Dilatational rheology of insoluble polymer monolayers: Poly(vinylacetate)

Abstract

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.

Dynamic Properties of Poly(styrene)–Poly(ethylene oxide) Diblock Copolymer Films at the Air–Water Interface

“…Note that better agreement with Eq. [2] was obtained for spread films of poly(vinyl acetate) where slower relaxation processes were discovered (46).…”

Dynamic Surface Properties of Poly(vinylpyrrolidone) Solutions

“…The deviation of the transverse surface viscosity from zero in contradiction to the theory is another problem of this method (11). Moreover, the SQELS method can be applied only at high frequencies (≥10 Hz) while the main relaxation processes for polymer films usually correspond to the lower range of the spectrum (12,16,17) where other methods of mechanical relaxation spectrometry of surface layers must be used.…”

Fourier-transform rheology of polymer Langmuir monolayers: Analysis of the non-linear and plastic behaviors

“…Each of these two in-plane motions are characterized by a frequency dependent elasticity modulus, ε (ω)=ε R (ω)+ε I (ω), where the first term is the real part or elasticity, and the second term is the imaginary or loss modulus, which is given by the product of the frequency, ω, and viscosity. In the case of polymer monolayers it has been clearly pointed out that the dilational elasticity and viscosity are orders of magnitude higher than the in-plane shear ones [13,14], thus one can safely neglect the contribution of the shear mode, and hereinafter we will write ε (ω)=ε(ω) +iωκ(ω), κ being the dilational viscosity.…”