Low Pressure Range Research Articles

Tunable and hierarchically porous self-powered sensor with high sensitivity

The remarkable potential applications of flexible and wearable devices in the fields of motion monitoring and preventative healthcare have garnered considerable attention in recent years. However, it is still an everlasting challenge to construct flexible sensors with high sensitivity over the detection range for smart wearable devices. Herein, a hierarchically porous sensor using self-foaming silicone rubber is designed and fabricated for motion monitoring and disease diagnosis. By adjusting the foaming formulations, the pore size and pore density could be controlled within a single sensor. This hierarchically porous sensor possesses a gradient compression characteristic, resulting in a remarkable sensitivity of 0.2988 kPa−1 in the low-pressure range and a maximum detection pressure of 63.75 kPa. Consequently, it can effectively identify signals from different pressing modes and compression distances. Furthermore, a smart insole is fabricated with a sensor array to provide precise information for motion monitoring and foot disease diagnosis. This work might provide a promising strategy to control foam morphology of pressure sensor, enabling precise pressure perception in the fields of sporting posture assessment, medical diagnosis, and healthcare monitoring.

A micro-dome array triboelectric nanogenerator with a nanocomposite dielectric enhancement layer for wearable pressure sensing and gait analysis.

The practical application of a triboelectric nanogenerator (TENG) as a self-powered sensor and an energy harvester is constrained by the need for a wide sensitivity range, significant output power, and structural flexibility. However, most research has focused on physical and chemical surface modifications of the charge-generating layer to enhance the TENG performance. Improving the charge storage ability could otherwise further enhance the overall performance. Here, we propose a flexible TENG design that incorporates a micro-dome array Ecoflex as the tribo-negative layer, coupled with a dielectric enhancement layer composed of a carbon black/Ecoflex composite. The addition of the CB/Eco composite layer to the micro-dome array triboelectric layer enhanced the output voltage performance by forming numerous micro capacitors within the dielectric layer. Furthermore, oxygen-containing fluorocarbon plasma treatment of the micro-dome array increased the surface energy, enhancing the interaction between the triboelectric layers. This leads to an enhancement in the output voltage and energy efficiency, exhibiting a power density of 197.4 mW m-2. The pressure sensitivity of the TENG was systematically investigated, demonstrating 2.57 V kPa-1 in the low-pressure range (0.612 to 8.58 kPa) and 1.70 V kPa-1 in the high-pressure range (8.58 to 20.83 kPa). Additionally, the encapsulated TENG sensor with spacers was integrated into insoles for self-powered gait analysis, providing real-time insights into walking patterns and frequencies. Exploring the TENG's energy harvesting capability revealed a peak-peak voltage of 89.4 V when two TENGs are connected in series. The comprehensive performance characterization of the TENG demonstrates its promising applications in wearable, self-powered sensing, and energy harvesting systems.

Mixture Adsorption in Nanoporous Zeolite and at Its External Surface: In-Pore and Surface Selectivity.

Using toluene, ethylene, and water as gas compounds with different representative molecular interactions, we perform atom-scale simulations for their mixtures to investigate the selectivity of the core nanoporosity and external surface in a prototypical zeolite. As expected, the overall behavior suggests that increasing the pressure of a given component promotes the desorption of the coadsorbing species. However, for water-toluene mixtures, we identify that the pseudohydrogen bonding between water and toluene leads to beneficial coadsorption as toluene adsorption in the low-pressure range promotes water adsorption. Moreover, when the zeolite is completely filled with water, toluene adsorption does not occur due to steric repulsion, and ethylene shows oversolubility as the amount of ethylene per water molecule is significantly larger than in bulk water. The underlying oversolubility mechanism is found to be due to localized ethylene adsorption in the density minima arising from the layering of water in nanoconfinement. Despite these specific effects, the relatively weak coadsorption effects in the zeolite nanoporosity, which are found to be reasonably captured using the ideal adsorbed solution theory, arise from the fact that adsorption of these gases having different molecular sizes occurs in distinct pore regions (channel type, channel intersection). Finally, in contrast to confinement in the nanoporosity, mixture adsorption at the external surface does not show coadsorption effects as it mostly follows the Henry regime. These results show that selectivity is mostly governed by the confinement effects as the external surface leads to a selectivity loss.

