-line quality control: Application to rubber seals Dr. Ernesto P. Danieli PostDoc supported by DFG Rubber gaskets are employed in multiple applications such as thermal isolations and seals in diverse areas including the building, aircraft, and car industry. Many are extruded profiles which can be monitored in-line to raise quality standards and optimize production cost. One of the few techniques suitable to inspect not only outer but also inner surfaces and rubber quality at the same time is magnetic resonance imaging (MRI). This contribution reports MRI experiments of rubber profiles measured with a portable MRI sensor built from permanent magnets arranged in a new way. The design combines Halbach rings with different geometric proportions optimized to minimize finite-size effects introduced by the limited length of the sensor. To properly control the magnetic field inhomogeneities, each ring is provided with mechanical shimming capabilities that modify the original Halbach design. They are composed of fixed trapezoidal elements used as guides for rectangular pieces that can radially be moved in and out to generate spherically harmonic correction fields in a controlled way. The homogeneity of the magnetic field obtained after shimming is better than 1 ppm across a spherical volume 40 mm in diameter. The length size of the magnet array is 32 cm with an outer diameter of 33 cm. The magnet is equipped with a solenoidal radio-frequency coil

28 25 to excite the homogeneous volume and with a three-axes actively shielded gradient coil system which allows fast switching times without introducing Eddy currents, to furnish the sensor with imaging capabilities. Figure 3.10a shows a typical 2D image of a cross section 1 cm thick of a static rubber profile measured with a spin-echo sequence. The image is composed of in-plane pixels which determine a nominal spatial resolution (pixel resolution) of mm 2. The total experimental time for one image averaged over 4 scans is 20 s. The grey scale of the image shows the density difference due to a change in the gravimetric density of the material from foamy to compact. The intersection of the dashed lines shown in Fig. 3.10a with the rubber sample determines the 1D profiles of Fig. 3.10b. The good sensitivity provides an image with high contrast between rubber and air, which is desired for the determination of the rubber-air interface with high accuracy. Once the edge points are obtained it is possible to reconstruct the rubber contour (Fig. 3.10c), from which internal and external geometric parameters can be extracted non-invasively. The precision of the location of the edge points depends on the signal-to-noise ratio (SNR) as can be seen from Fig. 3.10d. Since the different SNR values shown in the abscissa axis are proportional to the total acquisition time, a compromise between precision and measuring time must be found depending on the application. For an in-line implementation, the methodology proposed is to use the motion of the rubber gasket as a way to refresh the magnetization which continuously supplies the sensitive volume with polarized sample ready to be excited and detected. In this way it is possible to obtain a 2D image corresponding to a portion of the sample whose length would be proportional to slice Figure 3.10 : a) NMR image of a typical profile of a rubber gasket measured with a 0.5 T Halbach magnet. b) One dimensional profile corresponding to the dashed line observed in a). c) Reconstruction of the rubber profile contour based on the edge positions obtained in b). d) Error σ in the NMR measurement of the sample edge as a function of the SNR.

29 26 3 Individual Reports thickness and to the number of single experiments required. From one such image the material properties can be obtained and the geometric structure can be determined with micrometer precision, both in a non-invasive way in accordance with most quality standards. Parahydrogen induced polarization at low magnetic fields M. Sc. Qingxia Gong Ph. D. student supported by DFG Miniaturized NMR, is mobile and often inexpensive equipment. Its use promises new applications in bio-, chemical, and material sciences. The obvious disadvantage of NMR at low magnetic fields is low sensitivity due to the small differences in the thermodynamic equilibrium populations of the spin states. It can be overcome by the use of different hyper-polarization techniques. 2,3 Para-hydrogen induced polarization (PHIP) has become an established tool in NMR for investigating reaction mechanisms and the kinetics of hydrogenation reactions. 4,5,6,7 2 B. Blümich, F. Casanova, S. Appelt, Chem. Phys. Lett. 477 (2009) S. Appelt, F. W. Häsing, H. Kühn, B. Blümich, Phys. Rev. A 76 (2007) M. Stephan, O. Kohlmann, H. G. Niessen, A. Eichhorn, J. Bargon, Magn. Reson. Chem. 40 (2002) L. S. Bouchard, S. R. Burt, M. S. Anwar, K. V. Kovtunov, I. V. Koptyug, A. Pines (2008) Science, 319, R. W. Adams, J. A. Aguilar, K. D. Atkinson, M. J. Cowley, P. I. P. Elliott, S. B. Duckett, G. G. R. Green, I. G. Khazal, J. López-Serrano, D. C. Williamson (2009) Science, 323, K. D. Atkinson, M. J. Cowley, P. I. P. Elliott, S. B. Duckett, G. G. R. Green, J. López-Serrano, A. C. Whitwood (2009) (a) mmol phenylacetylene in 0.3 ml CD 2 Cl 2 (b) transverse magnetization frequency [Hz] time [s] Figure 3.11 : (a) Single-scan, proton-free induction decay (FID) after 90 impulse excitation at B 0 = 39 G. (b) khz 1 H NMR PHIP spectrum of styrene.

