Contact Experiments in Colloid-Polymer Mixtures
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- 作者：Jean Baudry and Wilson C. K. Poon
- 刊名：Langmuir
- 出版年：2003
- 出版时间：April 1, 2003
- 年：2003
- 卷：19
- 期：7
- 页码：2606 - 2611
- 全文大小：110K
- 年卷期：v.19,no.7(April 1, 2003)
- ISSN：1520-5827
文摘
We study the interpenetration of a polymer solution placed on top of a colloidal suspension. Directobservations show that at the interface, the depletion attraction induced by the polymer causes the colloidsto aggregate in a thin layer. This acts as a semipermeable membrane, through which the polymer osmoticpressure squeezes out solvent from the colloidal suspension like a cafetiere plunger. Observations usingfluorescent polymers show that despite the very high concentration gradients present, very little of thepolymer gets into the colloid. The movement of the colloid-polymer interface has two regimes at increasinginitial polymer concentration. First, the interface moves at a constant velocity with a constant thickness.In this regime, the interfacial velocity does not depend on the initial colloid volume fraction but increaseslinearly with the polymer osmotic pressure (
p). We show that these observations are consistent withDarcy-type flow through the interfacial membrane driven by p. At higher polymer concentration, a stronginstability occurs and the interfacial layer breaks and reforms regularly. The origin of this nonlinearbehavior is unclear. The relationship of our observations to fouling in ultrafiltration in an unstirred batchcell is discussed.
p). We show that these observations are consistent withDarcy-type flow through the interfacial membrane driven by p. At higher polymer concentration, a stronginstability occurs and the interfacial layer breaks and reforms regularly. The origin of this nonlinearbehavior is unclear. The relationship of our observations to fouling in ultrafiltration in an unstirred batchcell is discussed.