Civil Engineering Reference
In-Depth Information
15.4.3
Characterization Methods
Extensive research has already been done for the extraction of CNCs from various
sources. h ese are mainly of "rod-like" crystalline nanoparticles with dif erent dimen-
sions, morphology and topography; the degree of crystallinity depending on extraction
process, source and origin of cellulose, and hydrolysis conditions [67]. Morphological
and topographical characterizations of CNCs are usually performed by using trans-
mission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic
force microscopy (AFM). In these techniques, the same process can be used to prepare
the samples for measuring the dimensions of nanocrystals. In this way, a drop of nearly
0.1% (w/v) of aqueous suspension of CNCs was placed on carbon-coated grid (in case
of TEM), glass slide (in case of SEM) and mica or glass slide (in case of AFM) followed
by drying. Further, the dimensions can be measured by counting from TEM, SEM and
AFM micrographs at dif erent positions, manually. h e TEM, SEM and AFM images
typically show aggregation of the nanocrystals due to the drying during sample prepa-
ration. However, along with aggregation, usually instrumental artifacts (as tip-broad-
ening ef ect in case of AFM) lead to an overestimation of nanocrystals dimensions [88].
To prevent aggregation and to overcome the issues of artifacts, Elazzouzi-Hafraoui
et
al.
reported the TEM in cryogenic mode (cryo-TEM) for measuring precise dimen-
sions [89]. Kumar
et al.
[76] investigated the morphology and topography of sugar-
cane bagasse-based CNCs by using TEM, SEM and AFM techniques (as shown in
Figure 15.8 ). h e dimensions lie in the range of 250-480 nm in length and 20-60 nm
in diameter.
h e light scattering techniques such as dynamic (polarized) light scattering (DLS)
and dynamic (depolarized) light scattering (DDLS) [90, 91], static light scattering [92],
small angle X-ray scattering (SAXS) under shear [93] and small angle neutron scatter-
ing [37] have also been used for precise dimensions and morphological characteriza-
tions. In this sequence, De Souza Lima
et al.
calculated the dimensions of CNCs by
using DLS dynamic laser scattering for tunicate (L = 1160 nm; D = 16 nm) and cotton
(L = 255 nm; D = 15 nm) as similar to values obtained for tunicate (L = 100 - some
1000 nm; D = 15-30 nm) [94] and cotton (L = 100-150 nm; D = 5-10 nm) [95] by using
TEM. Braun
et al.
reported the dimensions of CNCs from cotton linter as 13 nm wide
and 272 nm long.
Figure 15.8
Morphology and topography of CNCs: (a) i eld emission scanning electron micrograph
(FESEM, 500 nm scale); (b) transmission electron microscopy image (TEM, 500 nm); (c) atomic force
microscopy (AFM, 2 μm scale) [76].
