Induced-Charge Enhancement of the Diffusion Potential in Membranes with Polarizable Nanopores

When a charged membrane separates two salt solutions of different concentrations, a potential difference appears due to interfacial Donnan equilibrium and the diffusion junction. Here, we report a new mechanism for the generation of a membrane potential in polarizable conductive membranes via an induced surface charge. It results from an electric field generated by the diffusion of ions with different mobilities. For uncharged membranes, this effect strongly enhances the diffusion potential and makes it highly sensitive to the ion mobilities ratio, electrolyte concentration, and pore size. Theoretical predictions on the basis of the space-charge model extended to polarizable nanopores fully agree with experimental measurements in KCl and NaCl aqueous solutions. © 2017 American Physical Society

On the origin of membrane potential in membranes with polarizable nanopores

We report a new mechanism for the generation of membrane potential in polarizable nanoporous membranes separating electrolytes with different concentrations. The electric field generated by diffusion of ions with different mobilities induces a non–uniform surface charge, which results in charge separation inside the nanopore. The corresponding Donnan potentials appear at the pore entrance and exit leading to a dramatic enhancement of membrane potential in comparison with an uncharged non–polarizable membrane. At high concentration contrast, the interaction between electric field and uncompensated charge at a low concentration side results in the development of electrokinetic vortices. The theoretical predictions are based on the Space–Charge model, which is extended to nanopores with polarizable conductive surface for the first time. This model is validated against full Navier–Stokes, Nernst–Planck, and Poisson equations, which are solved in a high aspect ratio nanopore connecting two reservoirs. The experimental measurements of membrane potential of dielectric and conductive membranes in KCl and NaCl aqueous solutions confirm the theoretical results. The membranes are prepared from Nafen nanofibers with ∼10nm in diameter and modified by depositing a conductive carbon layer. It is shown theoretically that the membrane potential enhancement becomes greater with decreasing the electrolyte concentration and pore radius. A high sensitivity of membrane potential to the ratio of ion diffusion coefficients is demonstrated. The described phenomenon may find applications in precise determination of ion mobilities, electrochemical and bio–sensing, as well as design of nanofluidic and bioelectronic devices. © 2017 Elsevier B.V

Influence of Modifying with Al2O3 Nanofibers on the Properties of Wall Building Ceramics Based on Quartzofeldspathic Technogenic Raw Materials

Изучено влияние модифицирования нановолокнами Al2O3 на свойства стеновой строительной керамики на основе кварц-полевошпатовых отходов обогащения медно-молибденовых руд. Установлено, что при добавлении 0,6 масс.% нановолокон Al2O3 прочность керамики, спеченной при 1000 °C, возрастает от 38,3 до 58,5 МПа, водопоглощение снижается от 12,8 до 10,6 %, наблюдается возрастание морозостойкости керамического материалаThe effect of modifying with Al2O3 nanofibers on the properties of wall building ceramics based on quartzofeldspathic wastes from the enrichment of copper-molybdenum ores were studied. It was found that with 0,6 wt.% of Al2O3 nanofibers addition the strength of ceramics sintered at 1000 °C increases from 38,3 to 58,5 MPa, water absorption decreases from 12,8 to 10,6 %, an increase of the frost resistance was observe

Modelling of ethanol pyrolysis in a commercial CVD reactor for growing carbon layers on alumina substrates

Chemical vapour deposition (CVD) is widely used for preparation of pyrolytic carbons from various precursors. The prediction of deposition kinetics requires deep understanding of all transport phenomena involved. In this work, we perform the computational modelling of ethanol pyrolysis in a commercial CVD reactor (a tube furnace). The reactor is employed for growing carbon layers on alumina substrates. The inlet gas flow is produced by evaporating azeotrope ethanol/water mixture and mixing it with inert gas (argon). The modelling is performed in 3D and 2D statements using Marinov mechanism with 57 species participating in 383 reactions. The heat and species transport is taken into account with temperature dependent physical properties. It is shown that the inlet gas velocity in the 2D statement should be corrected for a meaningful comparison with the 3D case. A good agreement is found between species mole fractions at the substrate position for 3D and 2D statements at low volume flow rates, while at high flow rates some deviations are observed. The temperature at the substrate position is found to be lower than at the reactor wall due to inflow of a colder gas. The main pyrolysis products at moderate temperatures (around 900 C) are water, ethylene, hydrogen, carbon monoxide, and methane. With increasing temperature, the mole fractions of hydrogen, acetylene, and carbon monoxide increase, while those of water and methane become smaller. With increasing ethanol/water volume flow rate, the mole fractions of ethanol and pyrolysis products saturate at some constant values due to incomplete thermal decomposition of ethanol in the reactor volume. The rise of argon flow rate leads to the decrease of pyrolysis products mole fractions due to decrease of residence time. The obtained results can be employed for simulating and analyzing pyrolysis processes in realistic CVD reactors with complex geometry as well as for the development of coupled gas phase and surface reaction model of carbon layer deposition on nanoporous substrates

