Polymer Monolayer Dynamics

Abstract

Polymer chain dynamics at interfaces of vapor/liquid and liquid/liquid have been probed by confining macromolecules as monolayers or thin films and examining their field induced and spontaneous capillary waves in addition to their lateral diffusion and in-plane steady shear viscosity, all in a Langmuir trough in conjunction with simultaneous surface pressure measurements. Various experimental methods have been used to examine the chain dynamics and this paper deals with two of such, namely surface quasielastic light scattering and surface canal viscometry.

Focus has been place on thin film viscoelastic properties of monolayers as examined by retardation effects of the surface films on the propagation and damping characteristics of the capillary waves. With the aid of a dispersion equation, two viscoelastic parameters, i.e., the surface dilation elasticity ε and the corresponding viscosity κ, are deduced from the observed spatial wave length or wave propagation rate and the wave damping constant. By virtue of ε and κ representing short-ranged, local packing states and the attending dynamics of polymeric monolayers, they are independent of molar mass. Thus we have chosen to examine structural parameters of some vinyl polymers together with polyethers and poly(dimethyl siloxane).

Parallel with this effort to understand the monolayer dynamics in terms of structural parameters, we present a very recent endeavor in determining steady shear viscosity of monolayers by observing the surface flow rate of monolayers through a narrow canal on a Langmuir trough, rather analogous to capillary viscometry under a constant driving head. Here the aim is to confirm the hydrodynamic coupling model of Harkin and Kirkwood, and probe the molar mass dependence of the in-plane steady shear viscosity η_s of a vinyl polymer, poly(t-butyl methacrylate)