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Poly(sodium acrylate) hydrogels: synthesis of various network architectures, local molecular dynamics, salt partitioning, desalination and simulation

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Abstract

Various poly(sodium acrylate) hydrogels with different architectures, such as single networks, interpenetrating double networks and surface crosslinked hydrogels, are synthesized with a systematic change in their degree of crosslinking. The influence of these 3D structures on the absorbency of aqueous NaCl solutions is investigated. The local polymer mobility in water is probed in the form of transverse (T2) 1H-relaxation at a low field, which allowed confirming the structural aspects of the studied network topologies. Salt partitioning between the gel and the surrounding solution phase in NaCl solutions with an initial salt concentration of c0 = 0.017–0.60 mol L−1 (≙1–35 g L−1) is investigated. The data are compared with an idealized mean-field Donnan model, which fit the experimental findings only under the assumption of a drastically reduced effective charge density of feff ≈ 25 mol% independent of the hydrogel used. The unequal salt distribution allows desalination of salt water by applying an external pressure to a swollen hydrogel to recover its water which has a lower salinity. The specific energy needed to desalinate 1 m3 was estimated to be 6–18 kW h m−3. This value decreases with a lower degree of swelling independent of the network topology. Besides the experiments, simulations based on a Poisson–Boltzmann mean-field model and MD simulations are performed to determine the degree of swelling and salt partitioning as a function of c0 for different hydrogels. Both simulations describe qualitatively the experimental data, where deviations can be ascribed to model simplifications and the imperfect structure of the hydrogels synthesized via free radical polymerization.

Graphical abstract: Poly(sodium acrylate) hydrogels: synthesis of various network architectures, local molecular dynamics, salt partitioning, desalination and simulation

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Publication details

The article was received on 19 Jul 2019, accepted on 06 Nov 2019 and first published on 14 Nov 2019


Article type: Paper
DOI: 10.1039/C9SM01468C
Soft Matter, 2019, Advance Article
  • Open access: Creative Commons BY-NC license
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    Poly(sodium acrylate) hydrogels: synthesis of various network architectures, local molecular dynamics, salt partitioning, desalination and simulation

    L. Arens, D. Barther, J. Landsgesell, C. Holm and M. Wilhelm, Soft Matter, 2019, Advance Article , DOI: 10.1039/C9SM01468C

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