부산대학교 도서관

Nonionic surfactants of the alkyl polyoxyethylene ether variety commonly form hexagonal (H1) or lamellar (Lα) lyotropic mesophases with water1. Less well-known is the frequent occurrence of I1 or V1 cubic mesophases.* No reports exist to date of the occurrence of reversed phases with these materials. While the surfactants are known to form several solid complexes with water, their melting points are below those of the anhydrous surfactants2. In an optical microscope study of the liquid crystals formed by water penetration into n-hexadecyl trioxyethylene glycol ether (C16EO3) we have observed a solid complex with a melting point above that of the pure surfactant. We also observe a cubic region which we classify as a reversed structure (V2). Moreover, the occurrence of a refractive index discontinuity within this region strongly suggests that two different phases are present. The cubic region coexists with water for part of the temperature range over which it occurs. When water droplets form within the cubic region on heating, they adopt angular shapes which suggest that a single, long-range structure exists, rather than a "powder" orientation of domains.