Cylindrical Pores Research Articles

The impact of secondary channels on the wetting properties of interconnected hydrophobic nanopores

Pores in nanoporous materials can be interconnected in different ways; preliminary evidence exists that connecting channels can affect the overall hydrophobicity of the material thus providing an additional parameter in designing applications that require controlled wetting properties. In this work, we show that the length of secondary channels is a key parameter to tune the overall hydrophobicity of the material: short secondary channels make the main pore effectively more hydrophilic than a simple cylindrical pore, while long secondary channels enhance its hydrophobicity, producing the macroscopic effect of superhydrophobic textures. This rich behavior is rooted in the spontaneous filling of the secondary channels, which is unexpected based on classical capillarity. This length-dependent filling is explained by the formation of hydrogen bonds bridging the main pores which becomes less frequent with longer channels. These findings could be useful for designing nanoporous materials with tailored wetting properties.

Energy localization efficiency in 1,3,5-trinitro-2,4,6-triaminobenzene pore collapse mechanisms

Atomistic and continuum scale modeling efforts have shown that the shock-induced collapse of porosity can occur via a wide range of mechanisms dependent on pore morphology, the shockwave pressure, and material properties. The mechanisms that occur under weaker shocks tend to be more efficient at localizing thermal energy but do not result in high, absolute temperatures or spatially large localizations compared to mechanisms found under strong shock conditions. However, the energetic material 1,3,5-trinitro-2,4,6-triaminobenzene (TATB) undergoes a wide range of collapse mechanisms that are not typical of similar materials, leaving the collapse mechanisms and the resultant energy localization from the collapse, i.e., hotspots, relatively uncharacterized. Therefore, we present the pore collapse simulations of cylindrical pores in TATB for a wide range of pore sizes and shock strengths that trigger viscoplastic collapses that occur almost entirely perpendicular to the shock direction for weak shocks and hydrodynamic-like collapses for strong shocks that do not break the strong hydrogen bonds of the TATB basal planes. The resulting hotspot temperature fields from these mechanisms follow trends that differ considerably from other energetic materials; hence, we compare them under normalized temperature values to assess the relative efficiency of each mechanism to localize energy. The local intra-molecular strain energy of the hotspots is also assessed to better understand the physical mechanisms behind the phenomena that lead to a latent potential energy.

Production of Noble-Metal Nanohelices Based on Nonlinear Dynamics in Electrodeposition of Binary Copper Alloys

Spatiotemporal pattern formation is dynamic self-organization widely observed in nature and drives various functions. Among these functions, chirality plays a central role. The relationship between dynamic self-organization and chirality has been an open question; therefore, the production of chiral nanomaterials by dynamic self-organization has not been achieved. Here, we show that the confinement of a two-dimensional spatiotemporal micropattern via the electrodeposition of a binary Cu alloy into a nanopore induces mirror symmetry breaking to produce a helical nanostructure of the noble-metal component although it is still not yet possible to control the handedness at this stage. This result suggests that spatiotemporal symmetry breaking functions as a mirror symmetry breaking if cylindrical pores are given as the boundary condition. This study can be a model system of how spatiotemporal symmetry breaking plays a role in mirror symmetry breaking, and it proposes a new approach to producing helical nanomaterials through dynamic self-organization.

Control of the Nanopore Architecture of Anodic Alumina via Stepwise Anodization with Voltage Modulation and Pore Widening.

Control of the morphology and hierarchy of the nanopore structures of anodic alumina is investigated by employing stepwise anodizing processes, alternating the two different anodizing modes, including mild anodization (MA) and hard anodization (HA), which are further mediated by a pore-widening (PW) step in between. For the experiment, the MA and HA are applied at the anodizing voltages of 40 and 100 V, respectively, in 0.3 M oxalic acid, at 1 °C, for fixed durations (30 min for MA and 0.5 min for HA), while the intermediate PW is applied in 0.1 M phosphoric acid at 30 °C for different durations. In particular, to examine the effects of the anodizing sequence and the PW time on the morphology and hierarchy of the nanopore structures formed, the stepwise anodization is conducted in two different ways: one with no PW step, such as MA→HA and HA→MA, and the other with the timed PW in between, such as MA→PW→MA, MA→PW→HA, HA→PW→HA, and HA→PW→MA. The results show that both the sequence of the voltage-modulated anodizing modes and the application of the intermediate PW step led to unique three-dimensional morphology and hierarchy of the nanopore structures of the anodic alumina beyond the conventional two-dimensional cylindrical pore geometry. It suggests that the stepwise anodizing process regulated by the sequence of the anodizing modes and the intermediate PW step can allow the design and fabrication of various types of nanopore structures, which can broaden the applications of the nanoporous anodic alumina with greater efficacy and versatility.

