Biomedical Engineering Reference
In-Depth Information
(Fig. 1.10). 65 Both TMC and NOSC polymers were synthesised from low-
viscous chitosan, which has an average molecular weight of 200 kDa. The
a
b
c
a
b
c
CH 2 OSO 3 -
CH 2 OH
CH 2 OH
O
*
O
O
O
*
n
*
O
O
n
n
OSO 3 -
OH
OH
*
*
*
+
NH
NH CO O Na
N(CH 3 ) 3
Cl
Figure 1.10 Chemical structure of some water-soluble derivatives of chitosan: (a)
carboxymethylated chitosan, (b) thrimethylchitosan chloride (TMC) and (c) N -octyl-
O -sulphate-chitosan (NOSC).
TMC and NOSC polymers present comparable thickness of coating,
respectively 3.7 - 4.4 nm and 4.7 nm, as observed by AFM imaging (Fig. 1.11).
Further studies should be carried out to identify the actual effect of coating
thickness on the stability and characteristics of the CNT-polymer composite.
Figure 1.11 An AFM image of SWNT treated with octyl chitosan (0.5 mg/mL) after
centrifugation. A = coated region (height = 6.6 ± 1.2 nm, n = 10) and B = uncoated
region (height = 1.9 ± 0.4 nm, n = 10). See also Colour Insert.
The use of chitosan as a suspending agent also provides a way of purifying
CNTs. Zhang et al. 53 reported that when chitosan-MWCNT composites
were analysed by TGA, the peak at 470°C, assigned to the degradation of
amorphous carbon impurities, disappeared. Chitosan has been shown not
only to separate CNTs from carbonaceous impurities but also to speciically
segregate CNTs according to their diameter and chirality. Yang et al. 52 analysed
the supernatant and the precipitate of a SWCNT suspension obtained by
sonication in the presence of high molecular weight chitosan, by Raman
 
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