A recently developed dynamic desorption technique is used for obtaining vapor isotherms on porous materials. This gravimetric technique does not require any preliminary calibration and is based on analyzing the kinetics of liquid evaporation from a porous sample under quasi-steady state conditions. The crucial feature of the technique is concerned with the fact that no vapor pressure measurements are necessary. The technique is illustrated by desorption of benzene vapors from mesoporous silica MCM-41. To calculate the pore size distribution, the Derjaguin-Broekhoffde Boer theory in its combination with the Wheeler model for capillary condensation is used. In the calculations, the reference data on benzene adsorption on a nonporous silica gel from two different sources (published by different authors) are applied. The mean mesopore sizes estimated from desorption isotherms are shown to be in a fair agreement with the calculations through the geometrical method based on the X-ray diffraction data. The dynamic desorption technique can serve as an additional tool for the characterization of a porous media.
An automated procedure was developed for monitoring fast changes in the size of spherical samples of polymers during their contact with a solvent or drying. The kinetics of bulk defor mation in these processes was studied for a series of cross linked polymers, viz., gel type and porous styrene-divinylbenzene copolymers and poly(divinylbenzenes), and hypercrosslinked polystyrenes. Gel, macroporous, and hypercrosslinked polystyrenes are substantially different in the rate, mechanism, and degree of swelling, which is associated with the principal differ ences in their physical structures. An unusual effect of a sharp decrease followed by a tempo rary increase in the volume of porous polystyrene and poly(divinylbenzene) materials were observed during desorption (evaporation) of organic solvents. Water desorption is accompanied by an excessive bulk compression of porous granules giving rise to negative deformations, which gradually relax to the state equilibrium for the dry polymer. The results of dynamic desorption porometry (for water desorption) are indicative of a bimodal size distribution of micropores in hypercrosslinked polystyrene.
We develop the universal technique of producing the mesoporous carbon nanomaterials. We manage to synthesize, in one and the same reactor, in the different regimes, carbon nanotubes and graphene. The technique consists in conversion of the carbon containing substances in the helium plasma flow generated by the plasma torch at low pressure. We investigate the samples using the scanning electron microscope and the synchronous thermal analysis. The studies, by the limited evaporation method, of the porous structure show that the graphene flakes and the balled nanotubes are mesoporous and thus provide the specific capacity value rather high for the electrochemical electrodes of the supercapacitor (125–133 F/g) at the charging/discharging resistance of 121/100 Ω.
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