Annual Report. Zentrum für Magnetische Resonanz. Editorial: 1 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie

Transcription

1 1 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Rheinisch-Westfälische Technische Hochschule Aachen Institut für Technische Chemie und Makromolekulare Chemie Lehrstuhl für Makromolekulare Chemie Zentrum für Magnetische Resonanz Annual Report 2003 Editorial: All members of the institute (editor: B. Blümich cover: Klaus Kupferschläger)

2 2 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Contents 1. A Review of The Institute Staff How to Reach the Institute 8 3. Teaching Lectures and Courses Practical Lab Courses Research Reports Public Activities Publications Talks Posters Honorary Activities Lectures of Visitors to the Institute Awards 87

3 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 3 1 A Review of 2003 NMR at ITMC Nuclear Magnetic Resonance (NMR) has many applications in chemical analysis of molecules in solution and in bulk, in biomedical imaging, in imaging of solids in materials science, in imaging and analyzing transport phenomena in chemical engineering and geosciences, and in process, and product and quality control. Apart from patient imaging all of these topics are pursued at the Institute of Technical Chemistry and Macromolecular Chemistry of RWTH Aachen. The main topic of research of Prof. Blümich s team is the development of NMR methods and applications in material science and chemical engineering. The research work focuses on NMR methods and hardware guided by applications to polymers and elastomers, to fluid transport in chemical engineering models and geological core samples, and to noninvasive product and process control in a manufacturing environment. Close contact to industrial and engineering partners defines the topics of diploma and doctoral work in the area of the applied sciences. Magnetic Resonance Center MARC Most of the NMR spectrometers are accommodated in the magnetic resonance center MARC (Fig. 1) and its annexes. The center serves the analytical needs of the chemistry research groups at the Seffent-Melaten campus of RWTH. At the same time it forms a nucleus for interdisciplinary research. The spectrometers available at MARC are listed in Tab. 1. Two 300 MHz spectrometers are used for routine high-resolution liquid-state NMR. Following the retirement of Dipl.-Ing. B. Dederichs, Frau Ines Bachmann now coordinates the user activities and service measurements. One 500 MHz spectrometer is dedicated to solid-state NMR spectroscopy. It is used for research and routine work and is accessible to the members of the chemistry department. Dr. Marko Bertmer is in charge of its operation. A 200 and a 300 MHz spectrometer are used for imaging and flow studies with Dr. D. E. Demco and Dr. S. Stapf as supervisors. Furthermore, Dr. Stapf has acquired a field cycling spectrometer, which further widens the broad range of NMR instruments at the center. In an annex to MARC, the so-called MOUSEoleum, work on the NMR-MOUSE is pursued, and the members of the DFG-Research consortium on Surface NMR of Fig. 1: View of the Magnetic Resonance Center MARC with the DMX 300, DSX 200, and DSX 500 and solid-state spectrometers. The DSX 200 and DMX 300 spectrometers are also suitable for imaging.

4 4 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Table 1. Spectrometers in MARC spectrometer Use manufactured/renovated DMX 300 imaging, flow NMR 1994/2000/2001 DSX 200 imaging, flow NMR 1997 DSX 500 solid-state NMR spectroscopy 1998 DPX 300 liquid-state NMR spectroscopy 1994 AC 300 liquid-state NMR spectroscopy 1995 Stelar field cycling relaxometer 2001 ESR electron spin resonance 1983/1992 Elastomers and Biological Tissues construct and test a unilateral NMR imager. A section of the annex has been reserved for setting up a LASER polarizer for NMR with hyperpolarized Xenon gas, an activity headed by Dr. Stephan Appelt from the Research Center in Jülich. Research Activities The research activities of the group can be divided into the three categories: NMR spectroscopy, NMR imaging including flow NMR, and mobile NMR. These respective NMR methods are applied in a variety of interlinked projects which predominantly concern materials and transport phenomena with applications ranging from engineering to the life sciences (Fig. 2). The central project work is coordinated by the senior staff members Prof. Dr. D.E. Demco, Dr. M. Bertmer, PD Dr. S. Stapf, and Dr. F. Casanova (Tab. 2). In addition to that, a promising new area of NMR activities arises in the context of hyperpolarized gas NMR in cooperation with Dr. S. Appelt from the Research Center in Jülich, where the physical basis of low- and high-field hyperpolarized gas NMR is investigated and applications of the method are explored in engineering and materials science. Each of the three main topics is addressed in a separate section of this report. spectoscopic Xenon imaging catalyst coking falling fluid film Bertmer, Demco spectroscopy morphology of Nylon-6 fibers order in tendon aging of rubber levitated drop drying of powders imaging and flow NMR mobile NMR morphology of PE porosity of rocks Stapf Casanova accuracy of moisture in plastic cheets diffusion imaging field cycling unilateral imaging laminar flow NMR Fig. 2: Research activities

5 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 5 Table 2. Projects, cooperation partners, and funding Project Coordinator Cooperation partners Funding Functional supramolecular Bertmer MnemoScience, INTECH BMBF materials Dynamically loaded Demco Bayer, DIK, Freudenberg, DLR Elastomers INTECH, Parker, Rheinchemie, TUHH, Vibracoustic NMR in Medicine and Demco MPI Köln, MPI Leipzig, Tel Aviv BMBF Material Science University Chemical extraction Stapf Engineering at RWTH Aachen DFG (SFB) and reaction Surface NMR Blümich Medicine, electrical and mech. Engineering at RWTH Aachen DFG (Forschergruppe) State assessment of electrical insulations Blümich Institute for High-Voltage Engineering DFG (Schwerpunktprogramm) Biocompatibility of Bertmer DWI, INTECH, MnemoScience BMBF implant materials Cultural Heritage Blümich Bruker, CNR Rome EUREKA The solid-state NMR activities have been centered on the topic of molecular order induced by self organization of molecules in a confining environment, of macromolecules in semi-crystalline polymers, and of molecules in biological tissues like tendon. NMR imaging was applied predominantly in the context of chemical engineering addressing the motion in levitated drops, multiphase flow, and microreactors. The capabilities of mobile NMR have been extended to 3D imaging and flow imaging. In addition, new and more sensitive MOUSE sensors have been developed. It can be anticipated, that some of the NMR topics in chemical engineering addressed today by NMR imaging in the laboratory can eventually be addressed by mobile NMR in the factory. Visiting Scientists and Awards Three scientist visited the NMR laboratory in 2003 for a research stay. These were Dr. Jagadeesh Bharatam from the Indian Institute of Chemical Technology in Hyderabad, India investigating the molecular dynamics of confined molecules, Dr. Alexander Khrapitshev from Wellington/St. Petersburg working on multiphase flow, and Dr. Ravindranatha Menon from Regional Research Laboratory (CSIR), Trivandrum, India, who studied the properties of novel rubber formulations by a variety of NMR methods and mechanical analysis in cooperation with Prof. Mang from FH Aachen. Radu Fechete received the DSM award. Teaching The teaching duties in Macromolecular Chemistry comprise courses and labs in Physical Chemistry of Macromolecules for engineering students and courses in Macromolecular Chemistry for Chemistry majors as well as for teachers to be. Furthermore, 1 diploma these was completed in 2003 and 3 dissertations (Tab. 3). Staff The NMR staff of ITMC related to Prof. Blümich s activities includes Prof. Dr. D. E. Demco and Dr. M. Bertmer (solid-state NMR), Dr. S. Stapf (imaging and flow), and Dr.

6 6 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Table 3. Diploma theses and dissertations completed in 2003 Name Thesis Iris Blomenkamp-Höfges Untersuchungen zur Wirkstoffbeladung und freisetzung an einem thermoplastischen Elastomer mit Hilfe der kernmagnetischen Resonanzspektroskopie Xiahong Ren NMR studies of molecular transport in model fixed-bed reactors Martin Klein Neue unilaterale NMR-Sensoren und ihre Anwendung Christa Gehlen Neue NMR-Methoden zur Untersuchung von Biomaterialien: Spektroskopie und Bildgebung unter Verwendung dipolarer Restkopplung F. Casanova (mobile NMR). Frau I. Bachmann-Remy operates the liquid-state spectrometers in MARC, Herr M. Adams designs NMR electronics and keeps all the spectrometers running, while Herr G. Schroeder has left the electronics workshop for his well-deserved retirement. Frau K. Charlier is the financial and in many ways also personnel officer, who keeps close watch in the finances and project management. The life savers of Prof. Blümich are Frau Gerlind Breuer and Frau Ingrid Schmitz who manage the daily work with him. The operating conditions of the group greatly benefit from the organizational skills of Dr. F. Kowaldt. Dr. H.-J. Helbig helps with different academic and safety issues. Funding Funding of the group derives largely from outstanding support by the Deutsche Forschungsgemeinschaft (DFG) in terms of personal projects by Dr. Stapf, Dr. Bertmer, Prof. Demco, and Prof. Blümich as well as by projects in context with the Sonderforschungsbereich on Chemical Extraction and the Forschergruppe Surface NMR. Further funding is received from a German-Israeli collaborative project (DIP), the Bundesministerium für Bildung und Forschung (BMBF), the Fonds der Chemischen Industrie (FCI), and from industrial cooperations. Förderverein Zentrum für Magnetische Resonanz e.v. Zentrum für Magnetische Resonanz e.v. is a non-profit organization associated with RWTH Aachen and the NMR group of Prof. Blümich. It supports the NMR activities by forming a link between industry and academic activities. One activity of the Förderverein is the support the Colloquium on Mobile NMR, which was organized in 2003 by Christa Gehlen and Kai Kremer. Furthermore, it partially covered the expenses for a German course for foreign students and acquired several valuable pieces of equipment for use of the NMR group.. Aachen, May 2003 Bernhard Blümich

