Under pressure: Quasi-high pressure effects in nanopores

Phenomena that occur only at high pressures in bulk phases are often observed in nanopores, suggesting that the pressure in such confined phases is large. We develop two models to study the pressure tensor of an argon nanophase confined in carbon micropores by molecular simulation, and show that the in-pore tangential pressure is positive and on the order of 104 bar, while the normal pressure can be positive or negative depending on pore width, with a magnitude of ∼103 bar at ambient bulk pressure. We find that the in-pore tangential pressure is very sensitive to the bulk pressure, suggesting that it should be possible to control the former over wide ranges in laboratory experiments. We also report results for porous materials other than carbon, and show that the pressure enhancement is smaller for pores with weakly attractive walls (e.g. silica and oxides), but larger for more strongly attractive walls (e.g. mica).

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► Pressure tensors for argon in carbon slit pores from molecular simulation.
► The tangential component of the pressure is enhanced by a factor of 104–107.
► A small increase in bulk pressure causes a huge increase in tangential pressure.
► Pressure enhancement arises from compression of adsorbate due to attractive wall.
► The sign oscillation of enhanced normal pressure expands or compresses the pore.