Equilibrium Onions?

TL;DR

This paper proposes a theoretical model demonstrating the stability of onion phases in pure lamellar systems through negative Gaussian curvature modulus and elastic moduli coupling, supported by experimental comparisons.

Contribution

It introduces a novel model explaining stable onion phases in pure lamellar systems without excess solvent, emphasizing the role of curvature and elastic moduli.

Findings

Stable onion phases can exist in pure lamellar systems due to negative Gaussian curvature.

The model aligns qualitatively with experimental observations on surfactant systems.

Polydisperse size distribution (Apollonian packing) enables space-filling without elastic distortion.

Abstract

We demonstrate the possibility of a stable equilibrium multi-lamellar (``onion'') phase in pure lamellar systems (no excess solvent) due to a sufficiently negative Gaussian curvature modulus. The onion phase is stabilized by non-linear elastic moduli coupled to a polydisperse size distribution (Apollonian packing) to allow space-filling without appreciable elastic distortion. This model is compared to experiments on copolymer-decorated lamellar surfactant systems, with reasonable qualitative agreement.