Removal of excess polymer from a suspension containing hybrids of thermoresponsive polymer and carbon nanotubes using aggregation phenomenon

Abstract

Hybrids of organic molecules and single-walled carbon nanotubes (SWNTs) are attractive candidates for nanobiodevices. The removal of organic molecules after dispersing the SWNTs in organic media is a significant step in the preparation of these hybrid suspensions. We investigated the aggregation phenomenon in hybrids of poly(N-isopropylacrylamide) (PNIPAAm) and SWNTs. Our results indicate that the hybrids efficiently precipitated when a buffer or salt solution was added to the suspension at 25 °C. 4 mM tris(hydroxymethyl)aminomethane hydrochloride (Tris–HCl) buffer was sufficient to precipitate the hybrids. Then, by repeated centrifugations and replacements of solvents, excess PNIPAAm molecules were efficiently removed from the suspension. Results of UV–vis spectroscopy and atomic force microscopy (AFM) suggest that the PNIPAAm–SWNT hybrids retained their hybridized structures even after the treatment process. However, the aggregation phenomenon was not observed at 4 °C.