Influencing Mechanism of Temperature on Coal Pores during the Artificially Thermal Evolution

The pores in coal are the primary storage sites of coalbed methane (CBM), and temperature is the critical factor affecting pore evolution during the thermal evolution. This paper investigates the evolution characteristics of different pores and the role of related molecular structures through the artificially thermal evolution of coal. The pore size distribution and morphology of unheated and heated coals were detected by combining the fluid injection technology and image analysis. The molecular structures of each sample are semi-quantitatively analyzed by X-ray diffraction and Fourier transform infrared spectroscopy. The results indicated that 300 °C is a turning point for the evolutions of micropores and macropores. Their respective volume remains steady approximately before 300 °C. Subsequently, the micropore volume increases gradually, while the macropore volume soars suddenly after 300 °C. Meanwhile, the mesopore volume constantly decreases during the artificially thermal evolution. On the other hand, the most mesopore morphology alters from the slit pore and wedge pore to the bottle-neck pore and cylindrical pore, while the macropore morphology alters from the wedge pore into the cylindrical pore and bottle-neck pore. Furthermore, during the artificially thermal evolution, the major factor affecting the evolution of micropore and macropore is the loss of −CH2 side chains from their edges, while the main factor affecting the mesopore evolution is the polycondensation of −CH2 side chains and carbonyl/carboxyl at its edge. These results could help understand the pore variation in CBM reservoirs during coalification.

Synthesis and properties of COK‐12 large‐pore mesocellular silica foam

AbstractLarge, ink‐bottle‐shaped pores in mesocellular foams (MCFs) are desired for various applications requiring enhanced mass transfer or the immobilization of larger compounds. Hence, the cylindrical pores of COK‐12, an ordered mesoporous silica structurally comparable to SBA‐15 but synthesized at room‐temperature at quasi‐neutral pH, are chemically swollen into ink‐bottle pores. Therefore, p‐xylene is used as a more sustainable swelling agent compared to popular alternatives. Its high boiling point allows for an additional thermal aging step to amplify the mesostructure enlargement without needing additional chemicals. For COK‐12, the MCFs obtained at room temperature reach an unprecedented plateau for the modal mesopore cell and window diameter of 19.9 and 5.5 nm, respectively, with an underlying broad pore size distribution and distorted hexagonal lattice up to 14.5 nm, involving hexagonal and spherical structures. The combined chemical and thermal swelling resulted in the selective enlargement of the window diameter to more than 200% and a slightly increased cell diameter, pore size distribution, and hexagonal lattice distortion in comparison to the room temperature synthesis. Such materials are thought to be promising alternatives to SBA‐15‐based MCFs, often utilizing toxic catalysts during synthesis. The presented results pave the way for enhanced adsorptive, catalytic, and drug delivery performances for COK‐12‐based materials.

О численном моделировании трековых мембран, используемых в качестве коллиматоров рентгеновского излучения

In this work, we present the results of numerical modeling of distribution of the field amplitude inside micron-sized through cylindrical pores in polymer track membranes in the soft X-ray wavelength range 13.5–30.4 nm. The calculations were performed by numerically solving the 3D parabolic equation with a finite-difference method using an exact transparent boundary condition. The dependences of the X-ray transmittivity through a pore on the incidence angle as well as on the pore diameter were computed. For the membranes with some thicknesses and pore diameters, calculated angular dependences of the transmittance are compared with the measurements known from the literature. It is demonstrated that the calculations agree with the measurements if a transition layer on the inner surface of the pores, which accounts for the finite surface roughness, is introduced.

Modified BET theory for actual surfaces: implementation of surface curvature.

The Brauner-Emmett-Teller (BET) theory was originally based on adsorbing surfaces of zero curvature. The theory is elaborated to include a curvature parameter. The theory has been developed for mono-size dense particles (spherical or rod-like) and porous materials with a sharp pore size distribution (spherical or cylindrical pores). Validation was performed considering 62 relevant published results. It is shown that for porous materials with cylindrical pores (15 cases), while the average error in the calculation of the specific surface area using the original BET theory is ca. 46%, that from the modified theory is ca. 11%. For porous materials with spherical pores (20 cases), an average error of 58% (BET theory) is reduced to 15%. To apply the new theory to dense materials, in addition to the probe-gas adsorption isotherm, skeletal density is needed. For meso-porous materials, the curvature parameter is calculated using the BJH theory.

