Polymer dynamics under nanoscopic constraints: the "corset effect" as revealed by NMR relaxometry and diffusometry.

A spinodal demixing technique was employed for the preparation of linear poly(ethylene oxide) (PEO) confined in nanoscopic strands, which in turn are embedded in a quasi-solid methacrylate matrix impenetrable to PEO. Both the molecular weight of the PEO and the mean diameter of the strands are variable to a certain degree. Chain dynamics of the PEO in the molten state were examined with the aid of field-gradient NMR diffusometry and field-cycling NMR relaxometry. The dominating mechanism for translational displacements in the nanoscopic strands is shown to be reptation. A formalism for the evaluation of NMR diffusometry is presented, which permits the estimation of the mean PEO strand diameter. Samples of different composition revealed diameters in the range 9-58 nm, in reasonable agreement with electron micrographs. The time scale of the diffusion measurements was 10-300 ms. On the much shorter time scale of field-cycling NMR relaxometry, 10(-9)-10(-4)s, a frequency dispersion of the spin-lattice relaxation time characteristic for reptation clearly showed up in all samples. An effective tube diameter of only 0.6 nm was found even when the strand diameter was larger than the radius of gyration of the PEO chain random coils. The finding that the tube diameter effective on the short time scale of field-cycling NMR relaxometry is much smaller than the diameter of the confining structure is termed the "corset effect", and is traced back to the lack of local free-volume fluctuation capacity under nanoscale confinements. The order of magnitude of the 'pore' diameter, at which the cross-over from confined to bulk chain dynamics is expected, is estimated.     

LokalNoethersche Gruppen

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Die unzerlegbaren,positiv-definiten Klassenfunktionen der abzählbar unendlichen,symmetrischen Gruppe

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Distributionen mit Werten in Topologischen Vektorräumen II

The research of [3] is continued. After some preparations on topological tensor products of algebras and modules, including a theorem for continuous bilinear operations on spaces of vector-valued distributions (cf. L. Schwartz [13]), we define the convolution for elements ofE(B) = L,(E(^N),B), where B denotes a complete locally pseudoconvex algebra with continuous multiplication. A Paley-Wiener-Schwartz theorem on the Fourier-Laplace transform (FLT) of vector-distributions enables us to reduce the convolution to a pointwise product of B-valued entire functions and to derive some properties of the convolution algebra (B), *).Those elements of a complete m-convex algebra, for which the analytic functional calculus can be continued to (E(B),*), are characterized by use of the FLT. In the last section, we look at representations of distributions in or with values in a complete topological vector space E by means of analytic E-valued functions.

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Während der Fertigstellung eines Teils dieser Arbeit Research Associate der University of Maryland, College Park, Md. 20742, USA.     

Kriterien für die Abgeschlossenheit endlicher Gruppen

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Microarrays by structured substrate swelling

A technique is presented for manufacturing surface microstructures on polymer substrates. It is based on the uptake of solvent vapors by a prestructured polymer, selective swelling, and the flow of the softened polymer. Prestructuring is done by evaporating material, UV illumination, or ion bombardment through a mask. As an application we describe the fabrication of two-dimensional ordered arrays of microvessels which can be of different shape, size, and material. The bottom of the microvessels can be functionalized by several means and it can be transparent to allow for optical analysis. Applications of the microvessel array are seen in combinatorial chemistry, as microreactors, and as confined spaces for controlling crystal growth.