Premicellar aggregation of amphiphilic molecules: Aggregate lifetime and polydispersity.

A recently introduced thermodynamic model of amphiphilic molecules in solution has yielded under certain realistic conditions a significant presence of metastable aggregates well below the critical micelle concentration-a phenomenon that has been reported also experimentally. The theory is extended in two directions pertaining to the experimental and technological relevance of such premicellar aggregates. (a) Combining the thermodynamic model with reaction rate theory, we calculate the lifetime of the metastable aggregates. (b) Aggregation number fluctuations are examined. We demonstrate that over most of the metastable concentration range, the premicellar aggregates should have macroscopic lifetimes and small polydispersity.