Shape of Mixed Micelles: Cylinders or Spheres? Theoretical Analysis

TL;DR

This paper presents a theoretical model to predict whether micelles formed by surfactants and phospholipids are cylindrical, spherical, or disc-like, based on thermodynamic and elastic properties, aligning with experimental observations.

Contribution

It introduces a comprehensive theoretical framework considering Helfrich energy and entropy to determine micelle shapes under various conditions, advancing understanding of micellization.

Findings

Cylindrical micelles are most probable for typical elastic parameters.

Conditions for formation of spherical and disc-like micelles are identified.

Model aligns well with existing experimental data.

Abstract

We develop a theoretical model for the solubilization of phospholipid bilayers by micelle-forming surfactants. Cylindrical micelles, disc-like micelles and spherical micelles are considered as alternative resultant structures. The main question addressed is what kind of micelles can be expected under various thermodynamical conditions. Our analysis is based on a theoretical model that accounts for Helfrich energy of curvature of amphiphile monolayers and for the entropy of mixing of lipids and surfactants in mixed aggregates. We conclude that for usual values of the elastic parameters of amphiphile monolayers cylindrical micelles are the most probable aggregates resulting from micellization of phospholipid by surfactants. This conclusion is consistent with available experimental data. Conditions of formation of disc-like and spherical micelles are also determined.