A molecular simulation study of freezing/melting phenomena for Lennard-Jones methane in cylindrical nanoscale pores

Abstract

A combination of grand canonical Monte Carlo and molecular dynamics simulation techniques are used to study the freezing and melting of Lennard-Jones methane in several different cylindrical pores. Two different types of pore wall are considered; a strongly attractive wall, and a weakly attractive wall, each with pore diameters in the range 1.5–3.5 nm. Freezing point depression is observed in the case of the weakly attractive pores, in agreement with several experimental studies. Freezing point elevation is observed at the walls of the strongly attractive pore, but freezing point depression occurs at the center of such pores, due to geometrical constraints.

Freezing of Lennard-Jones fluid in cylindrical nanopores under tensile conditions

“…The frozen particles have aligned in a concentric circles along the wall similar to those reported by Maddox and Gubbins (Maddox and Gubbins 1997). The freezing point was determined from the discrete changes in the density, enthalpy, arrangement, and structural functions against temperature .…”

“…In general, the freezing points depend on the strength of the attractive potential energy from pore walls, the fluid in a slit pore shows a freezing point elevation as well as depression; the critical strength to divide these two cases is the potential energy exerted by the solid state of the fluid. Maddox and Gubbins (Maddox and Gubbins 1997) and the authors studied the solidification of LJ methane within carbon cylindrical nanopores using molecular dynamics (MD) and GCMC simulations. They found a nonmonotonic dependence of the pore diameter on a geometric constraint of the cylindrical wall.…”

Freezing of hard spheres confined in narrow cylindrical pores

“…[1][2][3][4][5][6] Extensive studies of constrained species also indicate that the final behavior of the adsorbate depends on the interaction between the particles and the confining walls. [7][8][9][10] However, this is only a part of the problem since simulation results also suggest that in order to describe completely the involved phenomenology, one should take into account not only the energetics of the considered arrangement but also the steric influence of pure confinement in the properties under scrutiny. 11 In systems with soft attractive and repulsive interactions, such as Lennard-Jones-type adsorbates inside a carbon nanotube or a silica pore, the energetic and the entropic influences compete to produce a net effect whose relative contributions cannot be easily separated.…”

“…16 Nevertheless, there is profuse information about transitionlike transformations in narrow tubes. [5][6][7][8][9][10] Transformations in confined systems resembling the bulk liquid-solid phase transitions are commonly referred to as "freezing." 1 In this paper, freezing represents then a behavior qualitatively similar to a solid-liquid transition ͑driven by temperature changes or by purely geometrical packing effects͒, but in a context in which the existence of a real transition is not formally possible or cannot be demonstrated.…”

Application of density functional theory to capillary phenomena in cylindrical mesopores with radial and longitudinal density distributions

“…This strong mo- 41 noted that in most experimental systems adsorbents like pore glass had weak solid-fluid potential compared to the fluid-fluid potential. Theoretical analysis of methane adsorption in carbon buckytubes 41 and experimental studies of adsorption of different species on mica surfaces [42][43][44] and in graphitic micropores 45 show that the freezing temperature may be significantly higher than that in the corresponding bulk phase. However, all results described below should be considered with caution.…”