Flexible pressure sensor based on multi-layer with gradient structure P(VDF-HFP)/MXene/BaTiO3 composite film for human motion monitoring

In recent years, flexible pressure sensors have been widely used in fields such as human health monitoring, flexible energy storage, wearable electronic devices, and flexible sensing due to their advantages of simple and efficient preparation process, highly sensitive, fast response, and strong piezoelectric performance. In this paper, we studied a kind of polyvinylidene fluoride hexafluoropropylene (P(VDF-HFP))/MXene/BaTiO3 nanofiber prepared by electrospinning technology, and designed a multi-layer structure system with gradient to prepare a flexible pressure sensor. The piezoelectric properties, mechanical properties and dielectric properties are obviously improved. At the same time, the addition of nano fillers and structural design have increased the sensitivity of multi-layer composite fiber membrane-based sensors by 16.5 times compared to pure P(VDF-HFP) in the low-pressure range (<1 kPa), and by 1.5 times compared to PFP-0.5M5BT nanofiber-based sensors, reaching 0.23 kPa−1. When pressed by the palm of the hand, the output voltage of the three-layer gradient structure thin film sensor can be up to about 100 V. Compared with the output voltage of 5 V when the P(VDF-HFP) thin film is pressed by the palm, the output voltage of the flexible pressure sensor of the three-layer gradient structure thin film after adding the filler is 20 times higher. The flexible pressure sensor can analyze and recognize the form of human motion based on the peak, frequency, and shape characteristics of the voltage signals generated by different forms of human motion. This makes it possible for flexible pressure sensors to be used in pressure detection, flexible sensing, electronic skin sensors and other fields.

CO2 adsorption on carbonaceous materials obtained from forestry and urban waste materials: a comparative study.

The increasing emissions of gaseous pollutants of anthropogenic origin, such as carbon dioxide (CO2), which causes global warming, have raised great interest in developing and improving processes that allow their mitigation. Among them, adsorption on porous materials has been proposed as a sustainable alternative. This work presents a study of CO2 equilibrium adsorption at low temperatures (0, 10, and 20°C) over a wide range of low pressures, on activated carbon derived from Eucalyptus (ES) and Patula pine (PP) forest waste, and carbonaceous material derived from waste tires (WT). The precursors of these materials were previously prepared, and their physicochemical properties were characterized. ES and PP were thermochemically treated with phosphoric acid, and WT was oxidized with nitric acid. Additionally, these materials were used to obtain monoliths using uniaxial compaction techniques and different binding agents, with better results obtained with montmorillonite. A total of six adsorbent solids had their textural and chemical properties characterized and were tested for CO2 adsorption. The highest specific surface area (1405 m2g-1), and micropore properties were found for activated carbon derived from Eucalyptus whose highest adsorption capacity ranged from 2.27mmolg-1 (at 0°C and 100kPa) to 1.60mmolg-1 (at 20°C and 100kPa). The activated carbon monoliths presented the lowest CO2 adsorption capacities; however, the studied materials showed high potential for CO2 capture and storage applications at high pressures. The isosteric heats of adsorption were also estimated for all the materials and ranged from 16 to 45kJmol-1 at very low coverage explained by the energetic heterogeneity and weak repulsive interactions among adsorbed CO2 molecules.

The Parylene C as a Flexible Substrate and Passivation Layer: A Promising Candidate for a Piezoelectric, Piezoresistive, and Capacitive Pressure Sensor in Low-Pressure Range

The Parylene C as a Flexible Substrate and Passivation Layer: A Promising Candidate for a Piezoelectric, Piezoresistive, and Capacitive Pressure Sensor in Low-Pressure Range

