Phase Separation and Near-Critical Fluctuations in Two-Component Lipid Membranes: Monte Carlo Simulations on Experimentally Relevant Scales

By means of lattice-based Monte Carlo simulations, we address properties of two-component lipid membranes on the experimentally relevant spatial scales of order of a micrometer and time intervals of order of a second, using DMPC/DSPC lipid mixtures as a model system. Our large-scale simulations allowed us to obtain important results previously not reported in simulation studies of lipid membranes. We find that, within a certain range of lipid compositions, the phase transition from the fluid phase to the fluid-gel phase coexistence proceeds via near-critical fluctuations, while for other lipid compositions this phase transition has a quasi-abrupt character [1, 2]. The line tension characterizing lipid domains in the fluid-gel coexistence region is found to be ∼ 2 pN. When approaching the critical point, the line tension, the inverse correlation length of fluid-gel spatial fluctuations, and the corresponding inverse order parameter susceptibility of the membrane vanish [2]. All these results are in agreement with recent experimental findings for model lipid membranes. We observe transient subdiffusive behavior of lipids in the presence of near-critical fluctuations, which is a new result important for understanding the origins of subdiffusion in cell membranes. The effects of the interaction of the membrane with the cytoskeleton will be discussed as well.[1] J. Ehrig, E. P. Petrov, and P. Schwille, arXiv:1010.1207.[2] J. Ehrig, E. P. Petrov, and P. Schwille, arXiv:1009.4860.