Surface effects of lyotropic liquid crystalline phases of nonionic surfactants

Interfacial effects of structure and phase transitions in the lyotropic liquid crystalline phase of nonionic oligo(ethyleneoxide)-mono-n-alkylethers are summarized. In all phases investigated, we observed a coupling of the lattice planes of the liquid crystals to the interface, ranging over mesoscopic distances. In the case of the lamellar phase of the C12H4+water system we did not detect an influence of a solid/liquid interface either on the microscopic structure or on the phase transition temperature, while the properties of the hexagonal phase of the C12H5+water system are strongly influenced by the liquid/air interface. In a layer of about 300 nm thickness the lattice parameter is reduced and the isotropization temperature is increased leading to a shift of the hexagonal/isotropic coexistence line in the phase diagram with respect to the bulk curve.