Conductivity Of Liquids Research Articles

Design of Flexible Pressure Sensor Applied to Mechanical Gripper

Flexible electronic devices have emerged as a novel and popular research direction in the field of artificial intelligence, in which flexible sensor is an indispensable branch of flexible devices. In this article, a flexible pressure sensor is developed based on a liquid metal microchannel, which has the advantages of convenient measurement and easy integration. The sensor adopts Dragon skin 20 as the sensor matrix and Ga-In-Sn alloy as the conductive liquid. Meanwhile, there are two kinds of sensor structures are introduced which are the sensor only has a sensing layer and the sensor with an amplification layer. Through comparison of mechanical simulation models, the results suggest that adding the amplification layer structure can make the channel deformation more obvious, and the resistance change will be larger under the identical pressure, which indicating that adding amplification layer can effectively improve the sensitivity of sensor. We further demonstrate the basic characteristics of the sensor, and finally, it is proved by experiments that it can be installed on the mechanical gripper used to sense the pressure. This indicates that the flexible pressure sensor has relatively high sensitivity and the resistance value of sensor can well change with the size of pressure, which also indicates that the flexible pressure sensor has the possibility of applying in orchard manipulator picking for grasping force sensing to prevent peel breakage.

Electronic and ionic properties of sintered cathode of LiNi0.6Mn0.2Co0.2O2 (NCM622)

AbstractLi‐ion solid‐state batteries have the potential for high energy densities and improved safety. Oxidic all solid‐state batteries require co‐sintering of the Li‐ion conductive solid electrolyte, the active electrode material, and an electronic conductive additive to give a composite electrode. A first step for the realization of this complex system is the study of the sintering behavior of the active material itself as a single‐phase component and to investigate the electrochemical activity as well as the electronic properties after heat treatment. In this study monolithic NCM622 cathodes with a thickness of about 90 μm were sintered at temperatures up to 900°C by using a low‐melting glass as sintering additive. For these ceramic cathodes sintered at T = 800°C, an electronic conductivity of 3.0 × 10–3 S cm–1 and six orders of magnitude lower Li‐ion conductivity of about 10–9 S cm–1 were determined by DC conductivity measurement. To investigate the electrochemical performance of the sintered cathode material, the porous microstructure was infiltrated with liquid electrolyte and a charging capacity of 140 mAh g–1 (92% of the theoretical capacity) was measured with C/50 cycling rate. In comparison, the electrochemical performance without infiltration of a Li‐ion conductive liquid was tested with polyethylene oxide as polymeric separator. With these measurements the ability of the sintered cathode to charge/discharge as well as to provide sufficient high electronic conductivity has been demonstrated.

On Increments of Instability of Capillary Waves on the Surface of a Charged Electrically Conductive Jet Moving Relative to the Medium

For the first azimuthal modes of a charged jet of an electrically conductive incompressible liquid, the increments of the instability of capillary waves, their magnitude and dependence on the physical parameters of the task, the position of the instability zones on the set of wave numbers were investigated. In the conducted studies, it was found that the widths of the ranges of wave numbers of un-stable waves and the values of instability increments depend on the square of the intensity of an electrostatic field and the square of the speed of relative motion, increasing at a higher field strength and speed. In the absence of a charge on the jet, bending instability has a threshold character, and it is realized not at any low speed value but starting from some final value of it.

Specific Features of Detection of Electric Characteristics of Conductive Liquids Using Normal Acoustic Waves

Specific Features of Detection of Electric Characteristics of Conductive Liquids Using Normal Acoustic Waves

Dual‐Enhanced Effect of Ionic Liquid Incorporation on Improving Hybrid Harvesting Properties of Solar and Raindrop Energy

