For more than ten years now, many efforts have been done to identify and characterize nature of obstructed diffusion in model and cellular lipid membranes. Amongst all the techniques developed for this purpose, FCS, by means of determination of FCS diffusion laws, has been shown to be a very efficient approach. In this paper, FCS diffusion laws are used to probe the behavior of a pure lipid and a lipid mixture at temperatures below and above phase transitions, both numerically, using a full thermodynamic model, and experimentally. In both cases FCS diffusion laws exhibit deviation from free diffusion and reveal the existence of domains. The variation of these domains mean size with temperature is in perfect correlation with the enthalpy fluctuation.
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