Properties of colloidal hard spheres and monodisperse emulsions studied by light scattering.
Item
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Title
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Properties of colloidal hard spheres and monodisperse emulsions studied by light scattering.
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Identifier
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AAI9605595
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identifier
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9605595
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Creator
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Gang, Hu.
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Contributor
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Adviser: David A. Weitz
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Date
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1995
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Language
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English
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Publisher
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City University of New York.
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Subject
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Physics, Optics | Physics, Fluid and Plasma | Engineering, Chemical
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Abstract
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We have studied the properties of two different kinds of colloidal systems using laser light scattering techniques. One is a latex dispersion, which consists of hard sphere particles dispersed in a liquid; the other is an emulsion, which consists of oil droplets dispersed in water. Using recently developed diffusing-wave spectroscopy (DWS), we have investigated time dependent hydrodynamic interactions in concentrated hard sphere systems. By varying the particle size and the volume fraction, we can probe the self and collective diffusion coefficients and we first found the collective time-dependent diffusion coefficient shows clear evidence of scaling as well as the self-diffusion coefficient. The computer simulations further prove the scaling behavior.;The emulsions we fabricate in our laboratory have a very uniform droplet size. To compare with the hard sphere system, we have studied the dynamic properties of flexible liquid droplets. We find emulsions made of high viscosity oil droplets exhibit similar dynamic properties to hard sphere latex at relatively low volume fractions. As the volume fraction reaches {dollar}\phi\sb{lcub}c{rcub},{dollar} the critical volume fraction for the liquid-glass transition, emulsions also shows an ergodic to non-ergodic transition. We incorporate mode-coupling theory (MCT) of the glass transition and show that emulsions experience a liquid-glass transition similar to a hard sphere system. However, we find obvious difference between the two systems, i.e. in emulsions, {dollar}\alpha{dollar} relaxation persists on the glass side of the transition. We attribute this to the deformability and flexibility of the liquid droplets. We have investigated the dynamic properties on a wider range of length scales by combining the conventional dynamic light scattering (DLS) and DWS.;Finally, we focus our attention on the flexibility of liquid droplets. We have generalized the theory of DWS by incorporating the effects of amplitude fluctuations in the scattering intensity of the particles. We apply this new method to study the thermally induced fluctuations in the shape of spherical emulsion droplets whose geometry is controlled by surface tension. We study the volume fraction dependence of relaxation of the shape fluctuations, and find that higher modes of fluctuations can be excited, and that the interactions between the droplets can change the time scale of the relaxation. We find a remarkable scaling curve for the relaxation of the shape deformations of liquid droplets at different volume fractions.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
