Size dependent aqueous dispersibility of carboxylated multiwall carbon nanotubes

Abstract

The size dependent colloidal behavior of aqueous dispersions of carboxylated multiwall carbon nanotubes (c-MWCNTs) is presented. The presence of carboxylic groups provided electrostatic stabilization in water, where the size affected agglomeration. While aspect ratio did not show any definite correlation, the hydrophobicity indices (HI), zeta potential and aggregation kinetics showed dependence on the length of the c-MWCNTs where the shorter c-MWCNTs showed significantly lower HI values, smaller particle aggregates, higher zeta potential values and higher critical coagulation concentrations (ccc) in the presence of electrolytes. Although the diameter of the short c-MWCNTs did not appear to influence their aggregation behavior, the longer c-MWCNTs showed a dependence on diameter where stability decreased with increasing CNT diameter.

Fig. 1

Scanning electron microscope images of the c-MWCNTs.

Fig. 2

A (a) TGA data for purified MWCNTs, (b) representative TGA profile of the c-MWCNTs showing MWCNT83, (c); B (i) FTIR spectra of purified MWCNTs and (ii) representative FTIR spectra of the c-MWCNTs showing MWCNT₂₅₀.

Fig. 3

1-Octanol extraction of c-MWCNTs in (a) DI water, (b) 25 mM NaCl, and (c) 25 mM MgCl₂, and particle aggregation in the presence of (d) DI water, (e) 25 mM NaCl, and (f) 25 mM MgCl₂.

Fig. 4

Hydrophobicity index of the c-MWCNT as a function of (a) aspect ratio and as a function of diameter in the presence of 100 mM (b) NaCl and (c) MgCl₂.

Fig. 5

Particle size distribution in a 100 mM electrolyte solution as a function of tube diameter for the c-MWCNTs in the presence of (a) NaCl and (b) MgCl₂.

Fig. 6

Zeta potential as a function of diameter for the c-MWCNTs in the presence of (a) NaCl and (b) MgCl₂.

Fig. 7

Particle size as a function of time in the presence of (a) NaCl and (b) MgCl₂ and attachment efficiency as a function of c-MWCNT diameter in the presence of (c) NaCl and (d) MgCl₂.

Fig. 8

Colloidal stability as a function of c-MWCNT diameter for (a) short c-MWCNTs and (b) long c-MWCNTs.