A study on the structure of water in an aqueous solution by the solvent effect on a volume phase transition of N-isopropylacrylamide gel and low-frequency Raman spectroscopy

We introduce a new technique to investigate the effect of residual substances on the hydrogen-bonded network structure of water molecules. We have characterized the effect of very low concentrations of several alcohol and phenol compounds on the structure of water from observations of their effect on the volume phase transition of N-isopropylacrylamide (NIPA) gels. The alteration of the volume phase transition was observed as a remarkable drop of the transition temperature associated with the change in entropy of the gel fluid. In addition, we have investigated the effect of these same compounds on water structure using low-frequency Raman spectroscopy, the results verify quantitatively the increase in entropy of the gel fluid with the addition of the residual substances. We found the effect of phenols on the structure of water clusters was remarkably large compared to the effect of alcohols. We demonstrate there is a strong correlation between the measurements of the drop in transition temperature of the volume phase transition and the results obtained from low-frequency Raman spectroscopy. We conclude that the collapse mechanism of the NIPA gel is induced by the disruption of the tetrahedral structure of water.