Abstract
The dynamic behaviour of hard spherical silica particles of 70 nm radius in cyclohexane has been investigated with Photon Correlation Spectroscopy. In the diluted region, the obtained field autocorrelation functions could be described by single exponentials, but at particle concentrations above 0.30 g/cm3 deviations of the single exponential behaviour of the functions became pronounced. However, in this concentration range the experimental functions seem to be reasonably well described by a sum of two exponential functions. Recently WEISSMAN and PUSEY suggested that the occurrence of two different relaxation modes in concentrated systems might be due to optical polydispersity of the dispersed particles. One relaxation mode is attributed to the collective diffusion of the particles and is called the collective part, while the other relaxation mode is identified with the self-diffusion of the particles and is called the incoherent part. We were able to test the influence of the optical polydispersity experimentally with our system by performing optical contrast variation experiments in which we altered the difference between the refractive index of the particles and that of the solvent by varying the temperature. The results of these measurements appeared to be consistent with the theories of WEISSMAN and PUSEY. The concentration dependence of the two relaxation modes was studied.
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The situation given here can be compared to the long known “relaxation effect” of the electrical double layer in electrophoresis and self-diffusion. When the central particle is moving, the surrounding (ionic) atmosphere becomes asymmetrical because it takes some time to break down the old atmosphere and to build a new one. The asymmetrical atmosphere exerts a retarding force on the central particle.
M.M. Kops-Werkhoven and H.M. Fijnaut, J. Chem. Phys., accepted for publication.
M.M. Kops-Werkhoven, C. Pathmamanoharan, A. Vrij and H.M. Fijnaut, J. Chem. Phys., accepted for publication.
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© 1983 Springer-Verlag Berlin Heidelberg
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Kops-Werkhoven, M.M., Vrij, A., Fijnaut, H.M. (1983). Dynamic Properties of Silica Dispersions in Cyclohexane. In: Schulz-DuBois, E.O. (eds) Photon Correlation Techniques in Fluid Mechanics. Springer Series in Optical Sciences, vol 38. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-39493-8_37
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DOI: https://doi.org/10.1007/978-3-540-39493-8_37
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