NCAFM2023 Programme Booklet

Thursday 1400 - 1420

QTF BASED RAMAN SPECTROSCOPY OF CONFINEMENT INDUCED STRUCTURAL CHANGE OF WATER

Jonggeun Hwang 1 , Dongha Shin 1,2 , Manhee Lee 3 , Brendan T. Deveney 4 , Xingcai Zhang 4,5* & Wonho Jhe 1,* 1 Department of Physics and Astronomy, Seoul National University, Seoul 08826, Korea 2 Department of Chemistry and Chemical Engineering, Inha University, Incheon 22212, Korea 3 Department of Physics, Chungbuk National University, Cheongju, Chungbuk 28644, Korea. 4 School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA 5 School of Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA *Email: whjhe@snu.ac.kr, xingcai@mit.edu

Structural transformations originating from diverse rearrangements of the hydrogen bonding in water create various phases. Although most phases have been well investigated down to the molecular level, the molecular structure of the nanomeniscus, a ubiquitous form of nanoscale water in nature, still remains unexplored. For experimental study, we first demonstrated that the water nanomeniscus exhibits the stable, ice-VII-like molecular structure (Fig.) in ambient condition using surface-enhanced Raman spectroscopy (SERS) on trace amounts of water, confined in inter-nanoparticle gaps [1]. Recent first-principle molecular dynamic simulations showed water confined within nanoslits is expected to exhibit a bilayer ice-VII [2] at room temperature, but not the hexagonal ice structure. To address this, we then performed QTF-based atomic force experiment of confinement-induced structural change of water by employing tip-enhanced Raman spectroscopy (TERS) at room temperature. A novel DDAA molecular peak emerges in the OH-stretching band at sub-nanometer confinement, which exhibits the unit structure of ice-VII while the tetrahedral DDAA (ice-Ih) appears as the confinement lessens. Our results provide novel insights on water or ice that forms on Earth or in clouds and help deeper understand the peculiar sluggish dynamics of nano-confined water from molecular and biological aspects.

Fig. 1 Surface enhanced Raman spectroscopy for ultra-purified nanoconfined water between gold particles.

References [1] Ice-VII-like molecular structure of ambient water nanomeniscus, D. Shin, J. Hwang and W. Jhe, Nat. Commun. 2019, 10 , 286. [2] First-Principles Molecular Dynamics Simulations of the Spontaneous Freezing Transition of 2D Water in a Nanoslit. J. Jiang et al. J. Am. Chem. Soc. 2021, 143 , 8177.

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