Surface viscoelastic behaviour of polymeric Langmuir monolayers

Abstract

Viscoelastic behaviour in Langmuir monolayers of a photosensitive polyacrylate is investigated by a combination of surface quasielastic light scattering, and a new technique, which we call oscillating needle surface rheometry (ONR). The compressional modulus is determined over several time scales as a function of surface density and temperature, in the cis and trans conformations of the azobenzene side chain. Our results indicate that polymeric monolayers confined at the air–water interface provide interesting model systems for the study of glass transition phenomenology in a strongly confined two-dimensional geometry, without the hindrances to the glassy dynamics imposed by the more common two-dimensional confinements obtained by the deposition of a molecular layer onto a solid substrate.

Acknowledgement

The authors acknowledge Pietro Cicuta for the SQELS measurements and for useful discussions.