Boosting thermal energy transport across the interface between phase change materials and metals via self-assembled monolayers.

Thermal energy storage using phase change materials (PCMs) has great potential to reduce the weather dependency of sustainable energy sources. However, the low thermal conductivity of most PCMs is a long-standing bottleneck for large-scale practical applications. In modifications to increase the thermal conductivity of PCMs, the interfacial thermal resistance (ITR) between PCMs and discrete additives or porous networks reduces the effective thermal energy transport. In this work, we investigated the ITR between a metal (gold) and a polyol solid-liquid PCM (erythritol) at various temperatures including temperatures below the melting point (300 and 350 K), near the melting point (390, 400, 410 K, etc) and above the melting point (450 and 500 K) adopting non-equilibrium molecular dynamics. Since the gold-erythritol interfacial thermal conductance (ITC) is low regardless of whether erythritol is melted or not (<40 MW m-2K-1), self-assembled monolayers (SAMs) were used to boost the interfacial thermal energy transport. The SAM with carboxyl groups was found to increase the ITC most (by a factor of 7-9). As the temperature increases, the ITC significantly increases (by ∼50 MW m-2K-1) below the melting point but decreases little above the melting point. Further analysis revealed that the most obvious influencing factor is the interfacial binding energy. This work could build on existing composite PCM solutions to further improve heat transfer efficiency of energy storage applications in both liquid and solid states.

Bidirectionally promoting assembly order for ultrastiff and highly thermally conductive graphene fibres.

Macroscopic fibres assembled from two-dimensional (2D) nanosheets are new and impressing type of fibre materials besides those from one-dimensional (1D) polymers, such as graphene fibres. However, the preparation and property-enhancing technologies of these fibres follow those from 1D polymers by improving the orientation along the fibre axis, leading to non-optimized microstructures and low integrated performances. Here, we show a concept of bidirectionally promoting the assembly order, making graphene fibres achieve synergistically improved mechanical and thermal properties. Concentric arrangement of graphene oxide sheets in the cross-section and alignment along fibre axis are realized by multiple shear-flow fields, which bidirectionally promotes the sheet-order of graphene sheets in solid fibres, generates densified and crystalline graphitic structures, and produces graphene fibres with ultrahigh modulus (901 GPa) and thermal conductivity (1660 W m-1 K-1). We believe that the concept would enhance both scientific and technological cognition of the assembly process of 2D nanosheets.

Remarkable Thermal Conductivity Reduction of Silicon Nanowires during the Bending Process.

The one-dimensional geometry of silicon nanowire helps to overcome the rigid and brittle nature of bulk silicon and enables it to withstand substantial bending stresses. This provides exciting opportunities for the development of flexible electronics. The bending strain introduces atomic displacement in the lattice structure, which inherently has a significant impact on the thermal conductivity. The strain-dependent thermal conductivity of silicon nanowire is crucial to the thermal management and performance of flexible electronic devices. However, in situ thermal conductivity measurement of bending silicon nanowires remains challenging and unreported due to the varying thermal contact resistances between the sample and sensor/heat sink. In this study, the Raman spectroscopy-assisted steady state thermal conductivity measurement method is coupled with a micromanipulation system to successively monitor the thermal conductivity variation of silicon nanowires during the bending process. The result shows that the thermal conductivity of silicon nanowires steeply decreases 55-78% owing to the strain-induced structural deformation during bending. Furthermore, the proposed in situ thermal conductivity measurement method can also be extended to other nanomaterials.

Superior Large-Signal Piezoelectric Coefficient in Textured NBT-Based Piezoceramics by Template-Induced Structure and Composition Modulation.

