High Pore Density Research Articles

High resolution in turbid waters: Ampullae of lorenzini in the daggernose shark Carcharhinus oxyrhynchus (Valenciennes, 1839) (Elasmobranchii: Carcharhinidae).

The present work aimed to analyze the distribution of the electrosensory pores of the Daggernose Shark Carcharhinus oxyrhynchus identifying the organ's importance in the natural history of the species. By examining photographs and digital microscope videos, we found that C. oxyrhynchus possesses the highest abundance of pores among Carcharhiniformes. This suggests a well-developed electroreceptor system, which may have maximized its evolutionary success in high turbidity environments. Furthermore, as a morphologically derived species, C. oxyrhynchus comprises a more complex and specialized electrosensory system. Notably, the species exhibits ontogenetic variation in pore abundance, highlighting the importance of a high-resolution system for adults. The higher density of pores in the ventral region indicates a preference for benthic prey, despite also feeding on pelagic items. Moreover, the species has a high-resolution electrosensory system and a high density of pores in the snout, which emphasizes the importance of the elongated snout that expands the electroreception search area coverage. Evolutionary convergence was observed in the development of the electrosensory system, as C. oxyrhynchus shares characteristics of pore distribution and abundance with phylogenetically unrelated species.

Scalable Synthesis of Carbon Nanomembranes from Amorphous Molecular Layers.

Nanoporous carbon nanomembranes (CNMs) created by self-assembled monolayers ideally combine a high water flux and precise ion selectivity for molecular separation and water desalination. However, their practical implementation is often challenged by the availability of large epitaxial substrates, limiting the membrane up-scaling. Here, we report a scalable synthesis of CNMs from poly(4-vinylbiphenyl) (PVBP) spin-coated on SiO2/Si wafers. Electron irradiation of the amorphous PVBP molecular layers induces the formation of a continuous membrane with a thickness of 15 nm and a high density of subnanometer pores, providing a water permeance as high as 530 L m-2 h-1 bar-1, while repelling ions and molecules larger than 1 nm in size. A further introduction of a reinforced porous block copolymer layer enables the fabrication of centimeter-scale CNM composites that efficiently separate organic dyes from water. These results suggest a feasible route for large-scale nanomembrane fabrication.

Anomalous Mechanical and Electrical Interplay in a Covalent Organic Framework Monolayer Membrane.

Ion transport through nanoconfinement, driven by both electrical and mechanical forces, has drawn ever-increasing attention, due to its high similarity to stress-sensitive ion channels in biological systems. Previous studies have reported only pressure-induced enhancement in ion conductance in low-permeable systems such as nanotubes, nanoslits, or single nanopores. This enhancement is generally explained by the ion accumulation caused by the capacitive effect in low-permeable systems. Here, we fabricate a highly permeable COF monolayer membrane to investigate ion transport behavior driven by both electrical and mechanical forces. Our results show an anomalous conductance reduction activated by external mechanical force, which is contrary to the capacitive effect-dominated conductance enhancement observed in low-permeable nanopores or channels. Through simulations, we uncovered a distinct electrical-mechanical interplay mechanism that depends on the relative rate between the ion diffusion from the boundary layer to the membrane surface and the ion transport through the membrane. The high pore density of the COF monolayer membrane reduces the charge accumulation caused by the capacitive effect, resulting in fewer accumulated ions near the membrane surface. Additionally, the high membrane permeability greatly accelerates the dissipation of the accumulated ions under mechanical pressure, weakening the effect of the capacitive layer on the streaming current. As a result, the ions accumulated on the electrodes, rather than in the capacitive layer, dominating the streaming current and giving rise to a distinct electrical-mechanical interplay mechanism compared to that in low-permeable nanopores or channels. Our study provides new insights into the interplay between electrical and mechanical forces in ultra-permeable systems.

Influence of TPU/EVA Phase Morphology Evolution on Supercritical Carbon Dioxide Extrusion Foaming.

