Hongli Gao

Uniform distribution of low content BaTiO3 nanoparticles in poly(vinylidene fluoride) nanocomposite: toward high dielectric breakdown strength and energy storage density

BaTiO3/poly(vinylidene fluoride) (BT/PVDF) composite material, a promising dielectric material for capacitor, has recently attracted much attention because of the promising dielectric performance and its abundant availability. Insufficient control of the hierarchal morphology of the blend has yielded a precipitous decline in breakdown strength at high BT nanoparticles volume fractions. Here, we demonstrate that breakdown strength and energy storage density can be increased up to higher value by creating uniform distribution of low content of BT nanoparticles in PVDF matrix. The dielectric properties of BT/PVDF nanocomposite were measured as a function of BT nanoparticles loading. The nanocomposite displayed a 150% increase in dielectric breakdown strength and energy density increased to more than triple that of the pure PVDF even at the 1 vol% BT nanoparticles loading. It was attributed to the uniform distribution of low content BT nanoparticles in PVDF matrix, which lead to superior dielectric breakdown strength and energy storage density than those of composites filled with high content of BT nanoparticles. Furthermore, the nanocomposites films with low content of fillers were more flexible and cost-effective. The finding based on this research provides a low-cost method to achieve high performance in capacitor.

Recycling of asbestos tailings used as reinforcing fillers in polypropylene based composites.

In this work, asbestos tailings were recycled and used as reinforcing fillers to enhance the mechanical properties of polypropylene (PP). A silane coupling agent was used to chemically modify the asbestos tailings to increase the compatibility between asbestos tailings and polypropylene matrix. Both raw and chemically treated asbestos tailings with different loading levels (from 3 to 30 wt%) were utilized to fabricate composites. Mechanical properties of these composites have been investigated by dynamic mechanical analysis, tensile test and notched impact test. Results showed that hybridization of asbestos tailings in the composites enhanced the mechanical properties of neat PP evidently, and treated asbestos tailings/PP composites yielded even better mechanical properties compared with those of raw asbestos tailings/PP composites. This recycling method of asbestos tailings not only reduces disposal costs and avoids secondary pollution but also produces a new PP-based composite material with enhanced mechanical properties.

Enhanced adhesion and conductivity of Cu electrode on AlN substrate for thin film thermoelectric device

The Cu thin film electrode grown on aluminum nitride (AlN) substrate is widely used in the thin film thermoelectric devices due to its high electrical conductivity. We have developed a new type of buffer layer by co-sputtering Ti and Cu forming Ti–Cu layer. The Ti–Cu layer was sputtered on the Ti buffered AlN substrate so that the adhesion and electrical conductivity properties of the Cu film electrode on AlN substrate could be improved. The interface between the thin films and the substrate were characterized by the scanning electron microscope (SEM). Nanoscratch tests were conducted on a nanomechanical test system to investigate the adhesion between the Cu film electrodes and AlN substrate. Meanwhile, accelerated ageing test under thermal cycling was conducted to evaluate the reliability of the thin film electrode. The results show that the adhesion and the reliability of Cu film electrode on AlN substrate have been greatly improved by employing Ti–Cu/Ti buffer layers.

Scalable solution assembly of nanosheets into high-performance flexible Bi0.5Sb1.5Te3 thin films for thermoelectric energy conversion

Two-dimensional nanostructures, such as nanosheets and nanoribbons, represent excellent dimension for efficient transport of electrons and phonons and thus are ideal building blocks for hierarchical assembly of functional microscale electronic and phonic structures. We report a convenient and scalable solution approach for the hierarchical assembly of two-dimensional Bi2Te3&Sb2Te3 nanosheets compounds on polyimide substrates to obtain flexible Bi0.5Sb1.5Te3 thin films. We show that the nanosheets can be assembled into compact Bi0.5Sb1.5Te3 films by a solution-processed method followed by annealing treatment. Flexible thin films from two-dimensional nanosheets assemblies exhibit excellent thermoelectric properties and flexibility. The films of Bi0.5Sb1.5Te3/polyimide can be folded and even bent to a crease without cracking. The simple techniques involved in obtaining these films could help facilitate the rapid fabrication of flexible thermoelectric devices, heralding what promises to be a new approach toward the development of next-generation thermoelectric refrigeration and power harvesting technologies.Graphical abstractImage of the flexible high-performance thermoelectric thin film synthesized from the Bi2Te3&Sb2Te3 nanosheets compounds on polyimide substrates. Crease picture of the flexible thin film after folded by a pliers.