AbstractUbiquitous environmental energy has become an important energy source for ensuring long‐lasting operation of unattended monitoring systems. However, several technical bottlenecks remain for achieving improved collection performance of environmental energy. Herein, a transparent composite film comprising micro‐pyramid arrays (mp‐arrays) and a conductive ionic liquid (IL) based on polydimethylsiloxane (PDMS) is innovatively generated as a difunctional layer that acts as an antireflective coating for solar cells and an enhanced triboelectric layer for the raindrop‐harvesting triboelectric nanogenerator (RH‐TENG). The regular mp‐arrays fabricated using the template transfer technology according to the matched refractive index between IL and PDMS effectively inhibit the surface reflection and improve the light trapping ability of solar cells. Owing to a significant increase in transmittance, the power conversion efficiency of the solar cell is enhanced by 10.92% owing to the IL@PDMS coating with mp‐arrays (mp‐IL@PDMS). Further, the conductive IL significantly improves the dielectricity of PDMS film. Due to the improved dielectric constant, increased aspect ratio, and excellent hydrophobicity, the output voltage and current of the RH‐TENG with mp‐IL@PDMS are enhanced by ≈24‐ and 44‐fold, respectively. Overall, this study, which is based on the incorporation of transparent conductive IL, provides a new technical path for efficient multiclimate energy harvesting.

Membraneless Electrolyzers for the Conversion of Brine into High-Value Products

Desalination offers an approach to address the shortage of fresh water, however, the main concern is the generation of reject brine or concentrated saltwater that contains organic compounds, metals, and contaminants. Membraneless electrolyzers present a viable solution to convert the reject brine into H2 and O2, while simultaneously splitting it into acidic (HCl) and base (NaOH). They transport ions through a highly conductive liquid electrolyte instead of a membrane. The lack of a separator allows for operation in a wide range of pH environments and inhibits degradation and fouling issues found in conventional electrolyzers. In this study, a membraneless electrolyzer was 3D printed and a Pt|porous electrode and planar Pt|Ti-foil were used as the cathode and anode, respectively. The electrodes are a key component since that is where the reactions of interest (hydrogen and oxygen evolution reactions) occur. Hence, the distribution of Pt onto a carbon foam substrate in a uniform and asymmetric pattern was studied. Kinetic overpotentials and mass transfer limitations decrease when Pt nanoparticles are in a uniform pattern since it increases active sites resulting in faster kinetics. However, asymmetric catalyst placement controls where gaseous bubbles are generated and therefore decreases product crossover. The device’s ability to generate acid and base at different applied current densities and volumetric flow rates was investigated whereby at high current densities and low volumetric flow rates, the pH differential of the effluent streams broadens. However, at this condition, product crossover increases. Future work involves using in situ high-speed videography to determine the critical Damköhler number to unravel the achievable maximum pH while minimizing product cross-over.

Role of Agent Molecules for Low-Temperature Activation of Lithium-Ion Transport for Solid-State Polymer Electrolytes

The realization of all-solid-state lithium-ion batteries (LIBs) is often considered as the final challenge in the development of LIBs. Replacing Li-ion conductive liquid electrolytes with high-performance solid-state electrolytes is indispensable for the development of all-solid-state LIBs. Solid-state electrolytes under development fall into three classes: polymers, oxides, and sulfides. Polymer-based electrolytes have advantages over oxides and sulfides, such as formation of low-resistance electrolyte/electrode interfaces, good processability, and high energy-density owing to low density. Therefore, polymer-based solid-state electrolytes are being developed in both industry and academia as a practical route for realizing high-capacity LIBs.[1]For application in commercial LIBs, the electrolyte should have an ionic conductivity higher than 10-4 S/cm at room temperature. Conventional solid polymer electrolytes, such as polyethylene oxide (PEO)-based electrolytes, do not meet the performance requirements due to insufficient ionic conductivity in the range of 10-6 to 10-5 S/cm. Recently, polyphenylene sulfide (PPS)-based polymer electrolytes have been reported to yield ion conductivities as high as those of liquid electrolytes over a wide temperature range (> 1.0 × 10-4 S/cm at 25 °C, > 1.0 × 10-3 S/cm at 80 °C, and > 1.0 × 10-3 S/cm at −40 °C).[2] These electrolytes consist of base polymer chains containing PPS, Li salts that can dissociate into cations and anions, and neutral agent molecules. However, the detailed Li-ion transport mechanism in terms of the respective roles of the molecular components of PPS electrolytes is yet to be determined. This limited understanding hinders the further improvement of PPS-based electrolytes.In this study, we perform a series of first-principle calculations and demonstrate that certain types of neutral molecules (so-called agent molecules) accelerate solid-state lithium-ion migration when mixed with lithium salts.[3] We find that the intermolecular interaction in a selected agent-molecule/lithium-salt binary system is governed by the strong coupling between lithium and oxygen atoms. Upon the addition of agent molecules, the anionic species surrounding the lithium of lithium salts is replaced by the agent molecules. The resulting weakened Coulomb energy coupling between lithium and oxygen atoms is determined to be a key factor in enabling fast lithium-ion migration via facile dissociation of lithium salts and subsequent formation of ion-hopping sites in the form of lithium-free oxygen-cages. The structure-based interpretation of agent molecules suggests that neutral molecules with functional groups which enhance chemical resonance can be selected as potential agent molecules. We believe that the results obtained in this study serve as a theoretical basis for the future development of solid-state polymer electrolytes, particularly toward mitigating the dependence of lithium-ion transport on the movement of polymer chains.

