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.     

Structure of Conducting Polymer Films Prepared on the Surface and in the Pores of Poly(ethylene terephthalate) Track Membranes by Template Synthesis

The results of a structural study of conducting polymer coatings deposited onto poly(ethylene terephthalate) (PET) track membranes by template synthesis are reported. The following aspects of the quality of polymer coatings were studied: the ratio between film and granular polymers, the polymer distribution over the surface of track membranes, and the thickness of polymer layers on the opposite sides of track membranes. The fraction of granular polypyrrole (PPy) on the surface and in the pores of a film increased with pore diameter. A decrease in the polymerization temperature decreased the amount of granular PPy on the surface of membranes, whereas the effect of granular PPy on the water permeability of track membranes remained unchanged. A more homogeneous distribution of PPy over the surface of track membranes can be obtained by density equalization of reacting solutions; however, the fraction of granular PPy on the membrane surface increased in this case. It was found that polymer coatings on the two sides of the surface of a membrane template had different thicknesses. Poly(N-methylpyrrole) completely covered only one side of a track membrane facing a monomer solution.     

Hole Overlapping Statistics in Reactor Nuclear Track Membranes

Distributions of nuclear holes (cylindrical channels of an identical diameter) in reactor track membranes were studied by computer simulation taking into account the angular spread of an ion beam. The factors of angular decrease in the number of multiple-hole channels and their dependence on the overlap multiplicity and membrane porosity P at P = 0.01–0.30 and hole multiplicity of m < 4 were obtained. The simulation results were compared with predictions made using analytical models.     

Ion transport through track etched polypropylene membrane

The transport properties through track etched polypropylene (PP) of 25 μm have been examined. The asymmetric pores in PP have been prepared by track etching technique. The PP membrane was exposed by α-source (₉₅Am²⁴¹). Irradiated PP membrane placed into an electrolyte cell and etched from one side while stopping medium protected other side. The etching is controlled by monitoring the electric current and to be stopped shortly after the breakthrough, which, is observed as a sudden increase in current, indicating that the two chambers of cell are connected through the pores. Asymmetric etching condition allows the preparation of charged pores of conical shape. The resulting conical pores rectify ion current. The voltage current characteristics is strongly non-linear, comparable to that of an electrical diode.     

Synthesis of bilayer composite nanomembranes with conductivity asymmetry

The structure and electrochemical properties of polyethylene terephthalate track membranes modified in acetylene plasma are studied. It is found that polymer deposition on the track membrane surface using acetylene polymerization in plasma results in the case of formation of a semipermeable layer covering pores in formation of a composite nanomembrane featuring asymmetry of conductivity in solutions of electrolytes: a rectifying effect similar to that of a p-n junction in semiconductors. It is shown that the observed effect of conductivity asymmetry is caused by a significant decrease in the diameter of pores in the plasma-deposited polymer layer and a change in the pore geometry, same as existence of an interface between the initial membrane and polymer layer that have a different concentration of carboxyl groups in the surface layer. The impedance spectroscopy method allowed obtaining information on ion transfer in the studied membranes.     

Supported particle track etched polyimide membranes: a grazing incidence small-angle X-ray scattering study

Particle track etched polyimide membranes on silicon substrates covered with a native oxide layer are investigated. Preparation steps similar to the common classical particle track etched membrane production, giving rise to free-standing membranes, are successfully applied to the supported membranes. Polyimide films are used as a starting material for a template preparation based on high energy ion irradiation. The film/membrane structure is probed at different length scales by grazing incidence small-angle X-ray scattering at each individual preparation step. In addition, characterization with atomic force microscopy, variable-angle spectroscopic ellipsometry, Fourier transform infrared transmission, and attenuated total reflection spectroscopy is performed. An amount of 6 +/- 1 vol % pores inside the polyimide film is detected. The pores are oriented perpendicular to the substrate surface and have a conical shape, yielding a slightly reduced pore size at the substrate/film interface.     

Capillarity creates single-crystal calcite nanowires from amorphous calcium carbonate

Single-crystal calcite nanowires are formed by crystallization of morphologically equivalent amorphous calcium carbonate (ACC) particles within the pores of track etch membranes. The polyaspartic acid stabilized ACC is drawn into the membrane pores by capillary action, and the single-crystal nature of the nanowires is attributed to the limited contact of the intramembrane ACC particle with the bulk solution. The reaction environment then supports transformation to a single-crystal product.     

Anisotropic gas transport in a bilayer membrane in the free molecular flow regime

Asymmetric phenomena associated with gas transport in the free molecular flow in multilayer membranes have been investigated. Bilayer track membranes have been examined. A model describing anisotropic gas transport across a multilayer membrane has been constructed and analyzed. The interaction parameters characterizing the effect of the geometry of the inner surface of the pores on the gas flow through the membrane have been determined.     

