Wet-resilient graphene aerogel for thermal conductivity enhancement in polymer nanocomposites

Three-dimensional(3 D)graphene-based aerogels have significant potential for adsorption,sensors,and thermal management applications.However,their practical applications are limited by their disorganized structure and ultra-low resilience after compression.Some methods can realize a well-aligned structure,however,they involve high costs and complex technology.Herein,a 3 D graphene hybrid aerogel with an anisotropic open-cell and well-oriented structure is realized by unidirectional freeze casting,which combines the‘soft’(e.g.graphene oxide,Tween-80)and‘hard’(e.g.graphene assembly)components to realize full recovery after flattening.A graphene aerogel annealed at a moderate temperature(200℃)can possess superhydrophilicity and outstanding wet-resilience properties,including after being pressed under40 MPa.Furthermore,the graphene aerogel annealed at a high temperature of 1500℃exhibits excellent thermal conductivity enhancement efficiency in polydimethylsiloxane(PDMS).The resultant nanocomposites clearly demonstrate anisotropic thermal conductivity and promising applications as thermal interface materials.This strategy offers new insights into the design and fabrication of 3 D multifunctional graphene aerogels.

Enhanced ionic conductivity in LAGP/LATP composite electrolyte

Nasicon materials （sodium superionic conductors） such as Li1.5A10.5Ge1.5（PO4）3 （LAGP） and Li1.4Al0.4Til.6（PO4）3 （LATP） have been considered as important solid electrolytes due to their high ionic conductivity and chemical stability. Compared to LAGP, LATP has higher bulk conductivity around 10^-3 S/cm at room temperature; however, the apparent grain boundary conductivity is almost two orders of magnitude lower than the bulk, while LAGP has similar bulk and grain boundary conductivity around the order of 10-4 S/cm. To make full use of the advantages of the two electrolytes, pure phase Li1.5A10.5Ge1.5（PO4）3 and Li1.4A10.4Ti1.6（PO4）3 were synthesized through solid state reaction, a series of composite electrolytes consisting of LAGP and LATP with different weight ratios were designed. XRD and variable temperature AC impedance spectra were carried out to clarify the crystal structure and the ion transport properties of the composite electrolytes. The results indicate that the composite electrolyte with the LATP/LAGP weight ratio of 80：20 achieved the highest bulk conductivity which shall be due to the formation of solid solution phase Li1.42Alo.42Geo.3Ti1 .28（PO4）3, while the highest grain boundary conductivity appeared at the LATP/LAGP weight ratio of 20：80 which may be due to the excellent interfacial phase between Li1＋xAlxGeyTi2-x-y（PO4）3/LATE All the composite electrolytes demonstrated higher total conductivity than the pure LAGP and LATE which highlights the importance of heterogeneous interface on regulating the ion transport properties.

Thermal Property Enhancement of a Novel Shape-Stabilized Sodium Acetate Trihydrate-Acetamide/Expanded Graphite-Based Composite Phase Change Material

Phase change materials(PCMs)are a kind of highly efficient thermal storage materials which have a bright application prospect in many fields such as energy conservation in buildings,waste heat recovery,battery thermal management and so on.Especially inorganic hydrated salt PCMs have received increasing attention from researchers due to their advantages of being inexpensive and non-flammable.However,inorganic hydrated salt PCMs are still limited by the aspects of inappropriate phase change temperature,liquid phase leakage,large supercooling and severe phase separation in the application process.In this work,sodium acetate trihydrate was selected as the basic inorganic PCM,and a novel shape-stabilized composite phase change material(CPCM)with good thermal properties was prepared by adding various functional additives.At first,the sodium acetate trihydrate-acetamide binary mixture was prepared and the melting point was adjusted using acetamide.Then the binary mixture was incorporated into expanded graphite to synthesize a novel shape-stabilized CPCM.The thermophysical properties of the resultant shape-stabilized CPCM were systematically investigated.The microscopic morphology and chemical structure of the obtained shape-stabilized CPCM were characterized and analyzed.The experiment results pointed out that acetamide could effectively lower the melting point of sodium acetate trihydrate.The obtained shape-stabilized CPCM modified with additional 18%(mass fraction)acetamide and 12%(mass fraction)expanded graphite exhibited good shape stability and thermophysical characteristics:a low supercooling degree of 1.75℃and an appropriate melting temperature of 40.77℃were obtained;the latent heat of 151.64 kJ/kg and thermal conductivity of 1.411 W/(m·K)were also satisfactory.Moreover,after 50accelerated melting-freezing cycles,the obtained shape-stabilized CPCM represented good thermal reliability.