Ethylene-vinyl acetate copolymer (EVA) was added at different contents to the thermoplastic polyurethane (TPU) matrix to form a non-compatible blending system, and foaming materials with high pore density were prepared using the supercritical carbon dioxide extrusion method. The influence of the phase morphology and crystal morphology of the TPU/EVA blend on its foaming behavior was studied. The results show that EVA changed the phase morphology and crystal morphology of the blends, leading to the improved melt viscosity and crystallinity of the blend system. At the same time, interfacial nucleation increases the density of cells and decreases the cell thickness and size, which is beneficial for improving the foaming properties of the blends. For the EVA content of 10% (mass fraction), the cell size is small (105.29 μm) and the cell density is the highest (3.74 × 106 cells/cm3). Based on the TPU/EVA phase morphology and crystal morphology, it is found that the sea-island structure of the blend has better foaming properties than the bicontinuous structure.

A novel battery thermal management system utilizing ultrathin thermal ground planes for prismatic Lithium-ion batteries

Temperature significantly affects the energy efficiency, safety, life and performance of a lithium-ion battery pack in electric vehicles (EVs). High overall temperature and large temperature difference of the battery in fast charging (FC) can cause degradation in performance and even catastrophic failure like a thermal runaway. Besides, the increasing energy density of battery packs limits the space for the thermal management system. Therefore, we developed an ultrathin thermal ground plane-based battery thermal management system (UTTGP-BTMS), which utilizes 0.4 mm thick novel UTTGP with air cooling to dissipate the heat from the gap between batteries. Double-layer high pores per inch (PPI) mesh and wettability modification was adopted to enhance the thermal performance of the UTTGP. Before the evaluation test of the BTMS, the heat generation rates of the batteries in 2.2C to 4C fasting charging conditions are estimated by Bernardi’s model. Then, the thermal performance of the novel battery thermal management system (BTMS) is experimentally investigated under 2.2C to 4C FC regimes at ambient temperatures from 10 °C to 50 °C. The BTMS is able to maintain a battery surface temperature of 55Ah Lithium iron phosphate (LiFeO4, LFP) batteries below 42.7 °C under a 4C charge rate, 57.3 °C at 50°C ambient temperature, respectively, and still achieve good surface temperature uniformity in all cases studied. Compared to a BTMS with copper heat spreaders, the temperature rise temperature non-uniformity, and thermal resistance are reduced by up to 23.3%, 28.4%, and 62.6%, respectively. Besides this, the effects of the pores density of the mesh in the UTTGP-BTMS are also studied by changing the sieve number of mesh, showing that a higher pore density gives better performance under large C-rates. The proposed UTTGP-BTMS showed significant performance with only submillimeter thickness in the thermoregulation of a battery pack, with the potential of being a viable solution for high-power battery thermal management in EVs.

Experimental investigation on the performance of air–gap diffusion distillation with foamed ceramics

Air-gap diffusion distillation (AGDD) has been proposed as a novel type of thermal distillation technique, in which the hydrophilic porous media is used as a hot stream channel. Polyvinyl alcohol (PVA) sponge was first selected as the porous medium in our previous reports. To improve the thermal, chemical resistance and mechanical strength of the porous medium, some foamed ceramics (FCs) (alumina, zirconia, and silicon carbide foamed ceramic) are selected as the porous mediums which are used as hot stream channels of AGDD in this work. The effect of different FC materials on performances of AGDD is investigated by experiments. That the influence of FCs with pre-wetting and non-wetting treatments on the performances of AGDD is investigated first. Secondly, the influence of operation and structure parameters on the performances of AGDD and the stability of three FCs in long-term operation are explored. And finally, the performances of AGDD used FCs and PVA sponge are compared. Results show that the FC with pre-wetting treatment can improve the performances of AGDD, and the water production flux can rise to 23.7%, especially for the silicon carbide FC with high pore density. Furthermore, among the three FCs, ZrO2 FC can maintain higher water production flux and desalination rate during long-term operation. The desalination rate of AGDD with three different FCs is higher than 99.1%. The AGDD with FC is ideal for high-temperature and high-flow-rate working fluid environments, whereas the AGDD with PVA is suitable for low-temperature and small-flow-rate working fluid environments. This may be used as a reference for the industry to choose porous material for AGDD.

