Premicellar aggregation of amphiphilic molecules: Aggregate lifetime and polydispersity

TL;DR

This paper extends a thermodynamic model of amphiphilic molecules to analyze premicellar aggregates, revealing they can have long lifetimes and low polydispersity below the critical micelle concentration, with implications for experimental and technological applications.

Contribution

The study combines thermodynamic and reaction rate models to quantify aggregate lifetimes and examines aggregation number fluctuations, providing new insights into premicellar aggregate stability.

Findings

Metastable aggregates have macroscopic lifetimes below the critical micelle concentration.

Aggregates exhibit small polydispersity over most of the metastable concentration range.

Theoretical results align with experimental observations of premicellar phenomena.

Abstract

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.