Phase diagrams for monolayers of long-chain thioacetates

Brewster-angle microscopy has been employed to determine the phase diagrams of Langmuir monolayers of several long-chain thioacetates: S-hexadecyl acetate, S-octadecyl acetate, S-eicosyl acetate and S-docosyl acetate. The phases in S-octadecyl acetate were identified by carrying out a dilution study with octadecyl acetate. A composite thioacetate diagram could be established by superimposing the diagrams for the individual thioacetates with suitable shifts to account for the differences in chain length. Infrared reflection-absorption spectroscopic studies of monolayers of octadecyl acetate and S-octadecyl acetate show that the differences between their phase diagrams can be attributed, at least in part, to the extent of hydrogen bonding of the carbonyl group. (C) 2000 Elsevier Science B.V. All rights reserved.