Specific mechanical properties of highly porous Ti-Zr-Mo-Sn shape memory alloy for biomedical applications

Porous Ti-5Zr-3Mo-6.5Sn (at.%) shape memory alloy scaffolds were fabricated by fiber-sintering. Microstructural morphology of the scaffolds showed high density of three dimensional and interconnected pores ranging from 100 to 500 μm in diameter. β →α" martensitic transformation, which is induced by the applied stress, occurs at human body temperature. The porous shape memory alloy scaffold has excellent superelasticity and then exhibited the strain recovery ratio of 90%. An elastic modulus of the Ni-free shape memory alloy scaffold, which was prepared by fiber-sintering, was as low as 19 GPa due to the high density of pores. These mechanical properties of low elastic modulus and superelasticity matched well with those of human bone. Considering the specific mechanical properties, structural morphology and biocompatibility, the fiber-sintered Ni-free shape memory alloy scaffolds satisfy the major requirements of bone substitutes for damaged or diseased bones.

Improved NO2 gas sensing performance of nanoporous conjugated polymer (CP) thin films by incorporating preformed CP nanowires

Conjugated polymer (CP)-based organic field-effect transistor (OFET) gas sensors can detect gas molecules at room temperature with high sensitivity and selectivity. However, their performance, particularly when detecting oxidizing gases, has fallen behind that of their metal oxide counterparts. Hence, improving their sensing performance as well as understanding the correlation between it and the structural and electrical properties of the sensing materials is necessary. Herein, we demonstrate that gas sensing performance of an OFET sensor based on nanoporous poly(3-hexylthiophene) (P3HT) films can be improved simply by incorporating preformed P3HT nanowires (NWs), which act as an efficient charge transport pathway. It detects nitrogen dioxide (NO2) molecules with high sensitivity due to the efficient charge transport pathway as well as ultrathin nanoporous structure of the P3HT films. Upon exposure to 10 ppm NO2 at room temperature, the OFET gas sensor based on the P3HT-NW embedded nanoporous P3HT film exhibits excellent responsivity (34%), fast response and recovery times (∼69 and ∼133 s, respectively), and a low limit of detection of under 0.1 ppm, which are comparable to those of conventional metal oxide-based gas sensors. Based on the correlation study between the morphology, charge transport ability, and sensing performance of the P3HT-NWs embedded nanoporous P3HT films, it is revealed that the efficient charge transport ability is an important factor for realizing high-performance CP-based OFET gas sensors, along with excellent morphological features such as thinness and high pore density.

Effect of simultaneous electrical and mechanical stressing on porosity of Ti3C2T x MXene films

MXenes are atomically layered carbides and nitrides of transition metals that have potential for micro-devices applications in energy storage, conversion, and transport. This emerging family of materials is typically studied as nanosheets or ultra-thin films, for which the internal defects are mostly nanoscale flake-flake interface separation type. However, micro-devices applications would require thicker films, which exhibit very high density of microscale pores. Electrical conductivity of thicker MXenes is significantly lower than nanosheets, and the physics of defect size and density control are also different and less understood. Current art is to perform high temperature annealing to improve the electrical conductivity, which can structurally alter or degrade MXene. The key contribution of this study is a room-temperature annealing process that exploits the synergy between electrical pulses and compressive mechanical loading. Experimental results indicate over a 90% increase in electrical conductivity, which reflects a decrease in void size and density. In the absence of compressive loading, the same process resulted in a conductivity increase of approximately 75%. Analytical spectroscopy and microscopy indicated that the proposed multi-stimuli process kept the MXene composition intact while significantly decreasing the void size and density.

Flexible Film Bulk Acoustic Resonator Based on Low-Porosity β-Phase P(VDF-TrFE) Film for Human Vital Signs Monitoring.

