The effect of casting solvent quality on the structure of polymeric Langmuir-Blodgett films

The effect of casting solvent quality (good vs. [symbol: see text] solvent) on the structure of Langmuir-Blodgett films of a flexible-chain polymer [poly(dimethylsiloxane)] was examined on the basis of differences in the shape of Langmuir-Blodgett isotherms for two solvents, two temperatures, four polymer molecular weights, and three compression rates. The magnitude of a new index that describes the shape characteristics of the isotherm beyond the point of monolayer formation is found to be capable of separating all 48 isotherms studied into two groups, exclusively on the basis of the quality of the casting solvent. Experimental observations are supplemented by qualitative polymer physics interpretations regarding the structure of the films upon casting and compression.