pH-responsive re-dispersible dispersions of carbon black and single-walled carbon nanotubes in arabinogalactan solutions

The stability of colloidal and nanoparticle (NPs) dispersions is a prerequisite for their utilization in advanced technologies. Yet, disposal of large volumes of NPs-rich fluid is challenging for waste management and would benefit from the ability to induce controlled aggregation and sedimentation of the NPs. Here, we demonstrate that sterically stabilized dispersions of carbonaceous NPs (Carbon Black and Single-Walled Carbon Nanotubes) in aqueous solutions of Arabinogalactan (AG) are pH responsive: the dispersions are stable at pH = 7 but coagulate at pH = 2 and separate into NPs-poor fluid and NPs-rich sediment. The sediment can be easily re-dispersed at pH = 7. The molecular and colloidal origins of the unexpected pH responsiveness of the sterically stabilized AG dispersions are investigated using surface tension measurements and Small-Angle X-ray Scattering experiments. While the pH responsiveness, along with the re-disposability, opens new pathways for reducing the ecological footprint of the NPs dispersions, the molecular origins of the observed behavior are not resolved and would require further investigation.