Applying the Langmuir-Blodgett technique to a well defined model detergent system

The Langmuir-Blodgett technique is used to obtain a well defined model detergent system. Spreading monolayers of arachidic acid as a model organic contaminant are transferred onto glass plates untreated and treated with two silane coupling agents, gamma -aminopropyltriethoxysilane (APTES) and methyltriethoxysilane (MTES). Brewster angle microscopic images show that the LB films of arachidic acid are uniformly deposited on the substrate. Glass plates with the LB films are ultrasonically washed in various aqueous solutions, and the detergency is evaluated from the change in FTIR spectra of the substrate due to washing. The efficiency of detergency decreases as a result of the silanization of glass, especially for the APTES treated glass. The wettability and the surface charge of the substrate play important roles in the detergency, suggesting that the LB films of arachidic acid are removed directly from the substrate. Removal of LB films from the APTES-treated glass increases with increasing surfactant or ethanol concentration, and the removal rate strongly depends on temperature. As a removal technique without washing liquids, exposure of the substrates with LB films to 172 nm ultraviolet light is also attempted.