Abstract
The objectives of this research are the preparation and characterization of transparent conductive films (TCFs) by utilizing Multi-walled carbon nanotubes and graphene. There are five parts in this dissertation. The first part of this dissertation discusses the optically transparent and electrically conductive thin films composed of multi-walled carbon nanotube (MWCNT) reinforced polymethyl methacrylate/acrylic acid (PMMA/AA) which were fabricated using a wire coating technique. Poly(acrylic acid) controls the dispersibility of MWCNT in aqueous mixtures and retains the well-dispersion of MWCNT in the polymer matrix after solidification resulted from extended polymer chains by adjusting the pH value. It causes the lower surface electrical resistance at the same MWCNT content. The second part of this dissertation used Poly (acrylic acid) and Poly (N-vinyl pyrrolidone) as adhesion promoters to improve MWCNT coating significantly. The cross-linked polymer resulted in a better bond between the MWCNTs and substrates. The surface electrical resistance showed significantly lower than that of the original sheet after nitric acid (HNO3) treatment. The lower electrical resistance of PVP/PAA-g-MWCNT conductive films on the PET substrate was due to more complete conductive paths with the cross-linked polymer. Such the electrical resistance was enhanced from 8.83x104Ω/□ to 2.65x103Ω/□ with 0.90mg/cm2 PVP/PAA-g-MWCNT content deposited on the PET after acid treatment. The third part examines the intercalation reaction of graphite oxide (GO) with poly (acryl amide)/poly (acrylic acid) (PMA) as a method to control the spacing between GOs. The intercalated polymer chains of poly (acrylic acid) between GNSs efficiently inhibit GNS aggregation and restacking. The PMA grafted GNS (NE-PMA-GNS) composite films show the lowest sheet resistance of 2.11×102 Ω□-1, which is one order of magnitude less than that without grafting polymer (NE-GNS, 1.86×103 Ω□-1). The fourth part developes a simple method to assemble graphite oxide (GO) densely onto the electrospun (ES) Nylon 66 nanofibrous membranes, used as a guide for the deposition of graphene nanosheets (GNS) conductive networks for preparing the TCFs. The main advantage of this technique by comparison with previous methods is that graphene does not form a uniform coating, but a percolated conductive network is existed, when guided by Nylon 66 nanofiber templates. A low surface coverage of the transparent substrate by GNS resulted in high transmittance. The resulting PVP-GO material could adsorb well on Nylon 66 nanofibers due to stronger hydrogen bond. The TCF optical transmittance was improved after thermal annealing at 350°C above the Nylon 66 melting point. A fused film, obtained after electrospinning Nylon 66 solution for 120 s, and immersing in 0.050 wt% PVP-GO solution, exhibiting a surface resistance of 8.6 × 103 Ω/□, while maintaining 88% light transmittance. The fifth part demonstrates a simple method of integrating hybrid thin films consisted of graphene nanosheets (GNS) and silver nanoparticles (AgNps) via in situ chemical reduction (AgNps-GNS) for preparing the TCFs. In order to obtain conductive films without compromising much on transmittance, the polyurethane (PU) nanofibers were introduced as guides to build the two-dimensional conductive networks of AgNps-GNS. By taking the advantage of the flexible mechanical property of GNS and great conductivity of AgNps, the potential application of hybrid AgNps-GNS as a highly flexible and transparent conductive thin film was demonstrated. A fused film, obtained after electrospinning PU solution for 120 s, and immersing in 0.05 wt% AgNps-GNS (5:1) solution, exhibits a surface resistance of 150 Ω/□, while maintaining 85 % light transmittance.