Multiple light-scattering studies of attractively interacting and polydisperse colloidal suspensions

This work demonstrated the application of diffusing wave spectroscopy (DWS), a multiple light scattering technique, to study dynamics of turbid polystyrene latex suspensions with depletion induced attractive forces, caused by dissolved, non-adsorbing polyacrylic acid. For the low polymer concentration systems used, the DWS measured retardation of volume fraction dependent single-particle self-diffusivity matched the predictions of the Asakura-Oosawa model of depletion. In addition, it was shown that the use of the Baxter's adhesive hard sphere model, with attractive potential only at particle-particle contact, is a reasonable, single-parameter characterization of suspensions with depletion induced attractive forces. The results suggest that DWS can measure the self-diffusivity of suspensions with various types of interactions, which can be used in comparing theoretical models.; Opacity, defined as the reciprocal of the photon transport mean free path, was studied for bimodal and polydisperse colloidal suspensions. A computational investigation of bimodal system opacity found that the opacity of a mixture of two monodisperse colloidal species can be greater than that of the more opaque species within narrow total volume fraction regions associated with the crossover of the two pure-component, volume fraction dependent opacities. A reduction in opacity, lower than that of the least opaque monodisperse component, was not observed in the systems investigated.; Computed opacities for polydisperse alumina, based on single-parameter representations of the measured size distribution, did not predict, qualitatively or quantitatively, the measured values. In addition, the incorporation of cross-component partial structure factor contributions by extending the bimodal computational approach of Kaplan et al. (Kaplan et al., Phys. Rev. Lett., 68(3), 1992) to polydisperse systems also did not predict the measured values. In fact, the resultant predictions appeared to be similar to the single-parameter description methods.; These results are applicable to the characterization of potential interactions and size polydispersity of turbid suspensions such as those found in the pharmaceutical, ceramic and coatings industries.