Morphology Development in Asymmetric Poly (styrene-b-tert-butylacrylate) Thin Films by Solvent Annealing

Morphology dependence of asymmetric poly(styrene-b-tert-butylacrylate) [P(S-b-tBA)] thin film on casting solvent, annealing solvent and annealing time was investigated. Two casting solvents, toluene and propylene glycol monomethyl ester acetate (PGMEA), and two annealing solvents, p-xylene and tert-butylacrylate (tBA), were studied. The casting solvent dominated the initial morphology. P(S-b-tBA) film cast from toluene resulted in inverted phase (PtBA cylinders ill PS matrix) and the one cast from PGMEA led to normal phase (PS cylinders in PtBA matrix) morphology. The annealing solvents preference to either the majority or the minority block in combination with the annealing time controlled the orientation of the cylinders. When the annealing solvent preferentially interacted with the majority block in the as-cast film, a metastable highly ordered perpendicular cylinder morphology was trapped. The best conditions to obtain perpendicular PS cylinders were casting P(S-b-tBA) film from PGMEA and annealing in tBA vapor for 20 and 25 min on silicon and NaCl substrates respectively.