SPONTANEOUS BOILING UP AS A SPECIFIC RELAXATION PROCESS IN POLYMER-SOLVENT SYSTEMS

The phenomenon of spontaneous bubble nucleation in extremely supersatu rated (superheated) polymer-solvent systems has been studied experimen tally. Spontaneous boiling-up temperatures T for polystyrene and poly (ethylene glycol) solutions in a number of solvents have been measured at different values of pressure p and weight fraction of polymer c by the pulse heating method. The heating rate T varied from 10(5) to 10( 7) K/s. For all systems studied, the values of T have been found to i ncrease with increasing p and c. The T(p, c) dependence is discussed with the use of the data on the degree of compatibility of components. The peculiarities of polymeric solutions manifest themselves in the r egion c --> 1, as follows: (i) an abrupt increase (by 1-2 orders of ma gnitude) in the slope of the T(c) dependence, and (ii) the appearance of the dependence of T values on the heating rate. Our approach to t he interpretation of this result assumes a change in the initial compo sition of a solution in the course of heating due to polymer decomposi tion. An example of the extended phase diagram of a polymer-solvent sy stem including the kinetic surface of T(p, c) is given. (C) 1996 John Wiley & Sons, Inc.