Burnhamrice0163

The results showed that the electrical conductivity of nanocomposites with 42.5 wt% epoxy was 1500 S/m, and the thermal conductivity was 2.83 W/m K, which was 10.1 times of the neat epoxy. Its thermal resistance was as low as 1% of the pure epoxy. And the mechanical properties of composites were also investigated. These robust and flexible nanocomposites showed prospective applications as thermal interface materials (TIMs) in the electronic industry.Silica aerogel is almost transparent for wavelengths below 8 µm where significant energy is transferred by thermal radiation. The radiative heat transfer can be restricted at high temperature if doped with carbon powder in silica aerogel. However, different particle sizes of carbon powder doping have different spectral extinction coefficients and the doped carbon powder will increase the solid conduction of silica aerogel. This paper presents a theoretical method for determining the optimal carbon doping in silica aerogel to minimize the energy transfer. Firstly we determine the optimal particle size by combining the spectral extinction coefficient with blackbody radiation and then evaluate the optimal doping amount between heat conduction and radiation. Secondly we develop the Monte Carlo numerical method to study radiative properties of carbon-gradient-doped silica aerogel to decrease the radiative heat transfer further. The results indicate that the carbon powder is able to block infrared radiation and thus improve the thermal insulating performance of silica aerogel effectively.A novel positive temperature coefficient (PTC) effect nanocomposite by employing both of polyvinylidene fluoride (PP) and polypropylene (PVDF) intermixture in 1-1 volume ratio as host materials and Ni nanoparticles as conductive filler was prepared via a simple hot compaction method. This study focused on the effect of Ni content on percolation threshold and temperature dependence of direct current (DC) resistivity, as well as frequency dependence of alternating current (AC) resistivity of nanocomposites. This kind of material showed a very small percolation threshold value (about 6.0 vol% of Ni) and a novel strong PTC effect of electrical resistivity between temperatures ranging 150-167 °C, which coincided with the both melting temperatures of PP and PVDF. https://www.selleckchem.com/products/sbe-b-cd.html Close to the percolation threshold, abnormal electrical behavior was observed and interpreted based on the tunnel conductivity between Ni clusters. The curves of the AC resistivity versus the frequency, at different loadings of Ni and at different temperatures, offered a further image of the arrangement of conducting clusters within the host.Phase explosion is a phase change process that occurs during short pulse laser ablation. Phase explosion is a result of homogeneous nucleation of vapor in the superheated melt and results in a rapid transition from a superheated melt to a mixture of vapor and liquid droplets that expand from the surface. The sudden phase transition results in rapid material removal, and if occurring in an ambient gas, causes a shock wave to propagate away from the surface. Measurements of this shock wave are commonly used with the Taylor-Sedov blast wave theory to estimate shock wave pressure and temperature. At low laser fluences the Mach number of the shock wave can be small, resulting in significant errors in pressure and temperature. The paper will demonstrate conditions for which the more general form of the Rankine-Hugoniot relations for thermo-fluid parameters simplifies to the Taylor-Sedov similarity solutions and when the Taylor-Sedov solutions are applicable. The results are compared to experimental shock wave data from the literature to explain why using the Taylor-Sedov blast wave solutions can result in large errors at low Mach numbers.Thermal conductivity of natural rubber has been studied by classic molecular dynamics simulations. These simulations are performed on natural rubber models using the adaptive intermolecular reactive empirical bond order (AIREBO) and the Green-Kubo molecular dynamics (MD) simulations. Thermal conductivity results are found to be very sensitive to the time step used in the simulations. For a time step of 0.1 fs, the converged thermal conductivity is 0.35 W/mK. Additionally the anisotropic thermal conductivity of a specially-modeled natural rubber model with straight molecular chains was studied and values of thermal conductivity parallel to the molecular chains was found to be 1.71 W/mK and the anisotropy, 2Kz/(Kx + Ky), was 2.67.We have developed boiling emulsifier-free emulsion polymerization recipes for the synthesis of monodisperse polystyrene (PS) nanospheres with diameters between ca. 100 and 300 nm. The morphologies of the nanospheres during growth were characterized and the results showed that the PS nanospheres with uniform structures could be synthesized rapidly by modifying the reaction conditions. These nanospheres readily self-assemble into three-dimensionally colloidal photonic crystal film and whose photonic band-stop could be tuned over the entire visible spectral region by altering the sphere diameters.Pure and Ni-doped ZnO nanostructures have been synthesized by a solvothermal process. The structure, morphology and properties of as-synthesized samples have been investigated using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), selected-area electron diffraction (SAED), UV-vis spectrometer as well as by vibrating sample magnetometer (VSM). XRD and EDS studies indicated that the as-prepared products were well-crystallized wurtzite hexagonal structure. The SEM and TEM images show that the individual Zn0.96Ni0.04O nanostructure is composed of several nanorods with average diameter of 200 nm and lengths of 500 nm. The structure and morphology analyses show that Ni doping can influence the nanostructures morphology, but cannot change the crystal structures of ZnO samples. The UV-vis spectra showed that Ni dopant can result in an