| Summary: | 碩士 === 大葉大學 === 醫療器材設計與材料碩士學位學程 === 106 === In the present study, graphene oxides (GrO) were synthesized by the Modified Hummer method with natural graphite powder as the raw material. The chemical structures and the surface morphology of the as-synthesized GrO were characterized by Raman and FE-SEM, respectively where aqueous GrO dispersions were prepared by adding aliquots of alcohol as solvent. The GrO thin films were prepared by electrophoretic deposition (EPD) over Indium Tin Oxide (ITO) glass substrates in asymmetric alternating current (AAC) and direct current (DC) electric fields, respectively. A preliminary study was conduct to find the appropriate EPD operation window after which the as-deposited GrO films by different deposition duration (5, 10, 20, 30 s), at identical operation voltage and frequency were compared comprehensively to investigate the effects of various modes of electric fields on the properties of the deposited GrO films. For AAC-EPD mode, all the three common waveforms has been choose, including square wave, square wave and sine wave, respectively. The former (square wave) could be named as the unbalanced electric field whose waveform was asymmetric in which the positive and negative area of the same size. In contrast, the remaining two waveforms could not meet the requirement of unbalanced electric field, i.e., a net DC current flows toward a given electrode leading to a DC and/or pulse-DC mode-like electric field.
It shows that, compared to those deposited by DC-EPD, the deposition rate for those deposited by AAC modes were apparently much slower whereas different kind of waveform has made little difference in the rate of GrO film deposition. For those deposited by AAC-EPD with waveform of both square and sine wave, the behaver of rate increment about deposition time did follow the relationship of Hamker equation whereas the triangular wave did not show similar linear relationship. The complexity of the deposition behavior under the AAC electric fields could be attributed to the Stotz-Wien effect where the variation of electric filed strength with applied voltage were nonlinear, leading to different films structure and properties. It is noteworthy that for AAC-EPD films with square waveform, there is no hydrogen evolving on the cathode surface owing that all charges were flowed within the double layers in the vicinity of electrodes.
In summary, the best result was obtained by AAC-EPD with square waveform at 40V, 50Hz, 25% duty cycle with deposition duration of 30s under which the as-deposited GrO films has compact surface morphology with RMS surface roughness of 4.40 nm, lowest sheet resistance of 25.93 0.85(/), and optical transmittance of 84.591%. By applying AAC-EPD with waveform of sine and triangular wave, the wrinkle on film surface becomes prominent, whereas both the optical transparency and electric conductivity for the as-deposited GrO films were deteriorated accordingly which might be ascribed to the hydrogen evolution at cathode surface during the prolonging deposition process.
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