Yunchuan Xie

High Dielectric and Mechanical Properties Achieved in Cross-Linked PVDF/α-SiC Nanocomposites with Elevated Compatibility and Induced Polarization at the Interface

Remarkably improved dielectric properties including high-k, low loss, and high breakdown strength combined with promising mechanical performance such as high flexibility, good heat, and chemical resistivity are hard to be achieved in high-k dielectric composites based on the current composite fabrication strategy. In this work, a family of high-k polymer nanocomposites has been fabricated from a facile suspension cast process followed by chemical cross-linking at elevated temperature. Internal double bonds bearing poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE-DB)) in total amorphous phase are employed as cross-linkable polymer matrix. α-SiC particles with a diameter of 500 nm are surface modified with 3-aminpropyltriethoxysilane (KH-550) as fillers for their comparable dielectric performance with PVDF polymer matrix, low conductivity, and high breakdown strength. The interface between SiC particles and PVDF matrix has been finely tailored, which leads to the significantly elevated dielectric constant from 10 to over 120 in SiC particles due to the strong induced polarization. As a result, a remarkably improved dielectric constant (ca. 70) has been observed in c-PVDF/m-SiC composites bearing 36 vol % SiC, which could be perfectly predicted by the effective medium approximation (EMA) model. The optimized interface and enhanced compatibility between two components are also responsible for the depressed conductivity and dielectric loss in the resultant composites. Chemical cross-linking constructed in the composites results in promising mechanical flexibility, good heat and chemical stability, and elevated tensile performance of the composites. Therefore, excellent dielectric and mechanical properties are finely balanced in the PVDF/α-SiC composites. This work might provide a facile and effective strategy to fabricate high-k dielectric composites with promising comprehensive performance.

Linear-like dielectric behavior and low energy loss achieved in poly(ethyl methacrylate) modified poly(vinylidene-co-trifluoroethylene)

To realize linear-like dielectric characteristics in normal ferroelectric poly(vinylidene-co-trifluoroethylene) (P(VDF-TrFE)), poly(ethyl methacrylate) (PEMA) was grafted onto poly(vinylidene fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene) as side chains. The introduction of rigid PEMA segments resulted in the decreased crystallinity, crystal and ferroelectric domain size. As a result, reduced dielectric loss and improved modulus, therefore enhanced breakdown strength was obtained in the graft copolymers. Moreover, low energy loss (about 16.6%) and relatively high energy density (19.3 J cm−3) under high electric field (675 MV m−1) was achieved since the hysteresis induced by the ferroelectric relaxation of P(VDF-TrFE) has been completely eliminated.

Strong induced polarity between Poly(vinylidene fluoride-co-chlorotrifluoroethylene) and α-SiC and its influence on dielectric permittivity and loss of their composites

Interface polarization and interface zone have been widely utilized to account for the abnormally improved dielectric properties of composites although their formation is rather vague and their influence has never been directly measured. In this work, micro α-SiC was designed as the filler particles incorporated into poly(vinylidenefluoride-co-chlorotrifluoroethylene) with internal double bonds (P(VDF-CTFE-DB)) to construct polymer micro composites through solution casting method. The dielectric constant of the composites is found to be increasing linearly as SiC content increases at lower content and the highest value is obtained as 83 at 100 Hz, which is unusually higher than both pristine polymer (13@100 Hz) and SiC filler (17@100 Hz). By studying the dielectric properties of a bilayer model composite, the real dielectric permittivity of SiC sheet and P(VDF-CTFE-DB) layer has been directly measured to be significantly enhanced than their original value. The induced polarity between high polar PVDF unit...

