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Effective diffusion in partially filled nanoscopic and microscopic pores

I. ARDELEAN1,* , G. FARRHERA2, R. KIMMICH2

Affiliation

  1. Technical University from Cluj-Napoca, Physics Department, 400020 Cluj-Napoca, Romania
  2. Sektion Kernresonanzspektroskopie, Universität Ulm, 89069 Ulm, Germany

Abstract

The contribution of the vapor phase to molecular diffusion in porous silica glasses with nanometer (Vycor) and micrometer (VitraPor#5) pores partially filled with water (polar) or cyclohexane (non-polar) was investigated with the aid of pulsed gradient NMR diffusometry. The effective diffusion coefficient of water in nanometer pores (Vycor) decreases with decreasing filling factor, whereas that of cyclohexane increases due to the vapor phase contribution without exceeding its bulk liquid value. On the other hand the effective diffusion coefficient of cyclohexane in micrometer pores (VitraPor#5) was up to ten times larger than the bulk liquid value. This is in contrast to the effective diffusion coefficient in water which first decreases and then increases upon reduction of the pores filling factor. The experimental diffusion features are well represented by a two-phase liquid/vapor exchange model. It is concluded that the dependence of the effective diffusion coefficient on the pore-filling factor is strongly related to the pore dimension and the polar character of the confined fluids..

Keywords

NMR, Diffusion, Porous silica lass, Nanoscopic and microscopic pores.

Submitted at: Nov. 15, 2006
Accepted at: March 15, 2007

Citation

I. ARDELEAN, G. FARRHERA, R. KIMMICH, Effective diffusion in partially filled nanoscopic and microscopic pores, Journal of Optoelectronics and Advanced Materials Vol. 9, Iss. 3, pp. 655-660 (2007)