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Published on: December 9, 2022
Molecular structure and adsorption of dimethyl sulfoxide at the air/aqueous solution interface probed by non-resonant
Qianshun Wei1, Dexia Zhou, Hongtao Bian
1Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi'an, 710119, China. htbian@snnu.edu.cn.
Abstract:
In this study, non-resonant second harmonic generation (SHG) was used to investigate the molecular structure and adsorption of DMSO at the air/neat DMSO liquid and air/DMSO aqueous solution interfaces. The molecular orientation of interfacial DMSO as a function of the bulk DMSO concentration was investigated by quantitative polarization SHG analysis. For the air/neat DMSO liquid interface, the transition dipole moment of the S[double bond, length as m-dash]O group of DMSO is oriented 140° from the surface normal, where the S[double bond, length as m-dash]O group of DMSO is estimated to be 30° from the surface plane. The orientation of the S[double bond, length as m-dash]O group of interfacial DMSO is not dependent on the bulk DMSO concentration. Furthermore, the concentration-dependent SHG signal confirmed that the antiparallel double layer structure does not form at the air/DMSO water interface. The free energy of adsorption of DMSO at the air/DMSO aqueous solution interface was determined to be ΔGads = -5.6 ± 0.4 kJ mol-1.
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