Use of poly(ethylene terephthalate) track membranes as template matrices for the preparation of polymeric nanomaterials based on polypyrrole and poly(<Emphasis Type="Italic">N</Emphasis>-methylpyrrole)

The oxidative polymerization of pyrrole and N-methylpyrrole with the use of template synthesis on poly(ethylene terephthalate) (PET) track membranes was studied. By scanning electron microscopy (SEM), it was found that a polymer film was formed on the surface of membranes and on the walls of membrane pores. The rates of polymerization on the surface of membranes and pore walls, as well as the yield and structure of the polymer film, depend on the membrane parameters (pore length and diameter and membrane porosity), the chemical structure of the monomer, the diffusion of polymerized solutions through template pores, and the temperature.Translated from Khimiya Vysokikh Energii, Vol. 39, No. 1, 2005, pp. 15–20.Original Russian Text Copyright © 2005 by Dobretsova, Ermolaev, Jitariouk, Milinchuk.     

Analytical Description of the Hole Overlapping Process on the Nuclear-Track Membrane Surface

The classical problem of overlapping circular holes of equal diameters on one surface of a nuclear track membrane was considered. Using the Monte Carlo method, the probabilities of overlapping W _k(P) of nuclear pores with a multiplicity of k < 32 at a porosity of P < 0.30 were determined and analytical expressions for their approximation were derived. The results were analyzed in terms of an approach based on a kinetic equation for a discrete Markov process. It was shown that the W _k(P) values obtained for multiple pores with a multiplicity of k < 7 are consistent with the theory if two-step processes are taken into account.     

Asymmetrical nanopores in track membranes: Fabrication,the effect of nanopore shape and electric charge of pore walls,promising applications

The properties of asymmetrical nanopores prepared by chemical etching of tracks of accelerated heavy ions are studied. Procedures are developed for controlling the size and shape of pores within wide limits. The presence of charged functional groups on pore walls is an intrinsic property of track membranes, which makes them a convenient object for studying electrokinetic phenomena in nanocapillaries. In electrolyte solutions, the asymmetrical “track” membranes demonstrate the diode effect. Two methods for fabricating asymmetrical nanopores in polyethylene terephthalate films are proposed and introduced into practice. Specific features of both methods, their advantages and drawbacks are considered. In addition to the brief survey of available information on diode-like track membranes, the new results on the mechanism of pore formation and the peculiarities of their geometry and electrokinetic properties are discussed. The emerging and potential applications of track membranes with asymmetrical pores are discussed briefly.     

Adsorption of nonionic surfactant on porous and nonporous poly(ethylene terephthalate) films

The application of surfactants in the chemical etching of track membranes enables one to control their pore shape. To find out the mechanism of the surfactant action on the track etching in the nanometer range of pore sizes, the adsorption of a nonionic surfactant (polyoxyethyelene-4-nonylphenyl ether) on porous and nonporous poly(ethylene terephthalate) films has been studied. The experimental results have been analyzed in comparison with the data previously obtained on the adsorption of an anionic surfactant on similar films. It has been concluded that the behaviors of anionic and nonionic surfactants in negatively charged pores about 100 nm in radius are strongly different due to the electrostatic exclusion of co-ions from the pores, which is of significance only for compounds dissociating into ions.     

Metal–Organic Framework (MOF) Nanorods,Nanotubes, and Nanowires

New mechanisms for the controlled growth of one‐dimensional (1D) metal–organic framework (MOF) nano‐ and superstructures under size‐confinement and surface‐directing effects have been discovered. Through applying interfacial synthesis templated by track‐etched polycarbonate (PCTE) membranes, congruent polycrystalline zeolitic imidazolate framework‐8 (ZIF‐8) solid nanorods and hollow nanotubes were found to form within 100 nm membrane pores, while single crystalline ZIF‐8 nanowires grew inside 30 nm pores, all of which possess large aspect ratios up to 60 and show preferential crystal orientation with the {100} planes aligned parallel to the long axis of the pore. Our findings provide a generalizable method for controlling size, morphology, and lattice orientation of MOF nanomaterials.     

Metal–Organic Framework (MOF) Nanorods,Nanotubes, and Nanowires

New mechanisms for the controlled growth of one‐dimensional (1D) metal–organic framework (MOF) nano‐ and superstructures under size‐confinement and surface‐directing effects have been discovered. Through applying interfacial synthesis templated by track‐etched polycarbonate (PCTE) membranes, congruent polycrystalline zeolitic imidazolate framework‐8 (ZIF‐8) solid nanorods and hollow nanotubes were found to form within 100 nm membrane pores, while single crystalline ZIF‐8 nanowires grew inside 30 nm pores, all of which possess large aspect ratios up to 60 and show preferential crystal orientation with the {100} planes aligned parallel to the long axis of the pore. Our findings provide a generalizable method for controlling size, morphology, and lattice orientation of MOF nanomaterials.     

