472297 Field Alignment and Localized Field Screening in Block Copolymer Films Using Sub-1T Magnetic Fields (Invited Talk)
Here we report on the use of a simple mesogen blending approach which dramatically reduces the critical field strength required for producing well aligned block copolymer nanostructures during a given processing timeframe. Appropriately chosen mesogens effectively co-assemble with the existing mesophases formed by covalently attached moieties in two side-chain LC block copolymers. The resulting systems display rapid alignment upon cooling from disordered states in magnetic fields as low as 0.5 T. We show that the improved alignment response is principally due to enhanced mobility in the system due to the presence of non-bonded mesogens, rather than due to the increased grain sizes observed in the blended system. Sub-1 T field alignment permits two important developments. First, block copolymer alignment can be performed using low cost permanent magnets, and second, the applied fields can be effectively screened using nanoparticles of simple magnetic materials such as cobalt. We demonstrate field screening by nanoparticle chains as well as by arrays of magnetic nanostructures at interfaces with block copolymer films. The localized field screening by these magnetic materials results in localized variation of the orientational order of the block copolymer structure. These developments offer a new route to local control of block copolymer morphology in thin films.