7 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 7 2 Lehrstuhl für Makromolekulare Chemie 2.1 Staff 2003 Function Name +49-(0) extension Head of the institute Prof. Dr. Bernhard Blümich 26420/21 Secretaries Gerlind Breuer Ingrid Schmitz Staff scientists Dr. Marko Bertmer Prof. Dr. Dan Demco Dr. Hans-Joachim Helbig Dr. Siegfried Stapf Guest scientist Dr. Sofia Anferova Prof. Dr. Vladimir Anferov Dr. Federico Casanova Ph. D. students Dipl.-Phys. Andrea Amar Alina Buda (M. Sc.) Radu Fechete (M. Sc.) Dipl.-Chem. Christa Gehlen Sobiroh Kariyo (M. Sc.) Dipl.-Ing. Christian Kölker Dipl.-Chem. Kai Kremer Dipl.-Chem. Mirko Krüger Dipl.-Chem. Markus Küppers Dipl.-Chem. Kerstin Münnemann Dipl.-Phys. Juan Perlo Dipl.-Chem. Xiaohong Ren Dipl.-Chem. Shatrughan Sharma Mihai Vodã (M. Sc.) Dipl.-Chem. Mingfei Wang Diploma students cand. chem. Iris Blomenkamp-Höfgens Technical staff Dipl.-Ing. Michael Adams Ines Bachmann-Remy Klaus Kupferschläger Günter Schroeder Financial resources Karin Charlier 26464

8 8 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 2.2 How to reach ITMC Address: Prof. Dr. Bernhard Blümich Institut für Technische Chemie und Makromolekulare Chemie (ITMC) Lehrstuhl für Makromolekulare Chemie Sammelbau Chemie, Raum 38 B 121 RWTH Aachen Worringerweg 1 D Aachen Germany Phone: ++49-(0) Fax: ++49-(0) bluemich@mc.rwth-aachen.de WWW: and Airports: Köln/Bonn, Germany (85 km to Aachen via A4) Düsseldorf, Germany (90 km to Aachen via A44) Brussels, Belgium (143 km to Aachen) Maastricht-Aachen, The Netherlands (35 km to Aachen) Frankfurt, Germany (300 km to Aachen) The Airport-Aixpress is a direct bus connection between Aachen and the airports in Düsseldorf (12 times a day) and Köln/Bonn (4 times a day). The transfer takes about 60 to 90 minutes. Arriving by train Take a train to Aachen, preferably to station Aachen-West. On the left from the stations exit you will find a bus stop. Take line 33 (direction Klinikum or Vaals (NL) ) and leave at bus stop Wendlingweg (7 th stop) directly in front of the institute. At working hours there is a bus every 15 minutes. Not all trains stop at Aachen-West. If you have to leave at Aachen-Hbf (main station) you have to cross the square in front of the station. Across the street there are bus stops. Take line 3a to Klinikum. At working hours there is a bus every 15 minutes. Facing the Klinikum (factory-like hospital) turn to the right and walk about 200 m following the street. Follow the sign Chemische Institute. Arriving by car From Cologne (Köln) take freeway A4 or from Düsseldorf take A44. At the Aachener Kreuz take A4 towards Antwerpen/Heerlen. Leave the freeway at exit Aachen- Laurensberg (last exit before the border to The Netherlands, Fig. 1). Directly after the exit turn right towards Aachen. After about 1 km bear right and follow the sign Klinikum with a red cross. On that highway stay in the right lane and bear to the right following the signs to the Klinikum (about 2 km after the intersection and through a tunnel) until you are guided to the top of a bridge ( Valkenburger Str., Fig. 2). Stay right and make almost a U-turn following the signs RWTH-Melaten or MTZ. After

9 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 9 Fig. 1: Aachen and highway access. Klinikum SB Chemie about 100 m there are parking lots on the left, enter the fourth one with the sign Chemie. The institute is in Sammelbau Chemie across the parking lots and across the street. It is readily recognized by the octogonal green glass towers which accomodate stair cases. Figure 3 on the following page shows an aerial view of the building. P Fig. 2: Detailed location map.

10 10 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Fig. 3: Aerial view of the building.

11 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 11 3 Teaching 3.1 Lectures and Courses (Prof. Blümich) Introduction to Technical Chemistry and Macromolecular Chemistry (SS 03) V2, 2 hours/week (together with Prof. Dr. W. Leitner) General Technical Chemistry and Macromolecular Chemistry (SS03) V2, 2 hours/week (together with Prof. Dr. W. Leitner) Macromolecular Chemistry II (together with Physical Chemistry of Polymers ) (SS 03) V2, 2 hours/week Macromolecular Chemistry IV g NMR-Spectroscopy of Polymers (SS 03) V2, 2 hours/week (together with Prof. Dr. D.E. Demco) Physical Chemistry of Polymers (SS 03) V2, 2 hours/week Technical Chemistry and Macromolecular Chemistry I (WS 03/04) V2, 2hours/week (together with Prof. Dr. W. Leitner and Researches of Structures (WS 03/04) VÜ6 (together with Profs. Bettray, Dronskowski, Enders, Englert, Fleischhauer, Gais, Lueken, Maisch, Martin, Raabe, Runsink, Simon, Stahl) Macromolecular Chemistry IV h NMR-Imaging of Materials (WS 03/04) V2, 2 hours/week 3.2 Practical Lab Courses Together with Prof. Dr. H. Baumann and Prof. Dr. M. Möller: Technical Chemistry and Macromolecular Chemistry (SS 03 and WS 03/04) lab course for students of teacher s profession (by arrangement) Macromolecular Chemistry (SS 03 and WS 03/04) lab course for students of teacher s profession (by arrangement) Macromolecular Chemistry (SS 03and WS 03/04) practical course of research (by arrangement) Macromolecular Chemistry (SS 03 and WS 03/04) hall-course (by arrangement) Technical Chemistry (SS 02 and WS 02/03) hall-course (by arrangement) Seminar to all lab courses of Technical Chemistry and Macromolecular Chemistry (SS 03 and WS 03/04) S2, 2 hours/week

12 12 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 4 Research Reports Group photograph From left to right: First line: Middle line: Upper line: Elena Talnishnikh, Mihai Voda, Sofia Anferova, Andrea Amar, Juan Perlo, Mingfei Wang, Xiahong Ren, Ines Bachmann-Remy, Sobiroh Kariyo Susanne Rath, Ramona Orza, Cristian Hedesiu, Doru Gabriel Rata, Marko Bertmer, Federico Casanova, Karin Charlier, Silke Harms, Bernhard Blümich, Christian Kölker, Jürgen Kolz Ioan Botiz, Mihaela Ninu, Nicolae Gogá, Mirko Krüger, Christa Gehlen, Kerstin Münnemann, Kai Kremer, Siegfried Stapf, Klaus Kupferschläger, Vladimir Anferov, Dan Demco

13 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 13 Main Research Topic Solid-State NMR Solid-state NMR is an important tool in materials science, especially for the characterization of polymers. Information about the structure as well as the molecular dynamics can be obtained to establish correlations between the microscopic structure and the macroscopic properties. Samples can be accessed in the state of their use without the need to dissolve the materials which can change or mask important features. Solid-state NMR has attracted attention in a variety of branches in science, mainly in chemistry, physics, and biology, but also in chemical engineering, pharmaceutics, mineralogy, and geology. The big advantage of solid-state NMR compared to other analytical techniques is the high flexibility of the method. This provides access to information such as the chemical structure, the three-dimensional orientation and especially the mobility of the whole molecule or of individual functional groups. Furthermore, there is no limitation to crystalline materials. Amorphous materials and powders can be analyzed as well. Our focus is oriented on the investigation of modern polymeric materials to deduce relationships between the microscopic chemical structure and dynamics and their macroscopic properties like chemical composition or mechanical properties. Besides the spectroscopic characterization including two-dimensional correlation spectra, the main goal is to adapt or develop NMR methodologies tailored for certain materials and questions of interest. The spectroscopic characterization describes the local surrounding of each nucleus and correlation spectra indicate close contacts and help in identifying the structure. Different relaxation times are a significant tool for molecular chain motions in a certain frequency range. Most importantly 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 nuclei through space. On the one hand they reveal close contacts and distances between functional groups or individual atoms but on the other hand they are sensitive to motions of the whole molecule or certain functional groups. The latter yields information about segmental chain mobility and dynamics. Furthermore, dipolar

14 14 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie couplings are responsible for the process of spin-diffusion with which information about domain sizes in block copolymers or semi-crystalline polymers can be obtained. Functionalized Polymers Modern polymer materials contain highly functionalized polymers tailored for a certain application. Due to the trend to synthesize smaller objects down to nanoscale dimensions, the properties of polymers at interfaces is of increasing technological importance. Solid-state NMR is well suited to obtain information about details of interfaces including polymer interactions, domain sizes, and reduced mobilities. Three different types of functionalized materials are currently under investigation, i. e. grafted poly(dimethylsiloxane) (PDMS) on hydrophilic silica, nanocomposites from nylon-6 and montmorillonite clay and shape-memory polymer networks. Short-chain PDMS grafted onto hydrophilic silica consists of two components with largely different mobilities, a rigid interface close to the silica surface with constant size independent of the total PDMS chain length and a mobile part. Different experiments for measuring homo- and heteronuclear residual dipolar couplings show a bimodal behavior due to the two regions of the polymer. In a sample series with different total chain lengths the dynamic order parameter of both parts could be deduced. For the interface it is constant for all samples whereas for the mobile part the order parameter decreases with increasing total chain length. Temperature dependent measurements of 1 H double-quantum buildup curves show the crystallization of the chain parts in the interface at 220 K and indicate a phase transition of the mobile part at about 210 K. This study was performed by M. Wang. Polymer-clay nanocomposites exhibit extraordinary mechanical properties. A correlation between the macroscopic properties and the characterization of the microscopic structure and dynamics of nanocomposites made from montmorillonite clay and nylon-6 with solid-state NMR was investigated in the report of M. Wang. Among the different NMR characterization techniques, 13 C and 15 N spectra show the semi-crystalline nature of nylon-6. Furthermore, with increasing clay content the amount of g-crystalline phase increases which is a first indication for the improved stability. The characterization of the clay part with 29 Si and 27 Al spectroscopy also showed interesting changes between the pure clay and the nanocomposite.

