Papers by Author: Rong Sun

Abstract: In the present study, epoxy based composite filled with meso and non-porous silica microspheres with similar size were prepared respectively and their rheological and thermo-mechanical properties were studied systematically. The results showed that the mesoporous silica/epoxy composites showed much higher viscosity, storage modulus and glass transition temperature (Tg) while lower coefficient of thermal expansion (CTE) than did epoxy composites with nonporous silica particles, which could be attributed to the stronger interface interaction between the mesoporous silica filler with larger specific surface area (BET) and the epoxy matrix.

Abstract: A magnetite composite composed of the organic compounds and Fe₃O₄ nanoparticles was prepared with microemulsion method. The Tween 80 and ammonia were used as surfactant and reducing agent, respectively, in synthesizing the Fe₃O₄ nanoparticles. The experimental results showed that the composite possessed good stability while the volume ratio of Tween 80 to butanol was 0.4 and the molar ratio of NH₄OH to Fe³⁺ was 14.6. The saturation magnetization of the composite depends on the molar ratio of NH₄OH to Fe³⁺. The mechanism of this stable Fe₃O₄ paste was realized by the Fe₃O₄ nanocomposite film using TEM. The microstructures of the film show that the magnetic nanoparticles in the composite are surrounded by Tween 80, which separates the magnetic nanoparticles and leads to good stability.

Abstract: Magnetic composites, especially ferrite composites, are of great interest for embedded inductor applications. In this paper, the Ni-Zn ferrite particles (Ni1-xZnxFe2O4, x=0.2～0.8) with different zinc contents were synthesized via chemical coprecipitation method followed by modification with γ-glycidoxypropyl trimethoxysilane (KH-560). The particles were investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results show that the prepared Ni1-xZnxFe2O4(x=0.2～0.7) have good spinel structures, higher saturation magnetization (35.18～77.69 emu/g) and smaller hysteresis hoops, while Ni0.2Zn0.8Fe2O4 grains exhibit some paramagnetic behaviors, such as almost zero hysteresis and non-saturated magnetization. Next Ni1-xZnxFe2O4 magnetic/epoxy composites with different volume fraction of ferrite were prepared and their magnetic performances at high frequencies were characterized by an Agilent E4991A impedance analyzer (USA). It is found that with zinc content in Ni1-xZnxFe2O4 increasing from 0.2 to 0.7, the real part of the complex permeability (μ′) of these composites increase first and then decrease with the frequency increasing gradually from 10 MHz to 1 GHz. Of all, the epoxy composites with filler of Ni0.6Zn0.4Fe2O4 or Ni0.5Zn0.5Fe2O4 ferrite show good frequency stability, and the composites including Ni0.4Zn0.6Fe2O4 ferrite have the highest permeability, and the maximal value at the frequency of 100 MHz is 5.55 when the volume faction is 42.75%. The imaginary part of the complex permeability (μ′′) of all magnetic composites is low For the Ni0.2Zn0.8Fe2O4/epoxy composites, they have very low real permeability (μ′～1) and imaginary permeability (μ″≤0.2).

Abstract: Nano-capsules with organic-inorganic composite PMMA-SiO2 as the shell and paraffin as the core have been largely and rapidly synthesized by the cooperative reaction of interfacial hydrolysis and polymerization. Ammonium persulfate as the initiator and catalyst was used to make the polymerization and hydrolysis process occurring simultaneously and to improve the uniformity and controllability of capsule morphology. The prepared homogeneous core-shell structures of capsules with the grain size around 100 nm have small volume change and stable thermodynamic characteristics. The cooperative reactions of polymerization and hydrolysis process provide a convenient and efficient method for preparing homogeneous and stable organic-inorganic composite capsules.

Abstract: The composites composed of micro-sized calcium copper titanate (CCTO) and nano-sized metallic nickel (Ni) fillers in the polyvinylidene fluoride (PVDF) matrix (Ni/CCTO/PVDF) were prepared, in which the filler content (volume fraction) of Ni and CCTO was set at 60 %. The impedance spectra and a serial equivalent circuit model consisting three RC units were used to investigate the behaviors of the Ni/CCTO/PVDF three-phase composite system near the percolation threshold. The real (Z′) and imaginary (Z″) parts of the impedance dramatically decreased as the Ni content was increased from 22% to 24% indicating a transition from an insulating to a conducting state. This transition process has been realized by the changes in the capacitance derived from the model, and the investigation has been carried out to clarify the release mechanism of the entrapped electrons at the interfaces.