Biomedical Engineering Reference
In-Depth Information
composite. The obtained composite body is either used as the final
composite after heat treatment (de Andrade et al., 2007) or crushed,
ground, sieved and then sintered to obtain composite samples of the desired
shape (Thomas et al., 2009). Although earlier studies showed a degree of
CNT agglomeration (Ning et al., 2003b, 2004), later investigations showed a
better dispersion of CNTs in glass/glass-ceramic matrices, after functiona-
lization, at 3wt% (Thomas et al., 2009) and then 10wt% loadings (Otieno
et al., 2010). However, higher loadings of CNTs (15wt%) still produce
agglomerates (Mukhopadhyay et al., 2010). Different types of CNTs, i.e.
SWCNTs (Babooram and Narain, 2009, Chu et al., 2008, de Andrade et al.,
2007, 2008), DWCNTs (de Andrade et al., 2009) and MWCNTs
(Mukhopadhyay et al., 2010, Thomas et al., 2009) have been incorporated
in glass/glass-ceramic matrices by the sol-gel process including silica (Seeger
et al., 2001), borosilicate (Thomas et al., 2009) and aluminoborosilicate
(Chu et al., 2008).
In one of the earliest studies on sol-gel processing (Seeger et al., 2001),
tetraethoxysilane (TEOS) was used as the precursor in acidified water to
produce a silica glass matrix. CNTs were mixed with the solution and, after
condensation, produced a composite body containing 2.5wt% MWCNTs,
which was milled to powder and densified by pressureless sintering (Seeger
et al., 2002) and laser treatment (Seeger et al., 2003). In earlier attempts,
CNTs without functionalization were incorporated in the precursor of the
desired matrix (Gavalas et al., 2001); however, later investigations focused
on using appropriate surfactants or coupling agents for improved dispersion
(Hernadi et al., 2003). Most subsequent studies have used functionalized
CNTs in sol-gel processing to produce composites (Babooram and Narain,
2009, Berguiga et al., 2006, DiMaio et al., 2001, Zhan et al., 2003, Zhang
et al., 2006, Zheng et al., 2007, 2008).
Transparent silica glass matrix composites were also prepared by
reinforcing SWCNTs (DiMaio et al., 2001) and MWCNTs (Xu et al.,
2009) by sol-gel processing. CNT-SiO
2
glass composites for non-linear
optical properties (Xu et al., 2009, Zhan et al., 2005), microwave attenuation
(Xiang et al., 2005) and electromagnetic interference shielding (Xiang et al.,
2007) provide further examples of sol-gel processing. In addition to bulk
composites, thin composite films of CNT-SiO
2
were also produced by this
technique and deposited by spin coating (Loo et al., 2007) and dip coating
techniques (Berguiga et al., 2006, de Andrade et al., 2007, Lopez et al.,
2010). CNT-mesoporous silica composites were also produced by the sol-
gel technique to develop novel biomaterials (Vila et al., 2009).