Anomalously supercooled H₂–D₂ mixtures flowing inside a carbon nano tube

Abstract

H₂ and D₂ molecules condensed in a carbon nano tube (CNT) and their nonequilibrium flow through nano pores offer a key test to reveal mass molecular transport and separation of purely isotopic molecules that possess the same electronic potential but a two-times difference in mass inducing differently enhanced nuclear quantum effects (NQEs) such as nuclear delocalization and zero-point energy. Taking advantage of the non-empirical quantum molecular dynamics method developed for condensed H₂–D₂ molecules that can describe various kinds of condensed phases and thermodynamic states including uneven density and a shear flow, we investigated condensed isotopic H₂–D₂ mixtures flowing inside nanoscale adsorbable CNTs. We found that, in any mixture, the more delocalized H₂ molecules are more supercooled than the less delocalized D₂ molecules in a two-dimensional liquid film adsorbed around the CNT well, and that the stronger supercooling of the H₂ molecules than the D₂ molecules in an equilibrium state becomes more enhanced under the nonequilibrium flow due to the isotope-dependent flow-induced condensation, demonstrating the anomalous condensed-phase quantum sieving under the nonequilibrium flow and its dependence on the mixing ratio and temperature. The differently enhanced NQEs of the purely isotopic molecules essentially influence the condensed adsorption and their flows occurring in the nanoscale CNT, which should be distinguished from a dilute gas adsorption. The predicted properties and obtained physical insights in this paper will help in experimentally controlling condensed H₂–D₂ mixtures, and open a new strategy and innovative design of nanoporous materials for adsorptive separation of condensed-phase mixtures under a nonequilibrium flow not of a dilute gas mixture in an equilibrium state.