Al~tract
The pseudobinary phase diagram of DPPC/C~2E4 at excess water was investigated by DSC, 2H-, 31p-NMR and freeze fracture electron microscopy in a wide range of concentrations and temperatures. Compared with previously published papers on phase behaviour of DPPC/Triton X-100 and DMPCfl'riton X-100 [13,41], we do not find any total solubilisation of the bilayer membrane within the range of molar fractions x = 0 to x = 0.95. The estimated phase diagram implies a strong non-ideal mixing behaviour in the gel phases with peritectic and eutectic behaviour and complete miscibility in the liquid crystalline L a phase. Two mixing gaps were observed in the gel phase between x = 0.2 and x = 0.95. One peritectic point with an incongruently melting lamellar gel compound complex formation at a molar ratio of nDpvc/ncl2~ = 3:4 (X = 0.57) and one eutectic point at x = 0.9 are a peculiar feature of this system. 2H-NMR measurements employing selectively deuterated surfactant and 3~p-NMR experiments clearly indicate a lamellar liquid crystalline phase La for the high-temperature phase in the whole mixing range. At low surfactant concentrations 0 < x < 0.15 the formation of the rippled phase Pr in a defined region of temperature can be observed by freeze fracture electron microscopy.