Short-Term Penetration beyond Diffusion Spinodal of a Mixture: Interaction of Liquid-Liquid and Liquid-Vapour Transitions

The article considers a relaxation of the water/polypropylene glycol-425 solution with a lower critical solution temperature (LCST) following its pulsed superheating concerning liquid-liquid and liquid-vapor equilibrium lines, as well as the liquid-liquid spinodal. Superheating was performed using the pulsed heat generation method in a micro-sized wire probe. The main heating mode was the constant (over the pulse length) power mode. Characteristic heating rates ranged from 0.05 × 105 to 2 × 105 K/s, while the degree of superheating concerning the spinodal was up to 200 K. The temperature of spontaneous boiling-up and the amplitude of the corresponding signal were monitored as functions of the heating rate set by the power value. The results demonstrate an example of the interaction of liquid-liquid and liquid-vapor phase transitions, as well as the spinodal decomposition of a solution with LCST against the background of its unstable states. We proposed a physical model to explain the minimum spontaneous boiling-up temperature revealed within a certain range of heating rates, which is not typical of completely miscible solutions. Further research will focus on establishing a general criterion for the possibility of spinodal decomposition of such solutions under the conditions of rapid heating.