V. V. Berezkin

The charge of the pores of poly(ethylene terephthalate) nucleopore membranes

The electrosurface properties of nucleopore membranes are studied by the streaming potential and EPR spectroscopy methods. Large differences between the values of surface charge of pores obtained by these methods are disclosed. This effect can be explained by the presence of the developed gel-layer on the pore surface.

Pore formation in polyimide irradiated by high-energy ions and the properties of the obtained membranes

The optimum conditions are determined for etching latent Kr tracks in sodium hypochlorite solution to prepare polyimide track membranes (PI-TMs) with cylindrical pores and the electrosurface properties of the membranes are investigated. The stability of the porous structure of PI-TMs is studied at elevated temperatures (up to 250°C) in aggressive media (pH 1–12). It is shown that the porous structure of PI-TMs is characterized by enhanced chemical and thermal stability.

Application of track-etched membranes to synthesis of microcrystalline dielectric structures

The formation of oriented nanostructures of iodic acid (HIO3) on track-etched membranes has been studied. The study has shown that the method of forced filtration of supersaturated crystallization solutions through track membrane pores can be used to grow needlelike faceted microcrystals that have the cross size and preferential growth direction corresponding to those of the pores.

Electrical conductivity of KCl solutions in pores of track-etched polymer membranes

The dependence of electrical conductivity of KCl solutions in pores of poly(ethylene terephthalate) and polyimide track-etched membranes (PET TM and PI TM) on the solution concentration and pore diameter has been studied by impedance spectroscopy. It has been found that the conductivity values calculated from the experimental results substantially exceed the standard values in the case of small pore diameters and low concentrations of the solutions, with this difference being more pronounced for PET TM. As the solution concentration and pore diameter increase, the conductivity of the solution in pores tends to the standard value. The revealed effect is explained by the presence of a loose layer on the pore walls that results from the polymer degradation induced by irradiation with high-energy ions. The contact of this layer with the solution gives rise to the gel layer, which is filled with the electrolyte and reduces the measured impedance of the membrane.

Electrokinetic study of etching latent tracks of accelerated heavy ions in poly(ethylene terephthalate) and polyimide

The etching of latent tracks and pore formation in track membranes are studied. It is shown that the incorporation of K+ and Ba2+ ions into alkaline solutions accelerates the etching of poly(ethylene terephthalate) (PET) and latent tracks in it. The etching is accelerated due to a decrease in the negative surface charge of PET surface and the pores in track membranes. Isoelectric points are determined for PET and polyimide track membranes and it is established that they depend on pore diameter. As the pore diameter is enlarged from 30 to 70 nm, the magnitude of the negative surface charge rises seemingly due to the increase in the concentration of carboxyl groups on the pore surface. It is assumed that this effect is due to either a high mobility of carboxyl groups in a gel, which is formed on pore walls as a result of etching latent tracks, or a displacement of the slipping plane caused by a decrease in the thickness of the gel layer.

Modification of the surfaces of polymer films irradiated by heavy ions and nucleopore nanofilters by XeF2 vapors

The effect of xenon difluoride (XeF2) vapors on the surface properties of the polymer films irradiated by heavy ions and of the nucleopore nanofilters produced from these films is studied. The procedure for modifying nucleopore membranes made of poly(ethylene terephthalate) and polyimide in XeF2 vapors is developed. The hydrophilicity, electrosurface properties, and selectivity of modified membranes are investigated. It is shown that the water contact angle on the membrane surface decreases as a result of modification, and the extent of its change depends on the duration and temperature of membrane treatment. Electrokinetic measurements did not reveal any changes in the surface charge during the modification of the membranes prepared from poly(ethylene terephthalate), but their ion selectivity increased twofold. It is shown that the hydrodynamic diameter of the pores of modified membranes reversibly decreases with an increase in transmembrane pressure. The dislosed effects are explained by the presence of an elastoplastic gel-layer on the surfaces of the membrane and its pores. The gel-layer accumulates considerable surface and bulk charges and is characterized by the high hydraulic resistance hindering the convective ion transport.

Synthesis of the Crystalline Microstructures of Potassium Dihydrogen Phosphate on the Basis of Track Membranes

The possibility of employing track membranes as templates during the formation of the crystalline microstructures of potassium dihydrogen phosphate is investigated. The microstructures emergent toward an incoming flow are shown to arise in pores when a supersaturated crystallization solution flows through the track membrane. Their direction and lateral sizes are determined by the direction and diameter of the membrane pores.

Direct Current Conductometry of Track Membranes

The electrical conductivity measured for a KCl solution in pores of poly(ethylene terephthalate) track membranes has been studied as depending on electrolyte concentration and pore diameter with the use of a direct-current source. The difference between the experimentally determined conductivity and the standard value has been shown to decrease with increasing electrolyte concentration and pore diameter. At the same time, its value is significantly lower than that determined by impedance spectroscopy. This result is related to a decrease in the contribution of a gel layer formed on the pore surface upon coming into the contact with the electrolyte to the electrical resistance of a membrane.

Separation of suspensions by dielectrophoresis on metal-coated track-etched membranes

Nonuniform electric field formed near pores of a metal-coated track-etched membrane retains on the membrane surface particles having a higher dielectric permittivity compared with the surrounding medium. A feasibility of separating suspensions (for example, rutile slurry in distilled water) by dielectrophoresis on metal-coated track-etched membranes has been experimentally shown.

Methods for modification of track-etched membranes designed for separation of biological objects

The existing and promising methods for modification of track-etched membranes are considered and analyzed; they are compared for subsequent separation of biological objects. On the basis of the results of comparative analysis, the simplest and most producible method of modification of track-etched membranes has been chosen.