NEUTRON REFLECTOMETRY USING THE KINEMATIC APPROXIMATION AND SURFACE QUASI-ELASTIC LIGHT-SCATTERING FROM SPREAD FILMS OF POLY(METHYL METHACRYLATE)

Neutron reflectometry data for syndiotactic poly (methyl methacrylate) have been analyzed using the kinematic approximation. This has produced form factor and Guinier analyses of the data from which the thickness and composition of films spread at the air-water interface have been determined. The layer thickness remains remarkably constant at ca. 18 (±2) Å over a surface concentration ranging from 0.2 to 2.0 mg m -2. Water is always contained in the film at a very small volume fraction (≈0.1), the polymer volume fraction increases linearly with surface concentration up to ca. 1.5 mg m -2; thereafter the volume fraction of polymer is approximately constant at 0.9 for the higher surface concentrations in the range investigated. Surface quasi-elastic light scattering has been used to evaluate the surface viscoelastic parameters of the polymer film. The dilational modulus (ε 0) obtained from surface quasi-elastic light scattering has the same general features as that obtained from surface pressure data but is shifted to a lower concentration. There is evidence from the surface tensions obtained that there is anomalous behavior at low values of the surface concentration of polymer. Over the range of surface concentrations investigated, the loss modulus of the polymer film decreases linearly with the reciprocal of the polymer content of the film. © 1993 American Chemical Society