Summary: The effect of monovalent/divalent cation exchange on the structure and osmotic properties of chemically cross‐linked polyacrylate and DNA gels swollen in near physiological salt solutions has been investigated. Both systems exhibit a reversible volume phase transition in the presence of calcium ions. The small‐angle neutron scattering spectra of these gels display qualitatively similar features. At low values of q surface scattering is observed, while in the intermediate q range the signal is characteristic of scattering from rod‐like elements. At high values of q the scattering intensity is governed by the local (short‐range) geometry of the polymer chains. The competition between monovalent and divalent cations has been studied by anomalous small‐angle X‐ray scattering (ASAXS). The ASAXS results reveal that the local concentration of the divalent counter‐ions in the vicinity of the polymer chains significantly exceeds that of the monovalent counter‐ions.
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Horkay et al. (2007) studied this question.
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