Influences of concerted cluster diffusion on single-file diffusion of CF4 in AlPO4-5 and Xe in AlPO4-31

Abstract

Traditional models of single-file diffusion in zeolites assume that adsorbate diffusion mechanisms at high and dilute pore loadings are identical. Atomistic models of single file systems, in contrast, have shown that clusters of adsorbed molecules can diffuse via concerted motions that are not available to individual adsorbates. We report molecular dynamics simulations of CF 4 clusters in AlPO 4 -5 and Xe clusters in AlPO 4 -31. We have used these simulations to characterize the diffusion and dissociation mechanisms and rates of these clusters as a function of temperature and cluster size. We have also used our MD results to parametrize coarse-grained models of adsorbed cluster dynamics. Using kinetic Monte Carlo simulations of our coarse-grained models, we have simulated pores containing hundreds of interacting clusters on microsecond time scales. These simulations offer the first opportunity to examine single-file diffusion in models that accurately account for the existence of concerted cluster diffusion. Our simulations show that concerted cluster motions make large contributions to single-file mobilities. The deviations of the computed single-file mobilities from the well-known result for hard sphere diffusion are discussed, as are the implications of using the latter model to interpret experimental measurements of single-file diffusion.

Non-equilibrium statistical mechanics: from a paradigmatic model to biological transport

“…For example, Sholl and Fichthorn have shown using molecular dynamics (MD) simulations how concerted motions of clusters of water affects its overall transport in molecular sieves [238]. Similarly, Sholl and Lee also showed that concerted motions of clusters of CF 4 and Xe in AlPO 4 -5 and AlPO 4 -31 zeolites, respectively, contribute significantly to their overall mobilities [239]. Concerted motion has also been predicted to occur in transport across carbon nanotubes [240].…”

“…For example, coarse-grained treatments of concerted motion were developed by Sholl and Lee [239]. Concerted motion has also been implemented within lattice models of exclusion processes in a more draconian manner.…”

Zeolitik-İmidazolat İskelet Yapılarının Adsorpsiyon ve Difüzyon-bazlı Soy-gaz Karışımı Ayırma Potansiyellerinin Hesapsal Yöntemlerle İncelenmesi

“…ZIF-65 has heterogeneous pores with the size of 3.4/10.4 Å where steric hindrance and topology effects become dominant for Xe preventing its diffusion from the pores. Single file diffusion of Xe is also observed in zeolite AlPO4-31 by molecular dynamics study of Sholl et al [32]. Since we do not observe diffusion of Xe, Xe permeability and permeation selectivity values are not calculated for ZIF-65.…”

Crossover from normal diffusion to single-file diffusion of particles in a one-dimensional channel: LJ particles in zeolite zsm-22

“…The essential difference between the normal diffusion and SFD lies in the dependence of mean-squared displacement of particles on the time interval t. In normal diffusion, MSD is proportional to t, while in SFD, MSD grows as √ t with respect to time. Such a dependence of MSD on √ t has been observed in many single-file systems in experiments [25][26][27][28] as well as in molecular simulations [29][30][31][32].…”