Linear and nonlinear viscoelasticity of concentrated thermoresponsive microgel suspensions

JOURNAL OF COLLOID AND INTERFACE SCIENCE

卷:601

Article

Chaudhary, Gaurav^1,4,7  Ghosh, Ashesh^2,4,8  Kang, Jin Gu^3,4,9  Braun, Paul, V^1,2,3,4,5  Ewoldt, Randy H.^1,4,5  Schweizer, Kenneth S.^2,3,4,5,6 

[1] Univ Illinois, Dept Mech Sci & Engn, Urbana, IL 61801 USA

[2] Univ Illinois, Dept Chem, Urbana, IL 61801 USA

[3] Univ Illinois, Dept Mat Sci & Engn, Urbana, IL 61801 USA

[4] Univ Illinois, Mat Res Lab, Urbana, IL 61801 USA

[5] Univ Illinois, Beckman Inst Adv Sci & Technol, Urbana, IL 61801 USA

[6] Univ Illinois, Dept Chem & Biomol Engn, Urbana, IL 61801 USA

[7] Harvard Univ, Sch Engn & Appl Sci, Cambridge, MA 02138 USA

[8] Stanford Univ, Dept Chem Engn, Stanford, CA 94305 USA

[9] Korea Inst Sci & Technol, Nanophoton Res Ctr, Seoul 02792, South Korea

关键词: pNIPAM microgels;    Concentrated suspension;    Attractive microgels;    Colloidal rheology;    Thermoresponsive colloids;    Statistical mechanical theory;   

DOI  :  10.1016/j.jcis.2021.05.111

来源: Elsevier

【 摘 要 】

We present an integrated experimental and theoretical study of the dynamics and rheology of selfcrosslinked, slightly charged, temperature responsive soft poly(N-isopropylacrylamide) (pNIPAM) micro gels 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. (c) 2021 Elsevier Inc. All rights reserved.

【 授权许可】

Free