Adsorption hysteresis in narrow pores

Abstract

We present molecular dynamics computer simulation results for adsorption hysteresis in a cylindrical pore. The adsorption is examined by inducing pore filling and emptying by changing the pore length at constant number of particles. By calculating the full density profile of the fluid in the pore, one can observe both processes. Hysteresis, overshooting the thermodynamic transition, is observed for both pore filling and emptying. That is, we observe metastable one-phase states on either side of the transition. The end of the gas branch (pore filling) is signaled by the growth of an unduloid, resulting in the formation of a biconcave lens of liquid, while the end of the liquid branch (pore emptying) occurs by the formation of a bubble. However, the latter appears to be an artifact of the lack of pore ends in the model. In the presence of pore ends, the bubble formation is expected to be preempted by the receding of the meniscus.