P(VDF-TrFE) is a promising material for flexible acoustic devices owing to its good piezoelectric performance and excellent stretchability. However, the high density of internal pores and large surface roughness of the conventional P(VDF-TrFE) results in a high propagation attenuation for acoustic waves, which limits its use in flexible acoustic devices. In this paper, a novel method based on two-step annealing is proposed to effectively remove the pores inside the P(VDF-TrFE) film and reduce its surface roughness. The obtained P(VDF-TrFE) film possesses excellent characteristics, including a high breakdown strength of >300 kV/mm, a high-purity β-phase content of more than 80%, and high piezoelectric coefficients (d33) of 42 pm/V. Based on the low-porosity β-phase P(VDF-TrFE) film, we fabricated flexible film bulk acoustic resonators (FBARs) which exhibit high sharp resonance peaks. The pressure sensor was made by sandwiching the FBARs with two PDMS microneedle patches. Heartbeat and respiration rate monitoring were achieved using the pressure sensor. This work demonstrates the feasibility of high-performance flexible piezoelectric acoustic resonators based on low-porosity P(VDF-TrFE) films, which could see wider applications in the wearable sensors for both physical and chemical sensing.

Experimental investigation of the effect of copper foam pore structure on the thermal performance of phase change material in different centrifugal force fields

In this paper, composite phase change material (PCM) was fabricated by incorporating copper foam into paraffin wax. The effects of porosity (ε = 0.93, 0.95 and 0.97) and pore density (ω =10, 20 and 40 PPI) on the thermal performance of composite PCM were experimentally investigated in positive centrifugal force field (5 g), normal gravity field (0 g) and negative centrifugal force field (-5 g), respectively. The end-state isobar and buoyancy vector are introduced for the description of the heat transfer process. The results show that there are differences in the effects of metal foam pore structure on the heat transfer process of composite PCM under different force field conditions. At 0 g and 5 g, the isotherms of all experimental conditions gradually converge to the end-state isobars, but decreasing the porosity or increasing the pore density can slow down this evolution rate. At -5 g, the evolution of isotherms is mainly influenced by the buoyancy vector, and isotherms with lower porosity or higher pore density are less influenced by buoyancy. It was also found that reducing the porosity effectively shortens the melting time lags along the heat flow flux direction for all force field conditions. However, reducing the pore density at -5 g shortens the melting time lags in both the upper and lower regions in the heat flux direction, while it only shortens that in the upper region at 0 g, and it has no significant effect on that either in upper region or lower region at 5 g. In addition, in the positive centrifugal force field, lowering the porosity can more significantly improve the heat transfer efficiency, while lowering the pore density can more effectively improve the heat transfer efficiency in the negative centrifugal force field.

Boiling Heat Transfer in Copper Foam Bilayers in Positive and Inverse Gradients of Pore Density

Gradient metal foam is an advanced heat transfer material that decreases resistance to bubble escape and enhances the transfer of boiling heat. In this study, boiling heat transfer and bubble behavior were studied in an experimental set-up with copper foam bilayers configurated either in positive or inverse gradients, utilizing deionized water as working fluid. Positive gradient refers to arranging metal foam layers with high pore density at the bottom, above the heat source, and low pore density on the top. Results show that the heat transfer is higher for gradient metal foam surfaces, of 6.14×105 W/m2, versus a uniform metal foam surface, of 3.94×105 W/m2. For the positive gradient configuration, boiling heat transfer performance first increased with the pore density, then decreased when the pore density was higher than 60 pores per inch (PPI). By contrast, for the inverse gradient, the heat transfer performance was nearly constant with increasing pore density. At the low pore density, the inverse gradient performed better than the positive gradient during the whole boiling process. At high pore density, the positive gradient structure performed better in heat transfer at the early boiling stage. Three main types of bubble escape were observed: For the positive gradient bilayer, the bubbles moved up or down without lateral interference. In contrast, for inverse gradient, the bubbles mostly escape from the sides, which is easy to induce bubble merging. The inverse gradient surface generates larger bubbles, while the positive gradient surface produces a higher frequency of bubble detachment. Accordingly, two liquid replenishment models are proposed: for the positive gradient, external liquid replenishes from the side into the copper foam, while for inverse gradient, the liquid is mainly replenished from the top.

