Line tensions, correlation lengths, and critical exponents in lipid membranes near critical points

TL;DR

This study investigates the critical phenomena in lipid membranes near phase transition points, measuring line tension and correlation lengths to confirm they follow the two-dimensional Ising universality class.

Contribution

The paper provides quantitative measurements of critical exponents in lipid membranes, demonstrating their consistency with the Ising model predictions.

Findings

Critical exponent nu=1.2±0.2 matches Ising prediction nu=1.

Critical exponent beta=0.124±0.03 aligns with Ising value 1/8.

Line tension approaches zero near critical point.

Abstract

Membranes containing a wide variety of ternary mixtures of high chain-melting temperature lipids, low chain-melting temperature lipids, and cholesterol undergo lateral phase separartion into coexisting liquid phases at a miscibility transition. When membranes are prepared from a ternary lipid mixture at a critical composition, they pass through a miscibility critical point at the transition temperature. Since the critical temperature is typically on the order of room temperature, membranes provide an unusual opportunity in which to perform a quantitative study of biophysical systems that exhibit critical phenomena in the two-dimensional Ising universality class. As a critical point is approached from either high or low temperature, the scale of fluctuations in lipid composition, set by the correlation length, diverges. In addition, as a critical point is approached from low temperature, the line tension between coexisting phases decreases to zero. Here we quantitatively evaluate the temperature dependence of line tension between liquid domains and of fluctuation correlation lengths in lipid membranes in order to extract a critical exponent, nu. We obtain nu=1.2 plus or minus 0.2, consistent with the Ising model prediction nu=1. We also evaluate the probability distributions of pixel intensities in fluoresence images of membranes. From the temperature dependence of these distributions above the critical temperature, we extract an independent critical exponent beta=0.124 plus or minus 0.03 which is consistent with the Ising prediction of beta=1/8.