β-cyclodextrin and its hyperbranched polymers-induced micro/nanopatterns and tunable wettability on polymer surfaces

This paper reports an efficient strategy to fabricate micro/nanopatterns on the surfaces of polymers for obtaining tunable wettability. Tepee-like bundles as micro/nanopatterns, composed of irregular polygon “podium” and “valley” structures, are formed by adding β-cyclodextrin (β-CD) or its hyperbranched polymers [HBP(β-CD)s] into a polystyrene (PS) matrix in the process of anodized aluminum oxide (AAO) template wetting. The degree and region of micro/nanopatterns are evidently enlarged with the increase of β-CD content or the molecular weight (Mw) of HBP(β-CD). The formation of micro/nanopatterns is mainly dependant on the self-organization of long and flexible aligned nanofiber/nanotube arrays with high aspect ratios, which are generated by the enhanced nanoflow behaviors of β-CD or HBP(β-CD)-containing PS melts in AAO templates. The final topographies of micro/nanopatterns are determined by the dilation stress and the interactions of nanofibers/nanotubes during the templates removal and solvent evaporation process. The static and dynamic water contact angle measurements show that the wettability of micro/nanopatterned surfaces is systematically tuned from being merely hydrophobic to being highly hydrophobic, and to being finally superhydrophobic by simply adjusting the content of β-CD or the Mw of HBP(β-CD) due to the decrease of the contact area fraction of the water droplet and solid polymer. The reported novel method, using nanoparticles or hyperbranched polymers as processing aids to induce micro/nanopatterns and tunable wettability on polymer surfaces, may be extended to various polymeric matrices to realize nanopatterns, and is useful for tailoring artificial superhydrophobic surfaces as well.

Biocompatible amphiphilic hyperbranched nanocapsules with a functional core: Synergistic encapsulation and asynchronous release properties towards multi-guest molecules

To achieve an encapsulation–release property towards multi-guest molecules, amphiphilic hyperbranched nanocapsules (AHN) consisting of a functional hyperbranched poly(β-cyclodextrin) [HBP(β-CD)] core and a methoxy polyethylene glycol shell was first constructed by click chemistry. The encapsulation–release capacity and corresponding mechanism of AHN towards multi-guest molecules were investigated by fluorescence and UV-vis spectroscopy. The results indicated that the encapsulation–release properties of AHN were pH dependent and can be applied to multi-guest systems. The multi-guest encapsulation capacity of AHN was derived from the synergistic encapsulation phenomenon of different guest molecules and the molecular recognition property of the HBP(β-CD) core. Compared with single-guest systems, AHN displays a sustained release characteristic accompanied by an “asynchronous release phenomenon” in multi-guest release systems. The release rate can also be effectively controlled because of the molecular recognition property of the HBP(β-CD) core. Both in vitro cell apoptosis and in vivo systematic toxicity assays confirmed that AHN possessed good biocompatibility.

Significantly elevated dielectric permittivity of Si-based semiconductor/polymer 2-2 composites induced by high polarity polymers

To disclose the essential influence of polymer polarity on dielectric properties of polymer composites filled with semiconductive fillers, a series of Si-based semiconductor/polymer 2-2 composites in a series model was fabricated. The dielectric permittivity of composites is highly dependant on the polarity of polymer layers as well as the electron mobility in Si-based semiconductive sheets. The huge dielectric permittivity achieved in Si-based semiconductive sheets after being coated with high polarity polymer layers is inferred to originate from the strong induction of high polarity polymers. The increased mobility of the electrons in Si-based semiconductive sheets coated by high polarity polymer layers should be responsible for the significantly enhanced dielectric properties of composites. This could be facilely achieved by either increasing the polarity of polymer layers or reducing the percolative electric field of Si-based semiconductive sheets. The most promising 2-2 dielectric composite was found to be made of α-SiC with strong electron mobility and poly(vinyl alcohol) (PVA) with high polarity, and its highest permittivity was obtained as 372 at 100 Hz although the permittivity of α-SiC and PVA is 3–5 and 15, respectively. This work may help in the fabrication of high dielectric constant (high-k) composites by tailoring the induction effect of high polarity polymers to semiconductors.