Track membrane with immobilized colloid silver particles

A method for modification of track membranes by immobilization of polymer complexes of colloid silver nanoparticles on the surface of microfiltration membranes was developed. The antimicrobial properties of track membranes modified with silver nanoparticles were tested on E. coli, Ps. aeruginosa, St. aureus, and B. cereus.     

Transport properties of thermo-responsive ion track membranes

The permeation of orange G (MW 452), methylene blue (MW 319), and bovine albumin (MW 68000), through thermo-responsive ion track membranes was studied. For this purpose, poly-N-isopropylacrylamide (poly-NIPAAm) hydro-gel was chemically grafted onto single/multi-pore ion track membranes of poly(ethylene terephthalate) (PET).The local transport properties were studied by measuring the electrical current through single pore membranes. It was found that the incorporation of the hydro-gel into the pores does not influence the phase transition temperature. The switching of the responsive membrane was reversible over 200 switching cycles applied during 30–50 days. The closed pores represent a physical barrier excluding organic molecules larger than 2±0.2 nm. This fact is based on the size exclusion method using mixtures of polyethylene glycol (PEG) of various molecular weights and 0.1 N potassium chloride.The global transport properties were studied using multi-pore membranes with 5×10⁵ to 5×10⁷ pores per cm² and pore diameters between 0.6 and 4.5 μm. For bovin insulin permeation in the open state was 35 times above the level of the closed state corresponding to the detection limit of the used permeation cell. In the open state the transport rates of the solvent and the solute were identical implying that the free space in the open pores was larger than the size of the permeating bovine albumin molecules (about 7.3 nm). The linear relation between pressure and mass current enabled to determine an effective open-pore diameter between 0.2 and 1 μm. In the open state, the membrane this is not molecular selective.     

Uranium Content Measurements in Building Materials Using Track Detection

In order to use the wood building materials in dwelling construction, uranium content measurements were performed by one of the alpha or fission track methods. The investigated samples were tree and rush samples, collected from different Romanian sites, situated in the vicinity of zones with human radioactive activities, such as: Sapantza, Izvorul Izei (North Romania), Omer and Periprava (Danube River Delta). We have examined the U atom distributions in these samples in order to detect any U contamination due to radioactivity. For each analysed sample, two U track micromappings were obtained in the two track detectors which were put in intimate contact with the sample during reactor neutron irradiations. The obtained track micromappings were studied by optical microscopy. The U distribution and content measurement results are presented and interpreted according to the present norms referring to maximum permissible values of U in building materials in Romania.     

A Statistical Model for Hole Distribution on the Nuclear-Track Membrane Surface

A statistical model for analysis of overlapping nuclear pores (ring holes of equal diameter) on the flat surface of nuclear track membranes was developed. Statistical distribution of the probability of occurrence of double and triple pores were obtained for medium-porosity (below 0.5) membranes with allowance for configuration forms (for triplets). The results obtained by the analytical procedure are compared with computer simulation data.     

The effect of surfactant concentration on the geometry of pores resulting from etching of poly(ethylene naphthalate) films irradiated by high-energy ions

The influence of temperature and concentrations of an alkali and a surfactant in etching solutions on the structural and transport characteristics of membranes produced by etching latent tracks of high-energy heavy ions in poly(ethylene naphthalate) films has been studied. The presence of a surfactant provides the formation of spindle-shaped pores narrowing in the direction toward the film surfaces. A procedure has been developed for the quantitative assessment of the degree of widening of spindle-shaped pores in their central part. The transport properties of track membranes with spindle-shaped and cylindrical pores have been compared.     

Surfactant aggregation in solutions applied for track etching and its possible effect on the pore shape in track membranes

Surfactants are used for etching track membranes to form pores of peculiar geometries with the purpose of, e.g., producing membranes with enhanced performance. The knowledge of the state of surfactant molecules in process solutions, in particular, the regularities of their aggregation, is of importance for understanding the mechanisms of surfactant action on track etching processes. This work presents the data on sodium dodecyl( sulfophenoxy)benzene sulfonate and nonyl benzene deca(ethylene oxide) micellization in neutral and alkaline electrolyte solutions of different concentrations. The measurements are carried out using the small-angle neutron scattering. It is shown that cylindrical (ellipsoid) micelles are formed in the solutions. Characteristic sizes of micelles are determined as functions of surfactant and added electrolyte concentrations. The correlation of the data obtained with the geometry of track nanopores and the dynamics of their etching in surfactant-containing solutions is discussed.