TY - JOUR
T1 - Strain shifts under stress-controlled oscillatory shearing in theoretical, experimental, and structural perspectives
T2 - Application to probing zero-shear viscosity
AU - Lee, Johnny Ching Wei
AU - Hong, Yu Tong
AU - Weigandt, Katie M.
AU - Kelley, Elizabeth G.
AU - Kong, Hyunjoon
AU - Rogers, Simon A.
N1 - Funding Information:
The authors thank Professor Dimitris Vlassopoulos for invaluable comments on an early version of the manuscript. Discussions with Dr. David Bohnsack and Dr. Bharath Rajaram from TA Instruments and Dr. Abhi Shetty from Anton Paar are gratefully acknowledged. The authors thank Dylan Walsh and Professor Damien Guironnet for providing polystyrene samples. Access to NBG 30m-SANS was provided by the Center for High Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology (NIST) and the National Science Foundation (NSF) under Agreement No. DMR-1508249. This material is based upon work supported by the National Science Foundation (NSF) under Grant No. 1727605. Certain commercial instruments or materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and Technology nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. H.K. acknowledges the funding provided by the National Science Foundation STC-EBICS Grant CBET-0939511 Postscript: We have recently been made aware of the development of a theory based on the results presented here. While our work deals exclusively with the steady state alternating case, this new work, which confirms our major findings, considers the initial transience from startup.
Publisher Copyright:
© 2019 The Society of Rheology.
PY - 2019/11/1
Y1 - 2019/11/1
N2 - Rheological measurements in which the applied stress or strain is oscillated are widely used to interrogate viscoelastic properties due to the independent control over the time scale and length scale afforded by changes in amplitude and frequency. Taking a nontraditional approach, we treat stress-controlled oscillatory tests as creep tests with transiently varying stress and apply an analysis typically used for steady creep and recovery experiments. Defining zero strain as the state prior to external shearing, it is shown that strain responses to small-amplitude oscillatory stressing are naturally shifted from the starting point by an amount proportional to the phase of the applied stress. The phenomenology is experimentally observed with entangled polymerlike micelles and polyethylene oxide solutions. A theory of strain shifting in the steady alternating state is provided based on recovery rheology, where differences between total strain and recoverable strains are acknowledged. User-controlled variables, such as the amplitude of the stress, the angular frequency, and the phase of the stress, as well a lone material parameter, the zero-shear viscosity, are shown to dictate the amount of shifting. A rapid and efficient approach of determining the zero-shear viscosity is, therefore, presented. We investigate the microstructural evolution via in situ small-angle neutron scattering when strain shifting appears. The microscopic orientation is shown to correlate to the recoverable strain independent of the shifting. Additional measurements are carried out on collagen, pluronic-hyaluronic acid, alginate gels, and polystyrene melts to show the generic nature of the strain shift phenomenon. In addition, we demonstrate that the strain-shift knowledge can be applied to determine the horizontal shift factor in time-temperature superposition, free of any numerical fitting procedures.
AB - Rheological measurements in which the applied stress or strain is oscillated are widely used to interrogate viscoelastic properties due to the independent control over the time scale and length scale afforded by changes in amplitude and frequency. Taking a nontraditional approach, we treat stress-controlled oscillatory tests as creep tests with transiently varying stress and apply an analysis typically used for steady creep and recovery experiments. Defining zero strain as the state prior to external shearing, it is shown that strain responses to small-amplitude oscillatory stressing are naturally shifted from the starting point by an amount proportional to the phase of the applied stress. The phenomenology is experimentally observed with entangled polymerlike micelles and polyethylene oxide solutions. A theory of strain shifting in the steady alternating state is provided based on recovery rheology, where differences between total strain and recoverable strains are acknowledged. User-controlled variables, such as the amplitude of the stress, the angular frequency, and the phase of the stress, as well a lone material parameter, the zero-shear viscosity, are shown to dictate the amount of shifting. A rapid and efficient approach of determining the zero-shear viscosity is, therefore, presented. We investigate the microstructural evolution via in situ small-angle neutron scattering when strain shifting appears. The microscopic orientation is shown to correlate to the recoverable strain independent of the shifting. Additional measurements are carried out on collagen, pluronic-hyaluronic acid, alginate gels, and polystyrene melts to show the generic nature of the strain shift phenomenon. In addition, we demonstrate that the strain-shift knowledge can be applied to determine the horizontal shift factor in time-temperature superposition, free of any numerical fitting procedures.
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U2 - 10.1122/1.5111358
DO - 10.1122/1.5111358
M3 - Article
AN - SCOPUS:85072614736
VL - 63
SP - 863
EP - 881
JO - TRANS. SOC. RHEOL.
JF - TRANS. SOC. RHEOL.
SN - 0148-6055
IS - 6
ER -