(515i) Pressure-Driven Water Intrusion and Extrusion in Hydrophobic Nanopores

Nanoporous particles with lyophobic properties hold great promise as materials for energy absorption and storage. When subjected to mechanical compression, these particles allow non-wetting solvents to intrude into nanopores, effectively converting and storing impact energy. Upon solvent extrusion, this stored energy can be released when the compression force is removed. While various nanoscale energy absorption systems (NEAS) have been explored experimentally, the molecular-level mechanisms governing the intrusion-extrusion cycles are not understood. To investigate this, we employ atomistic molecular dynamics (MD) simulations. Specifically, we investigate shock impact-induced intrusion and extrusion in hydrophobic cylindrical as well as slit pores using MD simulations. Our simulations, conducted for rigid and flexible nanopores of varying sizes under quasi-static and dynamic conditions, reveal three distinct stages of the compression process: (1) Initial elastic compression of the solvent, (2) Fluid intrusion into the pore upon reaching a threshold intrusion pressure, and (3) Elastic compression of the solvent upon pore-filling (Figure 1). By developing adequate computational models of flexible pores, we show that water intrusion and extrusion in flexible pores exhibit negative compressibility. We also observe that the extrusion of solvent from a completely filled nanopore, upon pressure release, is initiated by bubble nucleation. These simulation results are closely correlated with experimental observations.