30 l pyridine in 0.3 ml d4-methanol l pyridine in 0.3 ml d4-methanol transverse magnetization frequency [Hz] transverse magnetization frequency (Hz) time (s) 0.75 l pyridine in 0.3 ml d4-methanol time (s) 0.37 l pyridine in 0.3 ml d4-methanol 600 transverse magnetization frequency (Hz) transverse magnetization frequency (Hz) time (s) time (s) 23.4 nl pyridine in 0.3 ml d4-methanol 300 transverse magnetization frequency (Hz) time (ms) Figure 3.12 : Single-scan proton FID of pyridine after 90 impulse excitation at B 0 = 39 G and corresponding 1 H PHIP spectrum. Recently, Simon B. Duckett and co-workers demonstrated a reversible interaction with parahydrogen to enhance the NMR sensitivity by polarization transfer. 6,7 This interaction offers the possibility to polarize a variety of substrates that are not amenable to polarization by the traditional hydrogenative route. In a recent study we worked on the application of PHIP spectroscopy at low magnetic fields. A hydrogenation reaction and a reversible reaction with parahydrogen were investigated. Phenylacetylene was hydrogenated using [Rh(COD)(BINAP)]BF 4 as a catalyst. An iridium complex [Ir(COD)(PCy 3 )(py)]pf 6 and pyridine as a substrate were taken as the reversible reaction model. With the hydrogenative PHIP, a trace of the hydrogenation product from µmol (0.003 ml) phenylacetylene was determined at 39 G (166 KHz 1 H NMR frequency) in a single scan (Fig. 3.11). The solution was exposed to hydrogen containing 50% para-hydrogen at 7 bar pressure. The NMR experiment was done immediately after shaking the sample intensely. Two lines (Fig. 3.11b) analogous to the ALTADENA spectrum which correspond to a chemical shift difference J. Am. Chem. Soc., 131,

31 28 3 Individual Reports of 1.5 ppm between the CH and the CH 2 groups are observed. Figure 3.12 shows the enhanced 1 H NMR signal of free pyridine acquired in a single scan after the polarization transfer from para-hydrogen. This technique appears to be suitable to determine pyridine concentrations as low as 20 nl in 0.3 ml d 4 -methanol at low magnetic field in a single NMR scan. molecules at low magnetic fields. This simple method greatly extends the detection limit of the small Non invasive depth profiling of ancient wall paintings by portable Nuclear Magnetic Resonance M. Sc. Agnes Haber Ph. D. student supported by DFG Conservation and restoration of art are of great interest in understanding the human history. Before performing these, it would be of great help to know the composition and the layer structure in these objects. The Profile NMR- MOUSE proved in many cases its suitability in analyzing and characterizing the layer structures of wall paintings. Depth profile measurements were performed on wall paintings that were recently excavated in the Papyrus Villa in Herculaneum, Italy. Because they were recently excavated, no restoration or conservation techniques were applied before the NMR measurements. The NMR measurements were taken using the Profile NMR- MOUSE with 25 mm depth access and a proton resonant frequency of 13.8 MHz. Figure 3.13 shows the set up of the measurements and the wall paintings that were analysed. Four depth profiles were taken, three in the room showed in Fig. 3.13a) and one from the wall showed in Fig. 3.13b) situated above the room in which the other profiles were taken. Next to the wall showed in Fig. 3.13a) is a wall a) b) Figure 3.13 : Experimental set up. a) One of the walls from the room that were analyzed. b) The exterior wall situated above the room shoved in a).

32 29 w [arb.u.] a) b) before 63 AD before 63 AD between AD exterior wall T 2 [ms] before 63 AD before 63 AD between AD exterior wall depth [mm] depth [mm] Figure 3.14 : a) Depth profiles for the four wall paintings that were analysed. b) Transversal relaxation times along the depth recorded during the depth profiling. that at the point were the volcanic eruption took place (79 AD), was under reconstruction from a previous earthquake (62 AD). The measurements were made using a 5 mm spacer, for a better sensitivity. The 16 mm depth range was covered in steps of 100 or 200 µm, each measurement lasting around one and a half hours. The profiles and the T 2 along the depth can be seen in Fig The profiles in red and black (Fig. 3.14a)) were made on the same wall, in different position with different surface colours. The matching of the two profiles is noticeable in the 4 to 16 mm depth range. The difference is remarkable in the first 4 mm, which is a trace for the different pigments used for the wall paintings, but also for different techniques in preparing the surface of a wall painting. The blue profile belongs to the wall painting that was in restoration processes when the volcanic eruption took place. The difference to the red and the black curve is obvious. The fourth profile (the green profile), belonging to the outside wall, situated above the room where the other profiles were recorded, reveals a similarity to the blue profile. The amplitude of both profiles is lower in the second part of the profile, suggesting a building material that blocks the uptake of water. A different technique was used for the profiles in blue and green, suggesting that this was a newer method used for wall paintings, reasoning the fact that the outside wall was build after 63 AD. Figure 3.14b) is in agreement with the information revealed in Fig. 3.14a), showing the same building material used for the red and the black wall paintings, and totally different for the other two wall paintings. In all four correlations of the T 2 values and depth it is noticeable that the materials used closer to the surface have bigger pores, so the protons relax much slower than the material used at the bottom of the wall painting, where the pores are smaller and the protons relax faster.

