Functionalization of Carbon Nanotubes: Characterization, Modeling and Composite Applications

• Other Authors: Wang, Shiren, 1972- (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Industrial engineering; Operations research; Systems engineering
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-1253

Single walled carbon nanotubes (SWNTs) have demonstrated exceptional mechanical, thermal and electrical properties, and are regarded as one of the most promising reinforcement materials for the next generation of high performance structural and multifunctional composites with tremendous application potentials. However, to date, most application attempts have been hindered by several technical roadblocks, such as poor dispersion and weak interfacial bonding. Functionalization of nanotubes was suggested to be an effective way to overcome these technical issues and then to realize the full potential of nanotubes as reinforcement materials. In this dissertation, several original functionalization methods were proposed, studied, analyzed and quantitatively compared. These functionalization methods included precision sectioning of nanotubes using an ultra-microtome, electron-beam irradiation, amino-group grafting, and epoxide group grafting. Short nanotubes with open-ends show rich chemistry, ballistic transportation properties and capability of good dispersion. However, current reported cutting methods are difficult to protect tube sidewalls from devastation and to achieve desired length control. This research has developed a technique to precisely section aligned SWNT membranes through ultra-microtome in order to produce short and open-end tubes. Aligned SWNT membranes were sectioned to 50nm and 200nm. The results of AFM characterization and length statistical analysis have found the measured lengths were centered at 87nm and 246nm, respectively. Raman and TEM characterization results confirmed the minimized damage to the sidewalls. The cut-SWNTs were applied to nanocomposites fabrications. Young's modulus and strength of the composite were improved by 20% and 7%, respectively, when using 0.5wt% cut-SWNTs. The SEM results also confirmed the improvement in dispersion. The enhanced tensile strength indicates that load-transfer was improved due to the enhanced interfacial bonding. This dissertation also proposed a unique covalent sidewall functionalization through epoxy-grafting. The characterizations of Raman, FT-IR and TEM have proved the successful grafting of epoxide-group to the carbon nanotubes. The SEM results of the epoxy-grafted SWNTs reinforced composite indicated that significant improvement of dispersion was achieved. Dynamic Raman tests also revealed the considerable enhancement in the interfacial bonding. The tensile strength of nanocomposites was enhanced 27.1% and Young's modulus 30% with only 0.5wt% loading of epoxy-grafted SWNTs. When composites were fabricated with 1wt% loading of epoxy-grafted SWNTs, the strength and Young's modulus were improved by 40.3% and 60%, respectively. These substantial improvements are among the highest in the reported literatures. Furthermore, this research also succeeded in grafting amino-group onto SWNT sidewalls through one-step diazotization. Improvements in both dispersion and interfacial bonding were achieved. Young's modulus and strength for the amino-functionalized SWNTs composites with 0.5wt% loading were enhanced by 25% and 21.9%, respectively. The electron beam irradiation on the thin SWNTs membrane was both experimentally and theoretically investigated. Experimental results suggested that there exists a critical dose of irradiation in acquiring a desirable cross-linkage, above which significant enhancement of the SWNT membranes properties can be acquired. The theoretic modeling indicates that the density of cross-linkage is a quadratic function of the irradiation dosages. The irradiation-induced inter-tube bridging significantly enhanced the Young's modulus and tensile strength of the SWNTs membrane by 2 folds and 6 folds, respectively. Electric conductivity was also increased more than 1 fold. Both mechanical and electric properties improvements make the irradiated SWNT membranes very promising in the versatile applications, including electronic device, energy storage, biomaterials, and nanocomposites. All the methods developed in the dissertation demonstrated effectiveness in improving dispersion and interfacial bonding, resulting in considerable improvements in composite mechanical properties. Modeling of functionalization provided in-depth understanding and offered reasonable explanations of SWNTs length distribution, as well as carbon nanostructure transformation upon electron-beam irradiation. Both experimental and theoretical investigations would facilitate full realization of the potential of nanotubes-reinforced nanocomposites. === A Dissertation Submitted to the Department of Industrial and Manufacturing Engineering in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy. === Fall Semester, 2006. === October 25, 2006. === Nanocomposites, Surface Modification, Carbon Nanotubes, Functionalization, Precision Cutting, Amino-Grafting, Epoxy-Grafting, Electron-Beam Irradiation, Nanotube Membrane, Dispersion, Interfacial Bonding, Buckypaper === Includes bibliographical references. === Zhiyong Liang, Professor Co-Directing Dissertation; , Professor Co-Directing Dissertation; James Brooks, Outside Committee Member.