Diffusion of chain molecules and mixtures in carbon nanotubes: the effect of host lattice flexibility and theory of diffusion in the Knudsen regime

A novel algorithm for modeling the influence of the host lattice flexibility in molecular dynamics simulations is extended to chain-like molecules and mixtures. This technique, based on a Lowe-Andersen thermostat, maintains the advantages of both simplicity and efficiency. The same diffusivities and other properties of the flexible framework system are reproduced. Advantageously, the computationally demanding flexible host lattice simulations can be avoided. Using this methodology we study the influence of flexibility on diffusion of n-alkanes inside single-walled carbon nanotubes. Furthermore, results are shown for diffusion of two mixtures (methane-helium and ethane-butane). Using these results we investigate the accuracy of theories describing diffusion in the Knudsen regime. For the dynamics in carbon nanotubes the Knudsen diffusivities are much too low. The Smoluchowski model gives better results. Interestingly, the extended Smoluchowski model can reproduce our simulation results obtained with a rigid host lattice. We modify this model to also treat collisions with a flexible interface correctly. As the tangential momentum accommodation coefficient is needed for the theoretical models, we introduce a simple concept to calculate it.     

Effect of Chain Length on the Adsorption Behavior of n-Alkanes in Ferrierite

¹³ C NMR spectroscopy and computer simulations have shown that the chain length of hydrocarbons has a surprising effect on where these molecules reside in the zeolite FER. Propane and butane can access the entire two-dimensional channel structure, while hexane only the one-dimensional substructure. This difference has important consequences for the catalytic activity and explains some of the experimental observations.     

Molecular order and disorder of surfactants in clay nanocomposites

Disorder of intercalated surfactant molecules in clay minerals causes gradual swelling, rather than commonly assumed swelling in discrete steps.     

Higher regularity of the free boundary in the parabolic Signorini problem

We show that the quotient of two caloric functions which vanish on a portion of an \(H^{k+ \alpha }\) regular slit is \(H^{k+ \alpha }\) at the slit, for \(k \ge 2\). In the case \(k=1\), we show that the quotient is in \(H^{1+\alpha }\) if the slit is assumed to be space-time \(C^{1, \alpha }\) regular. This can be thought of as a parabolic analogue of a recent important result in De Silva and Savin (Boundary Harnack estimates in slit domains and applications to thin free boundary problems, 2014), whose ideas inspired us. As an application, we show that the free boundary near a regular point of the parabolic thin obstacle problem studied in Danielli et al. (Optimal regularity and the free boundary in the parabolic Signorini problem. Mem. Am. Math. Soc., 2013) with zero obstacle is \(C^{\infty }\) regular in space and time.     

Adducts of vinyl ethers with arylsulfenyl chlorides as reagents for electrophilic alkylation of vinyl ethers

Conclusions A general preparative method for the chemically selective codimerization of vinyl ethers has been developed, the first stage of which is addition of arylsulfenyl chloride to one vinyl ether and the second is an Ad_E reaction between the adduct obtained and the other vinyl ether in the presence of a Lewis acid followed by treatment of the intermediate with some nucleophile.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 119–125, January, 1987.