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Manipulating morphology and orientation in thermally responsive block copolymer thin films

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  • This article is a U.S. Government work, and as such, is in the public domain in the United States of America.

Abstract

We demonstrate the use of combined thermal annealing and solvent vapor annealing (SVA) to tune the morphology of thermally responsive block copolymer (BCP) thin films. The BCP, poly(styrene-b-tert-butyl acrylate) (PS-b-PtBA), undergoes a chemical deprotection to poly(styrene-b-acrylic anhydride) (PS-b-PAH) above a temperature threshold, giving rise to a structural and morphological transition. Our experiments systematically examine different thermal annealing and SVA protocols with two solvents (tetrahydrofuran and acetone) and map the resulting morphologies. Assessments of these processing protocols were accelerated using temperature gradients. Our results demonstrate that the final nanoscale morphologies after SVA are determined by the changes in the relative solvent/polymer interactions and surface tensions of the polymer blocks that accompany deprotection. Because of these driving forces, certain processing combinations led to irreversible morphological states, whereas others present opportunities for further manipulation. Accordingly, our study reveals that the morphology of this thermally sensitive BCP can be altered through judicious choice of annealing protocol. The protocols that combine equal numbers of SVA and thermal annealing (TA) steps are not necessarily equivalent, and the order of the SVA relative to TA is a deciding factor in the final morphology. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

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