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Structural and Mechanical Hysteresis at the Order-Order Transition of Block Copolymer Micellar Crystals
Department of Chemical Engineering, Center for Complex Fluids Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
* Author to whom correspondence should be addressed.
Received: 30 November 2010; in revised form: 22 December 2010 / Accepted: 5 January 2011 / Published: 11 January 2011
Abstract: Concentrated solutions of a water-soluble block copolymer (PEO)20-(PPO)70-(PEO)20 show a thermoreversible transition from a liquid to a gel. Over a range of concentration there also exists an order-order transition (OOT) between cubically-packed spherical micelles and hexagonally-packed cylindrical micelles. This OOT displays a hysteresis between the heating and cooling transitions that is observed at both the macroscale through rheology and nanoscale through small angle neutron scattering (SANS). The hysteresis is caused by the persistence of the cubically-packed spherical micelle phase into the hexagonally-packed cylindrical micelle phase likely due to the hindered realignment of the spherical micelles into cylindrical micelles and then packing of the cylindrical micelles into a hexagonally-packed cylindrical micelle phase. This type of hysteresis must be fully characterized, and possibly avoided, for these block copolymer systems to be used as templates in nanocomposites.
Keywords: pluronic; block copolymer; order-order transition; SANS; SAXS; rheology; hysteresis
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LaFollette, T.A.; Walker, L.M. Structural and Mechanical Hysteresis at the Order-Order Transition of Block Copolymer Micellar Crystals. Polymers 2011, 3, 281-298.
LaFollette TA, Walker LM. Structural and Mechanical Hysteresis at the Order-Order Transition of Block Copolymer Micellar Crystals. Polymers. 2011; 3(1):281-298.
LaFollette, Theresa A.; Walker, Lynn M. 2011. "Structural and Mechanical Hysteresis at the Order-Order Transition of Block Copolymer Micellar Crystals." Polymers 3, no. 1: 281-298.