Low-temperature plasma treatment of magnesium stearate Langmuir-Blodgett films

Abstract

Ultrathin Langmuir-Blodgett (LB) multilayers have been the focus of interest for use as gas separation membranes because of their well-defined thickness and defect-free structure. A considerable drawback from a technological point of view is the low thermal, chemical and mechanical stability of these films. One solution to this problem is the conversion of an organic multilayer structure, containing inorganic ions, to an organo-ceramic ultrathin film by low-temperature plasma treatment. This article describes the interfacial behaviour and the deposition of magnesium stearate monolayers and their subsequent conversion to organo-ceramic structures. X-ray, FTIR and AFM measurements were used to characterize the Langmuir-Blodgett (LB) multilayer structures, chemical compositions and surface topographics respectively: The LB-films consist of highly ordered Y-type multilayer structures with a stepwise surface height profile and nearly all amphiphiles are complexed as the magnesium salt. The modification of these LB-films by both argon and oxygen plasma leads to a decrease in the content of organic material by physical ablation and chemical etching processes. Whilst an internal order is retained within the plasma-treated films, the surface roughness increases significantly. Two parameters of the plasma process, the radio frequency power and the exposure time, were varied in order to find suitable process conditions. It is shown that the non-uniform multilayer structure can be converted to a uniform grainy organo-ceramic structure by plasma treatment.