Two-dimensional (2D) small-angle X-ray scattering (SAXS) correlation spectroscopy for block copolymer consisting of microlamellar and liquid crystal (LC) structures

Abstract

Thermally induced variation of an ABA type block copolymer including microlamellar and liquid crystal (LC) structures was probed monitored by two-dimensional (2D) small-angle X-ray scattering (SAXS). By taking an advantage of strong X-ray light source of a synchrotron radiation facility, i.e. Spring-8, time-resolved SAXS spectra of the block copolymer sample based on PEMA and BB-5(3-Me) was collected during heat treatment well below isotropization temperature of the LC structure. A substantial level of change in the spectral feature are observed when the sample is subjected to the applied temperature. Fine features of the spectral changes are readily analyzed by 2D correlation method, including conventional and hetero-spectral correlation analysis. Hetero-spectral 2D correlation analysis of the spectra collected along and perpendicular to the fiber axis elucidated details of the thermally induced variation of the microdomain structure of the copolymer. Namely, it was revealed that the heating of the copolymer sample first induces the decrease in the diffraction peak intensity at 0.32 nm−1 and 0.42 nm−1 in the spectra collected along the direction perpendicular to the fiber axis. Further heating eventually leads to the development of the peak at 0.27 nm−1 in the spectra measured along the direction parallel to the fiber axis. Above observation suggests that the applied temperature first result in the rotation of the periodical lamellar structure initially aligned to the direction perpendicular to the fiber axis. This rotation eventually leads to the appearance of the periodical lamellar structure along the direction parallel to the fiber axis.