15 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 15 Degradable polymers that change their macroscopic shape with a change in temperature are promising implant materials towards minimal-invasive surgery. Furthermore, these materials can also be used as drug-delivery systems. The polymers studied are amorphous polymer networks of lactide-glycolide copolymers. The cross-linking occurs via UV-irradiation of olefinic bonds at the end of the oligomers. Using 13 C CPMAS spectroscopy, the cross-link density can be monitored directly by the intensity of a signal at 44 ppm indicating the 13 C atom at the crosslinking point. This enables for a detailed investigation of the cross-linking kinetics which is superior to the indirect techniques like transverse relaxation measurements or residual dipolar couplings employed e. g. for sulphur cross-linked elastomers. The degradation of these polymer networks in an atmosphere simulating the conditions in a human body can give interesting results on the chemistry of degradation. See report by A. Buda. Elastomers An important class of materials is that of elastomers. Due to the high mobility highly resolved spectra can be obtained. This enables the investigation of the chemistry of cross-linking as well as the site-selective determination of segmental and local motions. These measurements can even be undertaken under non-spinning conditions thereby avoiding the influence of the centrifugal forces present under MAS and allow for an easy and variable experimental setup. Correlation of experimental data is performed with macroscopic properties, i. e. the cross-link density, which is the most important parameter for elastomers. Residual heteronuclear dipolar couplings and from that dynamic order parameters were obtained in a series of natural rubber (NR) samples with different amount of sulphur und vulcanization accelerator, therefore different cross-link density. Heteronuclear double quantum (HeDQ), spin-echo double resonance (SEDOR) and the MAS-analogue rotational-echo double resonance (REDOR) were employed to deduced the dynamic order parameter site-selective for each functional group of the monomer unit of NR. A linear correlation with the cross-link density was obtained but furthermore differences between the individual functional groups indicate the superimposed effect of local motions. These studies were performed by M. Wang.

16 16 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie A different approach aims at the determination of the self-diffusion anisotropy of small linear molecules like n-alkanes swollen inside compressed natural rubber samples. Results of pulsed gradient spin-echo (PGSE) measurements show an increasing selfdiffusion anisotropy with increasing compression of the sample due to the deformation of the free volume. These results offer the access to information about the polymer network structure and polymer-solvent interactions. See report by D. G. Rata. Another approach to investigate homonuclear residual dipolar couplings is the use of multiple quantum buildup curves. To compare the sensitivity gain in the determination of differences in cross-link density between different natural rubber samples double, triple and four quantum buildup curves were recorded. The higher quantum coherence shows an increase in sensitivity but suffers from lower signal-to-noise ratios. See report by R. Fechete.

17 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 17 Main Research Topic NMR Imaging and velocity imaging The development of new NMR imaging techniques under a wide range of aspects such as fundamental simulations, spectroscopy, parameter imaging, motion imaging, and engineering applications remained a centerpiece of the activities of MARC also in The very understanding of the interactions between the distribution of main and rf magnetic field on the one hand, and the object properties itself on the other hand, are the motivation of the project of M. Voda which has as its main goal the quantitative determination of concentration distributions in miscible liquid mixtures which will enable one to follow interdiffusion processes in real-time for the derivation of diffusion parameters in otherwise inaccessible systems. Another fundamental study which possesses similar prospects for a wide field of applications, is the development of spectroscopic imaging techniques using hyperpolarized xenon by K. Münnemann. The extreme dependence of the 129 Xe isotope spectrum on its environment allows one, for instance, to monitor phase transitions in a spatially resolved fashion such as the complicated process of the melting of ethanol/water mixtures. The surprising properties found for Xe-containing ethanol/water ice open new possibilities for routine applications of hyperpolarized xenon NMR in materials and medical research. A field of great relevance in Chemical Engineering is the understanding and on-line monitoring of the transport properties in liquid extraction devices. Drops and films are typical geometries which are used for this purpose, and both are investigated within different groups of the Collaborative Research Centre SFB 540, a joint effort with engineers and mathematicians at the RWTH Aachen to model and understand transport in multiphase systems. The formation of water drops, the onset of oscillations and vortex structures of drops falling in air following different starting conditions, and the dynamics of a liquid-in-liquid drop levitated in a particularly shaped nozzle are described in the report by A. Amar. Related problems are treated for the vertically falling film, but requiring different solutions due to the geometrical conditions

18 18 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie which are unsuitable for classic NMR imaging devices. The velocity distribution in falling films are discussed in the report by M. Küppers while K. Kupferschläger provides the design and construction of the complex apparatus which had to fit into the institute s super wide-bore vertical magnet and yet allows variable flow rates, heights and sonic excitation of the film. One further step towards applications has been taken by X. Ren who investigates not only the flow properties of a fixed-bed reactor consisting of real, metal-containing pellets, but also has looked into the microscopic aspects of the catalyst performance such as clogging and tortuosity reduction. More recent results include the different degrees of pore space turtuosity increase if residues are deposited with and without the presence of catalyzing metal, and the use of (relaxation and diffusion) parameter images for visualizing the strongly heterogeneous regeneration of large catalyst pellets under suboptimal temperature conditions. Concentration imaging, and indirectly also the influence of transport properties, are again the topics investigated by M. Krüger in a collaborative project with Dr. O. Dicoi. Drying of a wide range of porous media under controlled conditions of air temperature and moisture has been followed by fast, high-resolution imaging techniques, where in most cases the interpretation of the results was complicated by the presence of different liquid states, and required the use of single-point acquisition techniques to cope with the short relaxation times e.g. in some concrete samples.

19 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 19 Interdisciplinary Research Topic Material studies by NMR relaxation In contrast to large-scale motion which is usually interrogated by employing constant or pulsed magnetic field gradients, motion on the molecular level can be studied by exploiting the spectral information in combination with manipulating the state of the spin system with appropriate sequences of rf pulses or field changes. Molecular dynamics will always be reflected in the relaxation behavior of a sample, which is a consequence of interaction modulations by reorientations. Determining the relaxation properties of a substance in its native state and comparing it to those in the presence of additional boundary conditions of any kind thus gives useful information about the way how these conditions affect the motion of the molecules. Varying the experimental conditions by modifying characteristic time and frequency scales allows one to sample the spectrum of motional parameters over potentially wide ranges. Relaxation studies were performed on all spectrometers available in the MARC. Topics discussing molecular dynamics in solid materials are presented in the appropriate solid-state chapter. Relaxation times investigations predominantly employing single-sided NMR equipment can be found in the section dedicated to mobile NMR. Molecular reorientation at surfaces The existence of interfaces reduces the mobility of molecules indirectly by restricting its translation and rotational diffusion process; the molecular structure of the interface potentially contributes to this restriction by partially immobilizing the adsorbed molecule. The combined effect, under some circumstances strongly increased by the presence of paramagnetic centers or large internal field gradients, results in an increased relaxivity of the adsorbate. Because restrictive effects and interactions can be attributed a certain timescale, the relaxation behaviour is furthermore made frequency-dependent and can be probed by suitable techniques, such as field-cycling relaxometry or measurements at different constant fields but varying inter-pulse separations.

