ISSN:
1435-1536
Keywords:
Microgels
;
thermal diffusion
;
self diffusion
;
forced Rayleigh scattering
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Thermal diffusion in solutions of polystyrene micro-network spheres (microgels) in toluene has been studied by the holographic scattering technique of thermal diffusion forced Rayleigh scattering (TDFRS) and by photon correlation spectroscopy (PCS). Size distributions of microgels of different crosslink ratios are obtained from TDFRS measurements on dilute solutions at very lowq-values around 4000cm−1. At low concentrations a single diffusive mode is observed and the diffusion coefficient increases with concentration. It is attributed to the collective diffusion of the microgels and the solvent. At high concentrations an additional slow mode appears whose diffusion coefficient decreases with increasing concentration. Both diffusive modes are observed with PCS and TDFRS. Contrary to PCS, heterodyne TDFRS-measurements reveal a negative amplitude of the slow mode. We attribute the slow mode to self-diffusion of the microgels, made visible by the polydispersity of their size distribution. It is discussed in terms of a fast coupled thermal diffusion with subsequent decoupling of the individual microgels and relaxation into a new Soret equilibrium by self-diffusion of the microgels.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01182429
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