The purified myelin membrane is the starting material for the biochemical studies such as isolation of detergent resistant membrane fractions. Normally, the last procedure involves the extraction of lipids on non-ionic detergents under cooling. The thermotropic behavior of purified myelin membranes is examined in the 5-46 ºC for a series of different solvent systems by SAXS/WAXS and DSC. Additionally we succeeded in producing planar multilayers of myelin on Si/SiO2 wafers by testing different spreading techniques. The objective here is to take advantage of planar scattering geometry in SANS experiments, controlling the ionic content of the aqueous media. The results with SAXS and SANS are consistent in showing that, regardless of the aqueous media, the myelin membrane becomes heterogeneous below room temperature. The heterogeneous state is further stabilized by ionic media like physiological solution, then phase coexistence persists up to the border of the physiological temperature. The extreme case is the one of Ca2+ at high concentration (over 20 mM), then the phase coexistence is permanent at least up to 46 ºC. Nevertheless, the relative proportion of the phases, and thus probably the phase composition, markedly changes with temperature. From a general point of view, it has been suggested by multiple authors that cell membranes are set at the border of phase transition or critical points for phase mixing. The results showed appear to fit into this general framework.