20 20 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Rocks and building materials are examples of porous structures which strongly affect the relaxation of imbibed liquids, predominantly through their high metal contents. Obtaining a distribution of relaxation times (T 1 as well as T 2) provides insight into the different relaxivities, pore size distributions, and wettabilities of the materials. The different magnitude of the effect on polar (water) and non-polar (oil) molecules allows to monitor of the fluid distribution in the pore space, even its spatial dependence if combined with NMR imaging techniques. Related studies are discussed in the report sby S. Sharma and Dr. S. Anferova. Of more fundamental interest is the behaviour of complex fluids in nanoporous media, where the high specific surface serves mainly as a way to provide a sufficiently large effect to make measurements of fluid amounts down to submonolayer coverage feasible. In a collaboration with J. Bharatam, IIT Hyderabad, the relaxation behaviour of adsorbed liquid crystalline molecules in the nanoscopic cylindrical cavities of Anopore membranes was investigated using field-cycling relaxometry and other techniques. Dispersion data can be interpreted in terms of ordering effects as a function of coverage, and a smoothening of the cross-over from isotropic to nematic states as observed in the bulk. Finally, an even more complex problem was approached where both pore size and surface interaction were changed simultaneously. This situation was investigated in the case of partially coked catalyst materials of nm-sized pores. With increasing amount of coke, both the pores shrink and the surface structure is affected, having different effects on polar and non-polar adsorbate liquids. The change of the dispersion behaviour has been monitored and interpreted in terms of a variation of the surface roughness; partial freezing changes the diffusion statistics of the remaining mobile molecules and gave further evidence of the properties of the fractal structure of the pore space. The studies are conducted by X. Ren, E. Talnishnikh, and S. Stapf. Segmental dynamics in chain molecules under external constraints If chainlike molecules are regarded in contrast to small molecules, the coupling between the individual repeat units already represents a restriction to motion. In the case of concentrated solutions or melts, intermolecular interactions lead to a further

21 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 21 slowing down of the molecular motion. Polymer melts can be described by certain motional regimes depending on the time and length scales involved, and field cycling relaxometry has been applied to probe these motions over several orders of magnitude in frequency. However, polymer mobility can further be reduced by geometrical or chemical restrictions. Permanent cross-links, as are found in networks and elastomers, were found to slow down the motional spectrum in natural rubber, while filler particles show a negligible effect. Deformation of the network could be proven to lead to a change in the frequency dispersion of the NMR relaxation times, while swelling at even small concentrations of solvents could be demonstrated to increase the mobility of the chains considerably. Swollen networks were compared to concentrated solutions with respect to relaxation dispersion and dipolar coupling constants. Selective labeling of the polymers facilitates the interpretation of the results, allowing a direct comparison of inter- and intramolecular contributions to the relaxation rate. Microstructural modifications, e.g. by connecting polymer chains of one kind with blocks of a more rigid component via copolymerization, were proven not only to reduce the mobility of the attached chains but also to alter the motional spectrum altogether. Finally, a systematic study of series of natural rubber and EPDM samples experiencing various combinations of curing times, sulfur content, and addition of an internal plasticizer was conducted, combining a wide range of different NMR characterization techniques. These studies were conducted as a collaborative research project with Dr. A.R.R. Menon, IIT Trivandrum, India. See report by S. Kariyo

22 22 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Fluid dynamics of falling and levitated drops Dipl. Phys. Andrea Amar (Doctoral student) Supported by Sonderforschungsbereich 540 (DFG) The potential of pulsed field gradient (PFG) NMR for the investigation of flow processes has been demonstrated by applications to fluid motion in different geometries such as flow through packed beds, natural rocks, or vertical film flow (see other reports). One particular case, which addresses both problems of technical and engineering relevance such as encountered in evaporators and condensers, is given by the fluid dynamics inside a liquid drop in different environments. Experiments on the oscillation and internal vortex patterns of free falling drops and levitated drops were done. In this last study, silicon oil drops were generated at the bottom of a glass tube filled with D 2O with a special pipette that guarantees the reproducibility of the experiment and also allows to control drop size. When the drop rises to the middle of the NMR resonator, it is stopped in the counter streaming continuous phase. Velocity patterns in this free scheme were studied. 1D, 2D, 3D NMR images and flow measurements were performed and the velocity distributions analysed. Figure 1 shows a 3D image of a levitated silicon oil drop. Falling water drops have been an important field of study in this group for a number years [1]. In these experiments the drop is caught in a non-equilibrium state where a balance between gravity and friction has not yet been reached, leading to a continuous acceleration of the drop, while at the same time, oscillations brought about by Fig. 1: 3D Image of a 3 mm diameter the separation from the tip of the originating silicon levitated drop. pipette have not been damped. Moreover, the internal motion of the drop was found to be very sensitive to the conditions of this separation process, affecting both the shape and the deformation dynamics of the drop. For this reason, the formation process of water drops is an interesting topic and has been studied by fast one- and two-dimensional NMR imaging techniques. Figure 2

23 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 23 shows a series of 2D images of a pure water drop during the formation process, which will be followed by flow measurements of the motion within the drop. Fig. 2: Series of fast 2D spin density images of a pure water drop during its formation at the bottom of a glass pipette (shown in the first image). The entire formation process lasts 50 s. [1] S. Han, S. Stapf, B. Blümich, Phys. Rev. Lett. 87, /1-4 (2001).

24 24 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Construction and features of a newly designed PC NMR spectrometer Dipl.-Ing. Michael Adams, Prof. Dr. Vladimir Anferov Electronic staff at MARC and ITMC Inside-out NMR denotes the type of NMR where the probe sits inside the sample and not the sample inside the spectrometer. A natural extension of inside-out NMR is its applications to the analysis of materials and to process and product control. For those measurements a new small mobile NMR spectrometer with a frequency range from 15 MHz to 25 MHz and suitable software were designed. Two major parts of the spectrometer hardware are inside a normal PC. A PulseBlasterDDS TM ISA-Bus card controls rf-frequency, phase, pulse length and shape. The second PC card is a dual-channel PCI-416F data acquisition card. Analogto-digital conversion is achieved by two independent converters with a maximum sampling rate of 2 MHz per channel. All other parts of the new spectrometer (Fig. 1), except the NMR sensor e.g. NMR-MOUSE, were developed in our RF lab and placed inside an external industrial housing. Fig.2: Program options Fig. 1: The external parts of the spectrometer The basic spectrometer components and possible program options of the software to operate the spectrometer are shown in Fig.2. The main program offers 7 subprograms. The Tune-, Wobble-, Echo-, and Optimal Pulse programs are utility programs to match and tune the NMR sensor to the desired measuring frequency and for parameter optimization. As an example for parameter optimization a screen dump of the ECHO program is shown in Fig. 3. Two pulse programs for measuring material

25 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 25 properties are implemented in the main spectrometer software. The pulse sequence of the Decay program uses phase cycling to decrease the effective dead time of the spectrometer. By incrementing the echo time the decay of the echo amplitude is measured as function of time (Fig.4). The transverse relaxation time T 2 is automatically determined with the build in fit functions. The CPMG program allows fast determination and comparison of soft material properties. No increment of the echo time is needed. The measured decay as a function of time provides an effective relaxation time T 2eff which is essentially a mixture of T 1 and T 2 (Fig. 5). Fig. 3: Screen dump of a detect echo sequence Fig. 4: Screen dump of a decay measurement Such of a small, mobile, and inexpensive NMR spectrometer is useful for rapid product quality analysis as well as the identification of material faults, changes, and defects. Fig. 5: Screen dump of a CPMG measurement

26 26 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Feasibility study of a mobile NMR scanner for porosity and permeability measurements on deep-sea ocean drilling core samples Dr. Sofia Anferova (Visiting scientist) supported by Deutsche Forschungsgemeinschaft DFG in collaboration with Prof. C. Clauser (Institute for Applied Geophysics) Information on rock porosity and permeability is crucial for understanding mass and heat transfer processes of the sub-sea ocean floor and of larger scale solid earth formations. At present, only rock porosity is measured routinely using two different methods with their respective advantages and disadvantages. We have shown that the NMR-MOUSE Ò could be successfully used for porosity measurements of water saturated, drilled core sections and water content in building materials. In water saturated samples, the number of spins in the fluid normalized to the sensitive volume of the NMR-MOUSE is proportional to the sample porosity. Because the sensitive volume of the NMR-MOUSE is well defined, absolute values of porosity can therefore readily be determined from unilateral NMR-MOUSE measurements. We adapt current NMR processing techniques to develop new measurement routines and to evaluate the precision and accuracy of this method. The main advantage of the NMR scanner compared to conventional methods is its small size and weight, which is particularly attractive for the shipboard use and on any drilling platform. Whereas conventional NMR employs homogeneous magnetic fields, the NMR-MOUSE Ò employs highly inhomogeneous magnetic fields with a gradient of about 20 T/m. A feasibility study of a mobile NMR scanner for measurements of pore size distributions in rocks showed some limits: The signal-to-noise ratio of the NMR-MOUSE is not good enough for investigation of the rocks with porosities less than 5 %, The diffusion of the water molecules in the large gradient of the external magnetic field shortens the transverse relaxation times in the big pores, and only pore sizes less than 1 µm can be detected reliably with this device. Ò NMR-MOUSE (Nuclear Magnetic Resonance Mobile Universal Surface Explorer) is registered trademark of RWTH Aachen University

27 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 27 It is advisable to employ more homogeneous magnetic fields while maintaining the mobility of the sensor. A magnet design of interest for measurement of pore size distributions directly from transverse relaxation decays, which is suitable also for analysis of large pores, is the Halbach magnet. The device is mobile, light-weight (< 3 kg) and a gradient of the magnetic field is less than 0.3 T/m. The sensitive volume of the device is 100 times lager than that of the NMR-MOUSE. An example of experimental distributions of T 2eff, which is proportional to the pore size in homogeneous field, is given in Fig. 1 for the NMR-MOUSE and a mobile Halbach magnet. The data for the water saturated limestone sample show that the relaxation time distribution is wider for long T 2eff values when measured with the Halbach magnet than when measured with the NMR-MOUSE at the same echo time. For the Halbach magnet the values of T 2eff are no longer shortened by the diffusion of water molecules, and the new mobile device can indeed be used for measurements of pore size distributions in sediment samples. Fig.1 T 2eff distributions a sediment sample obtained with the mobile Halbach system and with the NMR-MOUSE

