Ordering kinetics of cylindrical and spherical microdomains in an SIS block copolymer by synchrotron SAXS and rheology

Abstract

The ordering kinetics of cylindrical and spherical microdomains in a polystyrene-block-polyisoprene-block-polystyrene (SIS) copolymer were studied using synchrotron small-angle X-ray scattering (SAXS) and rheology upon quenching the sample from a disordered state to an ordered state having either spherical or cylindrical microdomains. The SIS exhibits an order to order transition at ≈181°C, a lattice disordering transition at ≈210°C and becomes disordered at higher temperatures. Higher order peaks in the SAXS profiles corresponding to hexagonally packed cylindrical (HEX) microdomains appeared after less than 1 h when the sample was quenched from 235°C to 170°C. When quenched from 235°C to 200°C. a broad higher order peak at ≈1.65 qm, corresponding to spheres with liquid-like short-range order, was persistent up to 4 h before higher order peaks corresponding to body-centered cubic (BCC) microdomains appeared. We repeated this experiment by changing temperature from one ordered state with BCC microdomains to another with HEX microdomains, and vice versa. The BCC microdomains were attained within 1 h when heating from 170°C to 200°C. The transition between HEX and BCC is thermoreversible. The time evolution of dynamic storage modulus G′ is in good agreement with that of SAXS intensity.