Modeling and design of dielectric elastomer actuated tunable lens with dual chambers

As a novel kind of focus tunable lens, dielectric elastomer actuated liquid lens has a compact structure, fast response, low cost, and outstanding tunability, which makes it attract extensive attention. Here, we present a computational model of a dielectric elastomer actuated lens with dual chambers that consist of three elastic membranes and two disconnected chambers filled with conductive and transparent liquid. The intermediate layer actuated by applied voltage deforms, changing the curvature of passive membranes and obtaining a new focal length. The simulation results calculated by the shooting method with two guessed values agree well with the experimental results. Based on this model, the effects of a set of parameters, including chamber radii, shear modulus, permittivity, prestretch ratios, and injected liquid volumes, on the tuning performance of the lens are analyzed. It is found that, by regulating the liquid volume in each chamber, both the initial focal length and the tuning range can be adjusted easily. Under the condition with specific liquid volumes, the lens possesses both positive and negative focal length during voltage actuation, indicating promoted tuning performance, which is acclaimed for optimal design.

Experimental Investigations on Heat Transfer Characteristics of Direct Contact Liquid Cooling for CPU

Cooling systems can effectively enable information and communication technology (ICT) equipment to utilize power more efficiently in data centers (DCs). Two-phase cooling provides a potential method to cool CPUs and other electronics and involves submerging them in a thermal conductive dielectric liquid or coolant. In this study, an innovative cooling structure and a two-phase immersion cooling system procedure are presented. The CPU is directly submerged in an engineered fluid, and an experimental test is conducted to obtain the boiling heat transfer and energy consumption data. A prediction equation for saturated boiling HTC in the pool, based on the influence of the characteristics of the heat transfer surface of the CPU and the physical parameters, is proposed. The average partial power usage effectiveness (pPUE) value of the proposed system is 1.036, indicating a significantly improved energy conservation effect compared to conventional air cooling systems. Studies have shown that direct-touch heat dissipation is suitable for supercomputer server CPU heat dissipation with low heat flux density, while for high-density CPU heat dissipation, it is easy to reach the maximum temperature limit of the CPU, thereby reducing the CPU frequency.

Muscle-Mimetic Highly Tough, Conductive, and Stretchable Poly(ionic liquid) Liquid Crystalline Ionogels with Ultrafast Self-Healing, Super Adhesive, and Remarkable Shape Memory Properties.

Here, we report a simple method for preparing muscle-mimetic highly tough, conductive, and stretchable liquid crystalline ionogels which contains only one poly(ionic liquid) (PIL) in an ionic liquid via in situ free radical photohomopolymerization by using nitrogen gas instead of air atmosphere. Due to eliminating the inhibition caused by dissolved oxygen, the polymerization under nitrogen gas has much higher molecular weight, lower critical sol-gel concentration, and stronger mechanical properties. More importantly, benefiting from the unique loofah-like microstructures along with the strong internal ionic interactions, entanglements of long PIL chains and liquid crystalline domains, the ionogels show special optical anisotropic, superstretchability (>8000%), high fracture strength (up to 16.52 MPa), high toughness (up to 39.22 MJ/m3), and have ultrafast self-healing, ultrastrong adhesive, and excellent shape memory properties. Due to its excellent stretchability and good conductive-strain responsiveness, the as-prepared ionogel can be easily applied for high-performance flexible and wearable sensors for motion detecting. Therefore, this paper provides an effective route and developed method to generate highly stretchable conductive liquid crystalline ionogels/elastomers that can be used in widespread flexible and wearable electronics.

