Dynamics of a colloid-stabilized cream

TL;DR

This study investigates the aging dynamics of colloid-stabilized emulsions using x-ray photon correlation spectroscopy, revealing novel ballistic-like motion, intermittent fluctuations, and a transition in relaxation behavior over time.

Contribution

It provides new insights into the aging and dynamics of colloid-stabilized emulsions, highlighting unique motion characteristics not previously reported.

Findings

Identification of two aging regimes with different dynamics

Observation of ballistic-like motion and intermittent events

Change in relaxation exponent from 1.5 to less than 1 as emulsion ages

Abstract

We use x-ray photon correlation spectroscopy to investigate the dynamics of a high volume fraction emulsion creaming under gravity. The dodecane-in-water emulsion has interfaces stabilized solely by colloidal particles (silica). The samples were observed soon after mixing: as the emulsion becomes compact we discern two regimes of ageing with a cross-over between them. The young emulsion has faster dynamics associated with creaming in a crowded environment accompanied by local rearrangements. The dynamics slow down for the older emulsion although our studies show that motion is associated with large intermittent events. The relaxation rate, as seen from the intensity autocorrelation function, depends linearly on the wave vector at all times; however, the exponent associated with the line shape changes from 1.5 for young samples to less than 1 as the emulsion ages. The combination of ballisticlike dynamics, an exponent that drops below 1 and large intermittent fluctuations has not been reported before.