Raman Spectroscopic Study on the Dynamic Structure at the Interface of Water-Organic Thin Films

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The state of water molecules sorbed to various kinds of polymer films was investigated by using FT-IR spectroscopy with ATR technique. The profile of O-H stretching band for the water vapor primarily sorbed to poly(methoxyethylacrylate) (PMEA) largely differed from that entrapped in the polymer matrix (secondary hydrating water originated from the liquid water in contact with the polymer), which suggested that highly biocompatible materials do not seem to affect the structure of surrounding water noticeably.Next, the structure and hydrogen bonding of water in various kinds of aqueous polyelectrolyte solutions were analyzed with contours of O-H stretching of polarized Raman spectra. The number of hydrogen bonding collapsed by the presence of one monomer residue (N value) of poly[3-(dimethylamino)propyl]methacrylamide was much larger than those for neutral polymers. On the contrary, the N value for zwitterionic polymer (carboxybetaine and sulfobetaine polymer) was small. The influence of carboxybetaine and sulfobetaine polymers on the structure of water became smaller with the increase in the degree of quaternization.As described above, using vibrational spectroscopy, we have revealed that the disturbing effect of the biocompatible polymers on the water structure is very small. However, these techniques detect the state of water both in bulk and at the interface. Therefore, to investigate the structure of water only at the solid-liquid interfaces, an attenuated total reflection Raman spectroscopic apparatus was constructed.