Slow dynamics in dense oil–water emulsions studied using dynamic light scattering

Abstract

The 3D-echo-DLS (dynamic light scattering) flat cell light scattering instrument(3D-echo-DLS-FCLSI) presents the possibility of measuring slow dynamics of turbid andconcentrated colloidal systems. It combines a modified 3D-DLS component and anecho-DLS component with the flat cell light scattering instrument. While the3D-DLS suppresses multiple scattering, the echo-DLS allows measurements of slowdynamics or even on non-ergodic systems. The advantage of the thin flat cell isthat it increases the transmission and reduces multiple scattering; i.e., singlyscattered light that is required by the 3D-DLS is still available from dense turbidsystems. In the first part of this contribution the 3D-echo-DLS-FCLSI is introducedand the instrumental performance is presented. The second part of the paper isconcerned with the ageing behavior of dense fluids in a flat cell, and with confinementeffects. Here, we show that ageing is strongly influenced by the process of filling ofthe flat cell. In some cases complementary methods can be utilized to measurespecial properties of the system; e.g., the multispeckle method is most appropriatefor measuring heterogeneity effects. In the last part of the paper we compareglass transition measurements of an index-matched emulsion carried out usingthe 3D-echo-DLS-FCLSI and using the multispeckle instrument. We still find anα-relaxation in the glassy state.