28 28 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Solid State NMR of Advanced Polymer Materials M. Sc. Alina Buda supported by Deutsche Forschungsgemeinschaft DFG Biodegradable implants of oligo [(L-lactide)-ran-glycolide]: degradation studies in vitro (in collaboration with Prof. Dr. A. Lendlein) Biodegradable polymers are an important class of synthetic biomaterials that are widely used in temporary therapeutic applications such as wound closure, tissue regeneration and drug delivery. Among the bioabsorbable polymers developed thus far, polyglycolide, poly(lactide), and their copolymers constitute promising materials for use in the field of surgery and pharmaceutics. By hydrolysis of esterbonds these materials degrade to harmless products and therefore obviate the need for another transection. The degradation of polymers is a complex chemical process that occurs under the influence of heat, oxygen, mechanical stress or in our case the swelling and hydrolysis in water, and results in a time-dependent change in their chemical and physical properties. To acquire a better understanding of the mechanisms responsible for changes in physical properties associated with hydrolitical degradation, which would ultimately permit the design of polymers with among other properties - biodegradation rates suitable for a given application, we have carried out solid-state NMR studies of amorphous copolymers of L,L-dilactide and diglycolide with different molecular weight and monomer ratio. The samples were kept in a phosphate buffer solution with ph 7 in a water bath at 37 0 C. Changes in structure and dynamics of the samples were monitored at regular time intervals where the samples were removed from the buffer and dried prior to NMR measurements. Different NMR techniques sensitive to changes in the structure and chain mobility like 1 H and 13 C spectra, T 1H and 2D-WISE were selected. The results indicate that the degradation progresses in different stages. First, the samples swell due to water uptake. This effect is directly reflected in an increase in chain mobility. In the second stage, chemical reactions occur such as hydrolysis of ester groups and cleavage of more mobile chains that are then released into solution. These effects can be seen in Figure 1 where changes in the intensity of peaks corresponding to different functional groups are seen at a later stage in the degradation process. Furthermore, investigations of different samples indicate that the degradation rate is faster for samples with longer chain length.

29 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 29 Figure 1. The effect of the degradation process on copolymers of lactide and glycolide as reflected in the changes in the 13 C intensities corresponding to different functional groups. An insight into the morphology of Nylon-6 fibres (in collaboration with Dr. V. M. Litvinov and Dr. J. P. Penning, DSM) Polyamide (PA) is the most commonly used engineering thermoplastic today. It is suitable for all major processing techniques, such as injection moulding, blow moulding and extrusion. Nylon-6 (PA6) is one of the most important synthetic fiberforming material used for high-speed melt spinning. These fibres have a morphology consisting of a complex distribution of crystalline and amorphous domains (see Figure 2). This distribution and the corresponding domain sizes are directly related to the macroscopic properties of the fibres. A correlation of these parameters with the processing conditions is needed for the production of fibres with properties taylored for a given application. Figure 2. Model morphology of Nylon-6 fibres proposed based on NMR spin-diffusion and SAXS data. The distance between the fibrils is D. The fibrils are separated within the aggregate by less-mobile amorphous domains. Along the fibrils crystalline/lessmobile amorphous domains are stacked and form lamellae. An NMR spin-diffusion approach to clarify complex morphologies of semicrystalline polymer systems was introduced and applied to Nylon-6 fibers. This new approach uses a combination of MAPE (MAgic and Polarization Echo) and double-quantum dipolar filters that select mobile and rigid domains of the

30 30 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie heterogeneous sample in separate experiments. In combination with one- and multidimensional analytical solutions of the spin-diffusion equation adapted to a specific morphology, domain sizes of both mobile and rigid phases can be estimated. The particular setup of the spin-diffusion experiment in which the source of magnetization is selected based on a MAPE dipolar filter in the mobile amorphous domains allows us to explore only some aspects of the complex morphology of the Nylon-6 fibers. The obtained results give information about the mobile amorphous regions in terms of size and distribution, but only global information about the aggregates of fibrils even if they have a well defined structure as shown by SAXS measurements. Inside an aggregate the less-mobile amorphous domains separate the fibrils while the fibrils have a lamellar structure with alternating crystalline and lessmobile amorphous domains. A more detailed picture is obtained by using a doublequantum filter which selects the initial magnetization in the crystalline regions. Based on this type of spin-diffusion experiment an evaluation of the domain sizes of the crystalline and less-mobile amorphous regions along and perpendicular to the direction of the fibrils can be performed. The estimated sizes for samples produced with different winding speeds and draw ratios depend on the processing conditions. They are in good agreement with WAXD and SAXS data.

31 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 31 Velocity distributions remotely measured with a single-sided sensor Dr. Federico Casanova (staff scientist) supported by Deutsche Forschungsgemeinschaft DFG Pulsed-Field-Gradient (PFG) NMR has proved to be a powerful tool to characterize molecular motion in a non-invasive fashion [1]. It has been widely used in biology, medicine, and material science offering for example, the possibility to measure vascular flow in steams and petioles, as well as vascular blood flow at various stages in the cardiac cycle. Also numerous applications in porous media such as natural sandstone have made it possible to elucidate models that describe the transport of fluids within the porous structure. A large family of PFG sequences has been developed for different applications, but they have been always implemented and tested in the homogeneous field of conventional magnets. These magnets offer limited volume for housing the flow setup restricting the application field of this technique. During the last years increasing interest has been observed in developing open sensors for ex situ experiments [2]. The extreme versatility of this type of devices gives access to NMR of a large number of applications hindered to the conventional closed magnet geometry. In this work the so-called 13-interval PFG stimulated spin-echo (SSE) sequence proposed by Cotts [3] was implement on a single-sided sensor to encode displacement along the pulsed gradient direction. A suitable phase cycling scheme is proposed to remove the distortions introduced by the off-resonance excitation, and it is shown that the sequence effectively reduces the signal attenuation due to diffusion under the strong static gradient of the unilateral magnet. To improve the signal-tonoise ratio a novel multi-echo acquisition scheme was implemented. By adding the echos of an echo train a reduction in the experimental time up to two orders of magnitude was achieved. The experiments were performed on a single-sided sensor equipped with an optimized U-shaped magnet that provides a uniform gradient along the depth direction optimized for slice selection, and with a suitable gradient coil system suitable to apply pulsed gradients along the two lateral dimensions. To show how the velocity distribution inside a selected slice is encoded by this method, two different pipe geometries with different velocity profiles were investigated.

32 32 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie The method was combined with the depth selection obtained by retuning the probe frequency to provide velocity profiles spatially resolved along the depth direction. Figure 1a shows a rectangular pipe 30 cm long, 3 mm high, and 30 mm wide. The velocity profile inside this tube change as a quadratic function of z being zero at the walls and maximum at z = 0. The complete pipe was scanned selecting 10 slices 0.3 mm thick. Figure 1b shows five profiles from the wall to the center of the pipe. It can be clearly observed how the velocity distribution increases in thickness reflecting the velocity shear is larger near to the walls. Figure 1c shows the complete velocity profile where the quadratic behaviour as a function of z can be clearly observed. The same experiment was repeated but scanning a cylindrical pipe (Fig. 1d). In this case the velocity distribution inside each plane goes from zero to a v max that depends on z 2, being maximum in the center of the pipe. Figure 1e shows the profiles of the first five slices together with the result of the addition of all of them, which approach the theoretical constant velocity probability characteristic of a cylindrical pipe. The complete velocity distribution is shown in Fig. 1f. a) b) Depth [mm] c) mm Intensity [a.u.] velocity [mm/s] Velocity [mm/s] d) e) 3 mm intensity [a.u.] Depth [mm] 3 f) velocity [mms] 0 10 Velocity [mm/s] Fig. 3: Velocity distribution of a rectangular a-b-c) and circular pipe d-e-f) spatially resolved along the depth direction by selecting different slices across the tubes. The velocity distribution inside each selected slice was obtained in an experimental time of about 3 minutes. The velocity resolution of these experiments is 1.5 mm/s.

33 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 33 Enhanced sensitivity to residual dipolar couplings on elastomers by high-order multiple-quantum NMR Radu Fechete, M.Sc. supported by Deutsche Forschungsgemeinschaft DFG The homonuclear and heteronuclear residual dipolar couplings in elastomers reflect changes in the cross-link density, temperature, the uniaxial and biaxial extension or compression, as well as the presence of penetrant molecules. The difficulties related to these measurements are due to the small values of the residual spin couplings compared to those of other spin interactions, the many-body character of the dipolar couplings, and the presence of molecular motions which produce a supplementary encoding of the spin system response. An enhanced sensitivity to the changes in the values of residual dipolar couplings by measurements of the higher-order multiplequantum coherences for static samples with a complex 1 H dipolar coupling network like elastomers was demonstrated. For a quadrupolar nucleus with spin I = 2 the sensitivity enhancements were simulated by considering four-quantum, triple-quantum, and double-quantum buildup curves. The increases in sensitivity for higher-order multiple quantum coherences (Fig. 1) were verified by measurements of buildup curves of 1 H DQ, TQ, and four-quantum (FQ) filtered signals of differently crosslinked natural rubber samples (Fig. 2). The MQ excitation pulse programs were written in a way to produce 2p (with p the order of highest coherence) separate data files Fig. 1 Sensitivity parameter (S NR7(t)-S NR1(t))/S NR1(t) as a each corresponding to one function of t in the initial region of the DQ, TQ and FQ buildup curves evaluated from the measured MQ buildup curves of Fig. 2. The values were normalized to the sensitivity parameter of the DQ coherences taken at the shortest t.

