Thermoresponsive Behaviors of Poly(oxypropylene)-amidoamine Functionalized Carbon Nanotubes

Abstract

Multiwalled carbon nanotube (MWNT) was organically grafted with poly(oxypropylene)-amine (POP-amine) of 2000 g mol-1 molecular weight and became highly dispersible in water and organic media such as toluene. The presence of the POP pendants may render to the MWNT an inverse temperature transition (ITT) for water dispersion, showing a higher dispersing ability at lower temperature below 21−27 °C, which is detectable by UV−vis transmittance and the naked eye. The temperature-responsive dispersion behavior was further demonstrated in the toluene/water biphasic system, taking advantage of its relative dispersing ability in both media. By varying the temperature around the ITT, the dark-colored carbon nanotube (CNT) was dispersed into either water or toluene phase, in a reversible manner for multiple cycles. The unique thermoresponsive property is attributed to the switching of noncovalent bonding forces of the tethered POP segments between the hydrogen bonding with water and the hydrophobic interaction with toluene. The distinctly different morphologies of dispersion and aggregation were further observed by using atomic force microscopy.