γ-irradiation induced effects on structural, morphological and photoluminescence properties of PEO-PVA blended polymer films

PEO/PVA blends have been prepared to investigate the effect of gamma rays on the structural, morphological and photoluminescence properties. The studies of non-irradiated and irradiated samples with radiation doses of 10 kGy were examined by using XRD, ATR-FTIR, Optical microscopy and PL. Gamma photons induced important chemical rearrangements, especially by PVA hydroxyl groups. We found that the crystallinity rate is strongly influenced by radiation. In this context, one could predict that the immiscibility of PVA with PEO and the interactions between the chains are of the electrostatic type. A structural-scale disturbance due to the radical formation leads to spherulitic texture modifications of the PEO. Due to the luminescence properties, the blend samples behave like core-shell nanoparticles. This phenomenon is due to the fact that the PVA polymer played the role of shell. Irradiation makes it possible to obtain well-ordered spherulites and to get a high pore density. The irradiated blend showed a higher quantum yield. The significant chemical and morphological changes caused by gamma radiation favored the optical recombination of hydroxyl groups.

How Loading of Co3O4-Cs on an Open-Cell Foam Influences N2O Decomposition

Co3O4 modified with Cs was deposited on an α-Al2O3 open-cell foam, characterized by X-ray diffraction (XRD), N2 physisorption, temperature-programmed reduction by hydrogen (TPR-H2), and scanning electron microscopy-energy-dispersive X-ray analysis (SEM-EDAX) and tested for the low-temperature decomposition of N2O. The aim was to study the effect of the amount of active phase on N2O conversion. Three different approaches were used: (i) the application of foam supports with different cell sizes, (ii) influencing catalyst loading using impregnation solutions with different precursor concentrations, and (iii) deposition of the active phase precursor by repeated immersion–calcination cycles. Increasing the geometric surface area of the support, and thus catalyst loading, was successfully done using the support with higher pore densities. A higher loading was also achieved by increasing the nitrate precursor concentration in the impregnation solution. In both cases, the catalyst activity increased with an increase in the amount of the active phase. Compared to that, a repeated impregnation procedure can ensure the deposition of a higher amount of active phase in comparison to that obtained with one-step impregnation, but only the last layer is used in the reaction and the rest of the active phase remains unutilized, which makes this type of preparation unfavorable. The high catalytic activity was preserved at 450 °C even in the presence of O2, H2O, and NO.

Graphene foam membranes with tunable pore size for next-generation reverse osmosis water desalination.

The development of carbon-based reverse osmosis membranes for water desalination is hindered by challenges in achieving a high pore density and controlling the pore size. We use molecular dynamics simulations to demonstrate that graphene foam membranes with a high pore density provide the possibility to tune the pore size by applying mechanical strain. As the pore size is found to be effectively reduced by a structural transformation under strain, graphene foam membranes are able to combine perfect salt rejection with unprecedented water permeability.

Size and Shape Exclusion in 2D Silicon Dioxide Membranes

2D membranes such as artificially perforated graphene are deemed to bring great advantages for molecular separation. However, there is a lack of structure-property correlations in graphene membranes as neither the atomic configurations nor the number of introduced sub-nanometer defects are known precisely. Recently, bilayer silica has emerged as an inherent 2D membrane with an unprecedentedly high areal density of well-defined pores. Mass transfer experiments with free-standing SiO2 bilayers demonstrated a strong preference for condensable fluids over inert species, and the measured membrane selectivity revealed a key role of intermolecular forces in ångstrom-scale openings. In this study, vapor permeation measurements are combined with quantitative adsorption experiments and density functional theory (DFT) calculations to get insights into the mechanism of surface-mediated transport in vitreous 2D silicon dioxide. The membranes are shown to exhibit molecular sieving performance when exposed to vaporous methanol, ethanol, isopropanol, and tert-butanol. The results are normalized to the coverage of physisorbed molecules and agree well with the calculated energy barriers.

On the effect of different placement schemes of metal foam as volumetric absorber on the thermal performance of a direct absorption parabolic trough solar collector

The main message of this paper is to answer the question of how the thermal efficiency of a direct absorption solar collector is affected by the placement scheme of porous foam in its absorber tube. Hence, ten different layouts of open cell copper porous foam are examined. The thermal efficiency of a constructed direct absorption parabolic trough solar collector is obtained in three different inlet temperatures (20, 30, and 40 °C) and five flow rates (40, 60, 80, 100, and 120 Lph) for various layouts. The results revealed that the placement of porous foam in the lower half of the absorber tube than the upper half leads to a higher thermal efficiency. The highest obtained thermal efficiencies for cases where the entire of absorber tube, center of it, and perimeter of it were filled with porous foam were 50.8%, 46.1%, and 44.7%, respectively. The placement of porous foam in the center of the absorber tube leads to higher pressure drop and thermal efficiency than peripheral placement. Considering the performance index, the peripheral placement of porous foam in the absorber tube is preferred. Moreover, porous foam with higher pore density (PPI) can lead to a higher thermal efficiency.

