Diffusing wave spectroscopy of dense colloids: liquid, crystal and glassy states

Abstract

Using intensity autocorrelation of multiply scattered light, we show that the increase in interparticle interaction in dense, binary colloidal fluid mixtures of particle diameters 0.115μm and 0.089μm results in freezing into a crystalline phase at volume fraction φ of 0.1 and into a glassy state at φ=0.2. The functional form of the field autocorrelation function g⁽¹⁾(t) for the binary fluid phase is fitted to exp[-γ(6k₀²D_eff t)^½] where k₀ is the magnitude of the incident light wavevector and γ is a parameter inversely proportional to the photon transport mean free path l^∗. The D_eff is the l^∗ weighted average of the individual diffusion coefficients of the pure species. Thel used in calculating D_eff was computed using the Mie theory. In the solid (crystal or glass) phase, the g⁽¹⁾(t) is fitted (only with a moderate success) to exp[-γ(6k²₀ W(t))^½] where the mean-squared displacement W(t) is evaluated for a harmonically bound overdamped Brownian oscillator. It is found that the fitted parameter γ for both the binary and monodisperse suspensions decreases significantly with the increase of interparticle interactions. This has been justified by showing that the calculated values of l^∗ in a monodisperse suspension using Mie theory increase very significantly with the interactions incorporated in l^∗ via the static structure factor.