Calcitropic Non-ionic Surfactant Lamellar Phases

Abstract

The aqueous non-ionic surfactant decaethylene glycol hexadecyl ether (C16EO10), in the presence of CaCl2, forms novel “calcitropic” lamellar liquid-crystal phases. Thin films of these materials display notable structure sensitivity to the hydrophobicity or hydrophilicity of the underlying support. A structure-bonding model of these materials is based upon Ca2+-crown ether-like coordination to the decaethylene glycol head group of one or two of the surfactant molecules. Ca2+ binding of two surfactant head groups, makes possible cis- and trans-conformations for the alkyl tails, resulting in normal and inverted structures with preferences for hydrophilic and hydrophobic surfaces, respectively. The extent of Ca2+ ion clustering in the head group determines the geometrical packing requirements of the surfactant and the overall dimensions of the resulting lamellar liquid-crystal phases. The effect of various phosphate reagents (H3PO4, KH2PO4, K3PO4) on these “calcitropic” liquid-crystal phases has also been inv...