Reliable and rapid ordering of block copolymers (BCPs) having low defect density and long-range vertical order is important for their applications in the nanotechnology industry. Long range vertical ordered BCPs can have applications in nano-porous membranes for clean water to nanolithography templates in the sub 10 nm regime for nanoelectronics applications. However, attaining long range vertical order in common BCPs such as Polystyrene-b-Polymethylmethacrylate (PS-PMMA) is a challenge as they have low thermodynamic interaction parameter, χ, and are susceptible to de-wetting with solvent processing. Herein we demonstrate how a common additive such as Ionic Liquid (IL) can help enhance thermodynamic interaction parameter chi and allow rapid solvent processing of PS-PMMA using a creative solvent design and altered diffusive motions. We have used two different solvent processing routes, an in house developed solvent immersion annealing technique we call direct immersion annealing (DIA) and a more established solvent vapor annealing (SVA) technique. The formation of the vertical morphological structure has been validated using AFM, grazing incidence SAXS technique and real space chemical imaging with ToF-SIMS. The enhancement of the thermodynamic parameter was estimated using neutron reflectivity. The altered diffusive motion due to the presence of IL in solvent processing impedes film from de-wetting and allows attainment of long-range order through longer annealing time. The unique combination of IL and solvent processing with BCPs such PS-PMMA can make these films more appealing for industrial applications.

Enhanced long range order in block copolymer films by ionic liquid and neutral solvent processing

ACS Fall 2021

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