Time Evolution of Structures under Shear-Induced Phase Separation and Crystallization in Semidilute Solution of Ultrahigh Molecular Weight Polyethylene

Abstract

We investigated shear-induced structures for a semidilute solution of ultrahigh molecular weight polyethylene (UHMWPE) with a paraffin wax as a solvent by means of shear small-angle light scattering, shear microscopy, birefringence, and rheology. The solution has a reduced concentration (c/c* where c and c* is concentration and the overlap concentration, respectively) of 11 and hence well-developed entanglements. The structures were investigated at temperature of 124 °C, which is approximately equal to the equilibrium melting temperature of crystals in the solution at quiescent state. We found both shear-induced liquid-liquid phase separation and shear-induced crystallization, when the solution was subjected to shear flow at shear rate larger than the critical shear rate γ ˘c,streak. Time change in the shearinduced structures after onset of the shear at γ ˘> γ ˘c,streak or after cessation of the same shear illuminated that the shear-induced phase separation triggers the shear-induced crystallization into fibrous structures: crystallization occurs through regions rich in polymer concentration that are built up by the shear.

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

“…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.…”

“…[20] The transient behaviors of these properties are also classified into four regimes (Regime I to IV) with respect to three characteristic times t c1 , t c2 , and t c3 or shear strains _ g c1 , _ g c2 , and _ g c3 , as will be also defined below in conjunction with Figure 3. The transient behaviors of the noncrystallizable UHMWaPS also are quite similar to those of UHMWPE.…”

Experimental Study of Pressure Loss and Rheo-Optical Behavior of CTAB/NaSal Aqueous Solution under Elongational Flow

“…They also showed that the value of birefringence fluctuates just after starting the flow and it settles down to an almost constant value smaller than that at the inception of the flow. SALS has also been used to investigate the change in the structure of CTAB/NaSal 12) and polymer solutions [13][14][15][16] in many shear flows but only in a few elongational flows.…”

“…10, and the corresponding real-space images of fluctuations in concentration which were made by referring to the paper for polystyrene solution in shear flow. [14][15][16] Fig.14 (c). 15) For CTAB/NaSal aqueous solutions it is suggested that the same kind of stringlike domain aligned in the flow direction occurs in region II together with some fluctuations in concentration which were formed in region I and still remain in region II.…”

“…[14][15][16] Fig.14 (c). 15) For CTAB/NaSal aqueous solutions it is suggested that the same kind of stringlike domain aligned in the flow direction occurs in region II together with some fluctuations in concentration which were formed in region I and still remain in region II. Such a combined pattern has been reported in elongational flows using a four roll mill 12) in the low elongational rate region (G = 1 1/s).…”