Processing and characterization of nano-engineered thin films

Abstract

Nanoparticle-based thin films are an emerging type of material with extraordinary electrical, mechanical, and physical properties. Because of their exceptional characteristics, these thin films can serve as reinforcement or conductive/semi-conductive sheets in composite and electronic systems. While most thin films comprise a structure of random nanoparticle network, the ability to produce high quality films depends on how to minimize inter-filler junction effects between filaments. This study presents a novel processing technique to fabricate thin films composed of functionalized carbon nanofibers (CNFs). The two-step process combines solution filtering and mechanical compression through a rolling process to form dense CNF thin films of uniform thickness. Electron micrographs show a remarkable change in surface morphology for all rolled films; the film morphology becomes more uniform and compact due to nanofiber displacement with mechanical compression. Test results show that tensile strength and electrical conductivity of surfactant-treated CNF films are inferior to those of oxidized CNF films. Based on these findings, it is suggested that surfactant significantly hinders the interaction between particles. Regarding the rolling effect on the oxidized CNF films, results show that strength and conductivity of rolled films improve by 400% with respect to the non-rolled films. By not having surfactant, it appears that the oxidized nanofibers can participate in higher intermolecular interactions and form an interlocking mechanism when forced into close proximity. Upon fracture, electron micrographs reveal significant pull-out and alignment of nanofibers for surfactant-treated CNF films as a result of particle slippage, while nanofiber fragmentation is identified for oxidized CNF films, suggesting higher fiber-fiber interaction within the dense entangled network. Hence, the methodology presented herein is an effective route to reduce inter-filler junction between nanofibers and to produce thin films with superior properties.