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UNIVERSITY OF WATERLOO
Waterloo Institute for Nanotechnology (WIN); Department of Chemical Engineering; Department of Physics & Astronomy
Prof. Mark W. Matsen

Researchers are now beginning to exploit the self-assembly of block copolymers as a means of fabricating nanoscale structures [1], either directly from the block-copolymer material, as scaffolds for arranging other molecules/nanoparticles, or as templates for nanolithography. Possible applications/devices include high-density information storage, waveguides, nanoporous membranes, and nanowires. Although the self-assembly process is exceptionally efficient, it does not always produce the desired pattern; the common examples being that lamellar and cylindrical domains tend to orient parallel to the substrate, as opposed to perpendicular where they exhibit a more useful lateral structure. Researchers have coated the substrates to negate the surface interactions that cause this, but the resulting structures are generally populated by numerous defects. One strategy for overcoming this problem is to orient the domains using strong electric fields that couple to the dielectric contrast between the different components of the block copolymer.

We have recently combined self-consistent field theory (SCFT) with an exact treatment for linear dielectric materials to produce a rigorous method of investigating the Landau-Ginzburg free-energy landscape of structured polymeric systems (e.g., polymer brushes, polymer blends, and block copolymers) with respect to their composition profile. In our first application [2,3], the method was demonstrated on a parallel lamellar layer of diblock copolymers sandwiched between two parallel conductors (see the figure). Two competing instabilities were identified, and the resulting kinetic pathways towards perpendicular lamellae were investigated. In our second application [4], we examined the ability of an electric field to convert a monolayer of spherical domains into cylindical domains that penetrate through the film. Our most recent publication [5] examines the equilibrium phase diagram for thin films of cylinder-forming diblock copolymer as a function of surface interaction and electric-field strength.