Papers by Author: Nyan Hwa Tai

Abstract: In this paper, carbon nanotubes were used as the reinforcements in the polymer composites for the application of electromagnetic interference, due to their outstanding mechanical and electrical properties. The multi-walled carbon nanotubes (MWNTs) synthesized by the chemical vapor deposition method were used to reinforce the epoxy resin by both mixing and spreading processes. The effects of the weight percentage and the reinforced form of MWNTs on electromagnetic interference shielding effectiveness, including the absorbance and the reflectance, were investigated. From experimental results, the electromagnetic shielding effectiveness of the nanocomposite specimens is improved with increasing content of MWNTs. The nanocomposites fabricated by the spreading process have better shielding effectiveness than those made by the mixing process. The nanocomposites, made by the spreading process with 2 wt% MWNTs, had up to 22.69 dB of electromagnetic shielding effectiveness. The reflectance percentage of electromagnetic shielding increases for higher content of MWNTs. The layerwise form of MWNTs in the nanocomposites, resulting from the spreading process and having a better electromagnetic shielding effectiveness, can be observed from the morphologies of the tensile failure surfaces of the nanocomposite specimens by filed emission scanning electron microscopy.

Abstract: Two processes, the floating catalyst chemical vapor deposition (CVD) process and the rapid heating and cooling (RHC) process, were adopted for synthesizing single walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). Batch production of SWNTs and MWNTs with the diameters of 0.8~1.5 nm and 15~40 nm, respectively, were prepared using the floating catalytic chemical vapor deposition (CCVD) process. The production rate is 70±20 mg every 10 minutes. The as-synthesized carbon nanotubes (CNTs) were used for fabricating carbon nanotubes reinforced composites and field emitter for lighting. On the study of nano-composites, around 70% enhancement of tensile strength was detected when 1.5 wt% MWNTs in the form of network structure were introduced to the phenolic matrix. Comparisons on the mechanical properties of the composites reinforced with the network MWNTs and SWNTs were made. Microstructures of the MWNTs and SWNTs were studied by Field Emission Scanning Electron Microscope (FESEM) and High Resolution Transmission Electron Microscope (HRTEM). In the RHC process for fabricating the device for lighting, the carbon nanotube array was grown on a silicon substrate which was pre-coated with a catalyst thin film. The synthesis process was performed in a thermal CVD chamber equipped with a rapid heating apparatus. The as-synthesized CNT array was then transferred onto the substrate which was coated with silver paste. After heat treatment, field emission properties of the CNT-based cathode were tested, high current density of 35 mA/cm2 and low turn-on voltage of 0.65 V/μm were achieved in this work.

Abstract: The multi-walled carbon nanotubes (MWNTs) and carbon fibers (CFs) were added to the phenolic resin to fabricate MWNTs/phenolic, MWNTs/CFs/phenolic nanocomposites and CFs/phenolic composites by hot press method. The differential scanning calorimetry (DSC) test was performed for the above-mentioned three kinds of composites. The valley points on the slope of endothermic responses correspond to the glass transition temperatures of the composites. The MWNTs/phenolic nanocomposites had the lowest glass transition temperature among the three kinds of composites discussed, which indicated a better thermal conductivity property of MWNTs. Phenolic-based composites reinforced by different weight percentages of MWNTs and CFs were also investigated. The tensile failure morphologies of nanocomposite specimens were examined using a scanning electron microscope to evaluate the possible effects on the glass transition temperature of nanocomposites..

Abstract: Atomic force microscopy (AFM) is widely used in many fields, because of its outstanding force measurement ability in nano scale. Some coating layers are used to enhance the signal intensity, but these coating layers affect the spring constant of AFM cantilever and the accuracy of force measurement. In this paper, the spring constants of rectangular cantilever with different coating thickness were quantitatively measured and discussed. The finite element method was used to analyze the nonlinear force-displacement behavior from which the cantilever’s normal and torsional spring constants could be determined. The experimental data and the numerical results were also compared with the results from other methods. By considering the influence of coating layers and real cantilever geometries, the more accurate force measurements by AFM cantilever can be obtained.

Abstract: Composites of phenolic resin reinforced by the multi-walled carbon nanotubes (MWCNTs) were fabricated and its mechanical properties were measured. The MWCNTs were synthesized by the floating catalyst method in a thermal chemical vapor deposition chamber. Benzene, hydrogen, ferrocene, and thiophene were used as carbon source, carrier gas, catalyst, and growth promoter, respectively. The nano-composites were made by the melt mixing and the resin infiltration methods. Tensile strength, Poisson’s ratio, and modulus were measured and the morphologies on the fracture surface were examined by the field emission scanning electron microscope (FESEM). The microstructure of the synthesized MWCNTs reinforced nano-composites was examined by FESEM. The influences of MWCNTs amounts on the mechanical properties of the nano-composites were discussed.

Abstract: Two different types of multi-walled carbon nanotube (MWNT), the dispersed and the network MWNTs, were used to reinforce the phenolic resin. The MWNTs/phenolic nanocomposites were tested by a dynamic mechanical analyzer (DMA) to characterize their dynamic mechanical properties. The results showed that increasing the MWNT content can increase the storage modulus, the loss modulus and the glassy transition temperature of the MWNTs/phenolic nanocomposites. A subambient loss transition is seen in the nanocomposites with network MWNTs which results in a better impact resistance property in the nanocomposites. The glassy transition temperature of the nanocomposites with network MWNTs is higher than that of nanocomposites with dispersed MWNTs. The MWNT additive in phenolic resin can be used to improve the dynamic mechanical properties of the MWNTs/phenolic nanocomposites. The tensile failure morphologies of MWNTs/phenolic nanocomposites were also examined using field emission scanning electron microscope (FESEM) to explain the difference between the two types of nanocomposites.

Abstract: The multi-walled carbon nanotubes (MWNTs) were added into the phenolic resin to fabricate MWNTs/phenolic nanocomposites. The pressure and temperature were applied to cure MWNTs/phenolic compound by hot press method, then followed by a post curing process. The results showed that post-curing of the nanocomposites specimen is necessary for better mechanical properties. The temperature used for post curing should be higher than the curing temperature. The higher curing pressure improved the Young’s modulus of the nanocomposites. The tensile failure morphologies of MWNTs/phenolic nanocomposites were examined using field emission scanning electron microscope (FESEM) to evaluate the effects of manufacturing processes on the mechanical properties of MWNTs/phenolic nanocomposites.