Theory of the asymmetric ripple phase in achiral lipid membranes

TL;DR

This paper develops a phenomenological two-parameter theory to explain the complex phase behavior and microstructure of achiral lipid membranes, especially the asymmetric ripple phase, which previous models could not fully describe.

Contribution

It introduces a coupled scalar and vector order parameter model that successfully captures all key features of the ripple phase and the overall phase diagram.

Findings

Reproduces the microstructure of the asymmetric ripple phase

Provides a unified description of phase transitions in achiral lipid membranes

Aligns well with experimental observations of phase features

Abstract

We present a phenomenological theory of phase transitions in achiral lipid membranes in terms of two coupled order parameters -- a scalar order parameter describing lipid chain melting, and a vector order parameter describing the tilt of the hydrocarbon chains below the chain-melting transition. Existing theoretical models fail to account for all the observed features of the phase diagram, in particular the detailed microstructure of the asymmetric ripple phase lying between the fluid and the tilted gel phase. In contrast, our two-component theory reproduces all the salient structural features of the ripple phase, providing a unified description of the phase diagram and microstructure.