Abstract
The double-chain cationic surfactant (dioctadecyl dimethyl ammonium chloride ; DODAC), is used as a fabric softener or for hair rinsing. The morphology of DODAC aggregates adsorbedon a hydrophilic surface were investigated by electron and atomic force microscopy.
An aqueous DODAC dispersion was dropped on a hydrophilic nitrocellulose membrane which was then observed by transmission electron microscopy using negative-staining. Multilayer vesicles (250 nm in mean diameter) were adsorbed on the hydrophilic surface. Following ultrasonication, small unilamellar vesicles could be seen on the surfaces.
The texture and thickness of vesicles on the mica surface were examined by atomic force electron microscopy. The thickness of ultrasonicated vesicles after drying was 4 nm. Interior water of the vesicles was eliminated by drying, and the closed-shell structure collapsed. And this may have caused the bilayer to take on an interdigitated structure.
By measuring the bending resistance and water absorption, it was found that both properties largely depend on the size of the vesicles. Smaller vesicles are superior for use in fabric softeners.
DODAC molecules do not form monolayers on a hydrophilic surface, but are adsorbed as vesicles.
