Dynamics of High Molecular Weight Cylindrical and Lamellar Block Copolymers with X‐ray Photon Correlation Spectroscopy

Abstract

The structure and dynamics of polystyrene‐b‐poly(ethylene oxide) (PS‐b‐PEO) block copolymers (BCPs) were studied. The BCPs exhibited microphase separated cylindrical and lamellar morphologies. Structural dynamics were measured with X‐ray photon correlation spectroscopy (XPCS) in the small‐angle regime. Morphologies and domain sizes were evaluated using small angle x‐ray scattering (SAXS), scanning electron microscopy, and atomic force microscopy. Different solvent processing conditions were investigated. Grain sizes evaluated using SAXS were found to depend on processing only for the rubbery majority BCP. The structural relaxation times were examined as a function of PS volume fraction, temperature, morphology, and structural sizes. Well above the glass transition temperature (Tg) of PS, all samples exhibited stretched autocorrelation decays and diffusive dynamics. Near Tg of PS the dynamics of all samples was anomalous with compressed autocorrelation decays and hyperdiffusive dynamics. This transition occurred at 153°C or 1.13Tg of PS. In the diffusive regime (at high temperature), structural relaxation times were dependent on the processing method. Near PS Tg (at low temperature), structural relaxation times scaled with the PS volume fraction. Structural relaxation times do not correlate with grain size, indicating that the out‐of‐equilibrium state of PS dominates structural dynamics of these strongly phase segregated BCPs.This article is protected by copyright. All rights reserved