| Abstrakt: |
The rotational relaxation of the solvent Aroclor 1248 (A1248) has been examined in solutions containing either polystyrene (PS), 0≤c≤0.269 g/cc, or polybutadiene (PB), 0≤c≤0.264 g/cc, by oscillatory electric birefringence. Measurements were performed at eight temperatures from -17.31 to 25.00 °C. In all cases the normalized solvent relaxation time τ/τ0, where τ0 was the value in neat solvent, was an exponential function of concentration. For PS/A1248, ∂ ln(τ/τ0)/∂c was independent of temperature and equal to 13±1 cc/g, whereas for PB/A1248, ∂ ln(τ/τ0)/∂c increased steadily with temperature and was negative for measurement temperatures of 2.81 °C and below. These observations were qualitatively consistent with a picture of solvent clustering or ordering, which was enhanced by the addition of PS but disrupted by PB. Although some features of the data were also consistent with changes in solution free volume, as indicated by measurements of the composition-dependent glass transition temperature, such considerations were not sufficient to reconcile all the observed behavior. The ratio τ/τ0 was interpreted as representing an effective, average solvent friction function ζ(c,T), which could also be used to define an effective solvent viscosity, ηe(c,T)=ηs(T)·ζ(c,T). It was shown that ∂ ln ζ/∂c, also equivalent to an intrinsic effective viscosity [ηe], was very close in magnitude and sign to the intrinsic high frequency limiting viscosity [η’∞] for both PS/A1248 and PB/A1248. This implies that the measured values ofη∞ reflect predominantly polymer-induced changes in solvent friction. Therefore, it may not be necessary to invoke additional sources of energy dissipation, such as chain stiffness or internal viscosity, to describe the high frequency viscoelastic or oscillatory... [ABSTRACT FROM AUTHOR] |
