micromod Partikeltechnologie GmbH modular designed particles T A sicastar silica based nano and micro particles

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1 chnological e T A tions and Re a ic vi l b s ew Pu modular designed tions ica pl p ntation in e Lif em l e p ces ien Sc Im based nano and micro

2 Product overview 20 nm 10 µm 1 µm Product matrix 500 nm dextran 80 nm bionized nanoferrite 2-12 µm Magnetic polystyrene 30 µm nm - 6 µm 150 nm poly(ethylene imine) 150 nm chitosan Fluorescent iron oxide 25 nm 20 µm 6 µm Fluorescent magnetic polystyrene, polymethacrylate albumin nm dextran bionized nanoferrite 30 µm - 6 µm 20 µm 25 nm White polystyrene, polymethacrylate latex albumin 1 µm 300 nm Coloured 1 µm polystyrene 10 µm Friedrich-Barnewitz-Straße 4, D Rostock Tel.: / , Fax: / Technical Support Tel.: / info@micromod.de, Internet:

3 4 in geo- and astrophysics Dr. Rainer Schräpler (Technical University Braunschweig, Institute for Geophysics and Extraterrestrial Physics), Dr. Cordula Grüttner () Long-duration experiments with clouds of micro are interesting research objects ranging from the simulation of aerosol behavior in Earth s atmosphere to the formation of planets in the early solar system. It is, however, even under microgravity conditions, impossible to sustain a cloud of free-floating, microscopic for an extended period of time, due to thermal diffusion and due to unavoidable external accelerations. As a part of the ICAPS (Interactions in Cosmic and Atmospheric Particle Systems) project for the International Space Station (ISS) a three-dimensional trap for clouds of micro should be developed. This trap for dust clouds is required to prevent the particle drift caused by thermophoresis and thermal creep. Because this drift terminates experiments by driving the to the chambers walls. Thermal diffusion provides a source of relative velocities between the dust grains and drives the particle coagulation. Steinbach et al. used 1 µm plain sicastar as model for dust, and developed a particle trap by using the photophoretic effect [1]. Highly porous materials made of micron-sized have attracted significant attention. One reason is that these materials allow the relation of microscopic properties such as adhesion and friction forces between individual to macroscopic quantities such as compressibility. One example for the interest in both, individual particle contact as well as properties of agglomerates consisting of these, is the formation of planetesimals. Furthermore the behavior of particle agglomerates is crucial in particle filtration, because the performance of fibrous and membrane filters is often limited by the formation of dust cakes. Blum and Schräpler used plain 1.5 µm for the development of macroscopic agglomerates formed by ballistic hit-and-stick deposition [2]. The agglomerates, produced with this experimental method, have a volume filling factor of f=0.15, matching very closely the theoretical value for random ballistic deposition. They are mechanically stable against unidirectional compression of up to 500 Pa. For pressures above that value, the volume filling factor increases to a maximum of f=0.33 for pressures above 105 Pa. The tensile strength of slightly compressed samples (f=0.2) is 1000 Pa. Blum et al. found that the maximum compression, equivalent to the highest protoplanetary impact velocities of ~50 ms-1, increases the packing density to Tensile strength measurements with the laboratory samples yielded values in the range of Pa for slightly compressed samples. The review of packing densities and tensile strengths found for primitive solar system bodies, e.g., for comets, primitive meteorites, and meteoroids showed a consistency between packing densities and tensile strengths of the laboratory samples with those from cometary origin [3]. 1

