Influence of Metal Ions on the Melting Temperature, Modulus, and Gelation Time of Gelatin Gels: Specific Ion Effects on Hydrogel Properties.

The impact of ions on hydrogel strength is not well understood, in particular with regards to specific ion effects for cations. Herein, we find that divalent and monovalent cations in most cases reduce the modulus and melting temperature while increasing the gelation time of gelatin hydrogels. This behavior is in contrast to the well-known stiffening effect of trivalent metals. The melting temperature, the logarithm of the gelation time, and the logarithm of the amplitude of the complex modulus were found to follow a power law dependence on ionic strength: kI x. The power law exponent, x, was found to be universal within the groups of monovalent and divalent cations. The prefactor k depended linearly on the ionic radius, which was used as a proxy for ion polarizability. The slope of this linear dependence was different for monovalent and divalent cations.