C R Kamala | PubMed Health

PubMed2005

Large distinct diffusivity in binary mixtures confined to zeolite Nay.

Mutual diffusion coefficients have been computed from molecular dynamics simulation of two different binary mixtures confined to zeolite NaY. In one of these mixtures, where one component is from the linear regime and the other from the anomalous regime of the levitation effect [S. Yashonath, P. Santikary, J. Phys. Chem., 1994, 98, 6368], the magnitude of distinct diffusivity, Dd, is unusually large and comparable to the mixture self-diffusivity Ds. Distinct van Hove correlations suggest that the large Dd seems to arise from the presence of distinct physisorption sites for the two components. The contribution from Dd might be important for achieving good separation of mixtures, for which zeolites are used extensively.

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PubMed2002

Mutual diffusion in a binary Ar-Kr mixture confined within zeolite NaY.

Molecular dynamics investigations of the mutual diffusion coefficients in an Ar-Kr mixture confined in the zeolite NaY are reported. Velocity auto- and cross correlations were computed at two different temperatures (200 and 600 K). The importance of the appropriate choice of reference frame while evaluating the time correlation functions is illustrated for argon in the zeolite NaY. Mutual diffusivities in the mixture were obtained in the barycentric reference frame. Recently, Zhou and Miller showed that the distinct diffusivity D(d) is zero for the Ar-Kr mixture in bulk. On confinement, it is seen that at 200 K the ratio R=D(11)/D(s)=0.77, where D11 is the mutual diffusivity and D(s) is the mixture self-diffusivity. However, at 600 K, R=0.97, implying that the contribution from distinct diffusion is only slightly negative. The large negative D(d) at 200 K could be attributed to strong localization of Ar and Kr in the physisorption sites within the zeolite cages. Analysis of error bars and an efficient computational algorithm for evaluation of the velocity cross correlation function are also presented. The results have implications in biology, chemistry, and other situations where transport of confined mixtures is encountered.

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