The addition of non-absorbing polymer to a suspension of colloidal hard-spheres causes phase separation via the depletion mechanism. At high enough concentration of polymer a variety of non-equilibrium aggregation behaviour are observed. Transient gels are one such behaviour observed at the highest polymer concentrations. Transient colloid-polymer gels are metastable space-filling particle networks. They persist for some finite time before suddenly collapsing to form a dense sediment. Thus transient gels exhibit "delayed sedimentation" which is a phenomenon observed in many weakly aggregated suspensions. We have studied the collapse process occurring in the bulk of a gelled suspension using dark-field imaging and ultrasonic concentration profiling. At low polymer concentrations we observe delayed sedimentation behaviour. At the highest polymer concentration we observe a change in the settling behaviour. The suspension continuously sediment at a rate comparable to the initial slow settling rate of gels exhibiting delayed sedimentation. This is known as "creeping sedimentation". We have also investigated the effect of varying suspension height and width on the delay time of a gel. We have found a critical height below which the gel exhibits a size-dependent delay time. Above this critical height the delay time is independent of height. The same behaviour is found when width is varied. We find good agreement between the results of this experimental study and a recent theory.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:662375 |
| Date | January 1999 |
| Creators | Starrs, Laura |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14483 |
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