Surface dynamic light scattering is used to deduce the surface viscoelastic properties of poly(vinyl acetate) (PVAc) and poly(n-butyl methacrylate) (PnBMA) spread at the air-water interface. The two polymers were selected as group representatives of expanded (PVAc) and condensed (PnBMA) type films. Surface longitudinal viscosity,k, and elasticity, e, for the two types were calculated from the frequency shift and line broadening of the power spectrum of the scattered light with a dispersion relation over a range of temperatures and surface concentrations. In some cases, the wavevector dependence of the spectral characteristics necessitated the incorporation of a transverse viscosity term, μ, in the dispersion equation, subject to the assumption that є andk didnot depend on the scattering wavevector. This transverse viscosity was shown to have an anomalous temperature dependence with characteristics different for the two polymers; an explanation of the temperature dependence in terms of a slow, collective transverse relaxation process is provided, which may be related to the orientational properties of the different polymers at the interface.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry