Understanding ice formation near solid interfaces is a problem of fundamental and technological importance. We studied the structure of ice as well as the freezing and melting transition temperatures of water next to solid surface by sum frequency generation (SFG) spectroscopy. We have observed that the structures of ice and water are a function of pH and the surface charge. At low pH, corresponding to a positive charged surface, we observed an increase in the SFG signal subsequent to ice formation. Contrary to expectations, at pH 9.8, the intensity of the ice SFG signal is about 10 times lower than that of water. Recent simulation studies have suggested that charge transfer and stitching bilayers are important for the high intensity of the ice peak at the ice-air interface. We believe that in high pH, the charge transfer and the stitching bilayer may be perturbed by the segregation of sodium ions next to the negatively charged sapphire substrate, resulting in the decrease in signal intensity. The freezing and melting transition temperatures are independent of the surface charge. The results offer novel insight on how ions next to solid surfaces affect the structure of ice.

Freezing of water next to solid surfaces probed by infrared: Visible sum frequency generation spectroscopy

246th National Meeting (2013)

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