Shear-induced long-range spatial correlation and banded texture in thermotropic copolyester. In situ light and X-ray scattering

Laboratorio de Nanopolímeros y Colóides, Instituto de Ciencias Físicas, UNAM Av. Universidad s/n, Cuernavaca, Morelos, C.P. 62210, México

Corresponding author: ARomo-Uribe@fis.unam.mx

Received: 29 March 2006
Accepted: 18 September 2006

Abstract

In situ small-angle light scattering (SALS) has enabled to elucidate shear-induced orientation correlations and monitor their relaxation in the thermotropic copolyester of hydroxybenzoic acid (B) and ethylene terephthalate (ET). At 280 °C B-ET displays a nematic polydomain texture, the SALS and WAXS patterns are amorphous and isotropic. Applying steady shear, optical defect multiplication occurred and the microdomain sizes were reduced. However, the SALS pattern now showed anisotropy, the SALS pattern transitioned from a unimodal to a bimodal orientation. After cessation of shear, the orientation correlation rapidly relaxed to a polydomain and the SALS pattern became again isotropic. Above a threshold shear rate of about shear now induced line defects oriented nearly orthogonal to the velocity axis. The texture relaxation above was also distinctly different, the well-known “banded texture” was formed upon cessation of shear. In situ X-ray scattering showed that the molecular chains always aligned along the flow direction regardless of the shear rate. However, the degree of macromolecular alignment improved significantly above and this is a condition to obtain the banded texture.