33 30 3 Individual Reports Relaxation in a Natural soil: Comparison of Relaxometric Imaging, T 1 - T 2 Correlations, and Fast-Field Cycling NMR Dr. Sabina Haber-Pohlmeier PostDoc supported by DFG Soils are natural porous media of highest importance for food production and maintenance of water resources. For these functions a prominent property is their ability to retain and transport water which is mainly controlled by pore-size distribution. The latter is related to NMR relaxation times of the water molecules filling the pores, for which different measurement methods can be used. Generally,imaging methods contain more information than relaxation methods, since imaging resolves the information in 2 or 3 dimensions which is especially important for irregular samples such as natural soil. The aim of this study is to investigate the multi modal nature of the relaxation distribution functions observed in relaxation experiments of macroscopic samples at low field and to find an answer to the question whether or not they are caused by macroscopic structures like fractures or by the inherent microscopic heterogeneity. For this purpose we measured T 1 and T 2 maps by relaxometric imaging and two-dimensional T 1 - T 2 correlation maps and compare them with available data from fast field cycling relaxometry (FFC) experiments 8 of a saturated natural sandy loam from Kaldenkirchen. Figure 3.15 shows T 1 and T 2 parameter images of four axial slices of the saturated Kaldenkirchen 8 Pohlmeier A, Haber-Pohlmeier S, Stapf S. A Fast Field Cycling NMR Relaxometry Study of Natural Soils. Vadose Zone J 2009; 8: Figure 3.15 : T 1 and T 2 maps for Kaldenkirchen soil sample (measured at 7 T with 1 H = 300 MHz, t E = 1.5 ms, < T I n <1 s, 0.5 mm resolution, 3 mm slice thickness).

34 31 distribution function (a.u.) d ( m) ] Figure 3.16 : T 1 and T 2 histograms of the relaxation maps in Fig For comparison a T 1 distribution function (line, normalized and off-set) obtained by fast field cycling experiments (FFC) at a Larmor frequency of 20 MHz is inserted in the figure. 8 soil. From these, relaxation-time distributions are extracted by calculation of histograms of the populations of relaxation times in the soil excluding the porous plate layer (Fig. 3.16). T 2 shows a comparably narrow distribution in the range between 1 and 8 ms, with an average of 2 ms, whereas the T 1 distribution is bimodal with a narrow peak at 7 ms and a broad peak between 10 and 300 ms. The narrow peak is near the shortest inversion time and may be an artefact of the inversion procedure. It collects all longitudinal relaxation processes faster than 10 ms which cannot be resolved. For comparison with the distribution functions measured directly in non-imaging mode, a T 1 distribution function measured with fast field cycling (FFC) NMR at a Larmor frequency of 20 MHz is also included. A broad main mode with an average T 1 of 70 ms is accompanied by a faster relaxing component at about 10 ms. Additionally, a small but very fast component at 2 ms is observed, which is likely to correspond to the clay component and arises from strongly confined water in this phase. Similar short values have already been Figure 3.17 : T 1 - T 2 correlation map of saturated Kaldenkirchen soil measured at 1 H = 24.3 MHz.

35 32 3 Individual Reports distribution function (a.u.) d ( m) Figure 3.18 : Pore-diameter distributions obtained by projections on the T 1 and T 2 axes from the 2D data of Fig The relaxation times were rescaled to pore size distributions by means of the Brownstein-Tarr equation assuming the capillary tube model and the average S/V ratio from BET. measurements 8 found in a different clayey soil 8. The slow modes of T 1 at low magnetic field correspond very well to the slow mode observed spatially resolved at high field (300 MHz). These modes are due to the relaxation in pores with size ranging between 1 to some tens microns 8. The two slow modes depend logarithmically on the Larmor-frequency in the low field range and this relation persists at high field of 300 MHz (data not shown). According to Korb 9 this linear dependence is interpreted as local, two-dimensional diffusion, where the basic relaxation mechanism is the dipole-dipole interaction of water molecules with paramagnetic centres at the pore walls. These results are compared to distributions extracted from a T 1 - T 2 correlation experiment map measured at 24.3 MHz (Fig. 3.17). The map shows bimodal distributions for both T 1 and T 2 which indicates two distinct pore-size classes. The maxima for T 1 are near 20 and 90 ms and correspond well to the FFC data at 20 MHz and the imaging data at 300 MHz (Fig. 3.16). The main transverse relaxation modes at 9 and 50 ms are much slower than the T 2 modes identified at 300 MHz. As the echo time is much shorter at low field and the internal gradients are higher at high field, this may be explained by the effect of molecular diffusion at high field. An important observation is the lack of any detectable cross-peak. A cross peak would indicate that for a given value of T 1 two or more values of T 2 exist indicating multiple transverse relaxation mechanisms, so that T 2 is affected also by parameters other than pore size. It is concluded, that such multiple relaxation sources are not observed in these samples and that the multimodal relaxation time distributions are due to pore-size effects and not to macroscopic heterogeneities. 9 Korb JP, Bryant R. Magnetic Relaxation Dispersion in Porous and Dynamically Heterogeneous Materials. Adv Inorg Chem 2005; 57:

