Viscoelastic model of phase separation: From polymer solutions to colloidal suspensions

Tanaka, Hajime
June 2000
AIP Conference Proceedings;2000, Vol. 519 Issue 1, p52
Academic Journal
We recently found a new type of phase separation in condensed matter, which we call "viscoelastic phase separation", for dynamically asymmetric mixtures such as polymer solutions and polymer mixtures whose components have very different T[sub g]. Conceptually it is rather easy to accept that viscoelastic effects play a key role in polymeric systems, since polymer itself is viscoelastic matter. Here we argue that it is the interaction network of the slow component of a mixture that is the physical origin of viscoelasticity responsible for viscoelastic phase separation and the viscoelastic nature of the component itself is not its primary cause. This idea naturally leads to the conclusion that phase separation of colloidal suspensions should also belong to viscoelastic phase separation, even though colloidal particles themselves are not viscoelastic matter. It is known that a transient gel is formed upon phase separation of colloidal suspensions and emulsions. We view this fact as a fingerprint of the formation of the interaction network of the slower component (colloidal particles) of a mixture. We discuss the basic physical origin of viscoelastic phase separation, focusing on the formation of a transient gel in the initial stage of of phase separation. The possible mechanism of the collapsing of colloidal gel under gravity is also suggested.


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