Relaxation Kinetics of Micellization in Micelle-Forming Block Copolymer in Selective Solvent

Relaxation kinetics of micelle-forming poly(α-methylstyrene)- block -poly(vinylphenethyl alcohol) (PαMS- b -PVPA) in a selective solvent, benzyl alcohol (BA), has been investigated by time-resolved static light scattering. The time evolution of apparent molecular weight ( M wapp ) and radius of gyration ( R gapp ) were measured in the course of micellar relaxation, which was induced by temperature jumps (T-jumps) within the micellar region. The following two types of T-jumps were performed: (1) type I, a T-jump from shallow T-depth to deep T-depth with the change in depth, Δ T, being defined by Δ T = cmt − T (cmt, the critical micelle temperature), and (2) type II, a T-jump from deep Δ T 0 to shallow Δ T with Δ T 0 > Δ T . In a type I T-jump, the majority of existing unimers form new micelles and some of unimers enter into existing micelles formed in the premicellization. In a type II T-jump, instead of monotonical changes in micellar fraction and size from the starting state to the final state, the micelles first decompose with dominantly decreasing micellar size, and then the micellar size recovers to approach the final size. The change of M wapp in the type I T-jump is characterized by a time constant (τ I ) which decreases with increasing the polymer concentration. The τ I is almost equal to the time constant of the fast process in the direct micellization from unimer state (τ 1 ). The relaxation processes in the type II T-jump are described by time constants τ D and τ R for micelle decomposition and recovery, respectively. τ D is much smaller than τ R, having no concentration dependence, while τ R has a concentration dependence, having almost the same value as τ 1 . The occurrence of micellar decomposition as the first process in the type II T-jump is thermodynamically interpreted by a phenomenological theory.