Anti-polyelectrolyte effect as a novel strategy to regulate the freezing point of zwitterionic hydrogels

2026-05-21

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Juan Zeng

DOI：10.1016/j.cclet.2026.112980

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Zwitterionic hydrogels as a new generation of functional materials are widely used in many frontier fields. However, zwitterionic hydrogels usually contain a large amount of active water and are inevitably frozen at low temperatures, thus sacrificing their mechanical properties and conductivity, which greatly limits their application. Herein, a novel strategy, namely the unique anti-polyelectrolyte effect (APE) of zwitterions is proposed to reduce the freezing point of zwitterionic hydrogels. The regulation mechanism of this strategy is that the electrostatic associated zwitterionic groups are exposed, thus increasing hydration by allowing these groups to establish strong hydrogen bonding with water molecules during the volume expansion process of zwitterionic polymer in salt. The overall water activity is decreased in the hydrogels, thus reducing the freezing point of the hydrogels. Sulfonic-based 2-(methacryloyloxy)ethyl dimethyl(3-sulfopropyl)-ammonium hydroxide (SBMA) and carboxylic-based 2-carboxy-N,N-dimethyl-N-(2′-methacryloyloxyethyl)ethanaminium inner salt (CBMA) zwitterionic monomers are selected as a proof of concept. SBMA based hydrogels with strong APE have a higher bound water content and a lower free water content than CBMA based hydrogels with almost no APE. Benefitting from the strong APE, the freezing point of SBMA based hydrogel (−20.9 °C) is significantly lower than that of CBMA based hydrogel (−12.4 °C). This work offers a practical and meaningful guidance for the design of anti-freezing zwitterionic hydrogels and further promotes the application of zwitterionic hydrogels in low temperature environments.

Anti-polyelectrolyte effect as a novel strategy to regulate the freezing point of zwitterionic hydrogels

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