Rheology of Polystyrene Solutions with Scarcely Entangled Chains; Role of Slow Relaxation Mode in Nonlinear Behavior

概要

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Linear viscoelasticity behavior was described with sum of two terms for semi-dilute polystyrene solutions in tricresyl phosphate with molecular weights (M) close to 2Me, where Me is the entanglement molecular weight in the solution. One was a Rouse-Zimm (RZ) term represented by the Rouse-Zimm theory with arbitrarily chosen value of the longest relaxation time (τRZ). The other (L term) consisted of a relaxation mode with single relaxation time, τL (>τRZ), and high-frequency limiting modulus (GL) proportional to square of concentration, c. The shear stress, σ, and the first normal stress difference, N1, in steady shear were described with simple formulas proposed previously for more dilute solutions. The stress due to L term was assumed to be given by a K-BKZ equation with damping function h(γ)= (1+0.2γ2)−1/2, where γ is magnitude of shear. Contributions to σ and N1 from RZ term were derived from the Rouse-Zimm model theory, in which the relaxation time in steady flow decreased with rate of shear, γ, as τst=τRZ0+(τRZ−τRZ0)/(1+0.35τRZ γ). Here τRZ0 is the longest relaxation time of the polymer at the infinite dilution limit. The result together with previous result for more dilute solutions implies that η and Ψ1 for any non-entangled solutions are well described with use of parameters derived from dynamic viscoelasticity.
一般社団法人　日本レオロジー学会の論文