Determination of the elastic constants of a polymeric Langmuir-Blodgett film by Brillouin spectroscopy

Abstract Brillouin scattering experiments have been performed and theory developed on polymeric uniaxial Langmuir-Blodgett films (poly(γ-methyl- d -glutamate-co-γ-n-alkyl- l -glutamate)) with their preferred molecular axis in the plane of the film. Surface acoustic modes, guided modes and bulk modes were obsersed. Samples with from 10 to 560 molecular monolayers were measured and the elastic constants were found to be of hexagonal symmetry and not to depend on the film thickness. The whole set of elastic constants of the Langmuir-Blodgett films was determined from the spectra: c 11 = 4.74 GPa , c 33 = 10.8 GPa , c 12 = 3.43 GPa , c 13 = 3.57 GPa and c 44 = 0.91 GPa .