Shape fluctuations of spherical micelles

Abstract

The thermal excitation of capillary waves on the surface of a spherical micelle has been analysed in an approximate manner using a series expansion in spherical harmonics and restricting the treatment to small amplitudes. The potential energy governing the dynamics of these motions is computed as the surface tension, γ, of the micelle multiplied by its surface area, A. It is found that a closed, ordinary surfactant micelle in aqueous solution with γ≈ 25 mN m^–1 exhibits a root-mean-square dispersion, σ_r/R, of its radius of several percent because of shape fluctuations on the time-scale 10^–10s. The present study also indicates that (closed) micellar or microemulsion droplets with γ≲ 1 mN m^–1 experience large fluctuations in geometry.