(751c) Controlling Carbon Nanotubes Dispersion Using Stimuli-Responsive Polymers

Despite their immense potential, the ability to control the dispersion and microstructure of carbon nanotubes remains a hurdle for their widespread use in nanotube-filled polymer composites. Stimuli responsive polymers exhibit conformational changes as a function of applied stimulus (pH, temperature, light etc.) which can be used to tailor SWNT microstructure. In this work, several pH-responsive polymers(i.e., weak polyelectrolytes) such as, poly(acrylic acid), poly(methacrylic acid), poly(allylamine),polyethleneimine and temperature responsive poly(N-cyclopropylacrylamide), poly(N-isopropylacrylamide) functionalized with varying concentrations of pyrene were used to stabilize aqueous SWNT suspensions. Studies performed on aqueous SWNT suspensions stabilized with these pH and temperature responsive polymers suggest exfoliated and highly networked nanotube microstructure a function of pH and temperature, respectively. Cryo-TEM, viscosity and UV-Vis spectroscopy were used to characterize the nanotube dispersion state in these suspensions. Furthermore, studies performed on the nanocomposite formed by drying these suspensions suggests that microstructure of nanotubes in these suspensions is preserved in the solid composite, as evidenced by SEM imaging and electrical conductivity measurements. This method of controlling the microstructure of SWNTs in liquid medium with external stimuli to tailor the properties of solid composites could have a significant impact on solution process polymer nanocomposites preparation. Many of the relationships described here could also be applied with other responsive polymers and for the tailored dispersion of other types of nanoparticles (e.g., inorganic nanotubes and nanowires).