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Title: Layering, melting, and recrystallization of a close-packed micellar crystal under steady and large-amplitude oscillatory shear flows

The rheology and three-dimensional microstructure of a concentrated viscoelastic solution of the triblock copolymer poly(ethylene oxide){sub 106}-poly(propylene oxide){sub 68}-poly(ethylene oxide){sub 106} (Pluronic F127) in the protic ionic liquid ethylammonium nitrate are measured by small angle neutron scattering (SANS) under flow in three orthogonal planes. This solution's shear-thinning viscosity is due to the formation of two-dimensional hexagonal close-packed (HCP) sliding layer structure. Shear-melting of the crystalline structure is observed without disruption of the self-assembled micelles, resulting in a change in flow properties. Spatially resolved measurements in the 1–2 plane reveal that both shear-melting and sliding are not uniform across the Couette gap. Melting and recrystallization of the HCP layers occur cyclically during a single large amplitude oscillatory shear (LAOS) cycle, in agreement with the “stick-slip” flow mechanism proposed by Hamley et al. [Phys. Rev. E 58, 7620–7628 (1998)]. Analysis of 3D “structural” Lissajous curves show that the cyclic melting and sliding are direct functions of the strain rate amplitude and show perfect correlation with the cyclic stress response during LAOS. Both viscosity and structural order obey the Delaware–Rutgers rule. Combining rheology with in situ spatiotemporally resolved SANS is demonstrated to elucidate the structural origins of the nonlinear rheology of complex fluids.
Authors:
 [1] ;  [2] ;  [3]
  1. ExxonMobil Chemical Company, Baytown Technology and Engineering Complex, Baytown, Texas 77520 (United States)
  2. Center for Neutron Science, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716 (United States)
  3. Institute Laue-Langevin, BP 156, F38042 Grenoble Cedex 9 (France)
Publication Date:
OSTI Identifier:
22413357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Rheology; Journal Volume: 59; Journal Issue: 3; Other Information: (c) 2015 The Society of Rheology; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; COPOLYMERS; CORRELATIONS; CRYSTALS; HCP LATTICES; LAYERS; MELTING; MICROSTRUCTURE; MOLTEN SALTS; NEUTRON DIFFRACTION; NONLINEAR PROBLEMS; POLYETHYLENE GLYCOLS; POLYPROPYLENE; RECRYSTALLIZATION; RHEOLOGY; SLIP; SMALL ANGLE SCATTERING; STRAIN RATE; STRESSES; TWO-DIMENSIONAL SYSTEMS; VISCOSITY