Fluids in porous materials: from fundamental physics to engineering applications
CECAM-HQ-EPFL, Lausanne, Switzerland
Liquid intrusion in nanoporous systems (“wetting”) is the process by which the fluid replaces the pre-existing vapor/gas phase present in the medium. Extrusion ("drying") is the opposite process. For long time, the theoretical description of intrusion/extrusion has been based on the capillary theory of multiphase systems (see, e.g., Ref. ). During the last 10-15 years, some progress has been made developing rigorous statistical mechanics approaches describing intrusion/extrusion as a rare event (see, e.g., ). Among other advancements, this led to the discovery of unconventional wetting paths of cavities that could explain some experimental results, but also highlighted mismatches with the empirical evidence . This suggested that the quasi-static description of the intrusion/extrusion process one obtains with well-established simulation techniques may be insufficient . Moreover, novel (sub)nanoporous materials attracted the interest of experimentalists, adding significant theoretical challenges: i) they cannot be described by continuum models, ii) are highly flexible, iii) might change configuration during the process (e.g., biological channels), iv) present shallow interconnected pores defeating classical Cassie-Baxter/Wenzel behavior, v) present an unusually low intrusion pressure, etc. Related problems and challenges are also encountered in the processes of solvent evaporation from nanoporous materials.
Nanoporous materials immersed in liquids are promising for their potential applicability to develop novel technologies. In some cases intrusion/extrusion may be accompanied by other phenomena, such as triboelectrification and heat flow, which call for a comprehensive description of these processes and make them potentially usable to scavenge low-grade energy available in the environment. The peculiar behavior of water in nanopores is central also for several phenomena of biomedical interest, including selectivity, conduction, and gating mechanisms of ion channels , which can serves as a source of inspiration for technologies for water purification, nanopore sensing, nanofluidic circuits, and drug delivery. Understanding the physical origin of these properties and developing quantitative tools to engineer them is the key for the progress of nanopore-based technologies.
Understanding intrusion/extrusion/evaporation in system with complex chemistry and topology, and their combination with other phenomena is still in its infancy. The objective of this workshop is to gather experimentalists and theoreticians to discuss fundamental and technological aspects of these processes, including:
- Fundamental questions on the intrusion/extrusion/evaporation mechanism, energetics, and kinetics in complex porous systems: disordered grafted porous systems, metal- or covalent-organic framework, porous polymeric materials , soft porous media – biological channels. This includes, for example, how liquid penetrates in porous materials - e.g., via condensation or via a cascade advancement? – and its dependence on the morphological characteristics of the porous media – e.g., cage-like vs channel-like systems – and their chemical nature – e.g., hydrogen bonding with some atoms of the material.
- Challenges in the simulation of intrusion/extrusion/evaporation: quasi-static (e.g., string method) vs “dynamical” methods (e.g., transition interface sampling), and multiscale aspects in time and space in general.
- Challenges in the experimental investigation of intrusion/extrusion/evaporation: in situ structural measurements, heat flux, charging/discharging of the liquid/solid interface, ionic conduction across nanopores, stability of ultrathin liquid films.
- Identify possible novel technological applications of these systems and establishing collaborations among the participants to tackle them.
Alberto Giacomello (Sapienza University of Rome) - Organiser
Simone Meloni (University of Ferrara) - Organiser
Yaroslav Grosu (CIC energiGUNE) - Organiser
Andriy Yaroshchuk (Polytechnic University of Catalonia) - Organiser