Microstructure and mechanical properties of BT/PVTC composite ferroelectric thin films.

CONTEXT: Ferroelectric ceramic polymer composites have become the preferred electrocaloric materials due to their light weight and high polarization strength. But the mechanical properties were desired to be improved. In this study, the polyvinylidene fluoride trifluoro ethylene chloride (PVTC) and barium titanate (BT) composites were prepared, and the microstructure and mechanical properties were investigated by molecular dynamics simulations and experiments. It was found that with the increase of BT ceramic content in the composites, the yield stress is significantly reduced, which can be reduced by 16.07%. By comparing with the experimental data, the agglomeration and stress mechanism of the composites were proposed. METHOD: The microstructure of the composite was analyzed using radial distribution function, self-diffusion coefficient, and glass transition temperature. The agglomeration mechanism of the composite was revealed from the microscopic point of view, and the rationality of the agglomeration behavior was verified by experiments. The calculations were performed by Material Studio 2019 software and the COMPASS force field was adopted.

Revealing mechanical property-strengthening micro-mechanism of Ni/Ni3Al-based alloys by molecular dynamics simulation.

In this study, the Ni/Ni3Al-based alloys were proposed, and their microstructures were established. Uniaxial tension was performed based on the γ' phase precipitates of alloys with different shape ratio by means of molecular dynamics (MD) simulations. We demonstrate that the crystal distortion induced by the transition from FCC to disordered structure can lead to the reduction of tensile strength. Besides, the structure, temperature, and strain rate effects on the mechanical properties were clarified, and the microscale mechanism was revealed. The results indicated that compared with Ni/Ni3Al structure with a γ' phase precipitate shape ratio of 1:1:1, the tensile strength of the structure with a shape ratio of 1:2:1 is smaller, and the mechanical property-strengthening effect is significantly determined by the structures of the γ' phase precipitates; besides, there is a clear secondary strengthening in the tensile process of Ni/Ni3Al structure with a γ' phase precipitate shape ratio of 2:1:2 due to the formation of disordered structures. The elastic modulus and tensile strength of the models with different γ' phase precipitates shape ratios all decrease with the increase of temperature, under the conditions of low strain rate; the tensile strength of the alloys decreases with the decrease of strain rate.

Thermal Properties of the Mixed n-Octadecane/Cu Nanoparticle Nanofluids during Phase Transition: A Molecular Dynamics Study.

Paraffin based nanofluids are widely used as thermal energy storage materials and hold many applications in the energy industry. In this work, equilibrium and nonequilibrium molecular dynamics simulations are employed to study the thermal properties of the mixed nanofluids of n-octadecane and Cu nanoparticles during phase transition. Four different nanofluids systems with different mass ratios between the n-octadecane and Cu nanoparticles have been studied and the results show that Cu nanoparticles can improve the thermal properties of n-octadecane. The melting point, heat capacity and thermal conductivity of the mixed systems are decreased with the increasing of the mass ratio of n-octadecane.

Temperature-dependent electrochemical capacitive performance of the α-Fe2O3 hollow nanoshuttles as supercapacitor electrodes.

The design and optimization of supercapacitors electrodes nanostructures are critically important since the properties of supercapacitors can be dramatically enhanced by tunable ion transport channels. Herein, we demonstrate high-performance supercapacitor electrodes materials based on α-Fe2O3 by rationally designing the electrode microstructure. The large solid-liquid reaction interfaces induced by hollow nanoshuttle-like structures not only provide more active sites for faradic reactions but also facilitate the diffusion of the electrolyte into electrodes. These result in the optimized electrodes with high capacitance of 249 F g(-1) at a discharging current density of 0.5 A g(-1) as well as good cycle stability. In addition, the relationship between charge storage and the operating temperature has been researched. The specific capacitance has no significant change when the working temperature increased from 20 °C to 60 °C (e.g. 203 F g(-1) and 234 F g(-1) at 20 °C and 60 °C, respectively), manifesting the electrodes can work stably in a wide temperature range. These findings here elucidate the α-Fe2O3 hollow nanoshuttles can be applied as a promising supercapacitor electrode material for the efficient energy storage at various potential temperatures.