Charge segregation in weakly ionized microgels

John S. Hyatt, Alison M. Douglas, Chris Stanley, Changwoo Do, Thomas H. Barker, and Alberto Fernández-Nieves
Phys. Rev. E 95, 012608 – Published 19 January 2017

Abstract

We investigate microgels synthesized from N-isopropylacrylamide (NIPAM) copolymerized with a large mol% of acrylic acid, finding that when the acid groups are partially ionized at high temperatures, competition between ion-induced swelling and hydrophobic deswelling of poly(NIPAM) chains results in microphase separation. In cross-linked microgels, this manifests as a dramatic decrease in the ratio between the radius of gyration and the hydrodynamic radius to 0.2, indicating that almost all the mass of the microgel is concentrated near the particle center. We also observe a concurrent decrease of the polymer network length scale via small-angle neutron scattering, confirming the presence of a dense, deswollen core surrounded by a diffuse, charged periphery. We compare these results to those obtained for a system of charged ultralow-cross-linked microgels; the form factor shows a distinct peak at high q when the temperature exceeds a threshold value. We successfully fit the form factor to theory developed to describe scattering from weakly charged gels in poor solvents, and we tie this behavior to charge segregation in the case of the cross-linked microgels.

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  • Received 5 October 2016

DOI:https://doi.org/10.1103/PhysRevE.95.012608

©2017 American Physical Society

Physics Subject Headings (PhySH)

Polymers & Soft MatterCondensed Matter, Materials & Applied Physics

Authors & Affiliations

John S. Hyatt1, Alison M. Douglas2, Chris Stanley3, Changwoo Do3, Thomas H. Barker4, and Alberto Fernández-Nieves1

  • 1School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430, USA
  • 2Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
  • 3Biology and Soft Matter Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
  • 4Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia 22908, USA

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Issue

Vol. 95, Iss. 1 — January 2017

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