Evaluation of Surfactants on Graphene Dispersion and Thermal Performance for Heat Dissipation Coating.

With the development of thin and high-power electronic devices, heat dissipation has become an important and urgent issue in thermal management. In this study, a water-based epoxy was used as a polymer matrix to prepare heat dissipation coatings utilizing low volatile organic compounds, which were environmentally friendly and had a high heat-dissipating performance. Graphene flakes, multi-walled carbon nanotubes and aluminum oxide particles were used as fillers for preparing the heat dissipation coating. The graphene flakes and multi-walled carbon nanotubes were dispersed in a water-based epoxy by adding sodium dihexyl sulfosuccinate and poly (dimethyldiallylammonium chloride). These two surfactants were combined as a dispersant to improve the dispersibility of the carbon nanomaterials in the water-based epoxy. The synergistic effect of the well-dispersed fillers improved the heat-dissipating performance. The experimental results show that the infrared emissivity of the heat dissipation film was 0.96 after filling 30 wt% aluminum oxide particles, 2 wt% graphene flakes and 2 wt% multi-walled carbon nanotubes into a water-based epoxy. The heat dissipation film reduced the thermal equilibrium temperature of the bare copper panel by 17.8 °C under a heating power of 10 W. The film was applied in a heat dissipation test on a 15 W LED bulb, and the thermal equilibrium temperature was reduced by 21.3 °C. The results demonstrate that the carbon nanomaterial-based heat dissipation coating with a water-based epoxy could significantly reduce the thermal equilibrium temperature, giving a high potential for the application of thermal management.

Carbon Dioxide Tornado-Type Atmospheric-Pressure-Plasma-Jet-Processed rGO-SnO2 Nanocomposites for Symmetric Supercapacitors.

Pastes containing reduced graphene oxide (rGO) and SnCl2 solution were screen printed on carbon cloth and then calcined using a CO2 tornado-type atmospheric-pressure plasma jet (APPJ). The tornado circulation of the plasma gas enhances the mixing of the reactive plasma species and thus ensures better reaction uniformity. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were performed to characterize the synthesized rGO-SnO2 nanocomposites on carbon cloth. After CO2 tornado-type APPJ treatment, the pastes were converted into rGO-SnO2 nanocomposites for use as the active electrode materials of polyvinyl alcohol (PVA)-H2SO4 gel-electrolyte flexible supercapacitors (SCs). Various APPJ scanning times were tested to obtain SCs with optimized performance. With seven APPJ scans, the SC achieved the best areal capacitance of 37.17 mF/cm2 in Galvanostatic charging/discharging (GCD) and a capacitance retention rate of 84.2% after 10,000-cycle cyclic voltammetry (CV) tests. The capacitance contribution ratio, calculated as pseudocapacitance/electrical double layer capacitance (PC/EDLC), is ~50/50 as analyzed by the Trasatti method. GCD data were also analyzed to obtain Ragone plots; these indicated an energy density comparable to those of SCs processed using a fixed-point nitrogen APPJ in our previous study.

A Facile Method for Batch Preparation of Electrochemically Reduced Graphene Oxide.

The electrochemical reduction of graphene oxide (GO) is an environmentally friendly and energy-saving method for improving the characteristics of GO. However, GO films must be coated on the cathode electrode in advance when usingthis technique. Thus, the formed electrochemically reduced GO (ERGO) films can be used only as sensing or conductive materials in devices because mass production of the flakes is not possible. Therefore, this study proposes a facile electrochemical reduction technique. In this technique, GO flakes can be directly used as reduced materials, and no GO films are required in advance. A 0.1 M phosphate buffered saline solution was used as the electrolyte, which is a highly safe chemical agent. Experimental results revealed that the as-prepared GO flakes were electrochemically reduced to form ERGO flakes by using a -10 V bias for 8 h. The ratio of the D-band and G-band feature peaks was increased from 0.86 to 1.12, as revealed by Raman spectroscopy, the π-π stacking interaction operating between the ERGO and GO has been revealed by UV-Vis absorption spectroscopy, and the C⁻O ratio was increased from 2.02 to 2.56, as indicated by X-ray photoelectron spectroscopy. The electrical conductivity of the ERGO film (3.83 × 10-1 S·cm-1) was considerably better than that of the GO film (7.92 × 10-4 S·cm-1). These results demonstrate that the proposed electrochemical reduction technique can provide high-quality ERGO flakes and that it has potential for large-scale production.

Characteristics of Graphene Oxide Films Reduced by Using an Atmospheric Plasma System.