36 33 2D Relaxation Exchange NMR M. Sc. Maxime Van Landeghem Ph. D. student ESPCI Paristech and RWTH Aachen University supported by Saint-Gobain Recherche Nowadays, energy is becoming a major issue in terms of sustainable development. One aspect concerns the improvement of thermal insulation for buildings where industries offer new high performance mortars. Not only these mortars must have a low thermal conductivity, but they must also be waterproof. To achieve these properties, the pore structure of such materials must be investigated. This work examines the use of NMR to characterize the pore structure of mortars and it changes during mortar curing, especially the delicate dessication period. The NMR MOUSE seems to be a suitable tool in this endeavour because it is a tool of nondestructive measurements directly at construction sites. T 1 and T 2 relaxation times have already been studied extensively on these materials, but less is known about the pore size distribution and the way the pores are connected. For that purpose, we have shown that in T 1 - T 2 correlation NMR maps and in T 2 - T 2 exchange NMR maps, the values of T 1 and T 2 are affected by the exchange of water between the pores. To extract the unbiased values of the relaxation times and the exchange rates between the pores, the following classical differential equation is solved: d [ M(t) M eq ] = (R + K) [ M(t) M eq] (3.1) dt where M is a vector containing the magnetization components of each sites, R is the relaxation a) b) Figure 3.19 : Experimental (a) and simulated (b) T 2 mixing time of 70 ms - T 2 exchange spectra of silica particles for a

37 34 3 Individual Reports a) b) Figure 3.20 : 2D relaxation exchange maps for three-site exchange. a) Symmetric map with 1/k 12 = 1/k 13 = 1/k 23 = 1/k 32 =250 ms. b): Asymmetric map with 1/k 12 =400 ms, 1/k 13 =20 ms, 1/k 23 =3000 ms, 1/k 32 =10 ms. The longitudinal relaxation times were set to 4 times the corresponding transverse relaxation time. rates matrix and K is the exchange matrix which mixes the magnetization components. As a model system with a two relaxation sites for water molecules, water saturated, home made, 500 nm diameter silica particles were investigated by relaxation exchange NMR. The exchange rate found was 110 ms (see Fig. 3.19). Besides, we show that when more than two sites are involved, the spectrum may become asymmetric (see Fig. 3.20). Such exchange maps are often observed, for example in soil. The inversion of multi-site exchange maps for the relaxation times and exchange rates is a topic of ongoing research. Measuring the ingress of model moisturizing formulations into the palm Dr. med. Dipl. - Phys. Jörg Mauler Ph.D. student supported by Virtual Helmholtz-Institute on Portable NMR (VIP-NMR) For the development and testing of new moisturizing solutions, the cosmetics industry needs techniques to measure the speed of ingress, the penetration depth, and the residence time of cream in the skin. Human skin consists of layers. The outer most stratum is the epidermis. It is attached to the dermis which connects to the sub-cutis. Because the epidermis forms the barrier that prevents harmful substances from entering the human body, moisturizing solutions do not permeate the skin deeper than this layer. Corresponding to the life cycle of its cells, the epidermis also bears a layered structure, comprising the strata basale, spinosum, granulosum,

38 35 and corneum where dead cells are shed. Depending on the anatomic position, the dry stratum corneum is from 20 µm minimum up to 200 µm thick and provides the barrier function of the epidermis. Creams penetrate the skin no more than up to this stratum. In order to localize the penetration depth with high resolution while maintaining low measurement time, a new pulse sequence was developed for the Profile NMR-MOUSE. By exploiting the Fourier transform of the spin-echo a frequency band with 100 khz width is evaluated in one shot. 4 profile sections of the whole profile are measured separately and then composed to produce one profiles up to 400 µm deep as for example in the case where the stratum corneum is swollen after application of moisturizing liquids. Measurements on the palms of 3 volunteers have been performed with a glycerol water solution as a model moisturizing liquid. After recording a steady-state skin profile, the solution was applied to the palm and profiles were measured until either no effect of the substance was detected any longer or the time limit of 9 hours total measurement time had expired. Figure 3.21 shows the chronologic sequence of profiles of the untreated skin measured immediately after applying the test solution and 35 min later. The moisturizing solution binds water which mainly leads to an increase in T 2 - time up to 100 µm depth, corresponding to a higher weighting function value than for untreated skin. 35 min after applying the liquid the weighting function peak has started to drop with respect to amplitude and penetration depth. From 50 to 100 µm depth the amplitude is lower than the curve of untreated skin which may be caused by water mobilization from this area. If one interprets a moisturizing solution with its ability to penetrate certain skin layers as a tailored probe to detect the very anatomical layers, one can non-invasively measure and compare the depth of these layers for different individuals in vivo. This is shown in Fig In weighting function [a.u.] 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 untreated skin 0 min 35 min depth y [ m] Figure 3.21 : Measuring the ingress of moisturizing solutions into the palm. Consecutive experiments show the maximum penetration depth and track the recovery back to the untreated skin profile.

39 36 3 Individual Reports w-function difference [a.u.] 0,35 0,30 0,25 0,20 0,15 0,10 0,05 0, depth y [ m] volunteer A volunteer B volunteer C Figure 3.22 : Subtracting the weighting function of untreated skin from the treated skin profile for different volunteers reveals individual penetration depths and changes in amplitude. order to compare the data from different individuals with different native skin profiles, the difference between treated and untreated skin profiles is calculated and plotted versus depth. Volunteer B reveals the largest penetration depth corresponding to the largest thickness of the stratum corneum. NMR Investigation of Polymer/Cement Dispersions M. Sc. Maria Alexandra Olaru Ph. D. student supported by BMBF Polymer cement dispersions (p/c) are pastes of polymer dispersed in a cement matrix. They promise to offer improvements in durability and versatility far beyond the properties of conventional cement-based materials. They are employed as coatings for glass rovings to produce composite materials free of macro defects and are ideal for use in the construction of buildings with critical loads. The time-dependence of the mechanical and chemical resistance of p/c, as well as their sensitivity to hydration, have been attributed to the influence the addition of polymer has on the macrostructure. The dispersions are prepared using only small amounts of organic solvent and the formation of the cement matrix takes place upon hydration. In order to understand the mechanical properties of these novel materials and to be able to improve them further, the physical and chemical changes associated with the water transport inside the p/c paste need to be elucidated.

