Liyuan Xie

Core-shell structured poly(methyl methacrylate)/BaTiO3 nanocomposites prepared by in situ atom transfer radical polymerization: a route to high dielectric constant materials with the inherent low loss of the base polymer

Core-shell structured BaTiO3/poly(methyl methacrylate) (PMMA) nanocomposites were successfully prepared by in situ atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) from the surface of BaTiO3 nanoparticles. A broadband dielectric spectrometer was used to investigate the temperature dependence of the dielectric properties of the nanocomposites in a frequency range from 0.1 Hz to 1 MHz. It was found that the nanocomposites not only showed a significantly increased dielectric constant when compared with pure PMMA, but also showed the inherent low loss of the base polymer in a wide range of frequencies. Only in the very low frequency/high temperature range, can a higher dielectric loss can be observed in the nanocomposites. It was also found that the effective dielectric constant of the core-shell structured hybrid nanoparticles can be tailored by varying the polymer shell thickness. The dielectric response of beta relaxation of PMMA was also studied and the results showed that the nanoparticles had no influence upon the relaxation activation energy. Fourier-transform infrared spectroscopy (FTIR) and 1H NMR spectra confirmed the chemical structure of the PMMA shell on the surface of the BaTiO3 nanoparticles. Transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) results revealed that the PMMA shell thickness could be well controlled by tuning the feed ratio of MMA to BaTiO3.

Ferroelectric polymer/silver nanocomposites with high dielectric constant and high thermal conductivity

Ferroelectric polymer nanocomposites with silver (Ag) nanoparticles as inclusions were prepared and the dielectric properties and thermal conductivity were studied. The results showed that the nanocomposites have high dielectric constant and high thermal conductivity. When the loading level of Ag nanoparticles is 20.0 vol %, the dielectric constant and thermal conductivity of the nanocomposites were 120 at 103 Hz and 6.5 W/mK, respectively. Our results also showed that there is no percolation in the nanocomposites when Ag loading range is within 20.0%.

Core-shell structured hyperbranched aromatic polyamide/BaTiO3 hybrid filler for poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) nanocomposites with the dielectric constant comparable to that of percolative composites.

Polymer nanocomposites with the dielectric constant comparable to that of percolative composites are successfully prepared by using core-shell structured hyperbranched aromatic polyamide grafted barium titanate (BT-HBP) hybrid nanofiller. Poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (PVDF-TrFE-CFE) was used as the polymer matrix because of its high intrinsic dielectric constant and easy processability. The BT-HBP hybrid nanofiller were prepared by a solution polymerization of diaminobenzoic acid on the surface of amino-funcationalized BT nanoparticles. Nuclear magnetic resonance ((1)H NMR) and transmission electron microscopy (TEM) were used to verify the chemical structure of the hyperbranched aromatic polyamide and core-shell structure of the hybrid filler, respectively. It was found that the nanocomposite with 40 vol % BaTiO3-HBP had a dielectric constant of 1485.5 at 1000 Hz, whereas the corresponding nanocomposite sample with untreated BaTiO3 only showed a dielectric constant of 206.3. Compared with classic percolative composites, the advantage of the PVDF-TrFE-CFE/BaTiO3-HBP nanocomposites is that the composites show high enough breakdown strength and high dielectric constant simultaneously. An enhanced interfacial polarization mechanism between the BT-HBP and the polymer matrix was suggested for understanding the observed unusually high dielectric constant.

