Characterizing grain structure in block copolymer thin films and shear aligned block copolymers with depolarized light scattering

Block copolymers consist of two or more chemically distinct polymer chains covalently bonded to one another. Repulsive interactions between the blocks cause these materials to self-assemble into nanometer-scale patterns. This behavior can be leveraged to create devices or template features that cannot be made efficiently using traditional fabrication techniques, but doing so requires a greater understanding of and control over the grain structure formed during self-assembly. Particularly of interest for this type of application are block copolymer thin films and aligned block copolymer samples.;This first part of this dissertation describes the development of a new optical scattering technique for characterizing the grain structure of block copolymer thin films, called guided wave depolarized light scattering (GWDLS). GWDLS is based on depolarized light scattering, a well established technique applicable to samples on the order of 1 mm thick. By coupling polarized light into a thin film of interest and using that film as a waveguide, depolarized light scattering can be measured in a sample of arbitrary thickness. Using GWDLS with a prism coupling system, the depolarized scattering produced by block copolymer thin films was shown to be correlated to the size of grains within those films. The measurement of an order-disorder transition temperature and the dynamics of this transition were demonstrated using GWDLS with diffraction grating couplers.;The second part of this dissertation focuses on the development and characterization of a new class of block copolymer materials that undergo a reversible aligned-to-unaligned transition when heated. A new optical scattering technique, dual wavelength depolarized light scattering (DWDLS), was designed to characterize these systems during cycling of this transition. A shear aligned lamellar block copolymer cross linked through exposure to a high energy electron beam demonstrated the desired behavior, losing and recovering its alignment through 20 heating cycles while showing no signs of degradation.