Grains and Defects in Block Copolymers

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9901951BalsaraAn experimental study, aimed at obtaining a fundamental understanding of the factors that control grain and defect structure in block copolymers, is proposed. Block copolymers belong to a general class of materials that exhibit a symmetry-breaking phase transition from a disordered phase to ordered nanostructures with liquid crystalline symmetry. Typical examples include lamellae, and cylinders arranged on a hexagonal lattice. However, coherent order in these materials is restricted to finite regions or grains, with concomitant defects. This proposal addresses three issues: nucleation of grains, defect dynamics, and the microscopic response of grains to macroscopic deformation. The primary tool that we will use to obtain the grain structure is depolarized light scattering. The relationship between optical properties and block copolymer grain structure (size, shape, and inter-grain correlations) was established in our laboratory. The optical experiments will be augmented by electron microscopy, neutron scattering, and rheology. Samples required for the initial studies have already been synthesized by high vacuum anionic polymerization; additional samples will be synthesized as necessary.The students who will be supported by this grant will be educated in the areas of polymer synthesis, polymer characterization by spectroscopy and chromatography, scattering of light, X-rays, and neutrons, and condensed matter physics. Such interdisciplinary training is become increasingly important in government and industrial research laboratories.