In this project we focus on porous lyophobic crystalline materials (PLCs) for energy storage.
The first objective is the determination of the dependence of intrusion/extrusion pressure hysteresis on the chemical nature and morphology of the cavities of PLCs. PLCs can store mechanical energy under the form of interface energy: interface energy is accumulated when an external pressure higher than the intrusion pressure forces the non-wetting liquid into the cavities of PLCs and is released when the pressure drops under the extrusion pressure and the liquid returns to its initial state. A difference between the intrusion and extrusion pressures implies an energy loss, which must be minimized to maximize the efficiency of the device. Developing a quantitative theory of the intrusion and extrusion pressure, and the thermodynamics and kinetics of the wetting/dewetting process will allow to design PLC materials with desired properties.
A second objective of the project is the characterization of the degradation of PLC materials with intrusion/extrusion cycles. The use of PLC for energy storage requires the stability of the material at the operative conditions, while empirical evidence shows that the performance of present systems degrades with time. The identification of the degradation mechanism will help to develop novel materials with improved stability.
The research proposed in this project will be conducted by an interdisciplinary team composed by engineering, physics and chemistry experts. The team will combine experiments and simulations, using an array of techniques including porosimetry, XRD, XAS, XES, Raman spectroscopy, AFM, calorimetry, classical and ab initio rare event simulations. The results of this project will help progressing the field of energy storage as well as shading light on fundamental aspects of liquid under extreme confinement.
The research we propose has a high potential impact on fundamental research of multiphase systems and on related technological applications, such as the mechanical energy storage and dumpers systems that are the applicative subject of the research we propose. Indeed, the scientific questions of the present proposal are central to the physics and chemistry of porous media, liquids under extreme confinement and nano-engineering, the three scientific areas involved in the project. So far materials for energy storage and shock damping applications have been designed with a trial-and-error approach. The success of the present project will represent a paradigmatic shift: novel materials with tailored properties will be designed on the basis of a solid theoretical knowledge which has been validated on a number of experimental results obtained with complementary techniques.
The results of the present project will have impact on other fields as well. For example, we will learn how extreme confinement affects the structural and functional properties of liquids. This might pave the way for novel uses of liquids in porous materials in chemistry, physics and engineering. For example, the change of the properties of water could be exploited in chemistry to promote reactions that could not take place in the bulk. Performing reactions in high confinement could be an alternative approach to the use of alternative, potentially expensive and non eco-friendly, inorganic or organic solvents. Water under high confinement in contact with bulk water can give rise to violent nucleation once the process is triggered by an increase of temperature, decrease of pressure, or any other suitable mean (e.g. ultrasounds). This process can be exploited in many fields, e.g. to catalyze chemical reactions (sonochemistry) or enhance drug delivery (cavitation can loosen endothelium increasing the rate and depth of delivery of drugs in zones with low blood irroration, like tumor matter), which are themes investigated by some of the applicants.
Concerning fundamental research, developing mesoscopic models of liquids under high confinement, such as the cDFT model we propose to develop/optimize, will allow to investigate the dynamics of liquids in other confined systems. An example is the collapse of the Cassie-Baxter state on nano-textured superhydrophobic surfaces. So far this process has been studied at an atomistic scale within the quasi-static approximation: it is assumed that the Cassie-Wenzel transition occurs very slowly, such that at each step along the process the system reaches the local equilibrium. A reliable confined cDFT model could be combined with fluctuating hydrodynamics to investigate the transition in more realistic conditions.
As for the second objective of the project, investigating the degradation of PLCs with intrusion/extrusion cycles, their degradation at high pressure and moderate (operative) temperatures, might help designing more resistant materials. We expect to learn more than the important but specific aspects of dependence of degradation on pressure/temperature and their cycling. We expect that the proposed combined experimental-theoretical approach will allow us to establish a relation between the thermodynamics and kinetics of porous crystals and the degree of thermal and mechanical stress they are subject to, what are the crystal sites involved in the reaction, whether the liquid or, more in general, molecules in the cavities play an active role in the degradation process, whether defects, which are formed during the intrusion/extrusion cycles, are responsible for the collapse of the material according to an avalange (non-linear) mechanism.