Dynamics of Spinodal Decomposition in Polymer Gels
The process of phase separation via spinodal decomposition has been the subject of extensive investigation in recent years(l). The dynamics of spinodal decomposition in binary phase separation processes has been shown to exhibit very similar behaviour in a wide variety of systems ranging from mixtures of simple fluids(2) to polymer blends(3–4). In all of these previous studies with polymers only linear, uncrosslinked polymers were investigated. However it is well known that linear polymers can crosslink and eventually form a gel. The process of gelation involves a percolation transition characterized by the sudden appearance of an infinite network at the gel-point which leads to a divergence of the shear viscosity from below the transition and the appearance of elasticity above it(5). Since the space inside a gel is compartmentalized into a mesh and since viscosity directly influences the diffusional movement it is possible that gelation may have significant effects on binary phase separation processes in polymers capable of forming a gel. To study this coupling between the thermodynamically driven binary phase separation process and the connectivity driven gelation transition we considered the system of gelatin in a poor solvent. Gelatin dissolved in a water-methanol mixture undergoes a binary phase-separation into a polymer rich phase and a polymer poor phase as the temperature is lowered and simultaneously undergoes a reversible sol-gel transition(6).
KeywordsPhase Separation Cloud Point Spinodal Decomposition Gelatin Concentration Transmitted Light Intensity
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