Dilatational rheology of insoluble polymer monolayers: Poly(vinylacetate (original) (raw)

The dilatational rheology of the poly͑vinylacetate͒ monolayer onto an aqueous subphase with pHϭ2.0 has been studied between 1°C and 25°C. The combination of several techniques, relaxation after a step compression, oscillatory barrier experiments, electrocapillary waves, and surface light scattering ͑SLS͒ by thermal capillary waves, has allowed us to explore a broad frequency range. The relaxation experiments show multiexponential decay curves, whose complexity increases with decreasing the temperature. A regularization technique has been used to obtain the relaxation spectra from the relaxation curves and the dilatational viscoelastic parameters have been calculated from the spectra. The oscillatory barrier experiments confirm the results obtained from the step compression experiments. The dilatational viscosity increases very steeply in the frequency range 0.1-0.001 Hz. The shapes of the relaxation spectra follow the qualitative trends predicted a model recently proposed by Noskov ͓Colloid Polym. Sci. 273, 263 ͑1995͔͒. The temperature dependence of the fundamental relaxation time follows a Williams-Landel-Ferry equation above 14°C. These results correspond to the many-chain dynamics regime. The kilohertz region has been explored by the SLS technique. These results are compatible with the existence of a single Maxwell mode, with a relaxation time that has an Arrhenius-type temperature dependence. In the intermediate-frequency regime ͑10 Hz to 2 kHz͒ a further Maxwell process is found. It might correspond to the dynamics of loops and tails out of the surface plane.

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