Coupling of mutual diffusion to viscoelasticity in moderately concentrated polyisobutylene solutions

Abstract

The normalized intensity autocorrelation function g (2)( t) were obtained by dynamic light scattering for moderately concentrated entangled solutions of polyisobutylene in n-heptane at 25.0 °C and in isoamyl isovalerate (IAIV) at 25.0 °C ( Θ). The obtained data have been successfully analyzed by the ‘procedure X’ familiar for determination of mechanical relaxation spectra on the basis of the recent theory for g (2)( t). The results have shown that while the mutual diffusion coefficient D increases in the n-heptane solutions and decreases in the IAIV solutions with increasing polymer mass concentration c, the friction coefficient ζ for both solutions increases with c showing the same power-law behavior irrespective of the weight-average molecular weight M w and solvent quality. It has been found that the instantaneous longitudinal modulus L 0 for n-heptane solutions increases in proportion to c 2, obeying the familiar relation for the plateau value (4/3) G N of the longitudinal stress relaxation modulus, but L 0 for the IAIV solutions becomes progressively smaller than the values predicted from the relation with decreasing c. The terminal relaxation time τ m has been found to follow the power-law τ m∝ M w 3.4 established by rheological measurements.