Mesh phases in tetramethylammonium perfluorodecanoate–water ternary systems

Abstract

The evolution of the phase behaviour and lyotropic phase structures formed in the tetramethylammonium perfluorodecanoate (C10TMA)–water system upon the addition of a third component (tetramethylammonium chloride (TMACl) or 1H, 1H-perfluoro-1-decanol (C10ol)) have been studied using optical polarizing microscope, 2HNMR and small angle X-ray scattering (SAXS) in order to understand the correlated mesh phase with R3barm space group. With increasing concentration of both additives, the Mh1(R3barm) phase changes to a random mesh phase Mh1(0) via a two phase region. The structure of the Mh1(R3barm) phase is essentially unaltered with addition of TMACl or C10ol until the phase change to Mh1(0). With higher additive concentration, the water fraction within a mesh layer of the Mh1(0) phase is decreased. It is proposed that the transition from the Mh1(0) to Mh1(R3barm) phases is driven by a reduction in the electrostatic interlayer interaction enabling non-electrostatic repulsive interactions to dominate. This is because of the strong association of the TMA counter ion with the head group region, the increase of water within the mesh layers and the decrease in separation of the mesh layers in the Mh1(R3barm) phase. It is also shown that the hydrophobic counter ion has to be small
relative to the surfactant for both mesh and correlated mesh to occur.