Phase transition, high polymer fluids

Polymer-Fluid Equilibria and the Glass Transition Most polymer systems fall in the Class HI or Class V phase diagrams, and the same system can often change from one class into the other as the polymer s molecular weight changes. Most polymers are insoluble in CO9 below 100°C, yet CO9 can be quite sohible in the polymer. For example, the sorption of CO9 into silicone rubber is highly dependent upon temperature and pressure, since these properties have a large influence on the density and activity of CO9. 

Cellulose acetate phthalate forms a pH-triggered phase transition system, which shows a very low viscosity up to pH 5. This system will coacervate in contact with the tear fluid (pH 7.4), forming a gel in few seconds and releasing the active ingredients over a prolonged period of time. The half-life of residence on the rabbit corneal surface was approximately 400 seconds compared to 40 seconds for saline. However, such systems are characterized by a high polymer concentration, and the low pH of the instilled solution may cause discomfort to the patient. 

For the design of new, innovative processes to separate low-volatile components such as drugs or polymers with supercritical fluids, experimental data are needed. We designed and built a new apparatus capable of investigating phase equilibria in the occuring complex systems up to 200 bar and 250°C. Phase transitions are determined optically. Samples of the coexisting phases even at high concentration and viscosity are taken. Solid particles can be collected. 

Experimentally the high-temperature and low-temperature LEV lines for a polymer-solvent mixture superpose onto the vapor pressure curve of the pure solvent. The EEV line at high temperatures is bounded at one end by a liquid -I- vapor fluid transition in the presence of a second liquid phase and, at the other end, by the intersection of the higher-temperature branch of the critical mixture curve where a liquid -I- liquid fluid transition occurs in the presence of a vapor phase. 

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