The Viscoelastic Properties of Polymer Solution in the MHz Region

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Abstract
The ultrasonic absorption in solutions of polystyrene in dibutylphtalate was measured in the frequency range from 1 to 52MHz. The measuring temperature range was from 5 to 65°C, and the concentration of the solution was up to about 8g/100ml. The molecular weight of the sample of polystyrene was 3.0×105. The ultrasonic velocity, density and absorption coefficient of the solution increased linearly with the increase of the concentration of polymer over the whole temperarture range. The plot Δα/f2 against the frequency showed a relaxation curve of single relaxation. With the temperature rise, the relaxation frequency fr increased, and the absorption maximum per wavelength μmax showed the maximum. The imaginary part of the bulk modulus K" and shear modulus, G" were calculated from the deta of ultrasonic absorption and those of Moore et al. ΔK" and ΔG" were increased were with the increase of the concentration and frequency. The ratio, ΔK"/ΔG" is far greater than 1, and the ratio of Δκ' (Bulk viscosity) to Δη' (Shear viscosity) was 2.2 at 25°C. From the temperature dependence of the partial specific compressibility and the partial molar volume, it is suggested that the polymer chains in the solution began to rotate freely above 35°C. The energy difference and the activation energy were estimated from the temperature change of the absorption on the bases of two-state model. The following values were obtained; the energy difference ΔH0=1.66kcal/mol, and the activation energy ΔH21=6.6Kcal/mol.

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