Time Evolution of Shear-Induced Structures in Semidilute Polystyrene Solutions

Abstract

We investigated time evolution of structures induced by imposing shear flow on semidilute solutions of high molecular weight polystyrene (PS) by means of both flow light scattering and rheology. PS with weight-average molecular weights of 5.48 × 10 6 and 2.89 × 10 6 were dissolved in dioctyl phthalate (DOP). After imposing shear flow with a shear rate γ > γ c (the critical shear rate for shear-induced concentration fluctuations), the unique butterfly-type scattering pattern appeared. The pattern had a scattering maximum along the flow direction. The wave number qm and the intensity Im at the scattering maximum decreased and increased, respectively, with time and eventually reached steady state values. The rheological experiments that were carried out on the same solution under the same shear flow revealed two stress overshoots. The second overshoot was found to be related to the development of butterfly pattern and its time change, i.e., to the formation and growth of shear-induced structures.

Flow-Induced Anisotropy in Mixtures of Associative Polymers and Latex Particles

“…1d) (13). Such a behavior can be observed when shearing homogeneous, semidilute polymer solutions near the onset of phase separation (14,15). In that case the structures develop because of a coupling between concentration fluctuations and stress, due to the unequal concentration dependence of viscosity and normal stress differences (16).…”

Shear‐Induced Phase Separation of Entangled Polymer Solutions: Formation of Optically Anisotropic Strings as Precursor Structures of Shish‐Kebab

“…The transient behaviors of the noncrystallizable UHMWaPS also are quite similar to those of UHMWPE. [1,21] Figure 3 summarizes the results shown in Figures 1 and 2 and expected dissipative structures formed under steady or step-up shear flow, commonly found for the noncrystallizable and crystallizable entangled solutions. Upon increasing _ g under steady shear or time t after the step-up shear from _ g ¼ 0 to _ g > _ g a , the critical shear rate for an onset of the anomaly to be described later -Regime I where _ g < _ g c;x or t < t c1 (corresponding to the terminal rheological relaxation time).…”

“…The sharp streak-like scattering pattern with strong intensity appears along the z axis (Figure 1c). [18,20,21,31] The streak pattern is superposed on the butterfly pattern as shown actually in the pattern at _ g ¼ 89.4 s À1 in Figure 1c and schematically in part (d), row (B) in Figure 3. This implies that the demixed domains tend to align into string-like structures oriented parallel to flow as schematically shown in part (d 0 ), row (C) in Figure 3.…”

Structural development of dynamically asymmetric polymer blends under uniaxial stretching

“…A large number of intriguing phenomena have been observed for binary mixtures with dynamical asymmetry between two constituent components such as polymer solutions or polymer blends with a large difference in glass transition temperatures: viscoelastic phase separation (Tanaka, 1993(Tanaka, , 1994(Tanaka, , 1996Takenaka et al, 2002), shearinduced enhancement of concentration fluctuations (Dixon et al, 1992;Hashimoto & Fujioka, 1991;Kume et al, 1997) and so forth. The key concept of these phenomena is the dynamical coupling between stress and diffusion (Doi & Onuki, 1992).…”

“…the butterfly pattern. (Dixon et al, 1992;Hashimoto & Fujioka, 1991;Kume et al, 1997;Koizumi, 2003).…”