The Viscoelastic Properties of Polymer Solution in the MHz Region

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.