Optical extinction and refraction of concentrated latex dispersions

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Abstract
Experimental details are given of an apparatus which has been used to measure the optical extinction of colloidal dispersions with concentrations as high as 50% solids. For all dispersions examined the optical extinction showed a maximum as a function of concentration. Optical extinction, or turbidity, is interpreted as the imaginary part of the complex refractive index, ñ. An approximate theory of ñ for concentrated dispersions is presented. The theory takes into account the effect of neighbouring particles on the scattering cross-section of a particular scatterer by using the concept of a local radial distribution of refractive index. Computer calculations based on an idealised refractive-index profile are compared with experimental data for both real and imaginary parts of ñ.

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