4 Langkowski et al. varied the porosity of the dust aggregates to study the collision effects for aggregates with a smooth surface (porosities between 85% and 93%) in comparison to aggregates with a molded surface and a decreased porosity of 80%-85%. The molding of the aggregates was performed such that the radii of the local surface curvatures corresponded to the projectile radii. The experiments showed that impacts into the highest porosity targets almost always led to sticking, whereas for the less porous dust aggregates, consisting of monodisperse 1.5 µm, the collisions with intermediate velocities and high impact angles resulted in the bouncing of the projectile with a mass transfer from the target to the projectile aggregate. For the impacts into smooth aggregates of the depth of intrusion and the crater volume were measured. From these results some interesting dynamical properties could be derived, which can help to develop a collision model for protoplanetesimal dust aggregates [4]. In further experiments the collisional behavior of the dust aggregates of the 1.5 µm sicastar was studied at velocities below and around the fragmentation treshold. Therefore two experimental setups with the same goal were developed: to study the effects of bouncing, fragmentation, and mass transfer in free particle-particle collisions. The first setup was an evacuated drop tower with a free-fall height of 1.5 m. The second setup was designed to study the effect of partial fragmentation (when only one of the two aggregates was destroyed) (Fig.1). elastic band thread halogen lamp dust agglomerates projectile mount camera solenoid Figure 1. Experimental setup for collisions of the dust cylinders. The solenoid accelerates the lower aggregate, which collides with the upper aggregate (left). Image sequence, that illustrates the collision between the cylindrical samples with a collision velocity of 1 m/s (right) [5]. The measured critical energy for disruptive collisions was found to be at least two orders of magnitude lower than given in the literature. The accretion efficiency on the order of a few percentage points of the particle mass depends on the impact velocity and the sample porosity. These findings will have consequences for dust evolution models in protoplanetary disks as well as for the strength of large, porous planetesimal bodies [5]. Heim et al. used the highly porous agglomerates of 1.5 µm, formed by random ballistic deposition, to analyze their compaction. The porous agglomerates were deformed inside 2

5 a scanning electron microscope (SEM) using the cantilever of an atomic force microscope (AFM). The applied force and structural deformations with single particle resolution could be obtained simultaneously. It was found that whole blocks of many move collectively upon compression. Within these blocks the relative positions of the remained fixed. This results in a discontinuous force-compression curve [6]. The analysis technique was further improved by implementation of a piezoelectric controlled nanomanipulator with increments of 5 nm in the rotational and 0.5 nm in the translational direction. This tool allows the precise positioning and movement of an AFM cantilever under SEM observation. The higher sensitivity of the method allows the study of different aspects of the deformation of dust-aggregate structure, e.g. the behaviour of single particle chains. These findings allow a deeper insight into mechanical properties of granular matter the second most handled material by men [7]. The fluence of dust < 10 µm in diameter was recorded by impacts on aluminium foil of the NASA Stardust spacecraft during a close fly-by of comet 81P/Wild 2 in Initial interpretation of craters for impactor particle dimensions and mass was based upon laboratory experimental simulations using >10 μm diameter projectiles and the resulting linear relationship of projectile to crater diameter was extrapolated to smaller sizes. For the experimental proof of this extrapolation Price et al. [8] developed a new experimental calibration programme firing very small monodisperse projectiles (470 nm to 10 μm) at ~ 6 km s-1. Projectile materials were plain 10 µm and smaller commercially available. The results show an unexpected departure from linear relationship between 1 and 10 μm. Using the new calibration, Price et al. could recalculate the size of the particle responsible for each crater and hence reinterpret the cometary dust size distribution [8]. References [1] Steinbach J, Blum J, Krause M. Development of an optical trap for microparticle clouds in dilute gases. Eur. Phys. J. 2004;E 15: [2] Blum J, Schräpler R. Structure and mechanical properties of high-porosity macroscopic agglomerates formed by random ballistic deposition. Phys. Rev. Lett. 2004;93(11): (4 pp). [3] Blum J, Schräpler R, Davidsson BJR, Trigo-Rodriguez JM. The physics of protoplanetesimal dust agglomerates. I. Mechanical properties and relations to primitive bodies in the solar system. Astrophys. J. 2006;652: [4] Langkowski D, Teiser J, Blum J. The physics of protoplanetesimal dust agglomerates. II. ; Low-velocity collision properties. Astrophys. J. 2008;675: [5] Beitz E, Güttler C, Blum J, Meisner T, Teiser J, Wurm G. Low-velocity collisions of centimeterust aggregates. Astrophys. J. 2011;736:34(11 pp). [6] Heim L-O, Butt H-J, Schräpler R, Blum J. Analyzing the Compaction of High-Porosity Microscopic Agglomerates. Aust. J. Chem. 2005;58: [7] Heim L-O, Butt H-J, Blum J, Schräpler R. A new method for the analysis of compaction processes in high-porosity agglomerates. Granular Matter 2008;10: [8] Price MC, Kearsley AT, Burchell MJ, Hörz F, Borg J, Bridges JC et al. Comet 81P/Wild 2: the size distribution of finer (sup-10 micrometre) dust collected by the stardust spacecraft. Meteoritics and Planetary Science 2010;45(9):

6 Editor: Registergericht: Amtsgericht Rostock HRB 5837 Steuernummer: 4079/114/03352 Ust-Id Nr. (Vat No.): DE Compilation date - September the 19th, 2013