Phase polymorphism by mixing of poly(oxyethylene)–poly(dimethylsiloxane) copolymer and nonionic surfactant in water

Abstract

The phase behavior of the water/poly(oxyethylene)–poly(dimethylsiloxane) copolymer (Si 25C 3EO 51.6)/pentaoxyethylene dodecyl ether (C 12EO 5) ternary system has been studied. Both the silicone copolymer and the surfactant have equal volumes of hydrophilic and lipophilic parts; i.e., these are balanced amphiphiles. Although only a lamellar phase is observed in water–Si 25C 3EO 51.6 and water–C 12EO 5 binary systems, a variety of liquid crystalline phases, including normal micellar cubic (I 1), hexagonal (H 1), bicontinuous cubic (V 1), lamellar (L α ), reverse bicontinuous cubic (V 2), and reverse hexagonal (H 2), are observed in the copolymer-rich region of the ternary phase diagram. The small C 12EO 5 molecules dissolve at the hydrophobic interface in the thick bilayer of the Si 25C 3EO 51.6 L α phase occupying a large area of the total interface of the aggregates and modulate the curvature of the aggregates. Hence a variety of self-assembled structures are observed. In contrast, Si 25C 3EO 51.6 is not dissolved in the thin bilayer of the C 12EO 5 lamellar phase (L ′ α ). Hence, the C 12EO 5 L ′ α phase coexists with copolymer-rich L α and H 2 phases. Consequently, small surfactant molecules are dissolved in a large silicone copolymer aggregate to induce a change in layer curvature, but a large copolymer molecule is hard to incorporate with surfactant aggregates.