Enhancing the Scale of Block Copolymer Lamellae Alignment using Ionic Liquid (IL) on a Planar Supporting Substrate

Symmetric Block Copolymers (BCP) such as PS-b-PMMA when cast on Silicon wafer and ordered using thermal annealing assume a parallel lamellar structure in thin films. However, as molecular weight and film thickness increases, attaining complete parallel lamellar structure becomes elusive. Previous study has shown that increasing the thermodynamic driving force for microphase separation, cN, where c is the Flory-Huggins interaction parameter between the polymeric blocks and N is the number of segments in the BCP, enhances the degree of BCP ordering and alignment parallel to substrate. In order to control the microstructure of ordering, increasing N or reducing temperature T could be applied at the expense of either slower kinetics, or higher defect formation due to entanglements, higher glass transition temperature (T_g) and surface tension. In this work we present a method for parallel alignment of lamellar PS-b-PMMA over notably higher Mw and film thickness regime using IL to enhance c, thereby propagating substrate driven parallel layering, while lowering T_g for enhanced molecular mobility for fast kinetics. Such films may be useful in in applications barrier materials and batteries, solid state dielectric capacitors.