Isoconversional kinetics of vaporization of nanoconfined liquids

Abstract

Isoconversional kinetic analysis is applied to thermogravimetry data on vaporization of n-decane and dimethyl sulfoxide from alumina nanopores and bulk. For bulk vaporization, the isoconversional activation energy is independent of conversion and equal to the enthalpy of vaporization. For vaporization from nanopores, the isoconversional activation energy varies strongly with conversion, passing through a minimum at midrange conversions. This behavior is shown to be consistent with the successive transition of the rate control from the Kelvin effect to Knudsen diffusion, and eventually to surface diffusion. All three phenomena are demonstrated to have their specific activation energies. It has been determined that the deceleration of vaporization from nanopores is due to a dramatic decrease in the value of the preexponential factor. The decrease is linked to the high frequency of collisions with the pore walls and to a possibility of adsorption on the walls.