A.M. Grekhov

Percolation of composite poly(vinyltrimethylsilane) membranes with carbon nanotubes

Recent years have seen a flurry of activity in research on the use of nanoparticles to improve the properties of polymeric membranes. It is known that the change in the macroscopic properties of these hybrid materials is associated with the parameters of the cluster of incorporated nanoparticles. The percolation threshold is higher than 15 vol % for the spherical particles and decreases with the increasing aspect ratio of the embedded nanoparticles of another shape. The paper presents the results of study on the permeability of gases (N2, O2, CH4 and C3H8) and a test liquid (ethanol) through hybrid membranes based on the glassy polymer poly(vinyltrimethylsilane) (PVTMS) with embedded multiwall carbon nanotubes (MWCNT) with a concentration of 0.3–3 wt %. It has been found that the permeability of gases and liquids alters at MWCNT concentrations above 0.4 wt %, which corresponds to the percolation threshold for the given particles as proved by calculations. In addition, the gas permeability coefficients measured indicate a change in the transport mechanism and selectivity of the membrane.

States of a dispersed nonwetting liquid in a disordered nanoporous medium

Three different states of a dispersed nonwetting liquid (water) in the Fluka 100 C8 and Fluka 100 C18 disordered porous media, as well as transitions between these states under variation of the temperature and the degree of filling, have been revealed. It has been shown that the appearance of such states is due to the broadening of the pore size distribution function f(R), fluctuations of configurations of neighbors in the system of pores and fluctuations in the configuration of a pore and its environment consisting of filled and empty pores in the percolation cluster. These states and transitions are caused by the competition between the effective repulsion of the nonwetting liquid from the wall of the pore, which is responsible for the extrusion of the liquid from the pore, and the effective collective multiparticle attraction of the liquid cluster in the pore to clusters in the neighboring connected pores. The observed difference in the behavior of the Fluka 100 C8/water and Fluka 100 C18/water systems and the previously studied Libersorb-23 (L23)/water system indicates a significant dependence of the state of these systems on the type of disorder in them.

Effect of carbon nanotubes on a gases permeability of polymer PMMA

Mixed matrix membranes (MMMs) with unique transport characteristics can be prepared by the addition of the minor amounts of carbon nanotubes. Changes in the membrane performance are shown to be provided by the formation of a percolation cluster composed of nanotubes. For MMMs based on Poly(methyl methacrylate) (PMMA) containing carbon nanotubes (CNT), due to the formation of the CNT percolation cluster, gas permeability increases by a factor of 2.5-10.