Surface modification of nanoparticles and nanotubes by plasma polymerization and properties characterization

by Gao, Yong.

Nanomaterials have many special properties including a high surface energy and a high specific surface area. Those properties also cause the agglomeration of the nanomaterials. A useful strategy is to use surface modification to change the nanoparticles surface properties to minimize the agglomeration problem and meet other applications of functional materials. In the last two decades, much more research has been devoted to the surface modification of nanomaterials. Plasma polymerization is the one of the main methods of surface modification of particles and has many benefits. However few publications investigate on the surface modification of nanoparticles by this method. In this thesis, two studies are done. In the first part (this part is finished under the guidance of Dr. William van Ooij and in his lab), a pyrrole-coated nano ZnO powder was prepared by plasma polymerization. The surface properties, microhardness and sinteriblity of pyrrole coated ZnO nanoparticles treated by plasma polymerization under different temperatures are studied. Those studies showed that at a suitable treatment temperature and time, the coated nanopaticles increase the surface microhardness and the modified nanoparticles change their surface properties from hydrophilic to hydrophobic. Higher pressure and higher treatment temperature during pellet compaction give higher mechanical properties. The polymer coating improves the sinteribility at low temperature. To achieve good mechanical properties, the polymer-coated nanoparticles need to be treated in a faster sintering and lower temperature environment. In the second part, the Carbon Nanofibers (CNF) are coated using two plasma power conditions. The relationship between the mechanical properties, mainly tensile strength and Young’s Modulus, and the dispersion time using ultrasonication and the carbon nanofiber i concentration are studied. The coating is also characterized by Differential Scanning Calorimeters (DSC), Thermogravimetric Analysis (TGA), Transmission Electron Microscopy (TEM), Time-of-flight Secondary Ion Mass Spectroscopy (TOF-SIMS), and Infrared Spectroscopy (IR). The results showed that plasma treated carbon nanofiber cast in a polymer matrix had better tensile strength and Young’s modulus comparing to the untreated carbon nanofiber if ultarsonication at relative shorter time. For the current experiment condition, 100w plasma power coated CNF cast in a polymer has better mechanical properties than that of 10w plasma power. The relationship between mechanical properties and dispersion time and carbon nanofiber concentration is also discussed. The CNF-Polymer composites increase their mechanical properties with the dispersion time under ultrasonication to a maximum value and then decrease again. After overnight dispersion, the mechanical properties increase again. For the shorter dispersion time (less than 12 hours), 1 wt% CNF-Polycarbonate (PC) composites give a 10% increasing of in tensile strength and 14% increase in the Young’s Modulus. For the very long dispersion time (more than 24 hours), the tensile strength of 1 wt% CNF-PC composites reaches 1.21 times that of pure PC while Young’s modulus increases 1.42 times. The mechanism is not clear but it is possible because of the change of dispersion velocity of the ultrasound during ultrasonication and the change of the surface status of the CNFs.