Rheological studies of shear-induced alignment of SBS block copolymer in the presence of organoclay

Abstract

The effect of an anisotropic silicate layer on the ordering behavior, the alignment, and its recovery to the initial state, of hexagonally packed cylindrical (HEX) microdomains of polystyrene-block-polybutadiene-block-polystyrene (SBS) triblock copolymer was studied. The nanocomposite samples were prepared by solution-blending a commercial montmorillonite, Cloisite 15A, with SBS block copolymer. Studies using X-ray diffraction and transmission electron microscopy (TEM) support the intercalation of the organosilicates by SBS. The rheological measurements showed that the order–disorder transitions (TODT) of the SBS nanocomposites slightly increased with the addition of 5 wt% organoclay and, by applying a large amplitude oscillatory shear (LAOS), the extent of cylindrical microdomain alignment toward the flow direction decreased. The linear viscoelastic measurement for different resting times after alignment indicated that the recovery of the cylinders orientation in the nanocomposite sample was lower than that in the neat SBS sample. The stress relaxation measurements and the applicability of time-strain separation principle for the SBS and its nanocomposite samples were conducted and, consequently, the damping functions were estimated. The results showed that the neat SBS sample at T < TODT deviated from time-strain separation at low strain amplitude, which can be associated with the orientation of ordered microdomains. The deviation increased in the presence of organoclay in the ordered state (190 °C) due to the orientation of both organoclay and the microdomains in the applied shear regime. We demonstrated that the damping function of SBS and its nanocomposites can be fitted well by the Soskey exponential model.