34 34 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie step in the phase cycle. These files were suitably processed so a) that the signals of various orders of MQ coherences were obtained. A sensitivity parameter of the residual dipolar couplings can be defined by the ratio (S NR7(t)-S NR1(t))/S NR1(t). This b) ratio can be evaluated from the MQ buildup curves of Fig. 2 and depends on the MQ excitation / reconversion parameter t. The sensitivity parameters evaluated from the DQ, TQ and FQ buildup curves of Fig. 2 are c) shown in Fig. 1 as a function of t for the initial region of the buildup curves. The measurement of higher-order coherences proves to be a method to enhance the sensitivity of the spin system response to changes in dipolar Fig. 2 Experimental 1 H DQ (a), TQ (b), and FQ (c) buildup curves for the samples NR1, NR4, and NR7 which and quadrupolar couplings. The differ in their cross link density, with NR7 having the possibility to excite 1 H higherorder coherences in elastomers largest value in cross-link density. The MQ signals are normalized to the integral intensity of the 1 H singlequantum spectrum. is due to the existence of the multi-spin dipolar network extended mainly along the polymer chain. In selecting the appropriate order of MQ coherences a trade-off between the gain in sensitivity and the reduction in the signal to-noise ratio with the increase in the order of the MQ coherences has to be taken into account for each particular polymer.

35 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 35 NMR Relaxation Dispersion of Elastomers under Uniaxial Deformation and Swelling Sobiroh Kariyo (Ph.D. Student) supported by Deutsche Forschungsgemeinschaft DFG The molecular dynamics of polymer melts with molecular weights above the critical value have successfully been described by a power law dependence of the spin-lattice relaxation time on the Larmor frequency. This so-called relaxation dispersion is explained, for instance, by the Doi/Edwards limits of the time dependence of the mean square displacement of a chain segment. Four different regimes of power laws describing the relaxation dispersion of polymers are distinguished and have been observed experimentally for several different polymer types. In the case of natural rubber (NR), the observed relaxation dispersions at low field, which can be described as a region of semi-local motion according to those power laws, were shown to have the same value of the exponent as observed for linear polyisoprene with high molecular weight; T 1 µ n g with g» 0.16 at low field and g» 1.20 at hight field. However, the values of the exponent at low field was smaller than that for the tube model as described in the literature. a) 10-1 b) 10-1 T 1 [s] K l = 1 l ~ 4 B 0 l ~ 4 ^ B 0 l ~ 7 ^ B n /MHz T 1 [s] K l = 1 l ~ 0.3 B n /MHz Figure 1. The relaxation dispersion curves under uniaxial deformation with elongation ratios of a) l > 1 and b) l <1 of NR samples with 1 phr of sulfur/accelerator contents. In this study, the influence of swelling and deformation on the relaxation dispersion of the same NR samples were investigated using a field cycling relaxometer which provided measurements in a frequency range from 5 khz to 20

36 36 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie MHz. At the same time, the results were also compared to T 1, T 2, and double quantum measurements at high field. The relaxation dispersion curves under uniaxial deformation with elongation ratios of l > 1 (stretching) and l < 1 (compression) of NR samples were obtained. The stretching axes were set to be either parallel or perpendicular to the magnetic field B 0 while the compression axis was only parallel to B 0. At high field, the relaxation times remained unchanged while they were reduced at low field. The exponents were found to increase gradually up to the maximum observed value g» 0.24 under the maximum stretching ratio l» 7 of this measurement (Fig. 1). The influence of different degrees of swelling, which were controlled by a mixture of two solvents, on the relaxation dispersion of three NR samples with different cross-link density was observed and compared to equivalent solutions of polyisoprene. At low field, the relaxation times were increasing with increasing degree of swelling. A transition from a power-law behavior to Rouse dynamics was observed for swollen and dissolved samples (Fig. 2) K a) b) K T 1 [s] NR samples with 1 phr of sulfur/accelerator contents n [MHz] weight percentage of solvent [%] T 1 [s] Linear Polyisoprene M w 735,000 in solution (Toluene) n [MHz] weight percentage of solvent [%] Figure 2. The relaxation dispersion curves of a) NR swollen samples and b) solutions of linear polyisoprene samples. Further investigations employing field cycling relaxometry focused on fully and partially deuterated polyisoprene samples. Moreover, these techniques were also applied to some other types of polymers, such as diblock and triblock copolymers of polybutadiene (PB) and polystyrene (PS), PB rubber, grafted polydimethylsiloxane (PDMS), silicone rubber, etc..

37 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 37 On-line monitoring with the NMR-MOUSE Dipl.-Chem. Kai Kremer (Ph.D. student) Tire Fabrication A particular application of the NMR-MOUSE is measuring rubber test samples of a rubber process analyzer (RPA) in order to obtain reference NMR parameters for nondestructive product and quality control. Usually the formulation of a technical rubber product is tested on a rheometer, where a test sample is vulcanized, undergoing small oscillatory shear deformation. During curing, the torque increases to a maximum and may decrease on further curing following reversion of the crosslinking reaction. From the theory of rubber elasticity, it is known that the torque at small deformation is a direct measure of the crosslink density. NMR relaxation measurements have turned out to be extremely useful for quality control of elastomer products in connection with a database of reference values for different formulations and curing parameters. In this project we followed the complete production process of a tire to investigate dispersions of CPMG fit parameters for the raw polymer, all intermediate products, steps and before and after the vulcanisation of a tire. Fig. 1: The NMR-MOUSE is testing a tire. We made non-invasive on-line measurements of T 2 with the NMR-MOUSE at all steps of the production and compared the data with those of standard RPA and MDR rheometer tests. The skillful use of the NMR-MOUSE can help to replace some of the expensive tests on the racetrack by measurements in the laboratory. Diagnostics of polymer isolators Due to mechanical, thermal and electrical stress non-reversible damages of the morphological texture can occur in polymeric materials used in cable systems (mainly

38 38 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie polyethylene and silicone rubber). Such damage may be inizialized by gas-filled microvoids and local inhomogenities of the cross-link-density. For state assessment and life time prediction, effective diagnostic methods are currently required, which should be nondestructive. Investigations carried out so far have shown that Ultrasound and Nuclear Magnetic Resonance (NMR) meet these requirements. Ultrasound testing rest on the observation of the soundpropagation in materials. NMR is based on the recording of spindependent relaxation processes and its characteristics. Both diagnostic methods are wellknown in materials science, whereas their use for monitoring insulation material of cable Fig. 2: Cable joints of silicon rubber systems has to be further developed. The current investigations focus on the detection, localization and characterization of defects. The analysis regarding the influence of mechanical stress which arises in the expansion of joints shows a non-reversibility of this impact. Further investigations have shown, that ageing phenomena can be followed.

39 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 39 Moisture measurements of porous media Dipl. Chem. Mirko Krüger (PhD) Methods that provide moisture distribution are of great interest for monitoring the processing of products which need to be dried. Currently the product quality is directly related to the moisture distribution as the product leaves the dryer. The product moisture is measured either by taking some samples out of the current charge or by online monitoring. But once the product is out of the dryer, it is too late to take corrective action on the drying process. To solve this problem, sensors are needed to measure the moisture in different places inside the dryer, so that adjustments can be made before the product exits the dryer. The NMR-MOUSE is one solution for this problem, because the measured signal is proportional to the content of 1 H nuclei e.g. those of water. But before using NMR-MOUSE as a sensor it is necessary to study the drying process in the laboratory at conditions comparable to those in the factory. Several different experiments and measurements can be performed to obtain information about the spatial distribution of the moisture content in different samples, the drying curves, the mass transport coefficients, the porous structure of solids in connection with water content, the hygroscopic behavior, the water migration and the sensitivity of the NMR-measurements. The main goal of the current work is to investigate the drying process for different geometries. Therefore the experimental devices are continuously optimized. Figure 1 shows the plot of the drying curves of a wet concrete sample. The length and diameter are 17 mm and 10 mm respectively and the sample is dried with a steam of warm air. Also the sample is fitted in a cylinder with both ends open and the air steam passing he sample.

40 40 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Figure 1: Drying curves of a wet concrete sample with warm air The drying curves in Figure 1 reveal, that the water is drawn towards the open ends where the air stream passes due to the capillary effect. The intensity decreases continuously with time until it reaches a minimum, where the sample is completely dry. Some more experiments like the one shown in Figure 1 have been made with different geometries and different samples.

41 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 41 Construction of a falling film device Klaus Kupferschläger In one of the projects of the collaborative research center 540 at RWTH Aachen falling fluid films are investigated by NMR (see report by Markus Küppers). The research results of the last year showed that the device should be optimized with respect to: manageability of the device when setting up experiments flexibility of the device with respect to position and thickness of the film geometry of the plate on which the film is running down possibility of excitation of the fluid with a speaker possibility to perform a reaction between a gas and the fluid Manageability, free choice of position, and excitation of the fluid could be optimized by splitting the device into two parts. One part, called the upper reservoir, is now mounted on a rack fixed to the magnet (Fig. 1). The second part consists of the lower reservoir and the encapsulated film plate. The upper reservoir is placed in a region where the magnetic field of the tomograph is already reduced. This considerably improves the excitation characteristics of the speaker. Because of the separation of the device into two parts only a lightweight pipe needs to be inserted into the magnet. The pipe can be shifted within the magnet to choose different positions for the measurements. A major improvement in the part of the encapsulated film plate of is a new construction for initiation of the film (Fig. 2). The film bearing plate is now designed without sidewalls and fixed in the device at the upper end so that it hangs freely. Due to this construction feature the film flows on the front side of the plate and distributed homogeneously over the full width of the plate. An easily accessible aluminum blade allows to select the film thickness very precisely at the point of initiation.