The field-induced-phase transition in (Na1/2Bi1/2)TiO3-based lead-free piezoceramics can be facilitated in the ⟨001⟩-crystallographic orientation, and the templated grain growth is an effective method to align polycrystalline ceramics along with specific directions. However, due to the low texturing degree and undesirable composite effect of the added templates, the textured ceramics using the templated grain growth (TGG) method usually require a higher driving field to trigger the phase transition instead. Here, ⟨001⟩-textured (Na0.5Bi0.5)0.935Ba0.065Ti0.978(Fe0.5Nb0.5)0.022O3 ceramics are prepared through a liquid-phase-assisted TGG process at a low sintering temperature (1000 °C), in which the NaNbO3 (NN) templates induce a strong crystallographic anisotropic structure (a high Lotgering factor of 95%) while dissolving into oriented grains. The dissolution of templates acts as a composition doping and contributes to reducing the driving electric field as proven by the phase-field simulation analysis. Furthermore, electrical and structural characterizations reveal that an increased ionic disorder occurs in the textured ceramic, causing highly dynamic polar nanoregions and a larger reversible phase transition. Thanks to the appropriate structure/composition control, the textured ceramic achieves a large d33* value of 907 pm/V at 40 kV/cm. The high-performance lead-free ceramic under low driving electric field benefits the development of multilayer piezoelectric actuators.

Reversible bipolar thermopower of ionic thermoelectric polymer composite for cyclic energy generation.

The giant thermopower of ionic thermoelectric materials has attracted great attention for waste-heat recovery technologies. However, generating cyclic power by ionic thermoelectric modules remains challenging, since the ions cannot travel across the electrode interface. Here, we reported a reversible bipolar thermopower (+20.2 mV K-1 to -10.2 mV K-1) of the same composite by manipulating the interactions of ions and electrodes. Meanwhile, a promising ionic thermoelectric generator was proposed to achieve cyclic power generation under a constant heat course only by switching the external electrodes that can effectively realize the alternating dominated thermodiffusion of cations and anions. It eliminates the necessity to change the thermal contact between material and heat, nor does it require re-establish the temperature differences, which can favor improving the efficiency of the ionic thermoelectrics. Furthermore, the developed micro-thermal sensors demonstrated high sensitivity and responsivity in light detecting, presenting innovative impacts on exploring next-generation ionic thermoelectric devices.

The cross-interface energy-filtering effect at organic/inorganic interfaces balances the trade-off between thermopower and conductivity.

The energy-filtering effect has been widely employed to elucidate the enhanced thermoelectric properties of organic/inorganic hybrids. However, the traditional Mott criterion cannot identify the energy-filtering effect of organic/inorganic hybrids due to the limitations of the Hall effect measurement in determining their carrier concentration. In this work, a carrier concentration-independent strategy under the theoretical framework of the Kang-Snyder model is proposed and demonstrated using PANI/MWCNT composites. The result indicates that the energy-filtering effect is triggered on increasing the temperature to 220 K. The energy-filtering effect gives a symmetry-breaking characteristic to the density of states of the charge carriers and leads to a higher thermopower of PANI/MWCNT than that of each constituent. From a morphological perspective, a paracrystalline PANI layer with a thickness of 3 nm is spontaneously assembled on the MWCNT network and serves as a metallic percolation pathway for carriers, resulting in a 5.56-fold increase in conductivity. The cooperative 3D carrier transport mode, including the 1D metallic transport along the paracrystalline PANI and the 2D cross-interface energy-filtering transport, co-determines a 4-fold increase in the power factors of PANI/MWCNT at 300 K. This work provides a physical insight into the improvement of the thermoelectric performance of organic/inorganic hybrids via the energy-filtering effect.

An Empirical Investigation of Virtual Networking Sites Discontinuance Intention: Stimuli Organism Response-Based Implication of User Negative Disconfirmation.