Preparation of thermally conductive flexible liquid silicone rubber composites by magnetic field‐induced self‐assembly of Fe3O4@C

AbstractEfficient heat dissipation is very crucial for the performance, service life, and reliability of modern electronic devices. It is very challenging to improve heat dissipation efficiency through innovative material structure design. Therefore, in the work, dopamine (PDA) is used to coat the surface of graphite (C) with its excellent surface coating modification ability, so that the C surface has oxygen‐containing groups to change its electronegativity, and Fe2+ and Fe3+ in the solution are attracted to the surface of C, and then in situ redox reaction occurs on the surface of C to generate magnetic graphite (Fe3O4@C). Fe3O4@C is uniformly dispersed into liquid silicone rubber (LSR) by solution blending, and Fe3O4@C performs integral directional filling in the LSR under the action of magnetic field (B = 140 mT), thus preparing Fe3O4@C/LSR composites. Through magnetic field orientation, the thermal conductivity of Fe3O4@C/LSR composites reach 1.25 W/m·K when the content of Fe3O4@C is 100 phr, which is 410% higher than that of pure LSR (0.2447 W/m·K). Infrared thermal imaging test shows that Fe3O4@C/LSR composites has good heat dissipation performance, Fe3O4@C/LSR composites have shown great potential in terms of flexibility and high thermal conductivity.

Low-Voltage Activation Based on Electrohydrodynamics in Positioning Systems for Untethered Robots

In recent years, untethered soft robots, free of the lines that restrict their mobility, have been studied extensively. Our research team has been focusing on the electrohydrodynamic phenomena (EHD) as a driving mechanism for untethered robots. EHD is a phenomenon in which a flow is generated by applying a high voltage to a dielectric liquid. We propose a method to drive a robot in an untethered manner using EHD by vertically stacking two types of liquids: conductive and dielectric. This method is simpler, more energy-efficient, and quieter than conventional systems. Although a lower voltage would prevent the enlargement of the system by limiting the electronic components, the generation of EHD requires a high voltage. Therefore, in this study, to realize the low voltage drive of untethered robots dominated by the electrostatic actuator, we tackled the reduction of the driving voltage by investigating the phenomenon. As a result, we achieved low voltage driving at 15 V and successfully drove with off-the-shelf batteries (18 V). We also investigated the output current flowing through the system to reduce power consumption. Therefore, in addition to improving the energy efficiency of the system, we confirmed that the difference of the generated current depended on the thickness of the dielectric liquid and the concentration of the conductive liquid.

Electropolymerization of Pyrrole-Based Ionic Liquids on Selected Wireless Bipolar Electrodes.

This paper describes an electropolymerization-based on-chip valving system, accomplished by electrosynthesis of conductive polymeric ionic liquid (CPIL) films at selected points within an array of bipolar electrodes (BPEs), in which each of these wireless electrodes spans an IL-aqueous phase boundary. The low viscosity and high hydrophobicity of the CPIL precursor allow it to be patterned by established microfluidic methods. This advancement has the potential to impact microscale analysis because it allows on-demand creation of solid CPIL microstructures at locations specified by microfluidics, phase boundaries, and electrode potentials. To achieve this outcome, an imidazolium-based IL was functionalized with a pyrrole moiety, and the viscosity was tuned by choosing the appropriate counterion to form a CPIL with the desired viscosity, hydrophobicity, and oxidation potential. This monomer species was then introduced into a microfluidic device, which was prefilled with an aqueous buffer solution. The device comprised many parallel microchannels lined with nanoliter-scale chambers. BPEs interconnected the channels such that the BPE tips were each aligned to a chamber opening. The electrodes contacting the outermost channels were connected directly to a power supply and functioned as driving electrodes. The CPIL displaced the buffer in the channels and established a phase boundary at the opening of each chamber, thereby digitizing the aqueous phase. Finally, an alternating square waveform (under mode 1) was applied for 5 min to yield immobilized polymer films at a location defined by the BPE poles. In total, three modes were developed and three corresponding polymer film patterns were formed. Under mode 2, a DC power supply was used to achieve a dissymmetrical polymer film pattern, and, under mode 3, a regional polymer film pattern was formed under an AC potential with a DC offset. Our preliminary results demonstrate that the generated polymer films are immobile and sufficiently thick to seal the chambers at room temperature over the duration of our observation window (50 min), and this seal is maintained even at elevated temperatures that induce partial evaporation of the chamber contents. A key point is that this method is compatible with a preceding step─dielectrophoretic capture of single melanoma cells within the nanoliter-scale chambers.

