Langmuir films cast from poly(dialkylsiloxanes) on water-ethylene glycol subphases

The behavior of monomolecular and thin films of poly(dimethylsiloxane) and poly(diethylsiloxane) spread on the subphases of ethylene glycol and its mixtures with water was studied by measuring surface pressure as a function of specific surface area per repeating monomer unit. It was shown that poly(dimethylsiloxane) forms monolayers on pure ethylene glycol with a thickness equal to two times the thickness of a molecule occurring in a flat conformation. The surface pressure isotherm shows a second step corresponding to the formation of a layer with a fourfold thickness of the monolayer. Films cast from mixed ethylene glycol-water subphases demonstrate characteristics intermediate between those of films formed on pure water and pure ethylene glycol. Poly(diethylsiloxane) forms stable monolayers on ethylene glycol. The mechanism explaining the formation of layers on the alcohol subphase is advanced.