Effect of Electric Field on Ion Transport in Nanoporous Membranes with Conductive Surface

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.The effect of an external electric field on the ionic conductivity and selective properties of ceramic membranes based on alumina nanofibers coated with a conductive carbon layer has been studied. It has been shown that the membranes are ideally polarizable in the polarizing voltage range of −500 to +500 mV and, therefore, can be used for implementing switchable ionic selectivity. Experiments have revealed that the membrane resistance decreases with a change in the applied potential from 0 to ±500 mV. It has been shown that the membrane selectivity can be switched from anion to cation by varying the external potential. The surface charge density of the membranes has been determined in terms of the Teorell–Meyer–Sievers model according to the experimental measurements of the membrane potential. © 2018, Pleiades Publishing, Ltd

In-situ ellipsometric characterization of the growth of porous anisotropic nanocrystalline ZnO layers

info:eu-repo/semantics/publishe

Coupled thermal analysis of carbon layers deposited on alumina nanofibres

Catalyst-free chemical vapor deposition is used to form thin (1–2 nm) carbon layers on the surface of alumina nanofibers resulting in carbon-alumina nanocomposites. Thermal analysis, X-ray fluorescent microanalysis, Raman spectroscopy, and electrical resistance measurements of these composites show that increasing of synthesis time not only increases the amount of carbon on alumina surface, but also the ordering and density of the carbon layers. Nitrogen adsorption data reveal the decrease of total pore volume with increasing the synthesis time. The obtained composite material could be employed for the preparation of ion-selective membranes with switchable ion transport, electroconductive ceramics, and electrochemical sensors

Increase Transparency of Single Walled Carbon Nanotubes Films by Structuring Using Self-Organized Silica Template

Продемонстрирована возможность заполнения трещин самоорганизованного шаблона на основе пленок кремнезема коллоидной дисперсией одностенных углеродных нанотрубок (ОУНТ). Методика позволяет увеличить соотношение прозрачность – поверхностное сопротивление пленок ОУНТ посредством их структурирования и капиллярного уплотнения. Показана возможность управления растрескиванием шаблона для получения оптимальной геометрии, позволяющей иметь качественные воспроизводимые структурированные пленки ОУНТ. Полученные образцы структурированных пленок ОУНТ имеют прозрачность на 4-5 % выше, чем у сплошных пленок ОУНТ, при близком поверхностном сопротивленииThe possibility of filling the cracks of self-organized pattern based on the silica films colloidal dispersion of single-walled carbon nanotubes (SWCNTs), the method allows to increase the ratio between transparency and surface resistance of the SWCNT films through their structure and capillary packing. The possibility of controlling the cracking of the template to create an optimum geometry that provides high-quality reproducible structured SWCNTs films. Obtaining a sample of structured SWCNT Ÿlms have transparency on 4-5 % higher relative to continuous Ÿlms of SWCNTs in a close surface resistanc

Sol-Gel Lithography Method for Production of Flexible Transparent Ir-Heater

Представлена перспективная малозатратная методика формирования прозрачных проводящих покрытий на основе металлической микросетки, формируемой при помощи самоорганизованного шаблона. Разработанный метод позволил создать основы технологии получения гибких прозрачных нагревательных элементов. Показана высокая однородность нагрева и стабильность микросетки при деформационных воздействияхA promising low-cost method of forming transparent conductive coatings based on metal micromesh formed using self-organized pattern. The developed method is will provide the framework technology of flexible transparent heating elements. The show high heating uniformity and stability micromesh during deformation effect

Technological Basis of the Formation of Micromesh Transparent Electrodes by Means of a Self-Organized Template and the Study of Their Properties

Текст статьи не публикуется в открытом доступе в соответствии с политикой журнала.This Letter presents the results of a study of the physical properties of micromesh transparent electrodes on a flexible substrate, obtained using a template in the form of silica layers subjected to controlled cracking. For the first time, a combined approach to the control of parameters of a micromesh structure (crack width and cell size) by varying the pH and the thickness of the sol layer is proposed. Using this approach, transparent electrodes with a surface resistance of 4.1 Ω/sq with a transparency of 85.7% were obtained. Micromesh electrodes are characterized by linear optical transmission in the visible and IR ranges, which opens up prospects for their use in optoelectronics