Momentum-varying optical technique unveils interfacial water structure that controls energy transfer and chemistry at interfaces
Charged water interfaces are responsible for many natural phenomena and of great importance in the development of advanced catalysts and energy storage devices. Microscopic interfacial processes, such as ion desolvation and charge transfer in reactions, are directly controlled by the interface-specific hydrogen-bonding network of water. However, knowledge on these bonded water layer structures and the interplay between ionic and molecular species therein is very limited. A research team led by Dr. Yu-Chieh Wen at Institute of Physics (IoP) now develop a nonlinear optical spectroscopic scheme with varying photon momenta for retrieving the vibrational spectra of the bonded interface water layer and the ion diffuse layer and, hence, microscopic structural and charging information about aqueous interfaces.
Using a model surfactant-water interface as a demonstration, the result revealed a hidden weakly donor hydrogen-bonded water species, suggesting an asymmetric hydration-shell structure of fully solvated surfactant headgroups. In another application to a zwitterionic phosphatidylcholine lipid monolayer–water interface, the team found a highly polarized bonded water layer structure associating to the phosphatidylcholine headgroup. This all-optic method offers an in situ microscopic probe of electrochemical and biological interfaces. The study further highlights the opportunities of applying momentum-resolved nonlinear optics to explore surface excitations in bulk backgrounds, which broadens the application of surface nonlinear optics to general condensed matter research.
This study has been published in Science Advances. The two leading authors, Yao Hsiao and Ting-Han Chou, are current and former research assistants at IoP, who carried out the research with supports from Dr. Animesh Patra from the same group. Funding was provided by Academia Sinica and the National Science and Technology Council.
Journal Links: https://www.science.org/doi/10.1126/sciadv.adg2823