Crystalline morphology of a thermotropic aromatic polyester crystallized from nematic melt

Abstract

The crystalline morphology of a thermotropic aromatic polyester crystallized from a nematic melt was investigtated by means of polarized optical microscopy (POM) and scanning electron microscopy (SEM). Due to POM measurements it was found that spherulites of two different types are formed within the two different temperature regions. When Tc was exceeding 170°C, spherulites of type-1 showing a negative birefringence grew with a radial fibrillar morphology and exhibited a clear Maltese-cross pattern. The radius growth rate of type-1 spherulites was about 2.2 μm/min at 185°C. When Tc was smaller than 160°C, spherulites of type-2 were formed and exhibited a radially outward growing structure but no evident Maltese-cross pattern. These spherulites could be seen by the naked eyes due to their size reaching several millimeters. SEM observations revealed that the spherulites of type-1 exhibited a ripple-like homocentric morphology with periodical compact fibrils having a diameter of about 150 nm perpendicular to the radial direction. In contrast, the spherulites of type-2 exhibited, as apparent from performed SEM images, radially growing crystallites of about 500 nm in size with no periodicity in the radial direction.