Diffusion in concentrated dispersions: a study with fiber-optic quasi-elastic light scattering (FOQELS) |
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Authors: | D Lilge D Horn |
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Institution: | (1) Present address: Polymer Research Division, Department of Polymer and Solid State Physics, ZKM, BASF AG, G201 6700 Ludwigshafen, FRG |
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Abstract: | A fiber-optic, quasi-elastic light-scattering instrument is described using single-mode fiber optical components, including a novel slanted exit face optode. The setup operates with homodyne signal detection. It enables the characterization of diffusion processes in concentrated dispersions up to volume concentrations of 50%.The performance of the instrument is exemplified with results obtained from latex spheres with diameters of 226 nm and 404 nm at volume fractions from =0.01 to =0.5. The correlation functions are analyzed according to the second order cumulants method and the Contin -procedure yielding an average and a distribution function of the short-time self-diffusion coefficient,D
eff
s
, respectively.At high ionic strength the concentration dependence ofD
eff
s
/D
0 is found to be in close agreement with theoretical predictions based on a multi-body interaction model of hard spheres up to =0.45. With decreasing ionic strength the negative slope of the virial expansion tends to increase, presumably due to enhanced repulsive electrostatic interactions.The described technology offers new experimental means for on-line remote control sensing of particle size in concentrated disperse systems.Presented at the 34. Hauptversammlung der Kolloidgesellschaft e.v., Bochum, Oct. 1–4, 1989 |
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Keywords: | Dynamic light scattering fiber-optics latex dispersions self-diffusion |
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