Colloidal Stability in Water of Modified Carbon Nanotube: Comparison of Different Modification Techniques

The colloidal stability of carbon nanotube (CNT) in water is an important property for several applications. Three different functionalization approaches defined as nondestructive techniques have been carried out to modify the CNT surface and the product CNT compared. First, admicellar polymerization is used to form a water-soluble polymer on CNT with two different polymers, polyacrylic acid and polyvinyl acetate (PVAc). Second, coatings of soluble biopolymers are applied using dextran and chitosan. Third, mild acid oxidation conditions from the literature are employed with hydrogen peroxide (H2O2) and with potassium permanganate (KMnO4) as oxidizing agents. The colloidal stability of modified CNT is examined by sedimentation and by turbidity measurements along with laser particle size analysis. Thermogravimetric Analysis, energy dispersive X-ray analysis, scanning electron microscope, and transmission electron microscopy are used to confirm that modification of the CNT is successfully implemented with each technique. Lastly, FT-Raman is used to assess damage to the CNT structure after modification. A focus of the turbidity measurements is quantitative analysis using numerical integration of variability to evaluate colloidal stability. All modified CNT samples clearly yield improved aqueous dispersions. For each of the three approaches, the better option is KMnO4 for mild acid oxidation, PVAc for admicellar polymerization, and chitosan for biopolymer deposition.