Dispersion of single-walled carbon nanotubes in aqueous solution with a thermo-responsive pentablock terpolymer

Single-walled carbon nanotubes (SWNTs) were dispersed in pure water with a thermo-responsive amphiphilic PNIPAM₁₅₀-F108-PNIPAM₁₅₀ pentablock terpolymer in comparison with its precursor PEO₁₃₆-PPO₄₅-PEO₁₃₆ (F108) triblock copolymer. The stability, dispersibility, and thermo-responsive behaviors of the polymer/SWNT hybrids were characterized by UV–vis–NIR spectroscopy, thermal gravimetric analysis, viscosity measurement, Raman spectroscopy, and high-resolution transmission electron microscopy. The pentablock/SWNT hybrids showed superior ability in stabilization over F108/SWNT hybrids, and no sign of sedimentation was found at room temperature for 6 weeks or even 2 months of storage. The pentablock terpolymer can efficiently disperse SWNTs into individual tubes or small bundles with average diameter of about 5 nm, and their chains were helically wrapped onto the nanotube surface, whereas the larger bundles of the nanotubes with sizes of 15–25 nm were observed in F108/SWNT hybrids. Moreover, the pentablock/SWNT hybrids switched reversibly between the well-exfoliated and the aggregated states when cyclically increasing and decreasing temperature.