| Summary: | 碩士 === 國立中興大學 === 材料工程學系所 === 94 === Abstract
Dispersion of multi-walled carbon nanotubes (MWCNTs) in pure water has been investigated using various organic surfactants. An optimal surfactant was selected by zeta potential measurement; from which, CTAB was determined the best surfactant among the surfactants examined. Rheological behavior of the MWCNT suspensions was then examined under various CTAB concentrations (0.2 – 5 wt. % of solvent) and CNT concentrations (1 – 3.5 wt.% of solvent) over a shear-rate range ( = 1 – 1000 s-1). The suspension viscosity appeared to decrease from 1.33 to 0.26 Pa．s at a shear rate of 10 s-1 when CTAB concentration varied from 0.2 to 2 wt.%. The viscosity increased adversely when the CTAB concentration exceeded 2 wt.%, revealing that the optimal CTAB concentration was ~2 wt.%. From adsorption isotherm, specific adsorption reached 95.34 mg/g, which is 87 % of saturation, at CTAB concentration of 1 wt.%. We suspect that the dispersion mechanisms involved in CTAB-MWCNT/water system is mainly due to the electrosteric and depletion stabilization.
The specific adsorption of CTAB on MWCNT was found similar in different pH values (2.8 and 10) with presence of HCl and NaOH. The CTAB adsorption was 100.51, 100.18 and 106.74 mg/g for NaCl concentration of 1, 10 and 100 mM, respectively. In comparison, the specific adsorption of pristine MWCNT suspensions was 109.69 mg/g. The CTAB specific adsorption was decreased at low NaCl concentrations (0.001 and 0.010 M) and was increased in the case of 0.1 M, while the zeta potential was decreased with increasing NaCl concentration up to 0.1 M, due presumably to the compression of electrical double layer. We suspect that the increase of CTAB specific adsorption at 0.1 M NaCl is due to ions strength screening effect.
At 2 wt.% CTAB concentration, MWCNT suspensions exhibited thixotropic behavior when the MWCNTs concentration is raised above 3 wt.%. The area enclosed by shear stress and shear rate appeared to decrease with NaCl concentration, suggesting that the thixotropic behavior is dependent on solids loading and zeta potential.
Finally, we presume that MWCNTs are individual and take advantage of theoretical equations of van der Waals forces, electrostatic forces and depletion forces to estimate interparticle potential energy (Vtotal).
Key Word : Carbon Nanotube, CTAB, Dispersion, pH, NaCl Concentration
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