Phase Separation of Polymer Blends Induced by an External Static Electric Field

The mechanism of the phase separation of polymer blends in the presence of a static electric field was investigated using the molecular dynamics with a modified coarse-grained polarizable model.Two electric field effects,i.e.,the promotion and hindrance of the phase separation,were found in the system of the upper critical solution temperature(UCST)by varying the dielectric properties of polymer components.Our simulation directly demonstrated that the electric field effects originate from the energy changes of intramolecular unit polarization,intermolecular van der Waals(VDW)and Coulomb interactions induced by the external electric field.The relationship of the energy change and the dielectric constant for the system under electric field is obtained.The interface orientation under electric field was found to happen even before the transition point of phase separation.By assuming that the relative order parameter of the phase separation undergoes the same fluctuations for a system with and without an electric field,the transition temperature under an electric field can be predicted,and quantitative consistency with simulations is obtained.

Mechanistic Insights into the Shear Effects on Isotactic Polypropylene Crystallization Containingβ-Nucleating Agent

The crystalline structures and crystallization behaviors of iPP containing β nucleation agent TMB-5 （iPP/TMB-5） were investigated by synchrotron radiation wide angel X-ray diffraction （SR-WAXD）, differential scanning calorimeter （DSC） and polarized light microscope （PLM）. It was found that α-crystallization lagged behind β-crystallization at normal temperatures, but the discrepancy reduced with increasing temperature. TMB-5 could not induce β-iPP when the nucleation agent is wrapped up with α-crystal that crystallized at high temperatures. The polymorphic composition of iPP/TMB-5 was susceptible to the introductory moment of shear. New crystallization process of β-nucleated iPP was proposed to understand the experimental phenomena which could not be explained by those reported in the literature. It was supposed that polymer crystallization initiated from mesophase, and the formations of iPP crystals involved the organization of helical conformation ordering within rnesophase. It was proposed that the iPP melt contained mesophases with stereocomplex-type ordering of right-handed and left-handed helical chains which could be disturbed by shear or TMB-5, leading to different polymorphic structures.