Shearing of islands and holes in block copolymer thin films



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Shearing refers to the occurrence of a shear strain, which is the deformation of a material substance in which parallel internal surfaces slide past one another. It is induced by a shear stress in the material. This project focuses on developing a detailed understanding of underlying polymer physics responsible for block copolymer ordering in thin films under the effect of shear stress. To observe the shearing phenomenon in microscale, the polymer film is annealed such that it has a lamellar morphology with islands and holes. The idea here is to track shearing by juxtaposing the AFM scanned pre sheared and post sheared images to note the increment in area and decrement in height of islands and holes. PDMS, a silicone elastomer, is placed on the polymer film that is intended to be sheared. PDMS is a vital tool in this operation because it expands when the polymer film is passed through hot zone and contracts when exposed to cold zone. As PDMS is placed on the polymer film, the expansion and contraction poses a shearing effect on the polymer film. Block copolymers under a stimulus self-assemble to make different morphologies, having applications in nanolithography, membranes, photonics and energy storage devices. Shear ordered block copolymers have minimum defects and high degree of alignment, the criteria needed for use of block copolymers in energy storage and other technological applications.