58
3 PVA/BC Bionancomposite Films with Particle Size Effect
Moreover, surface area and pore volume tend to be the other two important
controlling factors in effective BC reinforcements. As mentioned previously by Das
et al. [10], pore volume and pore number in BCs could enhance the absorption
capacity of polymer matrices to allow for their sufficient interfacial bonding with
BCs. All three measured major surface areas including Brunauer–Emmett–Teller
(BET) surface area (S BET ), micropore area (S micro ) and external surface area (S ext )
appear to be consistently higher for NBCs when compared with those of MBCs
despite comparable micropore volume (V micro ) and relatively low pore diameter
(D pore ) of NBCs. Such results imply that NBCs have much better adsorption capability towards surrounding media, and thus can yield more efficient load transfer
from polymer matrices to fillers, which is in good agreement with previous work
from She et al. [11]. The increase in NBC surface areas may be attributed to high
carbonisation temperature (≥1300 °C) and small particle size [11, 12].
3.2.2 Particle Size and Elastic Modulus
Topographical analysis in relation to morphological structures of as-received NBCs
and MBCs was conducted by means of peak force quantitative nanomechanical
mapping (PFQNM) via atomic force microscopy (AFM), Fig. 3.1. After the holistic
evaluation of 1356 near-spherical NBCs and 871 MBCs, it has been statistically
determined that average particle diameters are 69.43 and 406.8 nm for NBCs and
MBCs, respectively. In addition, the average thickness of NBCs is about 6 nm as
compared to 54.4 nm for that of MBCs. Figure 3.1a, c as well as Fig. 3.1b, d display
typical cases of NBCs and MBCs deposited on steel substrates from aqueous dispersion at different magnifications, respectively. It is clearly shown that NBCs are more
uniformly dispersed with disc-like particle shapes and smaller particle sizes when
compared with sharp-edge MBCs in a 2D view. The variations of particle size and
thickness visually confirm different surface areas listed in Table 3.1.
Young’s moduli of NBCs and MBCs are essentially used for the prediction of
elastic moduli of corresponding PVA/BC bionanocomposites. However, so far, there
has been no published literature to report such important parameters in an experimental manner. Nanomechanical properties of NBCs and MBCs have also been
determined by AFM using PFQNM to quantitatively measure the stiffness of BCs
as nanoreinforcements. Five different zones of interest on NBCs and MBCs were
selected in typical mapping images, illustrated in Figs. 3.2 and 3.3, respectively.
A set of elastic modulus values was estimated according to Derjaguin–Mueller–
Toporov (DMT) model [13, 14] for each targeted zone based on corresponding
modulus mapping distributions. With the aid of mapping Gaussian distribution
curves, elastic moduli of NBCs and MBCs were determined to be 84.5 ± 3.6 GPa
and 80.65 ± 2.1GPa, respectively. Such results suggested that particle size effects
are minor on elastic moduli of NBCs and MBCs. When compared with those of
other carbon-based fillers, elastic moduli of NBCs and MBCs are higher than that of
T300 carbon fibres [15], which is in range of 20–40 GPa as well as higher than the
3 PVA/BC Bionancomposite Films with Particle Size Effect
Moreover, surface area and pore volume tend to be the other two important
controlling factors in effective BC reinforcements. As mentioned previously by Das
et al. [10], pore volume and pore number in BCs could enhance the absorption
capacity of polymer matrices to allow for their sufficient interfacial bonding with
BCs. All three measured major surface areas including Brunauer–Emmett–Teller
(BET) surface area (S BET ), micropore area (S micro ) and external surface area (S ext )
appear to be consistently higher for NBCs when compared with those of MBCs
despite comparable micropore volume (V micro ) and relatively low pore diameter
(D pore ) of NBCs. Such results imply that NBCs have much better adsorption capability towards surrounding media, and thus can yield more efficient load transfer
from polymer matrices to fillers, which is in good agreement with previous work
from She et al. [11]. The increase in NBC surface areas may be attributed to high
carbonisation temperature (≥1300 °C) and small particle size [11, 12].
3.2.2 Particle Size and Elastic Modulus
Topographical analysis in relation to morphological structures of as-received NBCs
and MBCs was conducted by means of peak force quantitative nanomechanical
mapping (PFQNM) via atomic force microscopy (AFM), Fig. 3.1. After the holistic
evaluation of 1356 near-spherical NBCs and 871 MBCs, it has been statistically
determined that average particle diameters are 69.43 and 406.8 nm for NBCs and
MBCs, respectively. In addition, the average thickness of NBCs is about 6 nm as
compared to 54.4 nm for that of MBCs. Figure 3.1a, c as well as Fig. 3.1b, d display
typical cases of NBCs and MBCs deposited on steel substrates from aqueous dispersion at different magnifications, respectively. It is clearly shown that NBCs are more
uniformly dispersed with disc-like particle shapes and smaller particle sizes when
compared with sharp-edge MBCs in a 2D view. The variations of particle size and
thickness visually confirm different surface areas listed in Table 3.1.
Young’s moduli of NBCs and MBCs are essentially used for the prediction of
elastic moduli of corresponding PVA/BC bionanocomposites. However, so far, there
has been no published literature to report such important parameters in an experimental manner. Nanomechanical properties of NBCs and MBCs have also been
determined by AFM using PFQNM to quantitatively measure the stiffness of BCs
as nanoreinforcements. Five different zones of interest on NBCs and MBCs were
selected in typical mapping images, illustrated in Figs. 3.2 and 3.3, respectively.
A set of elastic modulus values was estimated according to Derjaguin–Mueller–
Toporov (DMT) model [13, 14] for each targeted zone based on corresponding
modulus mapping distributions. With the aid of mapping Gaussian distribution
curves, elastic moduli of NBCs and MBCs were determined to be 84.5 ± 3.6 GPa
and 80.65 ± 2.1GPa, respectively. Such results suggested that particle size effects
are minor on elastic moduli of NBCs and MBCs. When compared with those of
other carbon-based fillers, elastic moduli of NBCs and MBCs are higher than that of
T300 carbon fibres [15], which is in range of 20–40 GPa as well as higher than the