Surface Properties of Aqueous Dispersions of Bovine Serum Albumin Fibrils

The surface properties of aqueous dispersions of worm-like fibril aggregates of bovine serum albumin (BSA) differ from those of the adsorption layers of the native protein. The dispersions of BSA fibrils are characterized by slower changes of the surface tension and dynamic surface elasticity and also have different steady-state values of the surface properties. The fourfold compression of the adsorption layer of BSA fibrils leads to noticeably higher surface pressures than those of a compressed layer of the native protein, indicating the formation of a more rigid layer structure in the former case. The spreading of BSA fibrils onto a liquid surface from a concentrated dispersion reduces the effect of surface-active admixtures on the layer properties. The dependencies of the dynamic surface elasticity on surface pressure almost coincide for the spread layers of fibrils and the native protein in the range of low surface pressures, but only the spreading of the native protein can lead to surface pressures higher than 4 mN/m. This distinction is presumably caused by the formation of stable clusters of BSA fibrils at the interface and their slow propagation along the liquid surface.

Highly Sensitive Soft Pressure Sensors for Wearable Applications Based on Composite Films with Curved 3D Carbon Nanotube Structures.

Soft pressure sensors based on 3D microstructures exhibit high sensitivity in the low-pressure range, which is crucial for various wearable and soft touch applications. However, it is still a challenge to manufacture soft pressure sensors with sufficient sensitivity under small mechanical stimuli for wearable applications. This work presents a novel strategy for extremely sensitive pressure sensors based on the composite film with local changes in curved 3D carbon nanotube (CNT) structure via expandable microspheres. The sensitivity is significantly enhanced by the synergetic effects of heterogeneous contact of the microdome structure and changes of percolation network within the curved 3D CNT structure. The finite-element method simulation is used to comprehend the relationships between the sensitivity and mechanical/electrical behavior of microdome structure under the applied pressure. The sensor shows an excellent sensitivity (571.64 kPa-1 ) with fast response time (85ms), great repeatability, and long-term stability. Using the developed sensor, a wireless wearable health monitoring system to avoid carpel tunnel syndrome is built, and a multi-array pressure sensor for realizing a variety of movements in real-time is demonstrated.

Flexible capacitive and piezoresistive pressure sensors based on screen-printed parylene C/polyurethane composites in low-pressure range

The use of polymers to fabricate flexible pressure sensors as an alternative to conventional pressure sensors has led to the development of physiological monitoring of human body and the electronic skin. In particular, the fabrication of flexible capacitive and piezoresistive sensors using a variety of materials and the investigation of their electromechanical properties are further developments in these fields. Herein, parylene C is synthesized via chemical vapor deposition method. Pressure-sensitive inks are prepared with a composite of parylene C, polyurethane, polymethylmethacrylate, and activated carbon at certain weight ratios. Flexible capacitive and piezoresistive pressure sensors are fabricated by the screen printing method. The sensitivity, detection limit, linearity range, and response/relaxation time, which define the capacitive and piezoresistive properties are investigated and presented in this paper. The sensitivities of the flexible capacitive and piezoresistive pressure sensors are 0.124 kPa−1 and 0.074 kPa−1 in the pressure range of 0.07–1.39 kPa. This study enables parylene C to be used in the composite structure and shows that it can be used not only as a protective layer but also in flexible pressure sensor applications. It also ensures that the design of the flexible capacitance pressure sensor can measure low pressure with high sensitivity compared to the flexible piezoresistive pressure sensor.

Multi‐Mode Optical Manometry Based on Li4SrCa(SiO4)2:Eu2+ Phosphors

AbstractOptical manometry is a highly promising method for measuring pressure. However, its wider application is limited by the lower sensitivity and influenced by environmental factors. Herein, multi‐mode optical pressure sensors based on Eu2+‐doped Li4SrCa(SiO4)2 phosphors suitable for a variety of complex pressure‐measuring environments are designed. The phosphors contain two separate luminescence centers at 443 nm (EuSr) and 584 nm (EuCa), respectively. In the lower pressure range, the emission peak undergoes a massive redshift of 5.19 nm GPa−1 of EuCa, which is 14× better than commercially available ruby sensors. In order to improve the pressure response range and the accuracy of pressure measurement, for the first time, a new approach in the pressure readout method in which single Eu2+ ions doping based on fluorescence intensity ratio (FIR) pressure measurement is realized in designed materials. Meanwhile, the measured full width at half maximum (FWHM) as an indicator of pressure sensor performance also reveals that the sensing performance is d FWHM/d P ≈ 1.23 nm GPa−1 and d FWHM/d P ≈ 0.84 nm GPa−1 for EuSr and EuCa positions, respectively. Additionally, the structural stability of the phosphor is confirmed by in situ Raman spectrum. The above results indicate that the Li4SrCa(SiO4)2:0.04Eu2+ phosphor is a good candidate for multi‐mode optical pressure sensors.