42 42 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Fig. 1: Photo of the newly constructed falling film device. Mounted on the top of the rack the so called upper reservoir. On the left hand side of this reservoir is a shielded box containing the speaker. In about the middle of the rack there is a rig to store the encapsulated film plate while not in use for measurements. Both parts of the device are linked by two tubes, one for fluid flow and the other one for air exhaustion. Fig. 2: Upper end of the film plate. This part constitutes the top end of the lower reservoir. With the blade made from aluminium one can set the thickness of the film at its beginning. The features of this design force the film to run down on the front side of the plate.

43 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 43 Flow research of a falling film Dipl.-Chem. Markus Küppers supported by SFB 540 The extraction of components from a liquid or gas system is most commonly achieved in packed columns. In this work, which is a part of the collaborative research center 540 at RWTH Aachen, the aim is to investigate such an extraction reaction with a number of different techniques. For most of these techniques a packed column is not accessible. Fortunately one can convert the results obtained for falling films to account for those packed columns system. This conversion, other measurement techniques like LDA, PIV, and the simultaneous detection of fluorescence and phosphorescence are performed by several engineering departments of the RWTH Aachen. The research of the last year revealed some imperfections of the device used up to this time. For that reason a new device was constructed (see report by Klaus Kupferschläger). One of the major improvements was the construction of a film plate without side walls. Due to this change in construction there is now a much better steady flow of silicone oil on the plate (Fig. 1). Another, more methodic, change has been applied with using a newly designed pulse sequence. The used pulse program was improved to acquire 2D velocity data employing two orthogonal slice selection pulses to reduce the dimensionality of the measurement scheme by selecting a small volume element of the film. 1D velocity imaging was used to spatially resolve the depth direction of the film and the velocity component in the direction of gravity (Fig. 2). Also first researches with acoustic excitation have been performed. These measurements confirmed the success of another construction change. The speaker used for excitation was installed in an area of considerably lower B 0 field strength. Due to this improvement it was possible to acquire velocity encoded data with acoustic excitation and associated trigger. Other scans have been performed to detect all frequencies of the waves present in the silicone film with a given external excitation (Fig. 3).

44 44 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Fig. 1: Gradient echo image of a vertical cross-section through the falling film plate. The film flowing on the left hand side. A small amount of fluid is detected on the right hand side. Fig. 2: Velocity map of the falling silicone film acquired with the new pulse sequence. The horizontal axis is the space axis through the film thickness. The vertical axis denotes the velocity component in the direction of gravity intensity [a.u.] f [Hz] Fig. 3: Map showing the frequencies occurring in a free falling silicone oil film under condition of an external acoustic excitation of 10 Hz.

45 45 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Time resolved spectroscopic NMR imaging using hyperpolarized Xe Dipl.-Chem. Kerstin Münnemann (Doctoral student) In collaboration with the research centre Jülich NMR of Xe is known as a very sensitive method for monitoring chemical and structural environments. Due to the low signal-to-noise ratio of NMR from Xe in thermodynamic equilibrium the acquisition of a single NMR spectrum in materials is usually very time consuming, taking 10 min up to tens of hours. NMR with hyperpolarized Xe has overcome this problem and therefore the number of applications in material sciences and medicine has increased significantly in the last years. The large nuclear magnetization of hyperpolarized Xe allows the repetitive application of excitation pulses with very small flip angles consuming slowly the non-equilibrium magnetization and therefore eliminates the need of T 1 waiting periods between successive measurements. This makes time resolved Xe spectroscopy and imaging viable. We have visualized the melting and dissolution process of xenon ice into different solvents using the methods of nuclear magnetic resonance spectroscopy, imaging, and time resolved spectroscopic imaging (Fig. 1) by means of hyperpolarized 129 Xe. Starting from the initial condition of a hyperpolarized Xe ice layer frozen on top of an ethanol (ethanol/water) ice block we measured the Xe phase transitions as a function of time and temperature. In the pure ethanol sample pieces of Xe ice first fall through the supercooled viscous ethanol phase on to the bottom of the sample tube and then form a thin layer of liquid Xe/ethanol. The Xe polarization in this liquid layer is trapped over a time period of 11 min and exists up to room temperature. In the ethanol/water mixture (80vol%/20%) most of the polarized Xe liquid first stays on the top of the ethanol\water ice block, then starts to penetrate into the pores and cracks in the ethanol/water ice block. In the final stage, nearly all the Xe polarization is in the gas phase above the liquid and trapped inside the pores. NMR spectra of homogenous samples of pure ethanol containing thermally polarized Xe and the spectroscopic images of the melting process show that very high concentrations of hyperpolarized Xe can be stored or delivered in pure ethanol.

46 46 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Fig.1: One dimensional spectroscopic images of hyperpolarized Xe frozen on ethanol ice (left side) and on 80 vol% ethanol/water ice versus time. The localized spectra give information about all the phase transitions of Xe occuring during the melting and dissolution processes.

47 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 47 3D imaging with an open NMR tomograph Juan Perlo (PhD Student) supported by Deutsche Forschungsgemeinschaft DFG The application range of unilateral NMR has expanded considerably during the last years. The use of single-sided probes is not limited by the object size making NMR a truly non-invasive method suitable for near surface studies of arbitrarily large objects. To assess the degree of heterogeneity of samples, imaging methods are required. In the last years special efforts were made to develop new imaging techniques to be used in the presence of the strongly inhomogeneous magnetic fields generated by open magnet geometries and the stray field of superconducting magnets. Recently, two-dimensional images have been obtained by implementing a single-point imaging method on a NMR-MOUSE, but the principal limitation of the method for 3D imaging was the long experimental time. The particular imaging method acquires the single Hahn echo for each point in k space. Although in many cases further echoes can be generated using a CPMG-like sequence, the use of them for signal improvement in imaging experiments was initially hindered because the space encoding could not be preserved in all echos. During this project a new fast imaging method has been developed and depending on the sample it reduces the experimental time by up to two orders of magnitude. Combining this method with the slice selection provided by the static field gradient, 3D images have been obtained. The imaging method was first applied in rubber product analysis to determine the position of fibbers inside an air spring bellows used in modern car suspension systems. Figure 1 Figure 1. Slice-selective images of the shows a car equipped with these air crossed fibers inside an air spring springs, a schematic drawing showing bellows. The images obtained with the open tomograph have a spatial two crossed fiber layers in the rubber resolution of (0.2 mm) 2.. shell, and the measured slice-selective

48 48 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie images of each layer. The 1 mm diameter fibers can clearly be observed and the slices are well separated although only 1 mm apart. Another important target of this project is to use the open tomograph to image biological tissues. The new fast imaging sequence was used to image different sections of a human finger (Fig. 2.) The spatial resolution of each cross-section is (1 mm) 2 obtained in an experimental time of 9 minutes. In the images the dimension and shape of the bone can be identified as well as the positions of vessels, arteries, and the tendon. It shows that sensors with optimized portable geometries can be used for medical diagnostics of extremities like hands and feet without Figure 2. First images through a finger tip the necessity to use an expensive obtained with the unilateral imager at whole. different positions. The important innovation is the demonstration that generating multiple echoes and co-adding them achieves a dramatic reduction in measurement time. Previously only the feasibility of obtaining 3D images from a stack of multiple slice selective images has been shown but the acquisition times were prohibitive. It is anticipated, that the new unilateral imaging sensor will find applications in non-destructive quality control and product failure analysis, where it can be employed similar to a magnifying glass which is capable of looking inside a large object at a selected spot.

49 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 49 Enhanced Self-Diffusion Anisotropy of Linear Molecules in Compressed Elastomers Dipl.-Phys. Doru Gabriel Rata supported by Deutsche Forschungsgemeinschaft DFG Molecular self-diffusion provides important information about molecular structures and interactions in many polymer systems. The phenomenon of anomalous diffusion is of great interest in fundamental and applied research. The deviation from ordinary diffusion due to the presence of internal boundaries in polymer solution, melts, and solid samples has been investigated. These results can be used to obtain important information about the polymer network structure. In particular, for rubber elasticity the mechanism of deformation and orientation of network chains can be investigated by measuring the self-diffusion of small penetrant molecules. The purpose of this work is to show the existence of diffusion anisotropy of a series of alkane molecules in a compressed polymer network. In this investigation the pulsed gradient spin echo (PGSE) method has been used. For this purpose we have used different alkanes, like n-hexane, n-heptane, n-octane and n-decane swollen in natural rubber samples (NR1, NR4 and NR7) with different cross-link densities (with NR7 having the highest cross-link density). The isothermal absorption of alkanes as a function of time for the different types of rubber is shown in Fig. 1) a) b)

50 50 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie c) Fig.1: Mol percentage of hexane, heptane, octane, and decane uptake of NR (natural rubber) with different cross-link densities. The results of absorption experiments are expressed as moles Q t of liquid absorbed by 100 g of NR. An enhanced anisotropy was detected relative to the small penetrating molecule of toluene for the different alkane solvents in the rubber samples with different cross-link densities. This mainly reflects the deformation of the free volume in the rubber under compression. The size of the anisotropy increases with increasing cross-link density and compression ratio. Figure 2 depicts the evolution of the diffusion with progressive compression. The diffusion coefficients have been measured for the maximum concentration of solvent in the polymer. In conclusion, by using a linear solvent molecule like n- alkanes instead of cyclic, aromatic ring molecule like toluene we observe an enhancement of the self-diffusion anisotropy, in case of a compressed Fig. 2: Anisotropy of the selfdiffusion coefficient as a polymer network. function of the compression ratio in decane where λ is the compression ratio.

