Surface hydrodynamics on a freely standing layer of a polymer solution

Abstract

The dispersion relation and the power spectrum of the surface modes on a surface-active, freely standing film of a concentrated polymer solution are studied with a two-component fluid model of a viscoelastic material. The diagram of bending modes is obtained from an asymptotic analysis of the dispersion equation when the bending rigidity modulus is the main elastic effect on the layer interface. The resulting dynamical structure factor provides the characteristic squeezing and undulation surface modes of the interfaces driven by thermal fluctuations or by a weak external perturbation. The effect of interfacial and bulk elastic properties on the power spectrum of the scattered light is studied. In the regime of an elastic solution, finite-thickness effects and bulk elastic properties of the layer sustain a train of elastic peaks when the wavelength of thermal fluctuations is comparable to the thickness of the layer. Interfacial elasticity properties increase the strength and shift all resonance frequency peaks producing a less intense quasielastic spectrum around zero frequency. [S1063-651X(99)03010-X].