Mechanically strong and highly ion conductive graphene oxide liquid crystal film containing the poly(amic acid) salt

Mechanically strong and highly ion conductive graphene oxide liquid crystal film containing the poly(amic acid) salt

Measurement of complex shear viscosity up to 3 GHz using an electrodeless AT-cut quartz transducer

An experimental method is proposed to determine the frequency-dependent complex shear viscosity of liquids based on the quartz crystal microbalance with dissipation method. An AT-cut quartz transducer without metal electrodes is immersed in a sample liquid and the transducer is electrically coupled to the circuit through the dielectric response of the sample itself. After correcting for the apparent change in the resonance properties due to the dielectric coupling of the sample, our method is able to determine the viscosity of liquids of high polarity and low viscosity at frequencies as high as 3 GHz. The method was then applied to ethylene glycol and the viscoelastic relaxation in the GHz regime was observed. Furthermore, it was also applied to room-temperature ionic liquids to show that the dielectric correction of the resonance properties is valid for conductive liquids.

3D Architecturing Strategy on the Utmost Carbon Nanotube Fiber for Ultra‐High Performance Fiber‐Shaped Supercapacitor

AbstractFiber‐shaped supercapacitors (FSSCs) are the most state‐of‐the‐art power supplies suitable for wearable devices, but the intrinsically limited cylindrical space of fibers restricts their high electrochemical performance, which must be overcome with a delicate and systematic architectural process. Here, a simple but effective 3D architectural strategy for fabricating FSSCs with high performance and flexibility is proposed. Highly conductive liquid crystal spun carbon nanotube fiber (CNTF) is an excellent 1D core fiber for the electrophoretic deposition of graphene oxide (GO). The deposited GO forms a vertical 3D structure on the CNTF (VG@CNTF), which can be successfully preserved by a consecutive coating of pseudocapacitive active materials onto the surface of VG. Notably, a solid‐state asymmetric FSSC shows an outstanding performance of 65 Wh kg−1 at 100 kW kg−1 and exceptional stability and flexibility (capacitance retention of 98.60% at bending angles of 90° and 93.1% after 5000 bending cycles). This work can provide new insight into the development of high‐performance FSSCs for practical wearable applications.

Flexible Electronic Catheter Based on Nanofibers for the In Vivo Elimination of Circulating Tumor Cells.

Clearing circulating tumor cells (CTCs) that are closely related to cancer metastasis and recurrence in peripheral blood helps to reduce the probability of cancer recurrence and metastasis. However, conventional therapies aiming at killing CTCs always cause damage to normal blood cells, tissues, and organs. Here, we report a flexible electronic catheter that can capture and kill CTCs via irreversible electroporation (IRE) with high efficiency. The flexible electronic catheter is assembled from nanofibers (NFs) with liquid metal-polymer conductor (MPC) electrodes. The NFs were modified with an epithelial cellular adhesion molecule (EpCAM) antibody on the surface to improve specific biorecognition and cell adhesion. Whole-body blood can be screened by the catheter repeatedly, during which the EpCAM antibody on a nanofiber can enrich CTCs to the surface of the catheter. Taking advantage of the high specific surface area, the capture efficiency of NF-based catheters for CTCs is 25 times higher than previously reported cases. Furthermore, the number of nonspecifically captured WBCs is less than 10 per mm2 areas of the catheter, compared to their original large number of 4-11 × 106 mL-1 of whole blood, showing good specificity of the flexible electronic catheter. The flexible and biocompatible MPC electrodes have a high killing efficiency of 100% for the captured CTCs in a rabbit model. No noticeable hematologic index and morphological changes of the vessels and major organs were observed, indicating that this electronic catheter had good biocompatibility. The present functional electronic catheter offers an alternative strategy for improving the efficiency of clinical cancer therapy.

