Lamellae Formation and Reorientation in Diblock Copolymers

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0100903VinalsThis research project will use analytical and computational techniques to study the formation, stability and coarsening of lamellar phases in diblock copolymers. Although block copolymers are already widely used in industry, newer technologies that rely on high performance polymeric materials often require precise control of the polymer microstructure and its self-assembly. Processing by temperature quench or solvent casting from a high temperature isotropic phase always leads to the formation of a polycrystalline structure comprised of domains or grains of differently oriented lamellae. The focus of this research is on mechanisms controlling long-ranged orientational order, including the reorientation of lamellar phases by reciprocating shears, and the motion of topological defects and its effect on coarsening of the lamellar structure. A theoretical analysis is carried out at a mesoscopic level to find nonlinear solutions under imposed, reciprocating shears, as well as to elucidate their stability. Viscoelastic contrast between the microphases is explicitly taken into consideration. In addition, the longest relaxation times in the lamellar phase are likely to be determined by the spatial distribution and motion of topological defects. The motion of grain boundaries, disclinations (in two-dimensional samples), and dislocations is considered, as well as their effect on the coarsening times of the microstructure, and on the possible existence of asymptotic self-similarity.%%%This research project will use analytical and computational techniques to study the formation, stability and coarsening of lamellar phases in diblock copolymers. Although block copolymers are already widely used in industry, newer technologies that rely on high performance polymeric materials often require precise control of the polymer microstructure and its self-assembly. Processing by temperature quench or solvent casting from a high temperature isotropic phase always leads to the formation of a polycrystalline structure comprised of domains or grains of differently oriented lamellae.The focus of this research is on mechanisms controlling long-ranged orientational order and the motion of topological defects and its effect on coarsening of the lamellar structure.***