Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

Figure 5.21 Reaction between SWNT-COOH and GPTMS in
forming f-SWNT and its subsequent incorporation into silica
matrix via the sol-gel technique. Reproduced with permission
from [91]. Copyright Ó (2006) The Royal Society of Chemistry.
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morphology of SiO2/CNT thin film imaged by the atomic force microscopy (AFM) in
tapping mode. Good dispersion of MWNTs in silica matrix can be readily seen in
these micrographs.
Zhang et al.funtionalized SWNTs (f-SWNTs) covalently with silane agent and
incorporated them into silica matrix via the sol-gel process [91]. Figure 5.21 shows the
strategy of incorporating f-SWNTs into silica matrix. Pristine SWNTs were first
purified with sulfuric/nitric acids to form carboxylic groups, and then reacted with
(3-glycidoxypropyl)trimethoxysilane (GPTMS). The resulting mixture was stirred
and heated to 70 C for 24 h. The silica sol was prepared by hydrolysis of TEOS with
ethanol, water and hydrochloric acid. GPTMS sol containing f-SWNTs was prepared
by hydrolysis of the GPTMS/f-SWNT mixture with water, ethanol and formic acid.
These two sols were then mixed at the same molar ratio. The hybrid sol was finally
cast on a glassy carbon electrode followed by air drying. Once the functional groups
are formed on the nanotube surfaces, the electrostatic repulsion between nanotubes
can overcome van der Waals interactions, thereby forming a stable suspension in the
solvent [91].
Loo et al. studied the effect of surfactant additions on the dispersion of MWNTs in
SiO2 sol [86]. The surfactants used include hexacetyltrimethyl ammonium bromide