Supramolecular assemblies of surfactants and lipid derivatives on free-standing hybrid nanofilms.

Abstract

A large, free-standing hybrid nanofilm (thickness 35 nm) of zirconia and cross-linked acrylate is stably dispersed in aqueous media via assembly with surfactants and lipid derivatives. These amphiphiles showed three different behaviours. Category 1 is represented by single-chain ionic surfactants of SDS and CTAB and by non-ionic surfactant of Triton X100. In this case, the amphiphile is adsorbed onto the surface of the nanofilm to stably disperse the supramolecular assembly in water but it is desorbed upon further transfer to pure water. Similar behavior is found for double-chain ionic amphiphiles of 2C12N+Br- and 2C10sucSO3-Na+. In Category 2 of non-ionic surfactants of poly(oxyethylene)-based C18En and TWEEN 20, the amphiphile-nanofilm assembly, once formed in aqueous amphiphile solution, remains intact even after transfer to pure water. A similar result is obtained, when 2C12sucSO3-Na+ is used. In the third category, the nanofilm cannot be dispersed in aqueous amphiphiles, as the supramolecular assembly is apparently not formed. Double-chain amphiphiles of 2C18N+Br-, 2C14sucSO3-Na+ and egg yolk lecithin show this behaviour. Although amphiphile-nanofilm assemblies are formed invariably under amphiphile concentrations above their CMCs (Category 1 and 2), some of them show quite slow desorption rate in water (Category 2). This situation is desirable in the design of useful amphiphile-nanofilm assemblies equipped with certain properties of biomembranes, such as fluid molecular ordering on surface and robust nanofilm structure.