Modeling and simulation of magnetic-shape-memory polymer composites

Composites of small magnetic-shape-memory (MSM) particles embedded in a polymer matrix have been proposed as an energy damping mechanism and as actuators. Compared to a single crystal bulk material, the production is simpler and more flexible, as both type of the polymer and geometry of the microstructure can be tuned. Compared to polycrystals, in composites the soft polymer matrix permits the active grains to deform to some extent independently; in particular the rigidity of grain boundaries arising from incompatible orientations is reduced. We study the magnetic-field-induced deformation of composites, on the basis of a continuous model incorporating elasticity and micromagnetism, in a reduced two-dimensional, plane-strain setting. The aim is to give conceptual guidance for the design of composite materials independent of the concrete macroscopic device. Thus, on the background of homogenization theory, we determine the macroscopic behavior by studying an affine-periodic cell problem. An energy descent algorithm is developed, whose main ingredients are a boundary element method for the computation of the elastic and magnetic field energies; and a combinatorial component reflecting the phase transition in the individual particles, which are assumed to be of single-domain type. Our numerical results demonstrate the behavior of the macroscopic material properties for different possible microstructures, and give suggestions for the optimization of the composite.     

A characterization of subshifts with bounded powers

We consider minimal, aperiodic symbolic subshifts and show how to characterize the combinatorial property of bounded powers by means of a metric property. For this purpose we construct a family of graphs which all approximate the subshift space, and define a metric on each graph, which extends to a metric on the subshift space. The characterization of bounded powers is then given by the Lipschitz equivalence of a suitably defined infimum metric with the corresponding supremum metric. We also introduce zeta-functions and relate their abscissa of convergence to various exponents of complexity of the subshift. Our results, following a previous work of two of the authors, are based on constructions in non commutative geometry.     

Die Fluoreszenz in der mikrochemischen Analyse

Ohne Zusammenfassung     

Epoxidation of bacterial polyesters with unsaturated side chains. II. Rate of epoxidation and polymer properties

Poly(3-hydroxyoctanoate-co-3-hydroxy-10-undecenoate)s (PHOUs) with controlled amounts of unsaturated repeating units were epoxidized to various extents with m-chloroperbenzoic acid (MCPBA) in homogeneous solution. The epoxidation reaction was second order, with an initial rate constant of 1.1 × 10⁻³Lmol^−1.s⁻¹ at 20°C, regardless of the unsaturated unit content in PHOU. No substantial change in either molecular weight or molecular weight distribution occurred as a result of epoxidation, but the melt transition temperature and enthalpy of melting both decreased as the unsaturated groups were increasingly converted into epoxide groups. In contrast, the glass transition temperature (T_g) increased by approximately 0.25°C for each 1 mol % of epoxidation, irrespective of the composition of the PHOU. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2381–2387, 1998     

Investigations on the structure of regenerated cellulose fibers; Herrn Professor Janeschitz-Kriegl zum 70. Geburtstag mit den besten Wünschen gewidmet

A review is given on comparative investigations onto the structure of regenerated cellulose fibers of the regular viscose type (modal) and of solvent spun fibers of the lyocell type, namely the NMMO fiber spun from a solution of cellulose in N–methylmorpholine N–oxide and water. It was found that in the lyocell fiber the mechanical properties in the wet state detoriate less. This is explained by an increased length of the crystallites, less clustering of the crystalline regions, and a shorter and better oriented amorphous portion. These structural features could be caused by a different spinning mechanism due to a preordered spinning solution in which the stiff complexed cellulose molecules are oriented lengthwise in the spinning direction. This will greatly facilitate their orientation during fiber formation in the elongtional deformation velocity field of the draw down zone.     

Anionic and coordination polymerization of 3-butyrolactone

Aluminoxane catalysts and anionic initiators can polymerize 3-butyrolactone, 3-BL, to high molecular weight stereoregular polymers. With the racemic monomer, [R,S]-3-BL, anionic polymerization with alkali metal complexes can form syndiotactic polymers and aluminoxane catalysts can form either highly isotactic, syndiotactic, or atactic poly-3-butyrolactone, P-3-BL, depending on the composition and method of preparation of the aluminoxane and the conditions of polymerization.     

Thermotropic liquid-crystalline copolyesters containing substituted phenylene terephthalate and ethylene terephthalate units

Three series of aromatic, thermotropic copolyesters, based on terephthalic acid (TA), ethylene glycol (EG), and another diol were prepared. The third monomer was selected from three different hydroquinones including, ethoxyhydroquinone (EHQ), phenylhydroquinone (PHQ), and hydroquinone itself (HQ). The amounts of the different hydroquinone terephthalate units were varied while the amounts of ethylene terephthalate units remained constant. The copolymers and terpolymers were characterized for solubility, for morphology by polarized light microscopy (PLM), for molecular weight by solution viscometry, and by NMR, DSC, and TGA. At elevated temperatures all samples, when observed by PLM, displayed the characteristic texture of a nematic phase. The melting transition temperatures, T_m, were found to vary from 255 to 325°C, while the 5 wt % loss temperatures, T_d, were found to vary from 330 to 440°C. The inherent viscosities varied from 0.6 to 1.9 dL/g. Increases in the HQ monomer content caused a decreased solubility and an increase in melting point. Copolymer compositions determined by NMR showed that only about one-half of the EG added was incorporated into the copolymers. © 1997 John Wiley & Sons, Inc.