Diffusion statique de la lumière

Résumé

alt=Exemple de diffusion statique de la lumière utilisant le système du goniomètre.|thumb|Exemple de diffusion statique de la lumière utilisant le système du goniomètre. La diffusion statique de la lumière est une technique utilisée en physique et en chimie pour mesurer l'intensité de la lumière dispersée pour obtenir le poids moléculaire moyen M d'une macromolécule, comme un polymère ou une protéine en solution. Explications La mesure de l'intensité de diffusion à de nombreux angles permet le calcul de la racine carrée du rayon moyen, aussi appelé le rayon de giration. En mesurant l'intensité de diffusion pour de nombreux échantillons de diverses concentrations, le second coefficient du viriel A2, peut être calculé. La diffusion statique de la lumière est aussi couramment utilisé pour déterminer la taille des particules en suspensions dans la sub-µm et gammes supra-µm, via, respectivement, la Théorie de Mie et la diffraction de Fraunhofer. En ce qui co

Source officielle

https://fr.wikipedia.org/wiki/Diffusion_statique_de_la_lumi%C3%A8re

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Nonspherical assemblies generated from polystyrene-b-poly(L-lysine) polyelectrolyte block copolymers

Laurent Bourdillon, Harm-Anton Klok, Harald Nuhn, Markus Scholl, Christine Wandrey

This report describes the aqueous solution self-assembly of a series of polystyrenem-b-poly(L-lysine)n block copolymers (m = 8-10; n = 10-70). The polymers are prepared by ring-opening polymerization of e-benzyloxycarbonyl-L-lysine AT-carboxyanhydride using amine terminated polystyrene macroinitiators, followed by removal of the benzyloxycarbonyl side chain protecting groups. The critical micelle concentration of the block copolymers determined using the pyrene probe technique shows a parabolic dependence on peptide block length exhibiting a maximum at n = .apprx.20 (m = 8) or n = .apprx.60 (m = 10). The shape and size of the aggregates has been studied by dynamic and static light scattering, small-angle neutron scattering (SANS), and analytical ultracentrifugation (AUC). Surprisingly, Holtzer and Kratky analysis of the static light scattering results indicates the presence of nonspherical, presumably cylindrical objects independent of the poly(L -lysine)n block length. This is supported by SANS data, which can be fitted well by assuming cylindrical scattering objects. AUC analysis allows the molecular weight of the aggregates to be estimated as several million g/mol, corresponding to aggregation numbers of several 10s to 100s. These aggregation numbers agree with those that can be estimated from the length and diameter of the cylinders obtained from the scattering results. © 2005 American Chemical Society.

2005

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Aqueous solution self-assembly of polystyrene-b-poly(L-lysine) diblock oligomers

Harm-Anton Klok, Harald Nuhn

This paper reports on the dilute, aqueous solution self-assembly of two asymmetric polystyrene-b-poly(L-lysine) (PSnPKm) diblock oligomers with PS and PK number-average degrees of polymerization of eight, respectively, 40 and 60. The self-assembly of these diblock oligomers was investigated using static and dynamic light scattering in combination with analytical ultracentrifugation. Direct dissolution of the diblock oligomers in water generates a mixture of solution assemblies, part of which is cylindrical or rod-like in nature according to the light scattering experiments. This is surprising given the highly asymmetric nature of the diblock oligomers. Additional experiments in which the sample preparation conditions were varied and sample solutions subjected to a thermal treatment or prepared via dialysis from an organic/aqueous solution, however, suggest that direct dissolution results in kinetically trapped assemblies, which are (partially) converted into thermodynamically more favored assemblies upon varying the sample preparation conditions. (C) 2010 Elsevier Ltd. All rights reserved.

2011

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Poleable Nanoparticles as Fillers Towards Non-linear Optically Active Actuators

Yee Song Ko

A new type of poleable dielectric elastomer is introduced herein. The elastomer contains polymer nanoparticles with frozen molecular dipoles, which can be oriented at elevated temperatures in an electric field via poling. The aim is to provide a soft material with high, tunable optical properties suitable for actuator and flexible electronics applications. To that end poleable polymeric nanoparticles with high dipole concentrations and glass transition temperatures well above room temperature will be needed to be used as filler in an elastomer matrix. The synthesis and characterization of such particles is presented in this manuscript. Polyhydroxyethyl methacrylate (PHEMA) nanoparticles were synthesized using miniemulsion polymerization. The particles were loaded with 4-[ ethyl (2-hydroxyethyl) amino]-4-nitrobenzene, usually called Disperse Red 1 (DR1), which has a large dipole moment (mu = 7.5 - 9.5 D). (1) The maximum dipole loadings is limited by the solubility of the dipole in the monomer solutions prior to polymerization. All samples show a glass transition temperature around 95 degrees C. Secondary electron microscopy (SEM) revealed spherical particles, the size of which was confirmed by dynamic light scattering (DLS) measurements. A composite was prepared by dispersing the particles in polydimethyl siloxane (PDMS).

Spie-Int Soc Optical Engineering2015

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