Linear and nonlinear viscoelasticity of concentrated thermoresponsive microgel suspensions

Gaurav Chaudhary, Ashesh Ghosh, Jin Gu Kang, Paul V. Braun, Randy H. Ewoldt, Kenneth S. Schweizer

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish (US)
Pages (from-to)886-898
Number of pages13
JournalJournal of Colloid And Interface Science
Volume601
DOIs
StatePublished - Nov 2021

Keywords

  • Attractive microgels
  • Colloidal rheology
  • Concentrated suspension
  • Statistical mechanical theory
  • Thermoresponsive colloids
  • pNIPAM microgels

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Surfaces, Coatings and Films
  • Biomaterials
  • Colloid and Surface Chemistry

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