Porous zeolitic imidazolate frameworks assembled with highly-flattened tetrahedral copper(II) centres and 2-nitroimidazolates.

Cu(II)-based zeolitic imidazolates (Cu-ZIFs), Cu-ZIF-gis and -rho, formulated as Cu(nIm)2 (nIm = 2-nitroimidazolate) have highly-flattened tetrahedral coordination geometry. Cu-ZIF-gis has 2.4 Å cylindrical pores that can adsorb H2 gas, and Cu-ZIF-rho has 19.8 Å cages with a BET surface area of 1320 m2 g-1.

Brownian motion with radioactive decay to calculate the dynamic bulk modulus of gases saturating porous media according to Biot theory

We present a new stochastic simulation method for determining the long-wavelength effective dynamic bulk modulus of gases, such as ambient air, saturating porous media with relatively arbitrary microgeometries, i.e., simple enough to warrant Biot’s simplification that the fluid and solid motions are quasi-incompressible motions at the pore scale. The simulation method is based on the mathematical isomorphism between two different physical problems. One of them is the actual Fourier heat exchange problem between gas and solid in the context of Biot theory. The other is a diffusion-disintegration-controlled problem that considers Brownian motion of diffusing particles undergoing radioactive-type decay in the pore volume and instant decay at the pore walls. By appropriately choosing the decay time and the diffusion coefficient, the stochastic algorithm we develop to determine the average lifetime of the diffusing particles, directly gives the effective apparent modulus of the saturating fluid. We show how it leads to purely geometric stochastic constructions to determine a number of geometrical parameters. After validating the algorithm for cylindrical circular pores, its power is illustrated for the case of fibrous materials of the type used in noise control. The results agree well with a model of the effective modulus with three purely geometric parameters of the pore space: static thermal permeability divided by porosity, static thermal tortuosity, and thermal characteristic length.

Rheology of a Viscous-Plastic Liquid in a Porous Medium

The hydrodynamics of the capillary flow of a viscous-plastic liquid in cylindrical rectilinear pores is considered, as a result of which the structural velocity distribution over the pore cross section is obtained. Analytical solutions are proposed for the equations of hydraulic diffusion and nonlinear filtration for a non-Newtonian fluid in a cylindrical porous medium. It is noted that when a non-Newtonian fluid flows in a porous medium, the filtration equations take a nonlinear form due to the effective viscosity, shear, and yield stresses taken into account in its structure. The proposed solutions make it possible to evaluate the state of the porous medium and its main parameters (permeability, hydraulic diffusion, and effective viscosity coefficients). The obtained solutions are compared with existing experimental data for non-Newtonian oils.

Electron transparent nanotubes reveal crystallization pathways in confinement.

The cylindrical pores of track-etched membranes offer excellent environments for studying the effects of confinement on crystallization as the pore diameter is readily varied and the anisotropic morphologies can direct crystal orientation. However, the inability to image individual crystals in situ within the pores in this system has prevented many of the underlying mechanisms from being characterized. Here, we study the crystallization of calcium sulfate within track-etched membranes and reveal that oriented gypsum forms in 200 nm diameter pores, bassanite in 25-100 nm pores and anhydrite in 10 nm pores. The crystallization pathways are then studied by coating the membranes with an amorphous titania layer prior to mineralization to create electron transparent nanotubes that protect fragile precursor materials. By visualizing the evolutionary pathways of the crystals within the pores we show that the product single crystals derive from multiple nucleation events and that orientation is determined at early reaction times. Finally, the transformation of bassanite to gypsum within the membrane pores is studied using experiment and potential mean force calculations and is shown to proceed by localized dissolution/reprecipitation. This work provides insight into the effects of confinement on crystallization processes, which is relevant to mineral formation in many real-world environments.