40 37 Polymer/cement samples with different poly(vinyl acetate) [PVAC] to cement ratios (30:70 and 40:60) have been studied with a combination of solid-state and imaging NMR methods. T 1, T 2, and spin density images have been acquired during the hydration process using pulse sequences based on the SPI (Single Point Imaging) technique. By using SPI the water ingress into the dispersions could be monitored in real time, without interruptions of the curing process by weighting and other sample manipulations which are required with standard methods of analysis. Figure 3.23 : Spin density evolution in different voxels across cylindrical samples as a function of the hydration time 30:70 p/c (left) and 40:60 p/c (right). With the SPI data, the changes in the sample upon hydration and the influences of temperature and polymer amount on the hydration-associated phenomena could be evaluated. For example, the type of water diffusion at temperatures ranging from 20 C to 50 C has been determined. Irrespective of the temperature, the diffusion process takes place in two steps. The first step is short, of the order of hours and is characterized by anomalous diffusion for both batches of samples analyzed. The second step lasts of the order of days. There, the diffusion front moves proportional to the square root of time for the samples containing 30% polymer, which is characteristic of case I diffusion. When increasing the polymer amount to 40% the decomposition of the organic phase requires a larger amount of water, leading to slower water uptake and a case II diffusion. The evolution of the inorganic phase was followed in two ways: on one hand, the formation of cement crystals was assessed with relaxation-time maps, which show the gradual curing as a function of position. On the other hand, 29 Si MAS-NMR spectra confirmed the imaging results but also allowed to follow the amounts of reacted and un-reacted cement as a function of the hydration time. For samples containing large amounts of polymer and/or cured at high temperatures, the cement hardens before it is fully penetrated by the water front, leading to a layered, inhomogeneous composite (reacted, hardened cement and soft, non hydrated p/c paste). The combination of imaging and spectroscopic NMR techniques represents a powerful approach for studying the effects of water ingress on the macroscopic properties of polymer/cement

41 38 3 Individual Reports Figure 3.24 : 29 Si MAS NMR spectra of pc/c samples with different poly(vinyl acetate)-to-cement ratios: (a) dry, (b) fully hydrated 40:60 and c) fully hydrated 30/70. dispersions. Generally, these properties are dictated by the speeds of the diffusion front and of the hardening process, which, in turn, can be controlled by modifying the polymer amount and the curing temperature. NMR imaging and velocity mapping in microfluidic systems Dipl. - Chem. Eva Paciok Ph. D. student supported by DFG Microreaction technology is a vastly progressing new development in the field of chemical engineering. The simple but revolutionary idea is to perform large-scale chemical processing in microscopically structured vessels. The use of microdevices can maximize the efficiency and safety of a chemical production process, if the microstructures are tailored precisely to the requirements of a given chemical reaction. Therefore, a measurement method is needed, which can shed light on the happenings inside the microdevice. In past years, standard flow mapping techniques were shown to be of limited reliability, mostly due to their invasive nature. Computational Fluid Dynamics seemed the only alternative. But despite the accelerating progress

42 39 (a) setup (b) FLIESSEN flow-imaging results (c) performance at higher flow rates Figure 3.25 : FLIESSEN flow-mapping on a micro-structured phantom. (a) The planar phantom was made of Tefzel tubing (OD 1/16, ID 0.03 ), a surface coil was installed and acetone was used as a model fluid. (b) Using FLIESSEN, high-resolution images and velocity maps were obtained within seconds ( pixels, 2 scans, TR 8.5 s, (211 µm) 2 /pixel. The laminar flow exhibits a slight centrifugal distortion. (c) FLIESSEN was tested within a wide velocity range. There is nearly no deviation between the measured and expected average velocities up to a limit that is set by the average residence time of molecules inside the phantom. in computer technology, the complexity of microfluidic systems makes the prediction of reallife systems difficult, if not impossible, since phenomena that are negligible for large-scale flow dynamics play a major role on the micro-scale, e.g. wall-slippage, surface tension etc. In 2005 our group has already proved that NMR is a powerful tool for the investigation of microfluidic setups 10. Using a dedicated surface transmitter coil, the improvement in S/N allows to acquire high-resolution images and velocity maps of flow inside a micro-device non-invasively. The acquisition with standard NMR techniques, however, leads to long measurement times in the range of hours or even days. The familiar ultrafast imaging methods cannot be applied to micro-devices. EPI-based techniques fail in the B 0 -inhomogeneity of the micro-structures, RARE-based methods fail due to the B 1 -inhomogeneity caused by the surface coil 11 and both EPI and RARE are flawed concerning flow compensation. In our recent work, we applied a newly developed, RARE-based imaging and velocity-mapping technique, called FLIESSEN 12 to a phantom-setup that bears all the characteristics of a microdevice. We were able to show that FLIESSEN has a remarkable resilience to magnetic field inhomogeneities and that its implemented flow compensation allows flow mapping over a wide velocity-range (Figure 3.25). As a result, we continued our work on an actual micromixer. For this purpose, due to higher demands in terms of resolution and S/N, a segmented acquisition scheme for FLIESSEN was developed. Using FLIESSEN in combination with a surface coil, the 10 S. Ahola, F. Casanova, J. Perlo, K. Münnemann, B. Blümich, S. Stapf, Lab Chip, 2006, 6, S. Ahola, J. Perlo, F. Casanova, S. Stapf, B. Blümich, JMR, 2006, 182, Flow Imaging Employing a Single Shot Encoding, A. Amar, F. Casanova, B. Blümich, to be submitted.

