Nanostructural characterization of the dehydrated (NIPA/SA+additive ion) gels

In the present study, the authors have investigated ion-absorption effects on a nanoscopic structure of a dehydrated N-isopropylacrylamide/sodium acrylate (NIPA/SA) gel. First of all, the authors compared small-angle X-ray scattering (SAXS) profile of a dehydrated NIPA/SA gel with that dehydrated after absorbing Cu2+ ion. Then, in order to examine copper-ion distribution structure in the NIPA/SA gel dehydrated after absorption of copper-ion, an incident-X-ray energy-dependence of a small-angle X-ray scattering profile was observed, in which the anomalous dispersion effect was clearly perceived especially around a distinct SAXS-peak. Because the SAXS-peak is thought to come from a dehydration-induced microphase separation between hydrophilic and hydrophobic network-polymers in the NIPA/SA gel, such a feature indicates that the copper-ions gather in the dehydration-induced hydrophilic domains. In addition to this interesting copper-ion nanostructure in the dehydrated NIPA/SA gel, a difference in the SAXS-peak position between the dehydrated NIPA/SA gels with and without absorbing the copper-ion has shown a possibility of a controlling method of the nanostructure in relatively gentle conditions without special instruments. Along this line, in order to get further information on the ion-absorption effects on the nanostructure, the authors have compared the SAXS profiles of the several NIPA/SA gels which were dehydrated after absorbing respectively different kinds of ions. In the observation, the SAXS-peak positions have shown characteristic features which are different with the kind of the absorbed ions and found to be classified into several kinds according to the periodic-table group of the absorbed ion.