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Xu R.,Guangdong University of Technology | Lei C.,Guangdong University of Technology | Lei C.,Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter | Cai Q.,Guangdong University of Technology | And 2 more authors.
Gaofenzi Cailiao Kexue Yu Gongcheng/Polymeric Materials Science and Engineering | Year: 2015

Polypropylene thermal conductive composites with different hybrid fillers were prepared, and the thermal conductivity, electrical conductivity and rheological properties were tested. The results show that the thermal conductivity is improved by adding hybrid parts. By adding 10% of carbon black and carbon nanotube simple mixture and chemical bonded filler to PP/Al2O3 composite, the thermal conductivity is improved to 0.60 W/mk and 0.63 W/mk, respectively. Using pure carbon black and pure carbon nanotubes as hybrid parts, the thermal conductivity is only 0.36 W/mk and 0.45 W/mk. The volume resistance declines 106 order of magnitude for the composite using carbon nanotube and the simple mixture, whereas the composite filled with pure carbon black or chemical bonded fillers show insulation behavior. An obvious shear thinning phenomenon appears in η* vs. ω curves after adding hybrid parts. A second plateau at low frequency region is observed, but it is very weak for the chemical bonded filler modified composites. For this composite, the microstructure shows that the filler distributes well in the matrix and connecting bridges are formed between the fillers. The results show that the thermal conductivity cannot be improved pronouncedly by pure carbon black or pure carbon nanotube. The simple mixture of carbon black and carbon nanotube can induce better thermal conductivity, but it will also lead to some electrical conductivity. The application of chemical bonded carbon black and carbon nanotube can meet the demand of thermally conductive and insulated composites. ©, 2015, Chengdu University of Science and Technology. All right reserved.

Zhao Y.,Guangdong University of Technology | Zhao Y.,Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter | Wei A.-X.,Guangdong University of Technology | Wei A.-X.,Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter | And 2 more authors.
Wuli Xuebao/Acta Physica Sinica | Year: 2015

Junction temperature, as one of the most important properties of light-emitting diodes (LEDs), has great impact on LEDs' power efficiency, luminosity, reliability, life-time, and so on. Precise measurement of junction temperature for LED device is quite important in the research of chip's fabrication, device packaging and related applications. In this paper, we propose a new approach to measure the junction temperature of LEDs by using temperature-dependent capacitance. The capacitance of white LEDs at room temperature is measured and found to be decreased first and then increased with an increasing reverse bias. Equivalent model using vertical and horizontal capacitances connected in parallel is proposed to qualitatively explain the variation of capacitance under different reverse bias. Result obtained from the model fitting agrees well with the experimental result. The capacitance-temperature (C-T) curve of white LEDs under different reverse bias is measured and analysed. Results show that the capacitance of LEDs is sensitive to temperature at all biases. Under a reverse voltage of 0.5 V, the capacitance has the maximal response of 1.971 pF/℃ and a good linear temperature-dependent property. The C-T curve is used as the calibration for the measurement of junction temperature. By monitoring the change of capacitance of the working LEDs and comparing it with the C-T curve, the junction temperature of the LED device is successfully measured. The junction temperature of a white LED obtained by the proposed C-T method is compared with that by tranditional forward voltage method, and they are in good agreement. The C-T method is also used to measure the real-time junction temperatures of white LEDs under a constant current of 350 mA and a constant voltage of 3.2 V, respectively. In both conditions, the junction temperature of an LED needs approximately 110 sec to rise from room temperature to a steady value, and subsequently needs approximately 500 sec to fall back to room temperature after the LED is turned off. Compared with traditional methods, C-T method only needs to measure one calibration and this calibration can be applied to LEDs working at any current and voltage. Therefore, C-T method is a simple and flexible alternative to the existing technique of temperature measurement in electronic device. ©, 2015, Chinese Physical Society. All right reserved.

Tan J.,Guangdong University of Technology | Tan J.,Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter | Bai Y.,Guangdong University of Technology | Zhang X.,Guangdong University of Technology | And 2 more authors.
Polymer Chemistry | Year: 2016

The photoinitiated polymerization-induced self-assembly (photo-PISA) of 2-hydroxypropyl methacrylate (HPMA) is conducted in water by using poly(poly(ethylene glycol) methyl ether methacrylate) (PPEGMA) based macro-RAFT agents. Polymerizations were carried out at room temperature via exposure to visible light irradiation, and quantitative monomer conversions (>99%) were achieved within 30 min of visible light irradiation. A remarkably diverse set of complex morphologies (spheres, worms, and vesicles) have been prepared by aqueous photo-PISA under mild conditions (water medium, room temperature, and visible light). The morphology of nano-objects can be tuned by changing the reaction parameters (e.g. degree of polymerization, solids concentration), and two detailed phase diagrams were constructed. The polymerization can be activated or deactivated by a simple "ON/OFF" switch of the light source. A thermo-responsive behavior of PPEGMA14-PHPMA200 nanoparticles prepared at 15% w/w was investigated by changing the temperature from 25°C to 4°C. © The Royal Society of Chemistry 2016.

Ye Y.,Guangdong University of Technology | Zhang H.,Guangdong University of Technology | Zhang H.,Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter | Chen Y.,Guangdong University of Technology | And 10 more authors.
Journal of Alloys and Compounds | Year: 2015

Abstract Core-shell structure carbon coated ferric oxide nanoparticles (Fe2O3@C) were fabricated by the oxidation of carbon coated iron nanoparticles (Fe@C) prepared by a direct current carbon arc discharge method. Porous activated-Fe2O3@C was prepared by KOH activation of Fe2O3@C at the temperature of 750 °C. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize the structure and morphology of the Fe2O3@C and activated-Fe2O3@C. The specific surface area and pore size distribution of the samples were also tested. The activated-Fe2O3@C electrodes exhibited good electrochemical performance with a maximum specific capacitance of 612 F g-1 at the charge/discharge current density of 0.5 A g-1 with 5 M NaOH electrolyte. After 10,000 cycling DC tests at the charge/discharge current density of 4 A g-1, a high level specific capacitance of 518 F g-1 was obtained (90.6% retention of the initial capacity), suggesting excellent long-term cycling stability. © 2015 Elsevier B.V. All rights reserved.

Tan J.,Guangdong University of Technology | Tan J.,Guangdong Provincial Key Laboratory of Functional Soft Condensed Matter | Fu L.,Guangdong University of Technology | Zhang X.,Guangdong University of Technology | And 3 more authors.
Journal of Materials Science | Year: 2016

Herein, we report a photoinitiated RAFT dispersion polymerization for the preparation of highly monodisperse poly(glycidyl methacrylate) (PGMA) microspheres at room temperature. Fast polymerization rates were achieved, with near quantitative yields within 2 h of UV irradiation. The effect of reaction conditions (e.g., stabilizer concentration, monomer concentration and solvent composition) on particle morphologies was studied in detail. Amine-functionalized PGMA microspheres were prepared by treating PGMA microspheres with ethylene diamine (EDA) at 70 °C, and the obtained product was characterized by FT-IR and XPS. Such amine-functionalized PGMA microspheres were able to stabilize oil-in-water Pickering emulsions. Covalently cross-linked colloidosomes were formed by cross-linking primary amino groups on the particle surface using (tolylene 2,4-diisocyanate-terminated poly(propylene glycol) (PPG-TDI) as a cross-linker. Amine-functionalized PGMA microspheres were also employed as templates for the synthesis of PGMA/gold (Au) hybrid microspheres and large gold nanoplates. © 2016, Springer Science+Business Media New York.

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