Surface visco-elastic moduli of a Langmuir film of a polystyrene-polydimethyl siloxane block copolymer at the air-ethyl benzoate interface.
Surface quasi-elastic light scattering has been applied to a spread film of a block copolymer of polystyrene and polydimethyl siloxane. The influence of surface concentration (surface pressure) at a fixed surface wave number has been explored. The capillary wave frequency and damping showed a similar dependence on the surface concentration as values obtained earlier, but due to a more appropriate analysis of the correlation functions, surface visco-elastic moduli obtained were distinctly different. By correlating the values obtained with the variations in solvated polystyrene layer thickness from neutron reflectometry, the maximum in dilational modulus was shown to occur at the same nominal surface concentration where the layer begins to stretch and take on brush-like behaviour. This same surface concentration is where the relaxation time of the spread film also has a maximum value, the relaxation time being calculated using the standard linear model of visco-elasticity, which was found to fit the frequency dependence of the surface tension and dilational moduli at the resonant nominal surface concentration of 3.1 mg m(-2).
Cook
J T E
JT
Interdisciplinary Research Centre in Polymer Science and Technology, University of Durham, Durham DH1 3LE, UK.
Richards
R W
RW