HYDROGEN ACCUMULATOR IN AUTONOMOUS ENERGY DEVICES

The purpose of the research. One of the main difficulties into solving the issues of energy supply for autonomous consumers with heat and electricity in agricultural production is the inconsistency of supply schedules and energy consumption. The uneven nature of the operating modes of wind and solar power plants requires the creation of an energy storage system. In this connection, the task of creating autonomous power plants that use hydrogen and thermal energy storage systems arises. Results. A fundamentally new type of porous gas-reinforced materials − gazars, which are the basis of hydrogen batteries − have been investigated. They have unique properties that are very valuable for structural materials: strength and lightness, as well as a number of special properties. Consider the existing methods of hydrogen storage − in the form of hydrides, in liquid and compressed states, which have significant disadvantages for their use in energy devices. Thus, hydride batteries have a number of attractive aspects: comparative safety, soft storage mode and hydrogen yield. However, they have a low capacity and require expensive metals: La, Ni, Ti and rare earth metals, the reserves of which in the earth's crust are limited. The structure and properties of gas-reinforced metals, which have a monolithic matrix and a cellular structure of the porous space, have been investigated to determine the functional capabilities and prospective areas of their use. The dependence of the porosity on the relative size of the pores for various options for their placement in the sample was established. It is shown that in order to accelerate the processes of saturation and discharge of battery gases and to increase their capacity, battery cells with closed unidirectional cylindrical pores should be used. Hydrogen saturation is conducted when one of the ends of the battery is heated and the rest of the surface is cooled with a temperature difference of 573…773 K. Conclusions. Research in laboratory conditions showed that batteries based on porous metals, having a monolithic matrix and a cellular structure of the porous space, have advantages compared to the well-known ones: hydride, balloon, cryogenic. This is a relatively high hydrogen capacity; relative cheapness; possibility of multiple use; the possibility of using batteries as elements of power structures, as well as the use of unpurified technical hydrogen.

Optimising nanoporous supercapacitors for heat-to-electricity conversion

Innovative ways of harnessing sustainable energy are needed to meet the world’s ever-increasing energy demands. Supercapacitors may contribute, as they can convert waste heat to electricity through cyclic charging and discharging at different temperatures. Herein, we use an analytically-solvable model of a cylindrical pore filled with a single file of ions to identify optimal conditions for heat-to-electricity conversion with supercapacitors. We consider Stirling and Ericsson-like charging cycles and show that the former or latter yields more work when a supercapacitor operates under charge or voltage limitations, respectively. Both cycles yield the most work for pores almost as narrow as the size of the ions they contain, as is the case for energy storage with supercapacitors. In contrast to energy storage, which can be maximised by ionophobic pores, such pores do not yield the best heat-to-electricity conversion, independently of the applied potential. Instead, we find that for a given pore size, a moderately ionophilic pore harvests more work than ionophobic and strongly ionophilic pores.

Electrochemical impedance simulation of porous electrodes with variously shaped pores using 3-dimensional finite element method

Porous electrodes are widely used in many applications, such as enzyme electrodes, energy devices, and electrosynthesis. However, evaluation of porous electrodes using electrochemical impedance spectroscopy, one of the most promising methods for determining electrochemically relevant structural information, is challenging. Thus, in this study, impedance spectra were simulated using a three-dimensional, finite element method-based model for porous electrodes. The shape of the electrode pore was varied, and the effect on the resulting impedance spectrum was analyzed. The results indicated that for certain pore shapes, such as wide and shallow cylinders, a three-dimensional model was required to obtain accurate results. However, for narrow and deep cylindrical pores, a classical one-dimensional approximation was sufficiently accurate, and a 45º inclined line was observed in the impedance spectra with high frequencies, even when a three-dimensional model was employed. Moreover, wide and shallow or narrowing pores result in a higher inclination angle, whereas widening or branching pores result in a lower inclination angle. These features were also observed when charge transfer and diffusion processes were considered in terms of a mediator-type enzyme electrode reaction.

Porous TiO2-x/C Nanofibers with Axially Aligned Tunnel Pores as Effective Sulfur Hosts for Stabilized Lithium-Sulfur Batteries.

Hierarchically porous TiO2-x/C nanofibers (NFs) with axially aligned cylindrical tunnel pore channels were synthesized as a sulfur (S) host for lithium-sulfur batteries (LSBs) by a microemulsion electrospinning method. We explored a synergistic chemical trapping reinforced by coordinatively unsaturated Ti3+ nuclei with oxygen deficiency (or more broadly via polar O-Ti-O units) in combination with physical trapping in both narrow pores (<5 nm) and larger ordered pore tunnels (20-100 nm) separated by thin walls to allow for a large volume of active material and rapid diffusion within the channels while effectively blocking out the diffusion of soluble lithium polysulfides. Due to this unique architecture and enhanced conductivity, the prepared materials enabled a high S loading (∼72 wt %) and significantly reduced the shuttle effect. Hence, the composite TiO2-x/C@S cathodes exhibited a high utilization of active materials, excellent rate performance, and promising cycling stability (retention of up to ∼1010 mAh g-1 after 150 cycles for the aerial capacity of 1.5 mAh cm-2, with very stable performance even for the high S loading of 2.5 mg cm-2). By designing control nanomaterials that lack either the pore tunnels or the desired chemical compositions, we elucidated the importance of the synergistic effect of both factors. This work demonstrates a successful exploration of oxide NFs with tunnel pores via a simple single-needle microemulsion electrospinning method, which should pave the way for similar nanomaterials engineering with other chemistries for improved LSB performance.

