Phd in THEORETICAL AND APPLIED MECHANICS

Thesis title: Simulations and coarse grained techniques for wetting and drying of hydrophobic nanopores

Wetting and drying in nanoporous materials is a non-trivial multiscale problem. If the material is solvophobic, it can resist wetting (intrusion), sometimes requiring hundreds of atmospheres of pressure for liquid penetration to occur. If the pressure is removed, the liquid can dry (extrusion) from the material, "boiling" at room temperature. Several technological applications require pre- cise control of the intrusion (wetting)/extrusion (drying) pressure and the dynamics of the process. Modelling these processes requires atomistic details that can only be achieved with molecular dy- namics simulations, as nanoscopic processes often govern the macroscopic behaviour of the system. Because the transitions from the wet (liquid filled) to the dry (empty of liquid) states, and vice versa, are events that take significant time to happen (up to some microseconds) they are called rare events. These rare events are difficult to study in standard atomistic simulations, as they require very long simulation times. In this work we will look at standard atomistic simulations, coupled with rare event techniques, like Restrained Molecular Dynamics, as well as other coarse graining techniques, like Langevin Dynamics and stochastic simulations, to cover the multiscale problem of wetting and drying in hy- drophobic nanopores, giving insights into experimentally relevant phenomena while keeping atom- istic information about the system. This dissertation is structured as follows: in the first section I will give a theoretical introduction into the phenomenology of hydrophobic nanopores, relevant experimental questions and failures of current macroscopic models, as well as a brief introduction to nanofluidics and iontronic applications; in the second section I will describe all the methods used throughout the work, explaining in detail some of the theoretical and practical questions related to the application of such methods; in the third sections I will discuss published and unpublished results related to simulations of wetting and drying in hydrophobic nanopores, discussing the effect of pressure, of the topology of the material, deviations from macroscopic laws, modelling the intrusion and extrusion of water in a real material as well as discuss the effect of voltage on wetting and potential applications related to novel forms of computation; finally I will present a conclusion of the research I developed and consider some relevant open questions that may open new perspectives.