The chemical oxidation method can be used to mass-produce graphene oxides (GOs) from highly oriented pyrolytic graphite. However, numerous oxygen-containing functional groups (hydroxyl, epoxy, carbonyl, etc.) exist in typical GO surfaces, resulting in serious electrical losses. Hence, GO must be processed into reduced graphene oxide (rGO) by the removal of most of the oxygen-containing functional groups. This research concentrates on the reduction efficiency of GO films that are manufactured using atmospheric-pressure and continuous plasma irradiation. Before and after sessions of plasma irradiation with various irradiation times, shelters, and working distances, the surface, physical, and electrical characteristics of homemade GO and rGO films are measured and analyzed. Experimental results showed that the sheet resistance values of rGO films with silicon or quartz shelters were markedly lower than those of GO films because the rGO films were mostly deprived of oxygen-containing functional groups. The lowest sheet resistance value and the largest carbon-to-oxygen ratio of typical rGO films were approximately 90 Ω/sq and 1.522, respectively. The intensity of the C⁻O bond peak in typical rGO films was significantly lower than that in GO films. Moreover, the intensity of the C⁻C bond peak in typical rGO films was considerably higher than that in GO films.

Development of a multilayered polymeric DNA biosensor using radio frequency technology with gold and magnetic nanoparticles.

This study utilized the radio frequency (RF) technology to develop a multilayered polymeric DNA sensor with the help of gold and magnetic nanoparticles. The flexible polymeric materials, poly (p-xylylene) (Parylene) and polyethylene naphtholate (PEN), were used as substrates to replace the conventional rigid substrates such as glass and silicon wafers. The multilayered polymeric RF biosensor, including the two polymer layers and two copper transmission structure layers, was developed to reduce the total sensor size and further enhance the sensitivity of the biochip in the RF DNA detection. Thioglycolic acid (TGA) was used on the surface of the proposed biochip to form a thiolate-modified sensing surface for DNA hybridization. Gold nanoparticles (AuNPs) and magnetic nanoparticles (MNPs) were used to immobilize on the surface of the biosensor to enhance overall detection sensitivity. In addition to gold nanoparticles, the magnetic nanoparticles has been demonstrated the applicability for RF DNA detection. The performance of the proposed biosensor was evaluated by the shift of the center frequency of the RF biosensor because the electromagnetic characteristic of the biosensors can be altered by the immobilized multilayer nanoparticles on the biosensor. The experimental results show that the detection limit of the DNA concentration can reach as low as 10 pM, and the largest shift of the center frequency with triple-layer AuNPs and MNPs can approach 0.9 and 0.7 GHz, respectively. Such the achievement implies that the developed biosensor can offer an alternative inexpensive, disposable, and highly sensitive option for application in biomedicine diagnostic systems because the price and size of each biochip can be effectively reduced by using fully polymeric materials and multilayer-detecting structures.

DNA detection using a radio frequency biosensor with gold nanoparticles.

This study presents a novel method for DNA detection with multi-layer AuNPs to enhance overall detection sensitivity. This essay achieves not only an innovative radio-frequency biosensor but also a critical signal amplification methodology. Results show that bandwidth change for multi-layer AuNP with hybridization of DNA exceeds that for the double-layer AuNP up to 0.5 GHz. Furthermore, the developed biosensor detection limit for the DNA set employed in this essay is currently 10 pM. A single base-pair mutation of the wild-type target DNA could be distinguished from the perfect match target DNA at the melting temperature of 47 degrees C with a temperature controlling system. Experimental results in this study indicate that the proposed biosensor and the developed amplification methodology are successful. As health care becomes much more essential in modern life, this biosensor has potential applications in a screening kit for recognizing, sensing, and quantifying biomolecules in real samples.

Three dimensional electrode array for cell lysis via electroporation.

Microfabricated devices for cell lysis have demonstrated many advantages over conventional approaches. Among various design of microdevices that employ electroporation for cytolysis, most utilize Ag/AgCl wires or 2D planar electrodes. Although, simple in fabrication the electric field generated by 2D electrodes decays exponentially, resulting in rather non-uniform forcing on the cell membrane. This paper investigates the effect of electric field generated by 3D cylindrical electrodes to perform cell lysis via electroporation in a microfluidic platform, and compared with that by 2D design. Computational results of the electric field for both 2D and 3D electrode geometries showed that the 3D configuration demonstrated a significantly higher effective volume ratio-volume which electric field is sufficient for cell lysis to that of net throughflow volume. Hence, the efficacy of performing cell lysis is substantially greater for cells passing through 3D than 2D electrodes. Experimentally, simultaneous multi-pores were observed on leukocytes lysed with 3D electrodes, which is indicative of enhanced uniformity of the electric field generated by 3D design. Additionally, a single row of 3D electrode demonstrated a substantially higher lysing percentage (30%) than that of 2D (8%) under that same flow condition. This work should aid in the design of electrodes in performing cell lysis via electroporation.