| The self-assembly of block copolymers, arising from incompatibility of the connected blocks, may influence chain diffusion by creating a potential energy field that localizes the junction to the interface and confines each block to its respective domain. Such thermodynamic effects are further subject to the prevailing diffusion mechanism and the adopted ordered morphology.; An experimental study of this behavior was conducted, in which forced Rayleigh scattering was employed to measure the diffusion coefficient of chains in two copolymer systems. Morphologies were characterized by small angle x-ray scattering, transmission electron microscopy, and static birefringence.; A poly(styrene-b-isoprene) (PS-PI) diblock copolymer was examined in two states of lamellar alignment: shear-aligned and quenched. In the shear-aligned systems, diffusion was measured along, D{dollar}sb{lcub}rm par{rcub}{dollar}, and across, D{dollar}sb{lcub}rm perp{rcub}{dollar}, the lamellar planes. A large anisotropy of motion was observed, i.e., D{dollar}sb{lcub}rm par{rcub}{dollar}/D{dollar}sb{lcub}rm perp{rcub} approx{dollar} 40, which can be explained by thermodynamic penalties for PS/PI contacts and a large disparity in monomeric friction. In the quenched samples, one mode of diffusion was observed in the ordered and disordered states, attributable to complete averaging of D{dollar}sb{lcub}rm perp{rcub}{dollar} and D{dollar}sb{lcub}rm par{rcub}.{dollar} The tracer diffusion of PS and PI homopolymers was also investigated in a PS-PI diblock copolymer. In a quenched matrix, the PS and PI tracer diffusion was enhanced and reduced relative to self-diffusion, respectively. A significant anisotropy of motion was observed in the diffusion of PI in a shear-aligned PS-PI matrix.; The self-diffusion of a poly(ethyleneoxide-b-ethylethylene) (PEO-PEE) block copolymer was examined in the gyroid and cylinder phases. One mode of diffusion was observed in the bicontinuous cubic gyroid phase, whereas an anisotropy in mobility was found in the cylindrical morphology. The chain mobility across the cylinders was found to be 80 times slower than motion along cylinders, caused by thermodynamic penalties associated with PEO/PEE contacts.; A model system of PS-PI-PS-PI tetrablocks was utilized to study the monomeric friction coefficient, {dollar}varsigma{dollar}, in immiscible systems. Diffusion and viscosity measurements yielded {dollar}varsigma{dollar} values that were essentially dependent on (T-T{dollar}sb{lcub}rm g{rcub}){dollar} only, irrespective of composition. Predictions for {dollar}varsigma{dollar} were attempted using mixing rules that incorporated only PS and PI homopolymer values. |
