Further consideration of the spectral characteristics of interfacial water at hydrophobic surfaces

摘要

In-situ FTIR/internal reflection spectroscopy (FTIR/IRS) was used to spectroscopically characterize interfacial water at a hydrophobic surface of a silicon single crystal internal reflection element (IRE). The hydrophobic surface state was established by reaction of the silicon IRE with octadecyltrichlorosilane (OTS) in cyclohexane solution. In-situ FTIR/IRS spectra were examined by consideration of the O-H stretching region (3000-3800 cm~(-1)) associated with the vibrational spectra of interfacial water. The broad peak in this region was deconvoluted in order to isolate overlapping spectral features characteristic of the interfacial water. Three distinct bands were found; approx 3600 cm~(-1) (free OH), approx 3400 cm~(-1) (incomplete tetrahedral coordination), and approx 3240 cm~(-1) (complete tetrahedral coordination). as found in previous studies, these FTIR/IRS results reveal a distinct change in interfacial water structure at the hydrophobic silicon surface. Specifically the vibrational mode of the free OH at approx 3600 cm~(-1) was found to be accentuated.