The effect of pH and ionic strength on the dispersion of carbon nanotubes in poly(acrylic acid) solutions

The dispersion of three kinds of acid-treated carbon nanotubes (CNTs) in poly(acrylic acid) (PAA) aqueous solution of different pH and ionic strengths (varied by NaCl, KCl and ZnCl2) was investigated by visual observation, zeta potential, particle size analysis, transmission electron microscopy and scanning electron microscopy. Visual observation revealed that the dispersion of CNTs acid treated at 60 degrees C for 3 h and at 80 degrees C for 2 h was poor in aqueous solutions with pH < 2 or pH > 12. The poor dispersion of acid-treated CNTs may be improved by adding PAA. In particular, PAA improved the dispersion of CNTs with greater COOH content. In a low pH solution (pH 1.5), a higher PAA content resulted in poorer CNT dispersion while in a high pH solution (pH 12.5), a higher PAA content led to better CNT dispersion. For superior dispersion in a basic aqueous solution (pH 12.5), experimental data showed that a greater atomic radius or a higher cationic charge of the added salt may result in faster aggregation and thus precipitation of CNTs. Copyright (C) 2011 Society of Chemical Industry