Shear-induced Precursors of Fibrillar Crystals of Poly(butene-1): A Rheological Study

Strong preshear flow stretches poly(butene-1) chains to form flow-induced precursors of fibrillar crystals. The formation leads to further growth of shear/normal stress after the stress reaches the steady state. In this study, stress relaxation measurements are performed after intervals of a strong flow during which the precursors form. The small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) measurements are conducted to characterize the crystalline structure formed after the preshear and relaxation processes, each of different periods. A combination of the stress relaxation and scattering results reveal that for the precursors formed within 5 s, the stress can fully relax and the orientation of the subsequent crystals (formed upon quenching the sample at different stress levels) decays gradually with the relaxation. In comparison, for those precursors formed after 5 s, the stress hardly relaxes during ∼104 s, and the orientation of the subsequent crystals hardly decays, suggesting that the precursors have been somehow stabilized during the shear. These features have been discussed with respect to the percolation of the precursors to form a reversible network.