Gelled phase-separated system

Figure 1. Phase diagram of the gelling steroid/cyclohexane system. The upper full line is the saturation curve (T) and the saturation temperature for the initial concentration. The dotted line indicates the separation between the two zones k and B. The lower full line indicates the transition to the cyclohexane plastic phase.(Reproduced with permission from Ref. 17. Copyright 1985 Academic Press.)...

Nakanishi, K. and Soga, N., Phase-separation in gelling silica organic polymer-solution—Systems containing poly(sodium styrenesulfonate), Journal of the American Ceramic Society 74(10), 2518-2530, 1991. 

Based on phase-separation mechanisms, coacervation systems can be classified into two general types simple coacervation and complex coacervation. When only one polymer is involved, the process is referred to as simple coacervation, and when two or more polymers with opposite charges are involved, it is referred to as complex coacervation. In both cases, the coacervation takes place just before precipitation from solution. This separated phase in the form of amorphous, liquid droplets constituted the coacervate which is the polymer-rich solution. Deposition of this coacervate around the individual insoluble oil droplets or solid particles dispersed in the equilibrium liquid forms the embryonic capsules, and subsequent gelling of the deposited coacervate results in microcapsules. 

H. Kaji, K. Nakanishi, N. Soga, T. Inoue, and N. Nemoto, In Situ Observation of Phase Separation Processes in Gelling AUcoxy-Derived Silica System by Light Scattering Method, J. Sol-Gel Sci. Technol., 3, pp. 169-88, 1994. 

If any transient (dynamic) heterogeneity is present in a gelling solution, it will be arrested in the gel network when the timescale of the sol-gel transition is short enough to freeze the snap-shot structure of the heterogeneity. In the present sol-gel system, both the structural evolution due to phase separation and the structure freezing by sol-gel transition take place as a result of irreversible polycondensation reaction. The frozen stmcture depends, therefore, on the onset of phase separation relative to the freezing point by sol-gel transition. The earlier the phase separation is initiated relative to the sol-gel transition, the coarser the resultant structure becomes, and vice versa. 

Further addition of octanol produced a situation where the stability of the solubilizate-containing micelles (at this concentration in a laminar form) was sufficient to allow their separation as a distinct liquid crystalline phase. Continuing addition of octanol produced first a completely gelled liquid crystalline system, followed by the separation of an isotropic liquid in which water was the solubilizate. 

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