Oriented Structure in Isotactic Polystyrene Melt Induced by Shear Flow

We performed polarized optical microscope (POM), depolarized light scattering (DPLS) and small-angle X-ray scattering measurements on the structure formation process or the crystallization process of isotactic polystyrene (iPS) tinder shear flow below and above the nominal melting temperature T-m. It was found that a micron scale anisotropic oriented structure termed here as "string-like object" was formed even above the nominal melting temperature that is stable for more than 24 h, but melted at around 270 degrees C far above the nominal melting temperature. The string-like object acts as a nucleation agent for the folded chain lamella crystal (or the kebab). We also examined the shear rate dependence of the structure formation to find a critical shear rate and a critical strain for the formation of the string-like object, suggesting the orientation and relaxation of the chains plays an important role in the formation of the structure.