Poly phase transition parameters

In spite of the constant density of the gel, the friction of the poly(N-isopropylacrylamide) gel reversibly decreases by three orders of magnitude and appears to diminish as the gel approaches a certain temperature. This phenomenon should be universal and may be observed in any gel under optimal experimental conditions of the solvent composition and the temperature because the unique parameter describing the friction is the correlation length which tends to diverge in the vicinity of the volume phase transition point of gels. The exponent v for the correlation length obtained from the frictional experiment is far from the theoretical value. It will, therefore, be important to study a poly(N-isopropylacrylamide) gel prepared at the critical isochore where the frictional property of gel may be governed by the critical density fluctuations of the gel. 

D. Patterson in 1968 based on an analysis of Flory-Rehner theory. It took ten years for the phenomenon to be experimentally observed after prediction. It was found by T. Tanaka that, when a critical amount of an organic solvent was added to a water-swollen poly(acrylamide) gel, the gel collapses. Many gels of synthetic and natural polymers have been studied. Subsequent experiments showed that a volume phase transition (swelling/collapse) could also be brought about by changes in other environmental parameters such as pH, ionic strength, and temperature. 

For some thermosensitive polymers, whose properties in water depend on the temperature, such as poly(vinyl methyl ether) (PVME), the microphase separation can be induced directly during the irradiation process. Depending on the applied dose, the temperature of the solution increases. By choosing appropriate experimental parameters the irradiation can be performed above the phase transition temperature and the structure of the collapsed polymer chains will be fixed (Figure 3). Globular particles with diameters in the range of 250-600 nm can be obtained by static electron beam irradiation starting from a 4gT PVME solution. ... 

The nonisothermal crystallization process of isotactic poly(butene-l) as a function of cooling rate was investigated by Silvestre et al. [77]. The samples were melted at 160°C for ten minutes and cooled to room temperature at different rates 0.5, 1, 2 and 4°C/min. The induction time and the time required for the completion of the phase transition were found to decrease with cooling rate. The calculated CRC parameter was 18 h. ... 

---