Robustness of monolayers on the solids; comparative studies on thermal, solvent, pH, and mechanical resistance among 1-layer LB films of cadmium arachidate and alkylchlorosilanes

The resistance of Langmuir–Blodgett (LB) monolayers of n-alkylchlorosilane compounds against the external disturbances has been investigated. The silane compounds used as film materials are trichloro(octadecyl)silane (TCOS), dichloro(methyl)(octadecyl)silane (DCMOS), and chloro(dimethyl)(octadecyl)silane (CDMOS). Cadmium arachidate (CdA) monolayers are also employed for comparison. FT-IR transmission and reflection absorption spectroscopic analysis of 5-layer LB films of the silanes indicates that the film molecules have residual silanol groups. The results reveal that the silane molecules can be fixed on the hydroxylic solid surfaces with covalent bonds after the monolayers are transferred on such substrates. Thermal stability and dissolution resistance of the LB monolayers on glass slides are investigated by the change of wavenumbers and intensities of CH2 stretching bands in FT-IR transmission spectra. It becomes clear that the TCOS monolayers are very stable against heating, organic solvents and acid, whereas the DCMOS and CDMOS monolayers are very weak. The mechanical durability of the monolayers is investigated by following friction coefficient profiles. The results reveal that the friction coefficients for the silane monolayers begin to increase after a few transits under high normal loads although those for the CdA monolayers maintain lower values. These results can be interpreted from the view point of monolayer structures.