Change of the surface and structure of activated carbon as a result of HNO3 modification

In the paper the chemical modification of activated carbon was presented. The activated carbon was modified by nitric acid. For the tested activated carbons, the following physical and chemical properties were determined: bulk density, pH of the water extract, and effective diameter of the grains. Elemental and technical analyses were performed. The pore distribution was determined using mercury porosimetry. Low-temperature nitrogen isotherms were used to analyze the microporous structure. The chemical properties of the surfaces of the tested adsorbents were interpreted by means of the Boehm method. The water vapor adsorption isotherms at 303 K were determined and the adsorption capacity towards methanol was tested using the desiccator method. Thermogravimetric tests were used and, at the same time, the released oxidizing gases from the tested samples were analyzed using a mass spectrometer. As a result of the modification, activated carbon enriched with acidic oxygen functional groups was obtained. The resulting modified activated carbon showed worse structural parameters (when compred to umodified activated carbon), however it was characterized by a higher adsorption capacity in relation to polar adsorbates such as water and methanol, especially in the low pressure range.

A detailed thermodynamic analysis of CO2 hydrogenation to produce methane at low pressure

Evaluation of CO2, which is harmful to the environment, as an alternative energy source in CH4 production was investigated from a thermodynamic point of view. The methanation of CO2 is exothermic, however it does not occur at low temperatures due to the kinetic barrier. Thermodynamic modeling studies were carried out to determine the appropriate parameters in the reaction using the Gaseq software according to the Gibbs free energy minimization approach. For this purpose, the effects of H2/CO2 molar feed ratio (2, 3, 4 and 5), temperature (100–1100 °C) and pressure (1, 3, 5 and 10 atm) on CO2 conversion (XCO2) and CH4 selectivity (SCH4) were investigated. As a result, 99.87% XCO2 and 99.99% SCH4 were reached using the molar ratio of H2/CO2 = 4 at 1 at m and 100 °C. The CO2 methanation modeling study at low pressure range was studied in detail and low operating pressure proved to be appropriate.

How to evaluate hydrogen storage properties by Sieverts’ method in the pressure range up to 100 MPa

In order to develop suitable hydrogen storage materials for thermochemical hydrogen compressor using metal hydride, it is necessary to evaluate hydrogen storage properties in high pressure range up to 100 MPa. However, several unexpected issues arose for measuring P-C isotherms up to 100 MPa, which was not observed for the relatively lower pressure range. This led to strange shape of P-C isotherms. In order to solve these, in this paper, we considered the effect of the inner volume of the valve, the pressure increment by a valve operation, and the volume expansion of the sample upon hydrogen absorption. Taken into account these factors, reasonable P-C isotherms were successfully obtained.

On the importance of excited state species in low pressure capacitively coupled plasma argon discharges

In the past three decades, first principles-based fully kinetic particle-in-cell Monte Carlo collision (PIC/MCC) simulations have been proven to be an important tool for the understanding of the physics of low pressure capacitive discharges. However, there is a long-standing issue that the plasma density determined by PIC/MCC simulations shows quantitative deviations from experimental measurements, even in argon discharges, indicating that certain physics may be missing in previous modeling of the low pressure radio frequency (rf) driven capacitive discharges. In this work, we report that the energetic electron-induced secondary electron emission (SEE) and excited state atoms play an important role in low pressure rf capacitive argon plasma discharges. The ion-induced secondary electrons are accelerated by the high sheath field to strike the opposite electrode and produce a considerable number of secondary electrons that lead to additional ionizing impacts and further increase of the plasma density. Importantly, the presence of excited state species even further enhances the plasma density via excited state neutral and resonant state photon-induced SEE on the electrode surface. The PIC/MCC simulation results show good agreement with the recent experimental measurements in the low pressure range (1–10 Pa) that is commonly used for etching in the semiconductor industry. At the highest pressure (20 Pa) and driving voltage amplitudes 250 and 350 V explored here, the plasma densities from PIC/MCC simulations considering excited state neutrals and resonant photon-induced SEE are quantitatively higher than observed in the experiments, requiring further investigation on high pressure discharges.

