Abstract
Summary: We consider certain general features of aggreβ gation (micellization) processes in solutions of amphiphilic molecules, in particular, blockβcopolymers. We demonstrate that nonβequilibrium effects can be very important for micellization. In particular, we show that micelle formation at the conventional (equilibrium) critical micelle concentration (CMC, $c_c$) can be inhibited by high activation energy barriers. This is likely to be the case when the micelles are large. In this case an aggregation actually occurs at higher concentrations, above an apparent CMC, $c_{\rm a}$. The concentration $c_{\rm a}$ can be much higher than the equilibrium CMC. Hence significant hysteresis effects are inherent in amphiphilic systems since micelle formation and dissociation are activation processes. To further clarify this idea we consider relaxation of a micellar system after a temperature jump (or a jump of another essential parameter) and discuss qualitatively different relaxation times corresponding to the relaxations of the micellar sizes and of the total number of micelles. We also discuss different kinetic pathways of micelle formation and relaxation and show that in certain cases the idealβgas (combinatorial) contribution to the micelle free energy is significant for the kinetics.
Micelle association and dissociation times vs. reduced concentration.
magnified imageMicelle association and dissociation times vs. reduced concentration.