43 40 3 Individual Reports spin-echo image FLIESSEN image z dimension [mm] z dimension [mm] x dimension [mm] 4 6 x dimension [mm] (a) setup (b) imaging results Figure 3.26 : Imaging on the serpent micromixer. (a) The planar microstructure with a total inner volume of 13 µl was provided by Micronit Microfluidics BV. It was mounted into a self-made probe containing a heat-exchanger and a surface coil for detection. Acetone was used as a model fluid. Due to the surface coil, the sensitive volume amounted to a mere 2 µl in the region of interest. (b) Using classic spin-echo pulse sequences as well as FLIESSEN, high-resolution images were obtained with (55 µm) 2 /pixel. The step from the classic method to the ultrafast method shortened the measurement time noticeably (15 hours vs. 15 minutes) with only a slight loss in image quality. Thus, we can proceed to our next challenge: ultrafast velocity-mapping of flow inside the micromixer. acquisition time was reduced from 15 h with a standard method to 15 min with the ultrafast method and high-resolution spin-density images were obtained (Figure 3.26). Consequently, our next goal will be the ultrafast velocity-mapping of flow inside the serpent micromixer. Design and Characterisation of intelligent Hydrogels M. Sc. Markus Raue Ph. D. student supported by FH Aachen Hydrogels are three-dimensional polymer networks which have the ability to keep a high amount of water. With an external stimulus like ph, ion concentration in solution or temperature, the hydrogels can change their shape. The response is expressed in the deformation of the chemical designed network, resulting in swelling or shrinking of the gel samples. The goal of this work is to synthesis new hydrogel types on the base of acrylic acid and maleic

44 41 acid with its anhydride for a higher charge density and on the base of vinylphosphonic acid for a higher ionic strength which influence the mechanical properties and the swelling behaviour. The new types of hydrogels should be established as sensors, actuators and switchable porous media. The mobility of sodium ions and exchange reaction between different ions is investigated with NMR by 23 Na and 27 Al imaging, self-diffusion coefficient and their relaxation times T 1 and T 2 for a better understanding. New type of a hydrogel and their relaxtion times A new type of hydrogel were manufactured by condensation reaction of a prepolymer poly (acrylic acid-co-maleic acid) with hexandiole as a crosslinker by water separation, whereas the prepolymer with a mol ratio of 70:30 and with a moleculare weight of g/mol shows great promise for a fast swelling hydrogel. After the condensation reaction the hydrogels were neutralized by sodium hydroxid. Before measuring T 1 by saturation recovery and T 2 by CPMG the hydrogels were washed and dried two times by changing the water. In the following Tab.3.3 the results of the relaxation times of 23 Na of the poly (sodium acrylateco-sodium maleate) hydrogels are shown. Table 3.4: Relaxtion times T 1 and T 2 of a poly(sodium acrylate-co-sodium maleate) with 1% hexandiole as a crosslinker measuring 23 Na by 11,4 T (132 MHz) Sample swelling ratio T 1 uncertainty T 2 uncertainty temperature [%] [ms] [ms] [ms] [ms] [K] ,97 0,01 0,80 0, ,22 0,05 1,07 0, ,83 0,02 1,19 0, ,82 0,03 1,07 0, Compared with the relaxation times of 23 Na hydrogels based on sodium acrylate, (T 1 16 ms; T 2 5 ms) the T 1 s are a factor three shorter and the T 2 s a factor 5 shorter than the relaxation times of the poly (sodium acrylate-co-sodium maleate) hydrogels due to a higher charge density and a higher polarity. In the theory means, that the chains of the hydrogels are less mobile and this yields to a faster swelling and shrinking of the hydrogel. Furthermore shows the mobility of sodium in vinylphonate great promise for a fast swelling hydrogel, too. Intelligent membrane Switchable porous media including intelligent hydrogels were manufactured by in situ radical copolymerization of sodium acrylate with MPEG 350 (90:10; 50:50) and sodium 2-Acrylamido- 2-methylpropansulfonate with MPEG 350 (90:10; 50:50) with PEGDMA 750 as a crosslinker in glass frits with a pore size between µm. As in Fig is shown, it is possible to open and close the porous medium by changing the ph from 0 to 14 and backwards. Switchable porous media, which react on temperature and ion concentration, are still in progress.

