| AVS 54th International Symposium | |
| Applied Surface Science | Wednesday Sessions |
| Session AS+BI+NS-WeA |
| Session: | Fabrication and Characterization of Functional Soft Material Surfaces |
| Presenter: | K. Uosaki, Hokkaido University, Japan |
| Authors: | K. Uosaki, Hokkaido University, Japan H. Noguchi, Hokkaido University, Japan S. Nihonyanagi, Hokkaido University, Japan H. Minowa, Hokkaido University, Japan R. Yamamoto, Hokkaido University, Japan |
| Correspondent: | Click to Email |
Polymer brush and gel plays very important roles in biological systems. Information on the interfacial structure is essential to understand the function of these materials. Here we employed sum frequency generation (SFG) spectroscopy, which is known to possess high surface specificity, to investigate the molecular orientation/conformation of polymer brush under various environment and water structure at PVA gel/solid interface. SFG spectra of alkylated poly (vinyl pyridine) in contact with dry nitrogen, water vapor, and liquid water were obtained. The peaks due to CH vibration of CH3 dominated in nitrogen, showing that the side chains are highly ordered. When the polymer layer is in contact with water vapor, in addition to the two peaks due to CH3 group, two peaks of CH2 group were observed, indicating that many gauche defects existed. The SFG spectrum of the polymer brush in contact with liquid water showed no peaks in CH stretching region except for small shoulder due to the ring CH modes, indicating the alkyl side chain was completely disordered. SFG spectra of the polymer brush in OH stretching region were also obtained. A broad band assigned to the OH stretching was observed in water vapor. Two bands corresponding to the OH stretching of the interfacial water molecules at 3200 cm-1 due to “ice-like water” and at 3400 cm-1 due to “liquid-like water” dominated in liquid water. Poly vinyl alcohol (PVA) gel is considered to be one of the possible candidates for an artificial articular cartilage in artificial joints because of very low friction between PVA gel and solid. SFG measurement proved that while the fractions of the “ice-like” and “liquid-like” water were almost equal at water/quartz interface, the fraction of the “liquid-like” water became much higher when the PVA gel was pressed against the quartz surface, showing that the weakly hydrogen bonded water dominate at PVA gel/quartz interface where friction is very low. SFG measurement in Ar showed only weakly hydrogen bonded water was present at the PVA gel/quartz interface. The effect of PVA gel contact was less obvious at the octadecyltrichlorosilane (OTS) coated quartz, where the friction is much higher. These results suggest the important role of weakly hydrogen bonded water for very small friction at PVA gel/solid interface. In conclusion, SFG is demonstrated to be a very useful technique to characterize molecular structure at solid/liquid interfaces including biological interfaces.