Cyclical 'flipping' of morphology in block copolymer films
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Collins, Timothy W.
Holmes, Justin D.
Morris, Michael A.
American Chemical Society (ACS)
We studied the kinetics of nanopattern evolution in (polystyrene-b-polyethylene oxide) diblock copolymer thin films. Using scanning force microscopy, a highly unexpected cylindrical flipping of morphology from normal to parallel to the film plane was detected during solvent annealing of the film (with average thickness of 30 nm) at high vapor pressure. Using an in situ time-resolved light scattering device combined with an environmental cell enabled us to obtain kinetic information at different vapor pressures. The data indicated that there is a threshold value for the vapor pressure necessary for the structural transition. We propose a swelling and deswelling mechanism for the orientation flipping of the morphology. The cyclic transition occurs faster in thick films (177 nm) where the mass uptake and solvent volume fraction is smaller and therefore the driving force for phase separation is higher. We induced a stronger segregation by confining the chains in graphoepitaxially patterned substrates. As expected, the cyclic transition occurred at higher rate. Our work is another step forward to understanding the structure evolution and also controlling the alignment of block copolymer nanocylinders independently of thickness and external fields.
Block copolymer thin films , Cyclical morphology transition , Graphoepitaxial alignment , In-situ light scattering , Nanopattern evolution
Mokarian-Tabari, P., Collins, T. W., Holmes, J. D. and Morris, M. A. (2011) 'Cyclical “Flipping” of Morphology in Block Copolymer Thin Films', ACS Nano, 5(6), pp. 4617-4623. doi: 10.1021/nn2003629
© 2011 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Nano, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://pubs.acs.org/doi/abs/10.1021/nn2003629