The study's prime objective is to investigate the user discontinuance intention in the shed of the negative disconfirmation of user expectation. The study has derived the theoretical structure from the expectancy disconfirmation theory (EDT) enacted through the stimuli organism response (SOR) framework to study the actual cause and effect relationship of human behavioral response. To investigate the user discontinuance intention behavioral response, a total of 434 correct and complete answers were shortlisted for analysis. To examine the data set, the study has used the modern partial least square method technique or simply SmartPLS service package to run the structural equation modeling (SEM). Moreover, the study has implied the 80/20 rule run the mediating analysis of the SOR framework. The statistical results show that all three stimuli make significant positive disconfirmation of the user beliefs in terms of dissatisfaction and the anxiety that ultimately leads to the discontinuance intention in virtual network users. Further, these results are validated through the six mediating relationships, which partially mediate the relationship between the stimuli and response. Besides all these findings, this study has made some practical and realistic theoretical and practical implications for both researchers and service-providing managers.

Enhanced Dielectric Energy Storage Performance of 0.45Na0.5Bi0.5TiO3-0.55Sr0.7Bi0.2TiO3/AlN 0-3 Type Lead-Free Composite Ceramics.

Na0.5Bi0.5TiO3 (NBT) ceramic is the promising dielectric material for energy storage devices due to its high maximum polarizability and temperature stability. However, its low breakdown strength limits its application. Here, we prepared 0-3 type composite 0.45Na0.5Bi0.5TiO3-0.55Sr0.7Bi0.2TiO3/x wt % AlN (NBT-SBT/xAlN) to increase the breakdown strength. The effects of the various AlN contents on the phase composition, microstructures, dielectric, and energy storage properties of NBT-SBT were systematically discussed. The result showed that the enhanced energy storage properties were obtained by introducing AlN particles. The NBT-SBT/6AlN composite ceramics showed a high breakdown strength of 360 kV/cm, large energy density of 5.53 J/cm3, and energy efficiency of 90%. Meanwhile, the excellent frequency (10-500 Hz) and temperature stability (25-125 °C) were exhibited with the fluctuation of energy storage within 9% and energy efficiency more than 87%, suggesting that the 0-3 composite NBT-SBT/xAlN is a candidate dielectric material for the dielectric energy storage.

Selectively tuning ionic thermopower in all-solid-state flexible polymer composites for thermal sensing.

There has been increasing interest in the emerging ionic thermoelectric materials with huge ionic thermopower. However, it's challenging to selectively tune the thermopower of all-solid-state polymer materials because the transportation of ions in all-solid-state polymers is much more complex than those of liquid-dominated gels. Herein, this work provides all-solid-state polymer materials with a wide tunable thermopower range (+20~-6 mV K-1), which is different from previously reported gels. Moreover, the mechanism of p-n conversion in all-solid-state ionic thermoelectric polymer material at the atomic scale was presented based on the analysis of Eastman entropy changes by molecular dynamics simulation, which provides a general strategy for tuning ionic thermopower and is beneficial to understand the fundamental mechanism of the p-n conversion. Furthermore, a self-powered ionic thermoelectric thermal sensor fabricated by the developed p- and n-type polymers demonstrated high sensitivity and durability, extending the application of ionic thermoelectric materials.

Parallel anomaly detection algorithm for cybersecurity on the highspeed train control system.

With the rapid development of the high-speed train industry, the high-speed train control system has now been exposed to a complicated network environment full of dangers. This paper provides a speculative parallel data detection algorithm to rapidly detect the potential threats and ensure data transmission security in the railway network. At first, the structure of the high-speed train control data received by the railway control center was analyzed and divided tentatively into small chunks to eliminate the inside dependencies. Then the traditional threat detection algorithm based on deterministic finite automaton was reformed by the speculative parallel optimization so that the inline relationship's influences that affected the data detection order could be avoided. At last, the speculative parallel detection algorithm would inspect the divided data chunks on a distributed platform. With the help of both the speculative parallel technique and the distributed platform, the detection deficiency for train control data was improved significantly. The results showed that the proposed algorithm exhibited better performance and scalability when compared with the traditional, non-parallel detection method, and massive train control data could be inspected and processed promptly. Now it has been proved by practical use that the proposed algorithm was stable and reliable. Our local train control center was able to quickly detect the anomaly and make a fast response during the train control data transmission by adopting the proposed algorithm.