Morphology-controllable graphene–TiO2 nanorod hybrid nanostructures for polymer composites with high dielectric performance

High permittivity polymer-based materials are highly desirable due to their inherent advantages of being easy to process, flexible and light weight. Herein, a new strategy for the development of polymer composites with high permittivity and low dielectric loss has been proposed based on morphology-controllable graphene–TiO2 nanorod hybrid nanostructures. These hybrid nanostructures possess large aspect ratio, high surface area and high electric conductivity graphene sheets, which provide ideal electrodes in the construction of microcapacitors. In addition, the morphology-controllable TiO2 nanorod decoration effectively prevents direct contact between the graphene sheets in the composite, which give advantages for forming a large microcapacitor network and suppressing the leakage current. As a consequence, a polystyrene composite with 10.9 vol% graphene–TiO2 nanorod sheets exhibits a very high permittivity of 1741 at 102 Hz, which is 643 times higher than the value for pure polystyrene (2.7), and low dielectric loss (tanα) of only 0.39. The permittivity of the composites can be controlled by controlling the amount of nanorod decoration on the graphene substrates, which provides a new pathway for tuning the permittivity of polymer composites. We expect that our strategy of controlling filler interface will be applied to acquire more polymer composites with high permittivity and low dielectric loss.

Core-shell structured polystyrene/BaTiO3 hybrid nanodielectrics prepared by in situ RAFT polymerization: a route to high dielectric constant and low loss materials with weak frequency dependence.

A novel route to prepare core-shell structured nanocomposites with excellent dielectric performance is reported. This approach involves the grafting of polystyrene (PS) from the surface of BaTiO(3) by an in situ RAFT polymerization. The core-shell structured PS/BaTiO(3) nanocomposites not only show significantly increased dielectric constant and very low dielectric loss, but also have a weak frequency dependence of dielectric properties over a wide range of frequencies. In addition, the dielectric constant of the nanocomposites can also be easily tuned by varying the thickness of the PS shell. Our method is very promising for preparing high-performance nanocomposites used in energy-storage devices.

“Grafting to” route to PVDF-HFP-GMA/BaTiO3 nanocomposites with high dielectric constant and high thermal conductivity for energy storage and thermal management applications

The introduction of high dielectric constant ceramic nanoparticles into an insulating polymer is an important approach to prepare high dielectric constant nanocomposites for electric energy storage applications. A key to obtaining desirable properties is the homogeneous dispersion of the nanoparticles in the corresponding polymer. Conventional methods used to improve the nanoparticle dispersion enhance the physical interaction between the nanoparticle and the polymer matrix via nanoparticle surface modification. In this work, the covalent bonding between the nanoparticle and the polymer matrix was utilized to simultaneously enhance the nanoparticle dispersion and nanoparticle/polymer interaction by functionalizing both the polymer and the nanoparticles. The poly(vinylidene fluoride-co-hexafluoropropylene) [PVDF-HFP] was functionalized with glycidyl methacrylate (GMA) via atom transfer radical polymerization. The barium titanate (BaTiO3) nanoparticles were modified by amino-terminated silane molecules. Then the nanocomposites were prepared by a “grafting to” method. Namely, grafting GMA functionalized PVDF-HFP to the surfaces of the BaTiO3 nanoparticles. The introduction of GMA into the PVDF-HFP not only increases the dielectric constant, but also changes the dielectric response of PVDF-HFP. More importantly, this “grafting to” approach results in core–shell structured BaTiO3@PVDF-HFP-GMA and thus a homogeneous dispersion of BaTiO3 nanoparticles in the nanocomposites. The dielectric constant, electric energy density and thermal conductivity of the nanocomposites are significantly enhanced with the increase of BaTiO3, while the dielectric loss shows a slight decrease as the nanoparticle loading increases.

Electrical, thermophysical and micromechanical properties of ethylene-vinyl acetate elastomer composites with surface modified BaTiO3 nanoparticles

In this study, we investigated the influence of the surface modified BaTiO3 nanoparticles on the electrical, thermophysical and micromechanical properties of ethylene-vinyl acetate (EVM) vulcanizates. Gamma-aminopropyl triethoxysilane was used as a silane coupling agent for the surface treatment of the BaTiO3 nanoparticles. It was found that the incorporation of surface modified BaTiO3 nanoparticles into the EVM matrix not only increased the permittivity, thermal conductivity and the mechanical strength but also showed a comparative dielectric loss tangent with pure EVM vulcanizates. In particular, the nanocomposites exhibit relatively high dielectric strength and good ductility even at the loading level of 50 vol%. The improved properties not only originate from the homogeneous dispersion of BaTiO3 nanoparticles but also should be ascribed to the strong interfacial interaction between the surface modified BaTiO3 nanoparticles and EVM matrix. We also investigated the dielectric relaxation behaviour of the BaTiO3 filled EVM nanocomposites by using Jonscher’s theory of universal dielectric response. (Some figures in this article are in colour only in the electronic version)

