Temperature controlled dispersion of carbon nanotubes in water with pyrene-functionalized poly(N-cyclopropylacrylamide)

Suspensions of single-walled carbon nanotubes (SWNTs) are being studied for variety of applications that include biocompatible transportation, drug delivery systems, and optical sensors. As produced SWNTs are aggregated because of the van der Waals force of attraction and hydrophobic interactions in aqueous environments which severely limit their dispersion, especially in water. For this reason, both covalent and noncovalent techniques are used to stabilize SWNTs in water. Recently, the use of pH responsive polymers to stabilize SWNTs in water was examined where changes in conformation and degree of ionization of poly(acrylic acid) (PAA) as a function of pH were utilized for exfoliation and bundling of SWNTs. The ability to use temperature to control the level of nanotube exfoliation would be a much more convenient extension of this powerful concept. In this
communication, we report the use of a thermo-responsive poly(Ncyclopropylacrylamide) (PNCPA) copolymer with 5 mol % pyrene side groups (p-PNCPA), to stabilize aqueous SWNT suspensions. The changes in conformation (i.e., coil to globule transformation) as a function of temperature are believed to control the dispersion state of SWNTs (i.e., stabilized or bundled) in water.