Keynote Speaker
Prof. Dr. Ricardo Garcia
Interfacial liquid water on self-assembled monolayers,
biomolecules and 2D materials
Ricardo Garcia
Instituto de Ciencia de Materiales de Madrid, CSIC, Madrid, Spain
Solid-water interfaces have a prominent role in a variety of fields such as surface science, geochemistry, electrochemistry, energy storage or molecular and cell biology. Liquids near a solid surface form an interfacial layer where the molecular structure is different from that of the bulk. Yet the molecular-scale understanding of the interactions of liquid water with solid interfaces is unsatisfactory for the lack of high-spatial resolution methods. Here I will present an AFM-based method that provides atomic-scale resolution images of solid-liquid interfaces. The main finding is that the interfacial water structure and composition has a strong dependence on the hydrophobic properties of the solid surface.
The presentation is divided in three sections. The first section is an introduction to the relevance of solid-liquid interfaces. The second section, presents the features and capabilities of 3D-AFM instrument [1-3] to image with atomic resolution the three-dimensional interfacial structure of surfaces immersed in aqueous solutions. The third section reports the structure of interfacial water layers on hydrophobic systems such self-assembled OTS monolayers to 2D materials and hydrophilic surfaces (APTES monolayers, biomolecules). Those interfaces are characterized by the existence of a 2 nm thick region above the solid surface where the liquid density oscillates [4-6]. The distances between adjacent liquid layers on hydrophobic surfaces are ~0.50 nm. This value is larger than the one predicted and measured for water density oscillations (~0.30 nm). The experiments demonstrate that on extended hydrophobic surfaces water molecules are expelled from the vicinity of the surface and replaced by several molecular-size hydrophobic layers. The last section investigates the interfacial water structure on hydrophilic surfaces, in particular, collagen proteins. On hydrophilic the interfacial structure is characterized by the presence of hydration layers with an interlayer distance of 0.3 nm [7].
References
[1] T. Fukuma and R. Garcia, ACS Nano 12 11785 (2018).
[2] R. Garcia, ACS Nano 17, 51-69 (2023)
[3] S. Benaglia, et al. Phys. Rev. Lett. 15, 20574-20581 (2021)
[4] M.R. Uhlig, D. Martin-Jimenez and R. Garcia, Nat. Commun. 10. 2606 (2019).
[5] M.R. Uhlig, R. Garcia, Nano Lett. 21, 5593 (2021)
[6] M.R. Uhlig, S. Benaglia, R. Thakkar, J. Gomer and R. Garcia, Nanoscale 13, 5275 (2021)
[7] D.M. Arvelo, C. Garcia-Sacristan, R. Garcia (under submission)