Temperature controlled dispersion of carbon nanotubes in water with pyrene-functionalized poly(N-cyclopropylacrylamide).
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Despite their immense potential, the ability to control the dispersion and microstructure of carbon nanotubes remains a hurdle for their widespread use. Poly(N-cyclopropylacrylamide), containing 5 mol % pyrene-bearing repeat units (p-PNCPA), is shown to vary the dispersion state of single-walled carbon nanotubes (SWNTs) in water. This is a thermo-responsive polymer whose conformation changes with temperature, which in turn leads to changes in the nanotube dispersion state. Cryo-TEM micrographs show that SWNTs stabilized using p-PNCPA transitions from a more exfoliated to a more bundled state as the aqueous suspension temperature is raised above the lower critical solution temperature (LCST) of the polymer (approximately 30 degrees C). Viscosity measurements on SWNT/p-PNCPA aqueous suspensions show shear thinning and near Newtonian behavior at 10 and 50 degrees C, respectively. Drying of these suspensions produces composites whose microstructure and electrical conductivity vary with drying temperature. This behavior has significant implications for the processing of carbon nanotubes and tailoring of composite properties. Such stimuli-controlled dispersion of carbon nanotubes could have a variety of applications in nanoelectronics, sensing, and drug and gene delivery systems.