Growth of lithium-indium dendrites in all-solid-state lithium-based batteries with sulfide electrolytes.

All-solid-state lithium-based batteries with inorganic solid electrolytes are considered a viable option for electrochemical energy storage applications. However, the application of lithium metal is hindered by issues associated with the growth of mossy and dendritic Li morphologies upon prolonged cell cycling and undesired reactions at the electrode/solid electrolyte interface. In this context, alloy materials such as lithium-indium (Li-In) alloys are widely used at the laboratory scale because of their (electro)chemical stability, although no in-depth investigations on their morphological stability have been reported yet. In this work, we report the growth of Li-In dendritic structures when the alloy material is used in combination with a Li6PS5Cl solid electrolyte and Li(Ni0.6Co0.2Mn0.2)O2 positive electrode active material and cycled at high currents (e.g., 3.8 mA cm-2) and high cathode loading (e.g., 4 mAh cm-2). Via ex situ measurements and simulations, we demonstrate that the irregular growth of Li-In dendrites leads to cell short circuits after room-temperature long-term cycling. Furthermore, the difference between Li and Li-In dendrites is investigated and discussed to demonstrate the distinct type of dendrite morphology.

Usability Identification Framework and High-Throughput Screening of Two-Dimensional Materials in Lithium Ion Batteries.

Two-dimensional materials (2D materials) show great advantages in high-performance lithium ion battery materials due to the inherent ion channels and rich ion sites. Unfortunately, rare 2D materials own all desired attributes to meet complex scenarios. Further enriching the 2D materials database for lithium ion battery use is of high interest. In this work, we extend the list of candidates for lithium ion batteries based on a 2D material identification theory. More importantly, a usability identification framework leveraging the competitive mechanism between the adsorbability and reversibility of ions on a 2D material is proposed to assist the deeper screening of practicable 2D materials. As a result, 215 2D materials including 158 anodes, 21 cathodes, and 36 solid electrolytes are predicted to be practicable for lithium ion battery use. The comparison between the identified 2D materials with the known ones verifies the reliability of our strategy. This work significantly enriches the choices of 2D materials to satisfy the various battery demands and provides a general methodology to assess the usability of unexploited 2D materials for lithium ion batteries.

Chemical Synthesis and Integration of Highly Conductive PdTe2 with Low-Dimensional Semiconductors for p-Type Transistors with Low Contact Barriers.

Low-dimensional semiconductors provide promising ultrathin channels for constructing more-than-Moore devices. However, the prominent contact barriers at the semiconductor-metal electrodes interfaces greatly limit the performance of the obtained devices. Here, a chemical approach is developed for the construction of p-type field-effect transistors (FETs) with low contact barriers by achieving the simultaneous synthesis and integration of 2D PdTe2 with various low-dimensional semiconductors. The 2D PdTe2 synthesized through a quasi-liquid process exhibits high electrical conductivity (≈4.3 × 106 S m-1 ) and thermal conductivity (≈130 W m-1 K-1 ), superior to other transition metal dichalcogenides (TMDCs) and even higher than some metals. In addition, PdTe2 electrodes with desired geometry can be synthesized directly on 2D MoTe2 and other semiconductors to form high-performance p-type FETs without any further treatment. The chemically derived atomically ordered PdTe2 -MoTe2 interface results in significantly reduced contact barrier (65 vs 240 meV) and thus increases the performance of the obtained devices. This work demonstrates the great potential of 2D PdTe2 as contact materials and also opens up a new avenue for the future device fabrication through the chemical construction and integration of 2D components.

Investigation of Dropwise Condensation on a Super-Aligned Carbon Nanotube Mesh-Coated Surface.