appreciable blue-shift for the absorption edge of the Ni-doped ZnO samples. The band gap energy of the Zn0.96Ni0.04O nanostructure was about 3.23 eV. By magnetic measurements, it was observed that the pure ZnO nanostructure exhibits diamagnetic property while the sample of 4% Ni shows an obvious ferromagnetic behavior at room temperature due to the formation of solid solution Zn0.96Ni0.04O, sp-d and d-d carrier exchange interactions, and the presence of abundant defects and oxygen vacancies.Heat conduction in nanoscale systems has different behavior from bulk materials, which is applied to develop high performance thermoelectric material. The non-trivial behavior is caused by the ballistic-diffusive transport of heat carriers such as phonons. In this paper, we use the thermomass theory and phonon hydrodynamics model to establish a hydrodynamic model for phonon transport. In nanoscale systems, a Poiseuille flow of phonon gas is formed due to the boundary scattering. The thickness of boundary layer is proportional to the mean free paths of phonon. When the boundary layer thickness is comparable with the whole flow region, strong decrease of effective thermal conductivity happens. This method can serve as a fast evaluation method for nanoscale heat conduction.In this study, the channel size dependence of the shear stress between water droplets and solid walls in nm-order channel was analyzed. We considered a several different-sized and highly hydrophobic channel whose macroscopic contact angle was about 150 degrees. We have evaluated the shear stress and the normal pressure by molecular dynamics simulation. Analyzing shear stress and normal pressure based on the macroscopic model, we have discussed the difference between the macroscopic model based on hydrodynamics and the microscopic model. As a result, in the high hydrophobic case, it became clear that the shear stress depends on the channel size due to the large Laplace pressure. Furthermore, in the case that the channel size was less than 50 A, the normal pressure by the molecular simulation didn't agree with the expected value from the Young-Laplace equation. From this study it was clear that molecular simulation is needed when the channel size is less than 40 A.In this paper, two modified unit cell models, truncated octahedron and cubic array of intersecting square rods with 45-degree rotation, are developed in consideration of the tortuous path of heat conduction in solid skeleton of silica aerogel. The heat conduction is analyzed for each model and the expressions of effective thermal conductivity of the modified unit cell models are derived. Considering the random microstructure of silica aerogel, the probability model is presented. We also discuss the effect of the thermal conductivity of aerogel backbone. The effective thermal conductivities calculated by the proposed probability model are in good agreement with available experimental data when the density of the aerogel is 110 kg/m3.Vertically aligned carbon nanotube (VACNT) array/polymer composite has already been recognized as a promising candidate for advanced thermal pad in thermal management of high-power electronic devices. However, the thermal conductive performance of this composite was limited by the quality of CNTs arrays. In this study, pre-annealing treatment was used to purify CNT arrays and improve thermal conductive performance of VACNT arrays/silicone composite. The thermal conductivity of the composite was enhanced by 34.52% and the thermal interface resistance was also reduced by 65.94% at a pre-annealing temperature of 490 °C for 5 min. The annealing process could remove some amorphous carbon and open the tips of CNTs. As a result, the interfacial compatibility in composite between carbon nanotube and polymer matrix was improved. The cyclic compression and tension performance of VACNT/S160 composite was investigated for further application.The heat generated from tractive lithium ion batteries during discharge-charge process has great impacts on the performances of tractive lithium ion batteries pack. How to solve the thermal abuse in tractive lithium ion batteries pack becomes more and more urgent and important for future development of electrical vehicles. In this work, TiO2, ZnO and diamond nanofluids are prepared and utilized as coolants in indirect liquid cooling of tractive lithium ion batteries pack. The results show that nanofluids present superior cooling performance to that of pure fluids and the diamond nanofluid presents relatively excellent cooling abilities than that of TiO2 and ZnO nanofluids. During discharge process, the temperature distribution of batteries in batteries pack is uniform and stable, due to steady heat dissipation by indirect liquid cooling. link2 It is expected that nanofluids could be considered as a potential alternative for indirect liquid cooling in electrical vehicles.Accurately predicting the effective thermal conductivity of the fibrous materials is highly desirable but remains to be a challenging work. In this paper, the microstructure of the porous fiber materials is analyzed, approximated and modeled on basis of the statistical self-similarity of fractal theory. link3 A fractal model is presented to accurately calculate the effective thermal conductivity of fibrous porous materials. Taking the two-phase heat transfer effect into account, the existing statistical microscopic geometrical characteristics are analyzed and the Hertzian Contact solution is introduced to calculate the thermal resistance of contact points. Using the fractal method, the impacts of various factors, including the porosity, fiber orientation, fractal diameter and dimension, rarified air pressure, bulk thermal conductivity coefficient, thickness and environment condition, on the effective thermal conductivity, are analyzed. The calculation results show that the fiber orientation angle caused the material effective thermal conductivity to be anisotropic, and normal distribution is introduced into the mathematic function.