Nano–micro structure of functionalized boron nitride and aluminum oxide for epoxy composites with enhanced thermal conductivity and breakdown strength

Polymer-based composites with high thermal conductivity and breakdown strength have become increasingly desirable in both the electronic and electric industries. Herein, we have designed a nano–micro structure of 2-D micro-scale hexagonal boron nitride (h-BN) and 0-D nano-scale α-alumina (α-Al2O3) hybrid fillers for epoxy composites with high thermal conductivity and breakdown strength. So as to improve interface interaction, both fillers are functionalized with hyperbranched aromatic polyamide (HBP). It is found that both structure design and surface modification play important roles. Surface modification can enhance many physical properties of composites, such as thermal conductivity, thermal stability and breakdown strength. Importantly, the nano–micro structure presents noticeable synergistic effects on both thermal conductivity and ac breakdown strength. The obtained composite with 26.5 vol% fillers presents a high thermal conductivity of 0.808 W m−1 K−1 (4.3 times that of epoxy). In addition, the breakdown strength of the composite at 4.4 vol% content is up to 40.55 kV mm−1, 21.5% higher than that of neat epoxy (33.38 kV mm−1).

Influence of BaTiO 3 nanoparticles on dielectric, thermophysical and mechanical properties of ethylene-vinyl acetate elastomer/BaTiO 3 microcomposites

This paper reports on the effects of nano-BaTiO3 particles on the dielectric, thermophysical (thermal conductivity) and mechanical properties of ethylene-vinyl acetate (EVM) elastomer/BaTiO3 microcomposites. The EVM composites with nano-, micro- and nano/micro hybrid BaTiO3 fillers have been prepared by melt compounding. The results showed that the addition of nano-BaTiO3 particles to micro- BaTiO3/EVM composites could lead to an enhancement in permittivity, thermal conductivity and mechanical strength when compared with the micro-BaTiO3/EVM composites with the same total filler content, whereas the dielectric strength did not show significant difference and the dielectric loss tangent increased slightly. The Maxwell-Garnett effective medium model was used to analyze the BaTiO3 concentration dependence of relative permittivity of the composites.

Role of interface in highly filled epoxy/BaTiO 3 nanocomposites. Part I-correlation between nanoparticle surface chemistry and nanocomposite dielectric property

The interface is critical for the design of polymer nanocomposites with desirable properties. The effect of interface behavior on the properties of polymer nanocomposites with low nanoparticle loading has been well documented. However, our understanding of the role of the interface in highly filled polymer nanocomposites is still limited because of the lack of comprehensive research work. In this contribution, by using BaTiO3 nanoparticles with six kinds of surface chemistry, we have prepared highly filled epoxy nanocomposites (50 vol% nanoparticle loading). The role of nanoparticle surface chemistry on the dielectric properties of epoxy nanocomposites is investigated at a wide frequency and temperature range by using broadband dielectric spectroscopy. Combining the microstructure analysis of the highly filled nanocomposites with a comprehensive X-ray photoelectron spectroscopy characterization of the surface chemistry of the BaTiO3 nanoparticles, an understanding is formed of the correlation between the nanoparticle surface chemistry and the dielectric properties of the nanocomposites. The functional group density, functional group type, and electrical properties of the modifier-the three parameters that are inherent from the nanoparticle surface modification-have a strong impact on the temperature and frequency dependence of the dielectric constant and dielectric loss tangent. This work demonstrates the great importance of surface chemistry in tuning the electrical properties of dielectric polymer nanocomposites.