In search of physical meaning: defining transient parameters for nonlinear viscoelasticity

Rogers, Simon A.

doi:10.1007/s00397-017-1008-1

Cited by 102 publications

(69 citation statements)

References 48 publications

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“…Having observed some unclear characteristics and on the basis of the recent experimental evidence, a relaxation modulus that is based on the recoverable strain is proposed. Following the conventional definition, the proposed relaxation modulus G ( t ) can be formulated as

G ((), t) = \frac{σ ((), t)}{γ_{rec}},

where γ rec is the recoverable strain according to Equation .…”

Section: Resultsmentioning

confidence: 99%

“…To this end, the way one perceives and analyzes particular responses may be influenced by concepts central to the prevailing theory in the field, and emerging experimental studies that challenge the theory have been reported . Motivated by recent advances in understanding out‐of‐equilibrium responses to LAOS via recoverable strain, the disagreement between the prevailing polymer dynamics theory and experiments, and experimental insights obtained from the recovery rheology, we aim to study the step strain response of a polymeric system with a complex shear history within the framework of recoverable strain. We concatenate two often‐performed tests, using an integer number of periods of LAOS to induce a complex nonlinear flow which is followed after some time by a single‐step strain.…”

Section: Introductionmentioning

confidence: 99%

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Recovery rheology via rheo‐SANS: Application to step strains under out‐of‐equilibrium conditions

2019

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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.

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G ((), t) = \frac{σ ((), t)}{γ_{rec}},

where γ rec is the recoverable strain according to Equation .…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Recovery rheology via rheo‐SANS: Application to step strains under out‐of‐equilibrium conditions

2019

Self Cite

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“…This fitted value, in turn, allows us to use our defining relation for large-amplitude, Eq. (11). For more on the Spriggs relations, we direct the reader to §6.1 of [17], Appendix of [76], or §8.5 of [77]).…”

Section: A Corotational Jeffreys Fluidmentioning

confidence: 99%

Exact solutions for oscillatory shear sweep behaviors of complex fluids from the Oldroyd 8-constant framework

Saengow

Giacomin

2018

Physics of Fluids

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Large-amplitude oscillatory shear flow (LAOS) is a popular for studying the nonlinear physics of complex fluids. Specifically, the strain rate sweep (also called the strain sweep) is used routinely to identify the onset of nonlinearity. In this paper, we give exact expressions for the nonlinear complex viscosity and the corresponding nonlinear complex normal stress coefficients for the Oldroyd 8-constant framework for oscillatory shear sweeps. We choose the Oldroyd 8-constant framework for its rich diversity of popular special cases (we list 18 of these). We evaluate the Fourier integrals of our previous exact solution to get exact expressions for the real and imaginary parts of the complex viscosity, and for the complex normal stress coefficients, as functions of both test frequency and shear rate amplitude. For our comparisons with data, we use the Spriggs relations to generalize the Oldroyd 8-constant framework to multimode. We explore the role of infinite shear rate viscosity on strain rate sweep responses for the special case of the corotational Jeffreys fluid. We find that raising η ∞ , raises the real part of the complex viscosity, and lowers the imaginary. In our worked examples, we thus first use the corotational Jeffreys fluid, and then, for greater accuracy, we use the Johnson-Segalman fluid, to describe the strain rate sweep response of molten atactic polystyrene. Our generalization yields unequivocally, a longest fluid relaxation time, used to assign Weissenberg and Deborah numbers to each oscillatory shear flow experiment. We then locate each experiment in Pipkin space. () are the real and minus [10] the imaginary parts of the nonlinear complex viscosities, η n * , and first and second normal stress coefficients, Ψ 1,n * and Ψ 2,n * . Some prefer to write Eq. (6) as (see Eq.(3) of [11]):

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“…in Refs. [13,16]. Among more advanced constitutive models the following three have attracted most attention: the pom-pom model [17e21], the Giesekus model [16,22e25], and the Phan-Tien and Tanner model [26,27].…”

Section: Introductionmentioning

confidence: 99%

Flexibility of three differential constitutive models evaluated by large amplitude oscillatory shear and Fourier transform rheology

Pivokonský

Filip

Zelenková

2016

Polymer

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In search of physical meaning: defining transient parameters for nonlinear viscoelasticity

Cited by 102 publications

References 48 publications

Recovery rheology via rheo‐SANS: Application to step strains under out‐of‐equilibrium conditions

Recovery rheology via rheo‐SANS: Application to step strains under out‐of‐equilibrium conditions

Exact solutions for oscillatory shear sweep behaviors of complex fluids from the Oldroyd 8-constant framework

Flexibility of three differential constitutive models evaluated by large amplitude oscillatory shear and Fourier transform rheology

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