Enhanced vapor condensation is a critical issue for improving the efficiency of energy conversion, thermal management, water recovery, and treatment. Low-energy surfaces incorporating micro/nanoscale roughness have been reported to significantly promote vapor condensation. In this research, the mesh structures of super-aligned carbon nanotube (SACNT) films were prepared by crossing monolayer SACNT films on a copper substrate. Then, the sustaining dropwise condensation was achieved on the SACNT mesh-coated surface. The SACNT mesh-coated surface could obviously enhance the coalescence and sweeping departure of the condensing droplets. Additionally, the measured overall heat transfer coefficient (HTC) of the SACNT mesh-coated surface demonstrated a 36% enhancement compared to that on the bare copper surface. The parallel stacking of SACNT films with different groove structures was also studied, and a 15% enhancement in the HTC was shown as compared with the bare copper surface. Furthermore, we developed a morphology-based model to theoretically analyze the condensation-enhancement mechanism on a SACNT mesh-coated surface. The SACNT surfaces also have advantages of low cost, durability, flexibility, and extensibility. Our findings revealed that the SACNT films could be readily used as vapor condensation-strengthening surfaces, further extending their potential applications to industrial equipment.

Corrosion protection properties of different inhibitors containing PEO/LDHs composite coating on magnesium alloy AZ31.

Corrosion inhibitors 2,5-pyridinedicarboxilate (PDC), sodium metavanadate (SMV) and 5-aminosalicylate (AS) were impregnated into porous PEO coatings respectively via vacuuming process, followed by fast sealing treatment in a Ce containing solution. After that layered double hydroxides (LDHs) based nanocontainers were respectively prepared on them via hydrothermal treatment. In frame of this work it was shown, that sealing effect for the pore was provided by formation of new phase CeO2 on the surface of PEO coatings. And, hydrothermal preparation for preparing LDHs leaded obvious changes in structure and thickness of the coatings. In addition, impregnation of inhibitors was in favor of improving LDHs content in final composite coatings. EIS result indicated that AS/Ce-HT specimen exhibited a best corrosion protection.

Hollow MnFe2O4@C@APBA Nanospheres with Size Exclusion and pH Response for Efficient Enrichment of Endogenous Glycopeptides.

Enrichment and detection of glycopeptides are an important clinical measure for the diagnosis of complex diseases. Enrichment materials play a key role in this process; they must have an effective sample-screening ability to eliminate the interference of nonglycopeptides. In this work, novel hollow MnFe2O4@C@APBA nanospheres (HMCAs) with magnetic and pH responsiveness were prepared for glycopeptide enrichment. The as-prepared composites have a suitable hollow structure and large specific surface area, and the boron hydroxyl group in their cavities can fix or disconnect the hydrophilic groups of the glycopeptides at different pH, so the glycopeptides can be adsorbed or desorbed in a controllable way. Enrichment results showed that the HMCAs exhibited an excellent enrichment performance: ultralow limit of detection (approximately 0.5 fmol µL-1), perfect size-exclusion effect (HRP/BSA, 1:800, w/w), favorable universality (HRP, IgG, and RNase B), and high binding capacity (150 mg/g). In order to verify the application of materials in practice, the HMCAs were used for the analysis of complex samples and it was found that 474 glycopeptides were identified from 210 glycoproteins in three replicate analyses of 2 µL of human serum. The results showed that the HMCAs could be used as a promising enrichment material for glycopeptide characterization in MS-based glycoproteomics and related fields.

Fabrication of a Double-Shell Ag/AgCl/G-ZnFe2O4 Nanocube with Enhanced Light Absorption and Superior Photocatalytic Antibacterial Activity.