51 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 51 Effects of coke deposition upon pore structure and self-diffusion in an Al 2 O 3 catalyst Dr. Xiaohong Ren supported by Deutsche Forschungsgemeinschaft DFG In catalytic hydrocarbon conversion processes, coke deposition on the internal catalyst surface, which blocks the active sites and inhibits the molecular transport, is a major cause of catalyst deactivation. This kind of deactivation is reversible, and the catalyst can be regenerated by burning off the coke with oxygen diluted in nitrogen. However, due to the complex mechanism of the deactivation, the understanding of the fundamental mechanisms of the regeneration remains poor or inconsistent which has restrained the simulation and optimization for both procedures. Compared to the NMR study on a commercial naphtha reforming catalyst Pt/Re-Al 2O 3, a pure metal free Al 2O 3 catalyst was selected as a model system in this work in order to simplify the mechanism of the deactivation. Different NMR techniques were applied for characterizing the changing morphology of the catalysts during the deactivation (coking) and regeneration (decoking) processes. The pore size distributions of the catalyst samples were measured by 129 Xe chemical shifts and NMR cryoporometry using cyclohexane as the molecular probe. The results show a good agreement with those of BET measurements. Pulsed field gradient nuclear magnetic resonance (PFG NMR) has been applied to probe the molecular motion of n-heptane probe molecules in the deactivated and regenerated samples. The tortuosity was evaluated from the ratio of the diffusion coefficients of the confined and bulk liquids, and the dependence of the tortuosity on the coke content was determined. The total elimination of carbonaceous residues by coking and decoking induces changes in the pore size distribution and the tortuosity. Comparing the two catalysts (Pt/Re-Al 2O 3 and metal-free Al 2O 3), it was found that the tortuosity of the regenerated Pt/Re-Al 2O 3 is obviously larger than that of the deactivated one at the same coke content. For the pure Al 2O 3, however, a more closely linear dependence of the tortuosity on the coke content for both processes is observed. Moreover, NMR relaxation times for the protons of adsorbed n-heptane provide also information on the pore morphology changes which can be corroborated by the tortuosity measurements.

52 52 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie tortuosity (t) t = C C t = C C coke content (C C wt%) Fig. 1. Change of the tortuosity of the catalysts during deactivation and regeneration processes. : pure Al 2O 3 deactivation : pure Al 2O 3 regeneration : Pt/Re Al 2O 3 deactivation : Pt/Re Al 2O 3 regeneration T 1 images of partly regenerated Al 2O 3 catalysts at different temperatures were created by the spin-echo imaging using a series of images with varying TR (Fig. 2). By calibration of T 1 with the value of the fresh catalyst, the coke distribution within a single particle was obtained. It is comparable to that measured by an electron microprobe and that from the simulation (Fig. 3). Furthermore, through the combination of the PFG NMR and MRI techniques diffusion weighted images of the sample were acquired s 0s 0 s (a) (b) (c) Fig. 2. T 1 images of Al 2O 3 samples with different coke content C c.. (a) Partly regenerated at 700 C, C c = 7.65%; (b) Partly regenerated at 400 C, C c = 7.65%; (c) Fresh Al 2O 3, C C = 0. relative content of coke C / C r / r p Fig. 3. Radial coke profile of sample (a) in Fig. 2. : NMR result from the T 1 image : Electron microprobe measurement : Simulation

53 53 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie NMR of Porous Building Materials Dip.-Chem. Shatrughan Sharma (Ph.D. student) supported by Deutsche Forschungsgemeinschaft DFG The unilateral NMR sensors like the NMR-MOUSE can be employed to characterize the size distribution of water filled pores in building materials even in the case of ferromagnetic contaminations. The shapes and the positions of the relaxation time distributions are similar to those of the pore size distributions obtained by mercury intrusion porosimetry (MIP) unless the samples exhibit very strong ferromagnetic contaminations as sometimes observed in historic brick samples. For short echo times even the strong effect of internal gradient fields can be meliorated, so that the pore size distributions in weakly ferromagnetic bricks can be analyzed by NMR. Moreover, the relaxation time distributions measured volume selectively by NMR-MOUSE sensors with inhomogeneous fields show a better match with the pore size distributions from mercury intrusion porosimetry than those measured in homogeneous field (Fig. 1). The observation can be rationalized by noting that both NMR-MOUSE and MIP tail at large pore sizes: There the NMR signal is alternated by diffusive attennation MHz <G> = 20 T/m MHz G = 1.26 T/m probability [a.u.] probability [a.u.] relaxation time T 2 [ms] relaxation time T 2 [ms] probability [a.u.] MHz G = relaxation time T 2 [ms] norm. incremental pore volume [ml/g] MIP 1E pore diameter [µm]

54 54 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie Fig. 1: Comparison of relaxation time distributions acquired with different NMR-Sensors. Top left: small NMR-MOUSE at 21 MHz. Top right: large NMR-MOUSE at MHz. Bottom left: Minispec, no depth selection (homogeneous field). Bottom right: pore size distributions from mercuriy intrusion porosimetry (MIP). Brick number 4 was the ferromagnetic brick. Furthermore it has been shown that unilateral NMR sensors can be employed to assess the change in pore size due to treatment with stone strengtheners like Funcosil â 100, Funcosil â 300, and Tegovacon â 100 (Fig. 2), and their effect can be distinguished. With regard to the measurements of the fresco and the bricks in the walls in the cryptoporticus of Colle Oppio in Rome it is concluded, that as a consequence of the short echo times of 60 and 80 µs used in these experiments, the relaxation time distributions are only little attenuated for large values of T 2. probability [a.u.] MHz untreated fully treated partially treated relaxation time [ms] T 2 probability [a.u.] 0 21MHz partially treated fully treated untreated relaxation time [ms] T 2 Fig. 2: Relaxation time distributions of Mergelstone from the city hall of Aachen treated for stone conservation. The data were acquired with the 2.5 kg NMR-MOUSE at 21 MHz (right) and with the 36 kg NMR-MOUSE at MHz (left). Certainly, a comparative evaluation of the distributions is justified to assess the difference in contributions of water in small and large pores between different locations. The MIP scale used in this work are obtained from adjusting the shape of the MIP pore size distribution to the relaxation time distribution of terra cotta provides a useful start for interpretation of NMR relaxation data, if MIP data are not available like for the fresco and the bricks in the wall.

55 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie 55 Simulations of field distortions inside liquid samples Dipl.-Phys. Mihai A. Voda supported by Sonderforschungsbereich 540 (DFG) The interdiffusion process of two liquids is a result of matter transport from one component to another due to the random molecular motions. The investigation of this process with NMR is a difficult task and requires correction procedures in order to obtain an accurate result. It is known that any material placed in a magnetic field leads to a distortion of the spatial field distribution. The field inside the sample has an inhomogeneity depending on the magnetic properties and the sample volume. The first inhomogeneity is introduced by the glass tube into which the sample is placed. In the case of interdiffusion of two liquids, the magnetic properties of the sample are changing due to progressive mixing process, and, the field as well. We simulated the static magnetic field B 0 and the radio-frequency field B 1 using Vector Fields TM OPERA 3D. The liquid sample was placed in a glass tube with 5 mm outer diameter, 4 mm inner diameter, and 25 mm height. The external static magnetic field has been considered to be homogeneous and corresponding to a Larmor frequency of 200 MHz. NMR spectra were numerically simulated in Borland C based on the simulated field distortions. We have investigated two limiting cases: the z liquids are completely separated, which mark the time t = 0 in terms of the interdiffusion time scale and the x case of homogeneous mixture, which means t. For two separated liquids there are three interfaces of interest where the field can change from one medium Fig. 1: B 0 field map in the xz to another: air/top of the liquid, top of the liquid/bottom plane for two separated liquid, bottom of the liquid/glass/air, and the vertical liquids. air/glass/liquid interface. The relative magnetic permeabilities are for the bottom of the liquid and for the top of

56 56 Annual Report 2003 ITMC Lehrstuhl für Makromolekulare Chemie the liquid. The map of the field simulated in the xz plane is shown in Fig. 1. It can be seen that the field changes at the interfaces specified above, especially those which are perpendicular to B 0. Analysing the field profile along the z axis, the influence of the two liquids and the glass tube can clearly be observed (Fig. 2). The stronger effect appears for the liquid with the smaller magnetic permeability. The difference between the maximum and the minimum value of the field is less than 2 ppm B 0 [T] bottom top Intensity [a.u.] z [mm] Fig. 2: B 0 profile along the z axis hom mixture separated Fig. 3: B 1 field map for the sample inside a 20 mm birdcage resonator 30 The B 1 field was simulated 25 for a birdcage type resonator of mm diameter and 60 mm height. The 15 local field inside the sample is shown 10 in Fig. 3. From the field values we 5 0 determined the flip angle distribution ppm in the whole sample volume. The Fig. 4: The spectra in the presence of simulated B 0 and B 1 inhomogeneities spectra of the two liquids were simulated for the inhomogeneous static field (Fig. 4) using the same transverse relaxation times and amplitudes for the homogeneous mixture and the separated liquids. The simulations reveal a significant shift of the lines between the two limiting cases of completely separated liquids and a homogeneous mixture. During the interdiffusion process, the line position changes all the time. This means a reduction of the data accuracy in time, and thus a timedependent error in determining the concentrations profile, which requires a calibration procedure in order to find the real values of the interdiffusion coefficients.