The Liquid/Vapor Interface of Dimethyl Carbonate-Methanol Binary Mixtures Investigated by Sum Frequency Generation Vibrational Spectroscopy and Molecular Dynamics Simulation.

In the present work, the dimethyl carbonate-methanol binary mixture was used as a benchmark system to study the molecular structures of the liquid/vapor interface of organic-organic mixtures by the sum frequency generation vibrational spectroscopy (SFG-VS) and molecular dynamics (MD) simulations. It was discovered that both the methanol and DMC molecules are anisotropically oriented at the surface, yielding strong SFG-VS signals in the C-H stretching frequency range for both molecules. The detailed analyses on the spectroscopic and MD data reveal that the orientational orders of the interfacial methanol and DMC molecules change diffidently with the bulk mole fractions. Moreover, no obvious correlations were found between the room temperature orientations of the surface molecules and the azeotropic mole fraction. The present work paves the road for the future investogations on the molecular structures of the liquid/vapor interfaces of other organic-organic mixtures, especially of those that are important in the industrial separations.