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Title: Charge segregation in weakly ionized microgels

Journal Article · · Physical Review E
 [1];  [2];  [3];  [3];  [4];  [1]
  1. Georgia Inst. of Technology, Atlanta, GA (United States). School of Physics
  2. Georgia Inst. of Technology, Atlanta, GA (United States). Wallace H. Coulter Dept. of Biomedical Engineering
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biology and Soft Matter Division, Neutron Sciences Directorate
  4. Univ. of Virginia, Charlottesville, VA (United States). Dept. of Biomedical Engineering
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Here 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. Lastly, 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.

Research Organization:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division; National Science Foundation (NSF)
Grant/Contract Number:
AC05-00OR22725; DMR-1609841
OSTI ID:
1422543
Alternate ID(s):
OSTI ID: 1341312
Journal Information:
Physical Review E, Vol. 95, Issue 1; ISSN 2470-0045
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 11 works
Citation information provided by
Web of Science

References (24)

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Cited By (2)

Synthesis of smart dual-responsive microgels: correlation between applied surfactants and obtained particle morphology journal January 2019
Numerical insights on ionic microgels: structure and swelling behaviour journal January 2019

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