Polyelectrolyte hydrogel diffusiophoresis

When immersed in an aqueous solution, polyelectrolyte hydrogels swell more than regular gels due to the Gibbs-Donnan effect. Upon dissociation from the gel backbone, the counterions may interact with the charged polyelectrolyte network through electrostatic interactions. Recent theoretical and experimental work has established the gel diffusiophoresis mechanism, where hydrogels can deform superdiffusively, driven by the sharp gradient of released ions from the polymer network [1, 2]. In contrast to gel diffusiophoresis, where the gel strain rate is linearly proportional to the gradient of free ion volume fraction, the strain rate in a polyelectrolyte hydrogel must depend on the gradient of the logarithm of counterion volume fraction. We hypothesize that in a polyelectrolyte hydrogel, the diffusiophoretic deformation can emerge when counterions rapidly dissociate from the polymer backbone and diffuse out of the gel, potentially leading to high strain rates. To probe this mechanism, we have developed a continuum poroelastic theory coupled with reaction, diffusion, and electromigration of ions. This theoretical framework describes the potentially elevated strain rates of a polyelectrolyte gel upon release of ions from the gel.

1. [1] C. Katke, P. A. Korevaar, and C. N. Kaplan. Diffusiophoretic fast swelling of chemically responsive hydrogels. Phys. Rev. Lett., 132:208201, May 2024. doi: 10.1103/PhysRevLett. 132.208201. URL https://link.aps.org/doi/10.1103/PhysRevLett.132.208201.
   
   
   
   [2] P. A. Korevaar, C. N. Kaplan, A. Grinthal, and J. Aizenberg. Non-equilibrium signal integration in hydrogels. Nat. Comm., 11:386, 2020. doi: 10.1038/s41467-019-14114-0. URL https://doi.org/10.1038/s41467-019-14114-0.