TY - JOUR
T1 - Linear and nonlinear viscoelasticity of concentrated thermoresponsive microgel suspensions
AU - Chaudhary, Gaurav
AU - Ghosh, Ashesh
AU - Kang, Jin Gu
AU - Braun, Paul V.
AU - Ewoldt, Randy H.
AU - Schweizer, Kenneth S.
N1 - Funding Information:
This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award Nos. DE-FG02-07ER46471 and DE-SC0020858, through the Materials Research Laboratory at the University of Illinois at Urbana-Champaign. RHE thanks Anton Paar for providing the MCR702 rheometer which was used for some of the rheology experiments.
Publisher Copyright:
© 2021 Elsevier Inc.
PY - 2021/11
Y1 - 2021/11
N2 - We present an integrated experimental and theoretical study of the dynamics and rheology of self-crosslinked, slightly charged, temperature responsive soft poly(N-isopropylacrylamide) (pNIPAM) microgels over a wide range of concentration and temperature spanning the sharp change in particle size and intermolecular interactions across the lower critical solution temperature (LCST). Dramatic, non-monotonic changes in viscoelasticity are observed as a function of temperature, with distinct concentration dependence in the dense fluid, glassy, and soft-jammed regimes. Motivated by our experimental observations, we formulate a minimalistic model for the size dependence of a single microgel particle and the change of the interparticle interaction from purely repulsive to attractive upon heating. Using microscopic equilibrium and time-dependent statistical mechanical theories, theoretical predictions are quantitatively compared with experimental measurements of the shear modulus. Good agreement is found for the nonmonotonic temperature behavior that originates as a consequence of the competition between reduced microgel packing fraction and increasing interparticle attractions. Testable predictions are made for nonlinear rheological properties such as the yield stress and strain. To our knowledge, this is the first attempt to quantitatively understand in a unified manner the viscoelasticity of dense, temperature-responsive microgel suspensions spanning a wide range of temperatures and concentrations.
AB - We present an integrated experimental and theoretical study of the dynamics and rheology of self-crosslinked, slightly charged, temperature responsive soft poly(N-isopropylacrylamide) (pNIPAM) microgels over a wide range of concentration and temperature spanning the sharp change in particle size and intermolecular interactions across the lower critical solution temperature (LCST). Dramatic, non-monotonic changes in viscoelasticity are observed as a function of temperature, with distinct concentration dependence in the dense fluid, glassy, and soft-jammed regimes. Motivated by our experimental observations, we formulate a minimalistic model for the size dependence of a single microgel particle and the change of the interparticle interaction from purely repulsive to attractive upon heating. Using microscopic equilibrium and time-dependent statistical mechanical theories, theoretical predictions are quantitatively compared with experimental measurements of the shear modulus. Good agreement is found for the nonmonotonic temperature behavior that originates as a consequence of the competition between reduced microgel packing fraction and increasing interparticle attractions. Testable predictions are made for nonlinear rheological properties such as the yield stress and strain. To our knowledge, this is the first attempt to quantitatively understand in a unified manner the viscoelasticity of dense, temperature-responsive microgel suspensions spanning a wide range of temperatures and concentrations.
KW - Attractive microgels
KW - Colloidal rheology
KW - Concentrated suspension
KW - Statistical mechanical theory
KW - Thermoresponsive colloids
KW - pNIPAM microgels
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U2 - 10.1016/j.jcis.2021.05.111
DO - 10.1016/j.jcis.2021.05.111
M3 - Article
C2 - 34186277
AN - SCOPUS:85109419181
SN - 0021-9797
VL - 601
SP - 886
EP - 898
JO - Journal of Colloid And Interface Science
JF - Journal of Colloid And Interface Science
ER -