Investigation of Thermally Responsive Block Copolymer Thin Film Morphologies Using Surface Gradients
Jennifer Y. Kelly, Julie N. Albert, John A. Howarter, Shuhui Kang, Christopher M. Stafford, Thomas H. Epps, Michael J. Fasolka
We report the use of a gradient library approach to characterize the structure and behavior of thin films of a thermally-responsive block copolymer (BCP), poly(styrene-b-tert-butyl acrylate), that exhibits chemical deprotection and morphological changes above a thermal threshold. Continuous gradients in temperature and film thickness, as well as surface chemistry were used to examine trends in deprotection, nanoscale morphology, and chemical structure. Thermal gradient annealing enabled rate constants (2.16 × 10-5/s and 1.69 × 10-5/s) of the thermal deprotection to be extracted from a single BCP library on a catalytic and inactive surface, respectfully. A symmetric PS-b-PtBA was monitored through the deprotection front and had a morphology and orientation transformation from parallel structures to perpendicular cylinders. By using gradient techniques we are able to map morphological and chemical structural changes in a rapid fashion, determine reaction kinetics, as well as demonstrate that surface functionality affects the reaction time of the chemical deprotection reaction in our thin films.