Immiscible solvent demixing

Studies described in earlier chapters used cellular automata dynamics to model the hydrophobic effect and other solution phenomena such as dissolution, diffusion, micelle formation, and immiscible solvent demixing. In this section we describe several cellular automata models of the influence of the hydropathic state of a surface on water and on solute concentration in an aqueous solution. We first examine the effect of the surface hydropathic state on the accumulation of water near the surface. A second example models the effect of surface hydropathic state on the rate and accumulation of water flowing through a tube. A final example shows the effect of the surface on the concentration of solute molecules within an aqueous solution. 

Ternary solutions of immiscible polymers in a low-molecular solvent display wide miscibility gaps. Consequently, they invariably involve demixing above a critical concentration of total polymer by spinodal decomposition and subsequent coarsening processes. When solvent evaporation progresses the enhanced viscosity will slow down the rate of phase separation to a level at which no further phase changes can be observed. 

In this process phase inversion is introduced by lowering the temperature of the polymer solution. A polymer is mixed with a substance that acts as a solvent at a high temperature and the polymer solution is cast into a film. When the solution is cooled, it enters into an immiscible region due to the loss of solvent power. Liquid-liquid demixing occurs and the solution is separated into two phases, i.e., the polymer-lean phase is dispersed as droplets in the polymer-rich phase. Further, cooling causes gelation of polymer. Because the solvent is usually nonvolatile, it must be removed with a liquid that is miscible with the solvent but not miscible with the polymer. The membranes made by the TIPS method have pore sizes in the range of 0.1 and 1 pm and the pore structure is uniform in the depth direction. ... 

In general, due to the strong immiscibility of macromolecular blends, polymer mixtures demix during the rapid solvent-casting process thus leading to different surface structures [14,15,76,77]. The final surface structure depends on the spin-casting solvent [34], the blend [29,37,48,41,78-83] and polymer chemical composition [80], the polymer-polymer [6,14,30,35,80] and polymer-substrate [34,35,37,82,84,85] interactions in the formation of the domain structures [15,86], the thickness of the film [34,87-90], (e) tanperature [91] and (f) the evolution of the spin-cast structures toward... 

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