45 42 3 Individual Reports solution swollen hydrogel shrunk hydrogel porous medium T; ph; c(ion) flow T; ph; c(ion) min. / max. flow [g/min] 35,0 30,0 25,0 20,0 15,0 10,0 5,0 0,0 0,01 30,9 29,2 Results of intelligent membrans by ph switching 29,1 11,5 10,4 9,95 1,36 1,20 1,10 1,11 0,93 0,31 0,1 0,67 0,16 0,71 0,16 0,09 0,01 0,01 0,28 0,2 0,07 0,33 0,06 0,38 0,13 NaAc/MPEG 90/10 NaAc/MPEG 50/50 AMPS- Na/MPEG 90/10 AMPS- Na/MPEG 50/50 Figure 3.27 : (Left) Switchable porous media including hydrogel as a matrix. By an external stimulus like ph, temperature or ion concentration the pores open and close with the result of a flow or separation. (Right) The switching processes of different hydrogels were measured by the minimal and maximal flow. water 1.cyclus 1M HCl 1.cyclus 1M NaOH 2.cyclus 1M HCl 2.cyclus 1M NaOH 3.cyclus 1M HCl 3.cyclus 1M NaOH NMR Studies of partially saturated soils M. Sc. Oscar Elías Sucre Ph. D. student supported by DAAD A tool for logging moisture in laboratory soil columns has been developed and tested in a project wich is part of the transregional collaborative research center TR32 of DFG. The tool has the shape of a cylinder with a diameter 48 mm and a length of 220 mm. It is fitted with a radiofrequency coil to sense a NMR signal from a slice 9 mm away from the sensor external surface. With a depth of 9 mm. The sensor has been used in imbibition and drainage experiments by shifting it through a plastic pipe embedded in a soil column. A major task entailed the optimization of the rf coil with the use of damping elements to suppress magneto-acoustical ringing. At its current state, the sensor has shown its capability not only probing water content, but also determining relaxation time distribution to gain an insight into the microscopical conditions under which water is retained in partially saturated soils. To use this sensor for characterizing the hydraulic properties a model soil, an outflow experiment in model soil FH31, classified as sand in the German soil standard, was performed. The soil column had a height of 606 mm and initially is saturated as shown in Fig By placing the detector at a depth of 185 mm and letting the water to flow out of the tank, we can follow the column drainage with time (Fig. 3.29). After drainage, a moisture profile is measured again, once the column has reached its equilibrium state (Fig. 3.28). The modelling of such a process is well documented on books about soil physics 13. Using 13 Bear, J. D.,dynamics of Fluids in Porous Media, Dover, New York (1988).

46 43 0,40 0,35 Before Drainage After Drainage MvG Model Saturation 0,30 0,25 0,20 0,15 0,10 0, r 0.36 s n Depth (mm) Figure 3.28 : Evolution of water content in draining sand column FH31. 0,35 0,30 Experimental Data Ks=0.15 mm/sec l=0.5 Saturation 0,25 0,20 0,15 0,10 0, Time (sec) Figure 3.29 : Evolution of moisture at Depth=-185 mm. the Muallem-Van Genuchten (MvG) model 14 to model the experimental data with the partial saturation θ, hydraulical potential h and permeability K s as variables hydraulical parameters of the soil can be obtained. Acknowledgement are given to German Academic Exchange Service (DAAD) for my Ph. D. grant and the Deutsche Forschungsgemeinschaft for the financial support of this project. 14 Van Genuchten, M. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J., 44, (1980).

47 44 3 Individual Reports Crystallinity of Polyethylene Pipes by High- and Low-Field NMR M. Sc. Ning Sun Ph. D. student supported by DFG Since the 1980s, the use of polyethylene (PE) pipes for water and gas transport is rapidly increasing worldwide. They are predicted to last for 50 to 100 years under the normal conditions. However, the actual service life of a pipe depends on the operational and environmental conditions, and can vary in different parts of the network. Hence, it is necessary to develop efficient ways to estimate the remaining service of life. To this end, methods of nondestructive testing are needed which deliver chemical and morphological information of the pipe material. The aim of this work is to compare the crystallinity estimated by relaxometry in inhomegeous fields with that obtained at high field. The crystallinity of PE pipes aged for different times (0 h, 300 h, and 600 h) was estimated by high-field and low field NMR. At high field, the 1 H-FID and 13 C CPMAS spectra were measured on bulk samples. At low field, 1 H solid-echo decays and their variations with depth were measured with a Profile NMR-MOUSE. The high-field 1 H-FID could be decomposed into three components corresponding to the rigid (crystalline), interphase, and mobile (amorphous) phases. The aging analysis revealed that the amount of the rigid phase increased slightly with the aging time from % (0 h) to % (300 h), and % (600 h). The 13 C CPMAS spectra (Fig. 3.30a) show that for the PE pipe under investigation, the crystalline phase exists in both monoclinic and orthorhombic states. The spectra could be decomposed into using five distinct signals corresponding to the monoclinic, orthorhombic-1, orthorhombic-2, interphase, and amorphous phases. The estimated amounts of the crystalline phases (orthorhombic + monoclinic) are %, %, and % for the samples aged 0 h, 300 h, and 600 h, respectively. These CPMAS data confirm the previously observed increase of the amount of the rigid phase with the aging time. However, as cross-polarization is affected by site-specific relaxation, it is not a quantitative method of analysis, and the 1 H data need to be compared with crystallinities obtained by other methods. Figure 3.30b shows the variation of the amount of the rigid phase with the depth determined with the NMR-MOUSE at low field. The plotted values were estimated by fitting the solid-echo envelope with a sum of three exponentials corresponding to the three phases. We observe that the amount of the rigid phase increases from the outside to the inside. This is attributed to a more rapid cooling of the pipe surface during production which leaves less time to the surface material to crystallize. Furthermore, we observe that the aging process is affects the morphology through the entire depth of the pipe wall. A mount of the rigid phase has slightly increased after 0 h600 h of aging. When averaging the amount of the rigid phase across the depth of the pipe wall, values of %, %, and % are obtained

