Clay-mediated carbon nanotube dispersion in poly(N-Isopropylacrylamide)

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) is the most widely studied temperature-responsive polymer due to its lower critical solution temperature (LCST) near to that of the human body temperature (around 32 °C). Unlike many water-soluble polymers, PNIPAM exhibits little affinity for single-walled carbon nanotubes (SWNT), which is not sufficient for preparing stable aqueous suspensions. The present study makes use of montmorrilonite clay (MMT) to compatibilize SWNT in aqueous PNIPAM solution. The interactions of clay with SWNT and PNIPAM is probed using UV–vis spectroscopy and cryo-TEM of aqueous suspensions. Furthermore, zeta potential measurements and direct visual observation suggests stable dispersion of SWNT in PNIPAM. SEM micrographs show that nanotube dispersion state in the aqueous suspension is preserved to a large extent in the solid nanocomposite films formed with drying. PNIPAM nanocomposite hydrogels, containing clay and SWNT, were also prepared with better SWNT dispersion in the presence of clay. Mechanical measurements show a 96% increase in storage modulus at 25 °C for 0.45 wt% clay and 0.05 wt% SWNT containing hydrogels (as compared to pure PNIPAM hydrogels). This method of employing clay as a dispersing aid for stabilizing nanotubes in PNIPAM solution is expected to be very useful for other polymers that have low affinity for nanotubes and could open up even more applications for nanotube-filled polymeric materials. This method of using clay to disperse carbon nanotubes in PNIPAM will likely be useful for producing mechanically durable and also, electrically conductive, PNIPAM-based hydrogels, sensors and self-cleaning surfaces that should serve to open up more biological applications for nanotube-filled materials.