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Recovery rheology via rheo‐SANS: Application to step strains under out‐of‐equilibrium conditions
Author(s) -
Lee Johnny C.W.,
Porcar Lionel,
Rogers Simon A.
Publication year - 2019
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.16797
Subject(s) - rheology , shear modulus , shear (geology) , relaxation (psychology) , stress relaxation , shear stress , neutron scattering , modulus , nonlinear system , materials science , shear flow , mechanics , classical mechanics , thermodynamics , physics , scattering , optics , composite material , kinetics , psychology , social psychology , quantum mechanics
Stress relaxation from a step strain test provides important information about constituent dynamics, but if a material has experienced a complex shear history, the underlying physics is not straightforward to access. We use recovery rheology and rheo‐small‐angle neutron scattering to probe the nonlinear dynamics of an entangled wormlike micelle solution by applying step strains after complex shear histories enforced by large‐amplitude oscillatory shear (LAOS) flow. We show that a universal relaxation modulus can be obtained from step strain tests with complex shear histories, as long as the modulus is defined in terms of the recoverable strain. The shear and normal stresses, as well as the alignment of micellar Kuhn segments, are shown to be positively correlated with the recoverable strain. We identify re‐entanglement of polymeric chains after cessation of LAOS and show that this process occurs over the same timescales as linear‐regime stress relaxation. This work, therefore, lays the foundation of how to accurately probe out‐of‐equilibrium rheology in a consistent manner.