Unexpected Penetration of CO Molecule into Zeolitic Micropores Almost Plugged by CuCl via π-Complexation of CO-CuCl.

Carbon monoxide (CO) is a key reactant in several Fischer-Tropsch processes, including those used in light olefin and methanol syntheses. However, it is highly toxic and causes serious poisoning of noble metal catalysts. Thus, a solid adsorbent that can selectively capture CO, especially at low concentrations, is required. In this study, zeolite Y-based adsorbents in which Cu(I) ions occupy the supercage cation sites (CuCl/Y) are prepared via solid-state ion exchange. Volumetric adsorption measurements reveal that the Cu(I) ions significantly enhance CO adsorption in the low-pressure range by π-complexation. Furthermore, unexpected molecular sieving behavior, with extremely high CO/CO2 selectivity, is observed when excess CuCl homogeneously covers the zeolite pore structures. Thus, although CO has a larger kinetic diameter, it can penetrate the zeolite supercage while smaller molecules (i.e., Ar and CO2) cannot. Density functional theory calculations reveal that CO molecules can remain adsorbed in pseudoblocked pores by CuCl, thanks to the strong interaction of C 2p and Cu 3d states, resulting in the high CO/CO2 selectivity. One of the prepared adsorbents, CuCl/Y with 50 wt % CuCl, is capable of selectively capturing 3.04 mmol g-1 of CO with a CO/CO2 selectivity of >3370.

Heat transfer mechanism of electrostatic chuck surface and wafer backside to improve wafer temperature uniformity

Semiconductor manufacturing technology keeps toward scaling down to a few nanometers. To protect the process yield and achieve the success of chip manufacturing, the center-to-edge uniformity of the wafer's temperature has become a crucial parameter. The thermal characteristics of the wafer are dominantly affected by the electrostatic chuck, which is generally used to support the wafer in the manufacturing process. In particular, the backside gas, which passes through the interface between the wafer and electrostatic chuck, is important for cooling the wafer below a critical temperature. The heat transfer via a backside gas can be explained by the layer-bulk model, and its pressure is a key factor to determine the cooling effectiveness. In this paper, a one-dimensional thermal circuit model is established for a system including the wafer, electrostatic chuck, and backside gas to calculate the convective heat transfer coefficient caused by the backside gas. The numerical results showed that the uniformity of the wafer's temperature became worse as the backside gas pressure increased in a low-pressure range but significantly improved above a critical value of the gas pressure. Based on our findings, we concluded that the backside gas pressure should be optimized to improve the uniformity of the wafer temperature.

Melting Curve of Cobalt using Molecular Dynamics Simulation

Molecular dynamics simulation is used to estimate the melting point of cobalt using the embedded atomic model (EAM) potential by heat until melting, void, hysteresis and interface methods. For instance, the estimated melting temperature are 2102 K, 1944.15 K, 1731 K and 1725±25 K using these methods, respectively. Then, the melting points at different pressures are calculated. A graph depicting the variation of melting point with pressure is drawn and compared with the available simulation and experimental results. The melting point at a low-pressure range is similar to the previous diamond anvil cell experiments. Besides, using the Simon equation, we calculated the melting slope at 0 GPa pressure of 36 K/GPa for one phase and 40 K/GPa for two-phase methods.