48 45 for aging times of 0 h, 300 h, and 600 h, respectively. These values are in good agreement with those estimated from high-field 1 H-NMR measurements. The results obtained so far indicate the high potential of unilateral NMR for truly non-destructive characterization of polymeric pipes. Figure 3.30 : a) 13 C CPMAS spectrum of the unaged PE pipe measured with a 500 MHz NMR spectrometer. b) Variation of the amount of the rigid phase with depth from measurements with the Profile NMR-MOUSE. Investigations of Permeate Flow and Visualization of the Cake-Layer Formation in Micro-Filtration Processes using NMR Imaging M. Sc. Lavinia Uţiu Ph. D. student supported by DFG The investigation of fluid transport by nuclear magnetic resonance (NMR) imaging and pulsed field-gradient NMR techniques has attracted growing interest in recent years. These techniques have been recognized to have great potential as an experimental tool for engineering research due to their versatility and accuracy. In this study, a submerged micro-filtration process using a polymeric hollow-fibre membrane and silica suspensions of different solid concentrations is investigated by NMR imaging. Hollow fibre membranes have been widely employed for water and wastewater treatments. A major advantage of hollow fibre membrane modules over other configurations of membranes is the high membrane surface area to footprint ratio achieved by the low aspect ratio (diameter-tolength ratio) of fibres. Understanding the filtration behaviour of hollow fibres is important in order to improve the operation and design of the hollow fibres system. This is because the hydrodynamic conditions in hollow fibre membranes are more complex than those in other

49 46 3 Individual Reports Deaeration valve PI TI Peristaltic pump Inlet Permeate line Balance Buffer tank y Measurement range Data logging Hollow-fibre membrane L = 1 m Test cell Outlet Figure 3.31 : Schematic diagram of the experimental device. types of membranes. In submerged filtration, negative pressure is applied to the lumen side of the fibre to obtain permeate flow through the membrane. This leads to an internal pressure drop due to permeate flow along the fibre lumen. Thus, the trans-membrane pressure (TMP), which is the difference between inside and outside pressure, will be highest at the exit and lowest at the starting point of flow. Therefore, local flux at the permeate exit is highest and may result in the most rapid cake formation in this area. The overall objective is to evaluate the permeability distribution along the fibre and to determine the thickness of the layer of deposited matter (silica) continuously formed on the surface of the membrane. For all flow tests, single hollow-fibre membranes of PURON type were provided by Koch Membrane Systems GmbH (KMS). The length of the membrane samples was approximately 100 ± 1 cm. According to the manufacturer, these microfiltration membranes consist of polyether sulphone (PES) as a source material and show an outer diameter of 2.6 mm, an inner diameter of 1.2 mm and a nominal pore diameter of 0.04 µm. In order to reduce the T 1 relaxation time to the range of ms, distilled water doped with CuSO 4 was used for velocity measurements. In the case of cake layer studies for the filtration tests, alkaline, aqueous dispersions of colloidal silica particles with a particle sizes distributed

50 47 y dimension [mm] (a) x dimension [mm] y dimension [mm] (b) x dimension [mm] y dimension [mm] (c) x dimension [mm] velocity [mm/s] L/(m 2 h) 15 L/(m 2 h) L/(m 2 h) 25 L/(m 2 h) L/(m 2 h) (g) position [mm] velocity [mm/s] (d) x dimension [mm] velocity [mm/s] (e) x dimension [mm] velocity [mm/s] (f) x dimension [mm] velocity [mm/s] F 30 E 25 D 20 C 15 B 10 0 (h) position [mm] Figure 3.32 : (a, b, c) Two dimensional velocity maps of the cross-section of the test cell and (d, e, f) velocity profiles of a 2 mm slice of water flowing through a hollow fibre at different permeate fluxes: (a, d) 10 L/(m 2 h), (b, e) 20 L/(m 2 h), (c, f) 30 L/(m 2 h) for 30 cm position bellow the y=0 position. (g) Permeability distribution along the fibre as function of position and (h) permeate flux. Bulk phase t = 01:49 min Cake layer t = 09:14 min Membrane t = 16:38 min Permeate t = 24:01 min t = 31:25 min Degassing t = 38:49 min Figure 3.33 : Visualization of the cake layer formation on the surface of the membrane over time, for a solids concentration of 0.2 wt.% and a flux of 10 L/(m 2 h). between 20 and 150 nm were used. The stock suspension consisted of amorphous spherical SiO 2 particles with a slightly negative surface charge. The desired solid concentrations (0.2, 0.4, and 0.6 wt.%) were adjusted by adding distilled water to the stock suspension (stock solids concentration: 50 wt.%). The NMR experiments were performed on a DSX200 spectrometer with field strength of 4.7 T. For rf irradiation a 20 mm standard birdcage coil was used operating at a 1 H resonance frequency of MHz. The test system shown in 3.31 was used to measure filtration characteristics for submerged membranes. The experimental set-up consisted of a flexible tubing (ϕ 12 mm) equipped with a single hollow-fibre for the filtration processes. The permeate is extracted from the top end of a fibre membrane with a peristaltic pump while the other end of the membrane was sealed with epoxy. Fresh model substance is filled into the feed side of the cell by gravity. An electronic balance connected to a computer was also used to ensure constant flux operation. The TMP, defined above, was continuously measured using a pressure transducer