Non-Covalent Stabilization of Carbon Nanotubes Using Stimuli-Responsive Polymers
K.C. Etika, J.C. Grunlan
Texas A&M University, US
Keywords: stimuli-responsive polymers, nanotubes, dispersion
Abstract:Despite their immense potential, the ability to control the dispersion and microstructure of carbon nanotubes remains a hurdle for their widespread use. Stimuli-responsive polymers show conformation changes with applied external stimulus (pH, temperature, light etc.). Two methods for non-covalent stabilization/dispersion of carbon nanotubes are describe here. The first method utilizes the pH-responsive nature of poly(acrylic acid) to disperse carbon nanotubes. The dispersion of nanotubes with weak polyelectrolytes enables the macroscopic properties of aqueous suspensions to be tuned using pH. Microstructural changes as a function of pH were observed with cryo–TEM of aqueous SWNT-filled suspensions. With poly(acrylic acid), nanotube bundling increases with increasing pH and these microstructurally-induced changes are reversible. pH dependent interaction of PAA with carbon nanotubes in water were confirmed by Raman spectroscopy and liquid suspension conductivity. This behavior has significant implications for the processing of carbon nanotubes and tailoring of composite properties. The second method involves the use of thermo-responsive copolymers. Temperature responsive polymers based on poly(N-cyclopropylacrylamide), with varying amounts of pyrene functionality, were used to disperse carbon nanotubes in water. The dispersion state of nanotubes below and above the lower critical solution temperature (LCST) of the polymers was investigated. Such stimuli-controlled dispersion of carbon nanotubes could have a variety of applications in nanoelectronics, sensing, and drug and gene delivery systems.