Solvent-coagulant miscibility, coagulated

Fig. 9. Effect of the solvent-coagulant miscibility on polymer structure, (a) ei 2 = 0, (b) si-2 = 0.5, (c) ei-2 = 0.77, and (d) si-2 = 1.5. The structures are for a coagulation time t = 0.02 s, except (d) which is for t = 0.03 s. All the other parameters are the same as in Figure 8. The extent of shrinking of the poljrmer-coagulant interfaces with respect to their initial positions have not been represented. Courtesy of Journal of Polymer Science.

Importance of the Solvent-Coagulant Miscibility. To recall, the miscibility between solvent and coagulant is, in this model, controlled by the interaction energy parameter i 2- A study of the effect of that parameter on the morphology of the precipitated polymer is presented in Figures 9a-d, for approximately the same coagulation time t = 0.02-0.03 s. For perfect mixing (ei 2 =... 

Most of the membranes listed in Table 5.20 are formed through phase separation processes, i.e., melt extrusion or coagulation of a polymer solution by a nonsolvent. In melt extrusion, a polymer melt is extruded into a cooler atmosphere which induces phase transition. The melt extrusion of a single polymer usually gives a dense, isotropic membrane. However, the presence of a compound (latent solvent) that is miscible with the polymer at the extrusion temperature but not at the ambient temperature, may lead to a secondary phase separation upon cooling. Removal of the solvent then yields a porous isotropic membrane. Anisotropic membranes may result from melt extrusion of a dope mixture of polymers containing plasticizers. 

Water-miscible solvents such as acetone at high pH coagulate sodium silicate, precipitating it as a solid or semiliquid coacervate, w.hich can be reacted with acid. 

How does the choice 6f the solvent now influence the membrane structure when water is used as the nonsolvent and cellulose acetate as the polymer The first interesting point is that the slope of the tie lines, which connect the two phases in equilibrium in the two-phase region, is less steep when the mumal affinity (or miscibility) between the solvent and the nonsolvent decreases [35,43]. The binodal and tie lines are depicted in figure in - 43 for the system water/solvent/CA, where the tie lines become steeper as the miscibility with water increases in the order DMF > dioxan > acetone >THE Light transmission measurements conducted on the same water/solvent/CA systems are shown in figure III - 44. When DMSO (e , DMF (d) and dioxan (c) are used as the solvent, instantaneous demixing occurs. Only when the solvent is added to the coagulation bath is... 

In this process, a polymer dissolved in a water miscible solvent is coated thinly onto the fabric. The porous structure is developed by passing through a coagulation bath where water displaces the solvent. For example, the textile substrate is coated with polyurethane solution, where DMF is used exclusively as the solvent, and the fabric is passed through a coagulation bath containing water, where water displaces the solvent to give a porous structure. 

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