Coexistence of rigid crystalline and liquid crystalline phases in lecithin-water mixtures.

X-ray diffraction measurements show that the beta'-crystalline to liquid crystalline transitions of dipalmitoyl lecithin-water mixtures take place over temperature ranges of several degrees, and by the gradual disappearance of one crystalline state accompanied by the gradual appearance of the other. The narrowness of the low angle X-ray lines indicates that the two crystalline states exist in separate phases. At a given temperature, the liquid crystalline phase has the greater water content. The bilayers of the liquid crystalline phase are thinner than those of the beta'-crystalline phase while the distances between bilayers are essentially equal in the two phases.