Influence of shape and charged conditions of nanopores on their ionic current rectification, electroosmotic flow, and selectivity

The electrokinetic behaviors, including ionic current rectification (ICR), selectivity, and electroosmotic flow (EOF) of a nanopore play important role in applications such as nano sensing, salinity gradient power, and desalination of sea water. Since those behaviors can be influenced significantly by the shape and charged conditions of a nanopore, the influence of these factors on its performance is studied in detail by comparing the behavior of six types of nanopore (conical, cylindrical, cigar, funnel, hourglass, and dumbbell-shaped pores), each of them can be unipolarly or bipolarly charged. In addition to examining their performance under various conditions, the associated mechanisms are also discussed. We show that the internal volume of a nanopore is the most important factor influencing its ICR behavior. However, the selectivity of a nanopore depends both on its internal volume and the fraction of its narrow region. The bipolar and unipolar nature of a nanopore can yield interesting velocity profile, which is also influenced by the salt concentration and nanopore geometry.

Selective Trapping of Living Cells into Micropores within a Track-etched Membrane by Dielectrophoresis

In this study, an insulator-based dielectrophoresis device using a track-etched membrane was developed for selective trapping of living yeast cells. A high electric field was formed in cylindrical pores of 8-µm diameter within the insulating membrane between two transparent plate electrodes. At a frequency of 20 MHz, only a living cell could be drawn into the pore and trapped strongly by dielectrophoresis. For non-spherical cells with a diameter and length of 5 µm and 14 µm, respectively, it was found that a cell longer than the pore diameter was drawn into the pores with electro-orientation if the minor axis of the cell was shorter.

Effects of three-dimensional pore structure on effective thermal conductivities of thermal insulation materials

Pore three-dimensional structure and overlap are the key factors in decreasing effective thermal conductivities of the porous insulation material. However, this coupled effect of pore structure and overlap has not been intensively studied. In this work, many three-dimensional models are built to solve the coupled heat transfer in porous insulation materials. The effects of pore structure and overlap are investigated. The results indicate that the effective contact area between pore gas and solid matrix is a key factor for the thermal insulation performance of porous insulation materials. The effect mechanism of the pore overlap on the thermal insulation is affected by the pore shape. The effect of pore overlap on the heat transfer performance is determined by the overlapping direction. The decrease of pore content is also affected by the pore shape. Overall, the pore overlap reduces the thermal insulation performance of porous insulation materials, regardless of pore shape and content change. Cylindrical (⊥) pore has the largest thermal insulation performance in our cases. A quantitative correlation is built to predict the effective thermal conductivity of the porous insulation material with different pore shapes. This correlation is not only simple but also accurate.

Boiling in nanopores through localized Joule heating: Transition between nucleate and film boiling

The transition from nucleate to film boiling on micro/nanotextured surfaces is of crucial importance in a number of practical applications, where it needs to be avoided to enable safe and efficient heat transfer. Previous studies have focused on the transition process at the macroscale, where heat transfer and bubble generation are activated on an array of micro/nanostructures. In the present study, we narrow down our investigation scale to a single nanopore, where, through localized Joule heating within the pore volume, single-bubble nucleation and transition are examined at nanosecond resolution using resistive pulse sensing and acoustic sensing. Akin to macroscale boiling, where heterogeneous bubbles can nucleate and coalesce into a film, in the case of nanopores also, patches of heterogeneous bubbles nucleating on the cylindrical pore surface can form a torus-shaped vapor film blanketing the entire pore surface. In contrast to conventional pool boiling, nanopore boiling involves a reverse transition mechanism, where, with increased heat generation, film boiling reverts to nucleate boiling. With increasing bias voltage across the nanopore, the Joule heat production increases within the pore, leading to destabilization and collapse of the torus-shaped vapor film.