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Polymers 2011, 3(1), 281-298; doi:10.3390/polym3010281
Article

Structural and Mechanical Hysteresis at the Order-Order Transition of Block Copolymer Micellar Crystals

 and *
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 / Revised: 22 December 2010 / Accepted: 5 January 2011 / Published: 11 January 2011
(This article belongs to the Special Issue Nano-Structures of Block Copolymers)
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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   pluronic; block copolymer; order-order transition; SANS; SAXS; rheology; hysteresis  
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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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.

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