Divalent metal ion removal from simulated water using sustainable starch aerogels: Effect of crosslinking agent concentration and sorption conditions

This paper evaluates corn starch aerogels, studying different crosslinking agent (trisodium citrate) concentrations (1:1, 1:1.5, and 1:2) and sorption conditions (contact time, adsorbent weight, and initial concentration) regarding the potentially toxic elements (PTEs) [Cd(II) or Zn(II)] adsorption of the aqueous systems. Besides, other properties of aerogels, such as structural properties, specific surface area, and mechanical performance, were evaluated. For adsorption results, better values were observed in adsorption capacity and efficiency for the initial concentration of 100 ppm. In addition, an adsorption time of 12 h and an adsorbent weight of 3.0 g obtained better results due to the possible balance in this time and the high specific surface area available for Cd(II) adsorption. As for the type of adsorbent, the Aero 1:1.5 sample (intermediate crosslinking agent concentration) obtained better results, possibly due to the high porosity, smaller pore sizes, high pore density, and high specific surface area (198 m2·g−1). In addition, hydroxyl groups in the starch aerogel removed Cd(II) ions with 30 % adsorption efficiency. Lastly, Aero 1:1.5 obtained a high mechanical strength at compression and a satisfactory compressive modulus. In contrast, starch aerogels did not absorb the Zn(II) ion.

Effect of thermoelectric modules with different characteristics on the performance of thermoelectric generators inserted in the central flow region with porous foam copper

The recovery and utilization of waste heat by thermoelectric power generation technology can effectively improve energy utilization efficiency and solve the problem of environmental pollution and resource shortage. In this study, a thermoelectric power generation system is established to recover and utilize high temperature waste heat for thermoelectric power generation. In order to improve the conversion efficiency of thermoelectric generator, porous foam copper is inserted into the central flow region of thermoelectric generator to enhance the heat transfer effect at the hot side, and the thermoelectric generator Comprehensive Performance (TEGCP) as a evaluation standard is used to analyze the performance of thermoelectric generator under the porous foam copper central flow region inserted method. The results show that the thermoelectric module with low thermal conductivity and high electrical conductivity can play a better performance in the thermoelectric generator. Moreover, the heat exchange capability of the thermoelectric generator heat exchanger can be significantly increased when the porous foam copper is inserted in the central flow region. Compared with an insert-free thermoelectric generator, the output power of the thermoelectric generator using porous foam copper with high pore density and high volume ratio is increased by 2.3 times. Through the TEGCP that, the use of 15 mm thickness (75 % volume ratio), 20PPI porous foam copper with the module KTGM161-18 and the central flow region inserted method has the best influence of the thermoelectric generator.

A comparative study of the optical and microstructural properties of suspension and atmospheric plasma sprayed thermal barrier coatings

Thermal radiation is an increasingly important issue for thermal barrier coating (TBC) applications in aircraft engine components. As operating temperatures increase, the radiative part of the heat load increases significantly faster than the conductive portion; as such, TBCs may not be as efficient in protecting their underlying heat-sensitive metallic components. To address this issue, new coating morphologies must be investigated. In this study, we compare the optical performance of atmospheric plasma sprayed (APS) and suspension plasma sprayed (SPS) yttria-stabilized zirconia (YSZ) coatings. First, we extract their absorption and scattering coefficients from spectrophotometry measurements via the inverse adding-doubling (IAD) method. The microstructure of the coatings is then analyzed and compared using scanning electron microscopy (SEM) and mercury infiltration porosimetry (MIP). SPS samples are found to offer higher radiation blocking properties due to a more uniform distribution of pores with an average smaller pore diameter than the APS samples. This results in an overall higher pore density, with each pore interface acting as a scattering site, and therefore a higher propensity for scattering events.