Liquid metal droplet shuttling in a microchannel toward a single line multiplexer with multiple sensors

Multiple sensors and actuators integrated in a small space, especially an elongated thin structure, require equivalent number of signal lines between microdevices, but there is limited space for signal wires. Thus, we propose a mechanism using a single microchannel where a liquid metal droplet moves and shuttles. A shuttling droplet switches multiple terminals of signal lines along a microchannel based on a traditional switching mechanism using a liquid metal droplet. Electrically conductive gallium alloy liquid metals (Galinstan) can flow in a microchannel due to their fluidity. The terminals consist of opposing electrode pairs in a microchannel. A change in a variable impedance connected to a terminal as a pseudo sensor can be read when a droplet flows in and connects electrode pairs. This paper presents switching and addressing objective terminals of chromium electrodes by a shuttling conductive droplet (500 µm in diameter and 10 mm long) in a microchannel (500 µm in diameter and 100 mm long). A demonstrated simple mechanism enables communication between multiple microdevices along a microchannel. We anticipate wide application of proposed mechanism toward a multiplexer, especially in microfluidic devices because of the advantages of utilizing microchannels as common microstructures for both microdevices and signal lines.

Estimation of a eutectic composition of imidazolium chloride ionic liquids using video imaging and impedance methods

The eutectic temperature Te and composition Xe of binary systems composed of three ionic liquids, 1-ethyl-3-methylimidazolium chloride ([C2mim]Cl), 1-methyl-3-propylimidazolium chloride ([C3mim]Cl), and 1-butyl-3-methylimidazolium chloride ([C4mim]Cl), were estimated using a video imaging method, in which the formation of a liquid phase on solidified ionic liquids at a given composition stored in a vial was detected from time-lapse images taken during temperature scanning. The advantage of this method is that multiple samples (five samples in this study) could be measured simultaneously, whereas its disadvantage is a less accurate determination of the melting point compared with the conventional differential scanning calorimetry (DSC) method. The Te and Xe of [C2mim]Cl–[C3mim]Cl, [C2mim]Cl–[C4mim]Cl, and [C3mim]Cl–[C4mim]Cl binary systems were roughly estimated. Furthermore, the Te of the ternary system of the [C2mim]Cl–[C3mim]Cl–[C4mim]Cl with limited compositions was estimated, which was lower than that of the binary systems. The transition of the electrochemical impedance of [C2mim]Cl ionic liquids was also measured using two Pt wire electrodes as a function of temperature. The differential inversed resistance curve (dR–1/dT)-T shows an obvious peak corresponding to the phase transition from a low conductive solid phase to a highly conductive liquid phase. This peak was comparable with the peak obtained in the DSC measurement.

A Highly Stretchable and Permeable Liquid Metal Micromesh Conductor by Physical Deposition for Epidermal Electronics.

Stretchable electronics allow functional devices to integrate with human skin seamlessly in an emerging wearable platform termed epidermal electronics. Compliant conductors represent key building components for functional devices. Among the various candidates, gallium-based liquid metals stand out with metallic conductivity and inherent deformability. Currently, the widespread applications of liquid metals in epidermal electronics are hindered by the low steam permeability and hence unpleasant wearing perceptions. In this study, a facile physical deposition approach is established to create a liquid metal micromesh over an elastomer sponge, which exhibits low sheet resistance (∼0.5 Ω sq-1), high stretchability (400% strain), and excellent durability. The porous micromesh shows textile-level permeability to achieve long-term wearing comfort. The conformal interaction of the liquid metal micromesh with the skin gives rise to a low contact impedance. An integrated epidermal sensing sleeve is demonstrated as a human-machine interface to distinguish different hand gestures by recording muscle contractions. The reported stretchable and permeable liquid metal conductor shows promising potentials in next-generation epidermal electronics.