AbstractWeak colloidal gels formed by a depletion attraction are metastable for a finite time before undergoing a catastrophic collapse. This delayed-collapse phenomenon has been previously linked to ageing and the lifetime of a gel explained by the way of single particle-particle bond kinetics. Here we present the dependence of the delay time before collapse on temperature, with a striking two-regime dependence becoming clear, one at low and one at high temperatures. We compare delay time to the calculated Kramer's escape time and find that the single-bond model is not sufficient to explain the decrease in delay time observed.
To bridge the microscopic and macroscopic length-scales, we use the technique Particle Tracking Velocimetry (PTV) to probe the mesoscopic length-scale in colloidal gels. This allows us to probe changes in the gel structure using 25 micron fluorescent tracer beads. As well as gaining much more detailed information about the dynamics that occur within colloid-polymer gels, we can track this tracer movement before macroscopic collapse is observed. We find that in the low-temperature regime, tracers are quiescent for a period of time before heterogeneous tracer movement begins in localised regions, which eventually propagates throughout the sample to cause macroscopic collapse. At higher temperatures however, tracer movement is homogeneous and no tracer quiescence is observed.
|Date of Award||23 Jan 2019|
|Supervisor||Paul Bartlett (Supervisor)|