Experimental estimation of molecular structure of the water-rock interface inferred from in situ IR-Raman spectroscopy up to 40 °C, 50 MPa

In order to investigate the molecular effects of interfacial water on rock surface by infrared (IR) and Raman spectroscopy, high temperature-pressure cell (up to 400°C and 50 MPa) worked with optical microscopy was developed. This apparatus can measure IR and Raman spectra of water on a metal and quartz surface at high temperature and pressure (HT & HP) conditions in situ. As a result of IR spectroscopic measurements of water on a metal, the broad peak at ca. 3400cm^-1, attributed to OH stretching vibration of water molecules was observed at high temperature and pressure conditions. Continuous shift of the OH vibration mode was obtained from room condition to hydrothermal condition. Compared with the result of IR properties of water on a metal, IR properties of water on quartz surface exhibit different trend: the peak position shifted to higher wavenumber with increasing temperature and slightly shifted with pressure. In addition, IR spectra of water in mesoporous silica were measured. IR property of water in mesoporous silica was changed depending on pore diameter. Mesoporous silica having smaller diameter restrict the vibration of water molecules. IR property of water was changed by environmental conditions such as temperature, pressure and substrate. Molecular structure of interfacial water on solid material at elevated temperatures and pressures were not only changes due to physical conditions such as temperature and pressure but also interaction between water and solid surface.