水为洗脱剂的静电离子色谱-增强电导检测法测定常见无机阴离子(英文)

To enhance the conductivity detection sensitivity of common anions(Na-anions) in electrostatic ion chromatography(EIC) by elution with water,a conductivity enhancement column packed with strong acid cation exchange resin in the H-form was inserted between an octadecyl silane(ODS)-silica separation column modified with zwitterionic surfactant(CHAPS: 3-{(3-cholamidopropyl)-dimethylammonio}propanesulfonate) and a conductivity detector.Specifically,the Na-anion pairing is converted to H-anion pairing after the EIC separation and then detected sensitively by the conductivity detector.The effects of conductivity enhancement and suppression in the EIC by the enhanced conductivity detection were characterized for the common strong acid anions such as SO2-4,Cl-,NO-3,I-and ClO-4 and weak acid anions such as F-,NO-2,HCOO-,CH3COO-and HCO-3.For the conductivity enhancement effect in the EIC,it is found that the conductivity of measured for all strong acid anions(Na-anions) was enhanced according to the theoretical conductivity predicted for H-anions and that of the measured for weak acid anions was suppressed depending on their pKa of H-anions.For the calibration linearity in the EIC,the strong acid anions were linear(r2=0.99-1.00) because the degree of dissociation is almost 1.0 over all the concentration range and that of the weak acid anions was non-linear because the degree of dissociation decreased by increasing the concentration of the weak acid anions.In conclusion,the EIC by enhanced conductivity detection was recognized to be useful only for the strong acid anions in terms of conductivity detection and calibration linearity.

Thermal Conductance of Cu and Carbon Nanotube Interface Enhanced by a Graphene Layer

Thermal conduetances between Cu and graphene covered carbon nanotubes （gCNTs） are calculated by molecular dynamics simulations. The results show that the thermal conductance is about ten times larger than that of Cu- CNT interface. The enhanced thermal conductance is due to the larger contact area introduced by the graphene layer and the stronger thermal transfer ability of the Cu-gCNT interface. From the linear increasing thermal conductance with the increasing total contact area, an effective contact area of such an interface can be defined.

Conductivity modulation enhanced lateral IGBT with SiO_2 shielded layer anode by SIMOX technology on SOI substrate

A new lateral insulated-gate bipolar transistor（LIGBT） with a SiO_2 shielded layer anode on SOI substrate is proposed and discussed.Compared to the conventional LIGBT,the proposed device offers an enhanced conductivity modulation effect due to the SiO_2 shielded layer anode structure which can be formed by SIMOX technology.Simulation results show that,for the proposed LIGBT,during the conducting state,the electron-hole plasma concentrations in the n-drift region are several times larger than those of the conventional LIGBT;the conducting current is up to 37% larger than that of the conventional one.The enhanced conductivity modulation effect by SiO_2 shielded layer anode does not sacrifice other characteristics of the device,such as breakdown and switching,but is compatible with other optimized technologies.

Processing Compressed Expanded Natural Graphite for Phase Change Material Composites

Phase change materials(PCMs)are used in various thermal energy storage applications but are limited by their low thermal conductivity.One method to increase conductivity involves impregnating organic PCMs into highly porous conductive matrix materials.Of these materials,compressed expanded natural graphite(CENG)matrices have received the most attention.Despite this attention,the effect that CENG processing has on PCM saturation and overall matrix thermal conductivity has not been fully investigated.Therefore,the effect of the heat treatment process used to expand intercalated graphite flakes is evaluated here.Higher heat treatment temperatures yielded higher saturation rates and overall saturation at similar matrix porosities.For example,increasing temperature from 300℃to 700℃resulted in approximately 60%-70%increase in pore saturation after 100 minutes of soaking.The exposure time to heat treatment had less of an effect on PCM saturation.The exposure time had negligible effect above 30 min and above 500℃heating temperatures.However,because the expanded graphite was found to oxidize around 700℃,the use of longer exposure time in manufacturing applications can be beneficial if a shortened impregnation time is needed.Heat treatment conditions did not impact thermal conductivity.The composite latent heat of fusion was also reduced approximately proportionally to the PCM mass fraction.A local maximum in axial thermal conductivity was observed at around 83%porosity,which is similar to previous studies.The observed conductivity at this maximum was a factor of 81 times greater than the conductivity of the PCM.

Removing the Destructive Quantum Interference in Cross Conjugation System by Structural Restraint

Understanding the quantum effect in the cross-conjugated system is of fundamental significance in molecular electronics.In this study,four molecules Xa-O,Xa,BP and BP-O were synthesized to investigate the destructive quantum interference(DQI)of a carbonyl bridge.The single-molecule conductance measured by the scanning tunneling microscope break junction(STM-BJ)technique demonstrates an increase in the conductance from molecule BP-O to molecule Xa-O as the cross-conjugated system is extended.Theoretical calculations show that the explicit DQI feature is presented in BP-O but absent in Xa-O,which indicates the removal of DQI in the restrained structures and results in the conductance enhancement in Xa-O.

Bending-Induced Conductance Increase in Individual Semiconductor Nanowires and Nanobelts

Reliable ohmic contacts were established in order to study the strain sensitivity of nanowires and nanobelts.Significant conductance increases of up to 113%were observed on bending individual ZnO nanowires or CdS nanobelts.This bending strain-induced conductance enhancement was confirmed by a variety of bending measurements,such as using different manipulating tips(silicon,glass or tungsten)to bend the nanowires or nanobelts,and is explained by bending-induced effective tensile strain based on the principle of the piezoresistance effect.