(430a) Comparison of Line Tension Measurement Methods for Lipid Monolayers at Liquid-Liquid Coexistence

The line tension between monolayer and bilayer domains governs the distribution and size of lipid rafts in biological membranes and in lung surfactant and other monolayers. Several methods of measuring the line tension between phase-separated liquid ordered-liquid disordered domains in phospholipid-cholesterol systems have been proposed, including a method based on domain size distribution analysis (SD) proposed by Jacob Israelachvili based on a mass-action model combined with the opposing forces of line tension and domain electrostatic energy. A second method is based on the Fourier analysis of boundary fluctuations (BA), which is bet used near critical points where these fluctuations are large. Both these experimental techniques are internally self-consistent but the measured line tension values vary widely between these techniques. To date, no measurement of line tension has utilized multiple experimental techniques to look at the same monolayer system. Here we compare two non-perturbative methods, Fourier analysis of boundary fluctuations (BA) and domain size distribution analysis (SD), to extract the line tension in a 70 mol% DMPC – 30 mol% dihydrocholesterol mixture as a function of surface pressure. We show that BA predicts the expected variation in line tension measurements consistent with the theoretical critical exponent, while SD does not. We conclude that the size distribution of monolayer domains is metastable and primarily determined by the kinetics of domain nucleation and subsequent aging, especially near critical points.