Pressure Dependence of Superconductivity in a Charge-Density-Wave Superconductor Bi2Rh3Se2

The structural and superconducting properties of a Bi-based compound, Bi2Rh3Se2, are investigated over a wide pressure range. Bi2Rh3Se2 is a superconductor with a superconducting transition temperature, Tc, of 0.7 K. This compound is in a charge-density-wave (CDW) state below 240 K, which implies the coexistence of superconducting and CDW states at low temperatures. Here, the superconducting properties of Bi2Rh3Se2 are studied from the perspective of the temperature dependence of electrical resistance (R) at high pressures (p's). The pressure dependence of Tc of Bi2Rh3Se2 shows a slow increase in Tc at 0-15.5 GPa, and the Tc slowly decreases with pressure above 15.5 GPa, which is markedly different from that of normal superconductors because the value of Tc should simply decrease owing to the decrease in density of states (DOS) on the Fermi level, N(εF), driven by a simple shrinkage of the lattice under pressure. To ascertain the origin of such a dome-like Tc-p behavior, the crystal structure of Bi2Rh3Se2 was explored over a wide pressure range of 0-20 GPa on the basis of powder X-ray diffraction; no structural phase transitions or simple shrinkage of the lattice was observed. This result implies that the increase in Tc against pressure cannot simply be explained from a structural point of view. In other words, a direct relation between superconductivity and crystal structure was not found. On the other hand, the CDW transition became ambiguous at pressures higher than 3.8 GPa, suggesting that the Tc had been suppressed by the CDW transition in a low pressure range. Thus, the findings suggest that for Bi2Rh3Se2, Tc is enhanced through the suppression of CDW transition, which may be reasonable because the CDW-ordered state restrains the charge fluctuation to weaken the electron-phonon coupling and opens the gap to decrease the density of states on the Fermi level. The obtained dome-like Tc-p behavior indicates the possibility of Bi2Rh3Se2 being an exotic superconductor.

Characterization of kerogen molecular structure and its effect on methane adsorption behavior: A comparative study on outcrop and core samples from Longmaxi shale

It has been known that adsorbed gas, mainly CH4, serves as the dominant source of shale gas yield in the middle and later stages of reservoir exploitation. Therefore, it is of great significance to study the microstructure of kerogen (organic matter rich in shale) and its effect on CH4 adsorption characteristics. In this paper, for the first time, a comparative study was conducted to experimentally characterize the microstructure of both outcrop and core kerogen samples from Longmaxi Shale, Sichuan Basin, SW China, using 13C NMR, FTIR, and XPS. Great differences in the chemical structure such as carbon skeleton (e.g., aromaticity, aliphatic branch) and heteroatoms (e.g., distribution and proportion of various types of functional groups) between the two kerogen samples have been identified. Molecular models of the outcrop and core kerogen samples were constructed based on the experimental data, that is, C237H219O21N5S4 for the former and C239H175O27N5S4 for the latter. CH4 adsorption isotherms obtained from gravimetric adsorption test and molecular simulation using proposed kerogen molecular models are in reasonable agreement with each other, especially at low-pressure range. Interestingly, the adsorption capacity of CH4 in the core sample is found higher than that in the outcrop sample under the same condition, indicating the effect of kerogen microstructure on CH4 adsorption behavior. As a result, to precisely evaluate the adsorbed gas content in shale gas reservoirs, it is strongly recommended to use a core sample rather than an outcrop sample.

Simple measurement of the pressure dependence of density for fatty acid esters.

A simple variable-volume method using a polytetrafluoroethylene capsule as a sample cell was applied to measure the pressure dependence of liquid density (ρ). The method was applied to 2-ethylhexyl benzoate at 313, 333, and 353K, and the reproducibility of its volume change was confirmed at pressures of up to 400 MPa. A correction term for the apparatus was also estimated. The uncertainty in the high-pressure ρ measurements was estimated to be ∼±1%. Using the developed method, the ρ values of methyl laurate at pressures of up to 400 MPa at 313 and 333K, as well as those of methyl linoleate at pressures of up to 400 MPa at 313, 333, and 353K, were measured. The results were in good agreement with the literature values in the low-pressure range. The proposed method enables the determination of the high-pressure ρ of liquids with greater ease than previously possible.