Development of highly efficient photocatalysts is a primary goal in the photocatalysis domain among which reusable composites with a synergistic photocatalytic effect have attracted extensive interest. The ability of catalysts to capture light determines their photocatalytic effect, and porous or hollow photocatalysts are more conducive to the entry and reflection of light. The goal of this research is to develop a type of visible-light-driven, double-shell photocatalyst with high antibacterial activity and excellent cycling stability. Photocatalysts were fabricated using hollow graphitized ZnFe2O4 nanospheres (G-ZnFe2O4) as the carrier. After G-ZnFe2O4 was functionalized with a polydopamine (PDA) template layer, Ag nanoparticles (NPs) and cubic AgCl NPs were in situ generated on the surface of the PDA/G-ZnFe2O4 nanospheres successively. Then, the PDA template was removed using KOH solution, and double-shell Ag/AgCl/G-ZnFe2O4 nanocubes (referred to as DAGZNs) with excellent photocatalytic antibacterial activity were constructed. The DAGZNs showed excellent antibacterial properties against Staphylococcus aureus and Escherichia coli. The efficient synergistic photocatalytic antibacterial activity coupled with magnetic separability and recyclability of DAGZNs make them potential for practical application in water purification and environmental protection. The method of designing and synthesizing double-shell structures to enhance photocatalysis may also be extended to synthesis of other photocatalytic and optical materials.

Spontaneous rectification and absolute negative mobility of inertial Brownian particles induced by Gaussian potentials in steady laminar flows.

We study the transport of inertial Brownian particles in steady laminar flows in the presence of two-dimensional Gaussian potentials. Through extensive numerical simulations, it is found that the transport is sensitively dependent on the external constant force and the Gaussian potential. Within tailored parameter regimes, the system exhibits a rich variety of transport behaviors. There exists the phenomenon of spontaneous rectification (SR), where the directed transport of particles can occur in the absence of any external driving forces. It is found that SR of the particles can be manipulated by the spatial position of the Gaussian potential. Moreover, when the potential lies at the center of the cellular flow, the system exhibits absolute negative mobility (ANM), i.e., the particles can move in a direction opposite to the constant force. More importantly, the phenomenon of ANM induced by Gaussian potentials is robust in a wide range of system parameters and can be further strengthened with the optimized parameters, which may pave the way to the implementation of related experiments.

A switched vibrating-hot-wire method for measuring the viscosity and thermal conductivity of liquids.

A method involving a vibrating hot wire is proposed for measuring the viscosity and thermal conductivity of liquids. A platinum wire is bent into a semicircular shape and immersed in the sample liquid in the presence of a static magnetic field. Alternating current is then applied to the wire, causing it to vibrate and generate heat. At low frequency, the frequency response of the vibration is used to calculate the viscosity. At high frequency, the vibration amplitude of the wire is less than the molecular free path, and the thermal conductivity of the sample is obtained from the temperature dependence of the resistance. The proposed method is validated using water, toluene, anhydrous ethanol, and ethanediol as the test samples. The measurement uncertainty is estimated to be 1.5% (k = 1) for thermal conductivity and 0.7% (k = 2) for viscosity.

Laser Flash Raman Spectroscopy Method for Characterizing the Specific Heat of a Single Nanoparticle.

Nanoparticles are widely used in composite materials, nanoscale devices, biological detectors and medical treatment. The thermophysical properties of a single nanoparticle are, therefore, important for both nanotechnology and nanoscience applications. However, property measurements are limited by the spatial resolution of conventional measurement methods, so there are not yet any effective measurement methods to characterize the thermophysical properties of a single nanoparticle. This paper describes a laser flash Raman spectroscopy method for measuring the specific heat of a single nanoparticle supported on a free-standing substrate based on a lumped parameter model for the nanoparticle coupled with a transient 2D thermal conduction model for the suspended substrate. A series of square laser pulses are assumed to be used to heat the supported single nanoparticle in a vacuum. The temperature increases in the single nanoparticle and the suspended substrate are then measured based on their Raman band shifts. The laser absorption coefficients of the nanoparticle and the substrate are then eliminated by comparing the temperature increases measured using different laser pulse widths. The specific heat of the nanoparticle and the thermal contact conductance between the nanoparticle and the substrate can then be extracted by fitting the temperatures of both the nanoparticle and the substrate. Case studies show that the method can accurately measure the specific heat of a single nanoparticle about 100 nm in diameter using ~1 ns pulse widths. The influence of the nanoparticle geometry and the thermophysical properties of the substrate are also discussed.