| Abstract
| - Intermediate phases in lyotropic liquid crystalline systems provide fascinating topological links betweenthe hexagonal and lamellar phases. The formation of intermediate phases has been shown to result froma delicate balance of interaction in amphiphilic systems. Their structures fall into one of three broadclasses: ribbon, mesh, or bicontinuous. In concentrated binary mixtures of nonionic surfactants and water,the intermediate phase is observed to replace the bicontinuous cubic phase under certain circumstances.In this paper we present more detailed scattering results from the mesh intermediate phases in theC30EO9/2H2O and C16EO6/2H2O systems. We show that the space group is indeed R3̄m and consists of athree-connected mesh structure with no interlayer connections. Three different mathematical models forthe structure, a minimal curvature surface, a rod-box model, and a simple rod model, are fitted to therevised lattice parameters. All give good values for the surface area per molecule and the aggregate thicknessparameter. They show that the progressive decrease in the ethylene oxide hydration with increasingtemperature causes the progressive decrease in surface curvature. Also in this paper we address thestructural relationship between the R3̄m mesh phase and adjacent phases in both surfactant systems.
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