Defesa de Tese de Doutorado #422 – Raphaela de Oliveira Gonçalves – 23/10/2023

Water is the matrix of life and its confinement in nanocavities is a central topic from geophysics to nanotribology. Phyllosilicate layered minerals are natural nanocavities for water due to their capacity to hydrate by confining water molecules in the interlamellar space. Abundant on Earth, the occurrence of phyllosilicate minerals on other planets is a signature of water presence. However, the hydration of phyllosilicates at nanoscale is not a fully understood process and depends on the geological specimens. On the other hand, phyllosilicate minerals are insulators with a large bandgap and associated low-cost that have been recently explored in the fabrication of nanodevices. Because they are of natural origin, the presence of impurities is common. Thus, it is crucial to understand how impurities and hydration by the nanoconfinement of water change the fundamental properties of phyllosilicates in their few-layer form for two-dimensional (2D) applications.

Exploring clinochlore from the chlorite group and phlogopite from the trioctahedral mica group, this thesis aims to expand the understanding of the fundamental properties and hydration of phyllosilicates in their few-layer form. First, a robust experimental characterization of the structure, morphology and defects and impurities of the samples was carried out. With this, it was possible to provide a complete description of the 2D structure of clinochlore and phlogopite and their fundamental properties from their bulk form. To elucidate how variations in the atomic structure of these barely explored specimens of phyllosilicates favor the geo-confinement of water and its properties, a deep analysis of the nanoconfinement of water in both phyllosilicates was conducted. Using advanced nanoprobe techniques, it was possible to obtain the vibrational properties of phyllosilicates in their few-layer form and to determine that nanoconfined water changes the mechanical and dielectric properties of the minerals. The results obtained suggest that the confined water can condense forming ice-like arrangements at room temperature, being stable to relative humidity variation, but unstable to temperature increase. As a unique result, a controlled method for mechanical nanomanipulation of interlamellar water was demonstrated.

Notably, this thesis opens doors to the multifunctionalization of phyllosilicate minerals in their few-layer form aiming applications at the frontiers of nanotechnology – from catalysis, microfluidics, and patterning of biomolecules to sensing, and fabrication of optoelectronic nanodevices.