Tunable sound absorption of silicone rubber materials via mesoporous silica

In this contribution, a new pathway for the regulation of sound absorption properties of silicone rubber (SR) materials was presented using worm-like mesoporous silica (MS) with nanoscaled channels and pores. The MS enhanced the sound absorption coefficient of SR in a wide range of sound frequency from 1 to 5 kHz. By introducing the MS with an average pore diameter of 5.56 nm and a specific surface area of 1026 m2 g−1, the sound absorption coefficient of the MS/SR composite was as high as 0.83 at a sound frequency of 1.8 kHz, which is nearly triple that of the pure SR. Moreover, the mechanical and thermal properties of the SR were retained in the composite. The reflection and friction of sound waves between the pore walls and the depleted energy by viscous absorption were suggested as the main mechanism responsible for the enhanced sound absorption coefficient. It is helpful to design and fabricate rubber materials with tunable sound absorption properties.

Enhanced Mechanical and Dielectric Properties of PU Networks with Hyperbranched Structures

We report a new polyurethane (PU) dielectric containing hyperbranched structures and metal nanoparticles. Silver nanoparticles were incorporated into the PU networks by using hyperbranched polyester (HBP) as a reductive template as well as the cross-linker. Simultaneously enhanced mechanical and dielectric properties were observed in the hyperbranched PU dielectrics. The branched macromolecular fractal provides a “covalent bridge” between the PU matrix and Ag nanoparticles, which contributed to the simultaneously enhanced mechanical and dielectric properties.

Effect of Nanoparticle Surface Treatment on Nonisothermal Crystallization Behavior of Polypropylene/Calcium Carbonate Nanocomposites

Polypropylene (PP)/CaCO3 nanocomposites were prepared by melt-blending method using a Haake-90 mixer. The CaCO3 nanoparticles were surface modified with a coupling agent before compounding. A fine dispersion of the modified nanoparticles in the nanocomposites was observed by transmission electron microscopy (TEM). Effects of surface treatment of CaCO3 nanoparticles on the nonisothermal crystallization behavior and kinetics of PP/CaCO3 nanocomposites were investigated by differential scanning calorimetry (DSC). Jeziorny and Mo methods were used to describe the nonisothermal crystallization process. It was shown that the crystallization temperature of the nanocomposites increased due to the heterogeneous nucleation of the surface-treated nanoparticles. It was found that the nanoparticles modified with a proper content range of coupling agent could facilitate the nonisothermal crystallization of the nanocomposites under certain conditions (the cooling rate and the relative degree of crystallinity). This may be a potential application for the crystallization controlling of composites in manufacturing. In addition, the activation energy of crystallization for the nanocomposites and the nucleation activity of the nanoparticle were estimated by using Kissinger and Dobrevas methods, respectively. It could be concluded that the surface-treated nanoparticles had a strong nucleating activity, which caused the decrease of the activation energy of the nanocomposites.

Effects of Heating, Tensile, and High Pressure Treatments on Aggregate Structure of a Low Density Polyethylene

The effects of heating, tensile, and high pressure treatments on the aggregate structure of a low density polyethylene (LDPE) are studied via modulated DSC (MDSC) and dynamic mechanical technique (DMA). The results indicate that the nonreversing heat flow can reflect the relative thermodynamic stability for crystalline structure of the polymer, and this makes nonreversing heat flow be a novel useful tool to qualitatively characterize the perfect degree of crystalline structures. During thermal treatment, it is found that there exists a low temperature melting endotherm at about 35°C. It presents an endothermal peak in nonreversing heat flow and a simultaneous glasslike transition in reversing heat flow, which behaves a feature of physical aging far above the glass transition temperature of the polymer. This suggests the existence of so-called “rigid amorphous fraction” (RAF). The structural changes of polyethylene induced by different treating methods are also investigated by DMA, and the relaxation characteristics of macromolecular chains are analyzed.