Enhanced Vertical Orientation in Cylindrical PS-b-PMMA Using Ionic Liquid and Direct Immersion Annealing
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Block copolymer thin films have gathered much attention due to their well-defined structures and interesting surface morphology. Surface of the thin films depend on several factors like self-assembly of the polymers and interaction of polymer with solvent and substrate. The variables effecting the ordering of a block copolymer into perpendicular cylinder to the thin dimension of the film are crucial for its applications. This thesis presents a systematic study of ionic liquid (IL) as an additive on the perpendicular cylindrical ordering of a well-studied PS-b-PMMA (55K-22K) block copolymer (BCP) thin film. IL addition was varied in weight percentage of 0 – 15 relative to the mass of the BCP. Four different thickness of 40 nm, 100 nm, 200 nm and 400 nm of BCP films with varied concentration of IL were studied using atomic force microscopy (AFM) and grazing incidence small angle X-ray scattering (GISAXS) techniques. Contact angles were measured for 100 nm and 400 nm thick films to calculate surface energy. BCP films of four different thickness with IL additive were then annealed by direct immersion annealing (DIA) method. DIA was studied in a solvent mixture of toluene and heptane by varying volume ratio and immersion time. The variables were examined by using the same characterization techniques to explore the viability of the DIA method in attaining desired ordering of the BCP films.