Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 118, Issue 37, Pages -Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2109560118|1of11
Keywords
soft colloids; polymer networks; volume phase transition; coarse-grained modeling
Categories
Funding
- European Research Council [681597]
- European Union [731019]
- Italian Ministry of Education, University and Research (FARE Project) [R16XLE2X3L]
- Agence Nationale de la Recherche [ANR-20-CE06-0030-01]
- European Research Council (ERC) [681597] Funding Source: European Research Council (ERC)
- Agence Nationale de la Recherche (ANR) [ANR-20-CE06-0030] Funding Source: Agence Nationale de la Recherche (ANR)
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Thermoresponsive microgels are soft colloids that can undergo a Volume Phase Transition (VPT) close to ambient temperature. A recent study found that microgel collapse occurs through a two-step mechanism due to electrostatic effects, with the emergence of a minimum in the ratio between gyration and hydrodynamic radii at the VPT. Peripheral charges arising from the synthesis were identified as responsible for this behavior, and a universal master curve was constructed to predict the two-step deswelling process.
Thermoresponsive microgels are one of the most investigated types of soft colloids, thanks to their ability to undergo a Volume Phase Transition (VPT) close to ambient temperature. However, this fundamental phenomenon still lacks a detailed microscopic understanding, particularly regarding the presence and the role of charges in the deswelling process. This is particularly important for the widely used poly(N-isopropylacrylamide)-based micro gels, where the constituent monomers are neutral but charged groups arise due to the initiator molecules used in the synthesis. Here, we address this point combining experiments with state-of-the-art simulations to show that the microgel collapse does not happen in a homogeneous fashion, but through a two-step mechanism, entirely attributable to electrostatic effects. The signature of this phenomenon is the emergence of a minimum in the ratio between gyration and hydrodynamic radii at the VPT. Thanks to simulations of microgels with different cross-linker concentrations, charge contents, and charge distributions, we provide evidence that peripheral charges arising from the synthesis are responsible for this behavior and we further build a universal master curve able to predict the twostep deswelling. Our results have direct relevance on fundamental soft condensed matter science and on applications where microgels are involved, ranging from materials to biomedical technologies.
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