Relaxation spectra of concentrated polystyrene solutions

Abstract

Abstract The relaxation modulus G ( t ) and the stress decay after cessation of steady shear flow were measured on concentrated solutions of polystyrenes in diethyl phthalate. Ranges of concentration c and molecular weight M of the polymer were from 0.112 to 0.329 g/ml and from 1.23 × 10 6 to 7.62 × 10 6 , respectively. The relaxation spectrum H (τ) as calculated from G ( t ) for the solution of very high M was found to be composed of two parts. One, at relatively short times, was a broad distribution (plateau zone) with height proportional to c 2 . The second, at the long‐time end, was very sensitive to concentration and gave rise to a maximum in H (τ) for very high concentrations. The behavior of H (τ) at long times was examined quantitatively by evaluating the longest relaxation time τ 1 0 and the corresponding relaxation strength G 1 0 from G ( t ) and from the stress decay function, on the assumption of a discrete distribution of relaxation times at long times. The longest relaxation time was approximately proportional to M 3.5 , even at relatively low concentrations where the zero‐shear viscosity was not proportional to M 3.5 . The strengths of relaxation modes with the longest few relaxation times are proportional to the third power of concentration.