28
1 Introduction to PVA-Based Bionanocomposite Films
interphase thickness based on molecular dynamic (MD) simulations, which implied
that the interphase thickness appeared to be relatively insensitive to nanoparticle
diameters and contents. Li et al. [183] reported that the volume fraction of interphases
could be size independent by using a modified hierarchical multi-interphase model
(MHMM). However, the interphase thickness might be influenced by the reinforcing
efficiency of nanoparticles when their lengths were over 40 nm. On the contrary, Gu
et al. [184] and other co-workers [185, 186] inferred that the interphase thickness
could be non-constant in nanocomposites systems. So far, nanointerphase properties
and features have not been explicitly quantified in a systematic manner by means of
direct topography of nanomechanical characterisation. As a matter of fact, nanomechanical techniques using tip–sample interactions such as atomic force microscopy
(AFM) [187], nanoindentation and nanoscratch tests [188, 189] are vital as effective
and relatively straightforward approaches to determine nanomechanical properties
of interphase. In addition, interphase dimensions and sizes can be clearly specified
due to their distinct mechanical properties from those of bulk materials. The interphase width of glass fibres coated with coupling agents was previously determined to
be around several microns [188, 190]. Nonetheless, a quantitative analysis of interphase dimensions associated with nanomechanical properties still undergoes limited
lateral resolutions and positioning capability of indenter probe used in nanoindentation and nanoscratch techniques. In particular, interphase regions of thermosetting
polymer/glass fibre composites are much thinner than those of individual fibre and
matrix components [191]. Plastic deformation usually takes place under a high fraction of applied load, thus resulting in an increase in the minimum allowable distance
between tow indentation spots, as well as the reduction of lateral resolutions of such
tests [190, 192]. The peak force quantitative nanomechanical mapping (PFQNM)
becomes a relatively new and powerful technique to quantitatively measure nanomechanical properties of materials such as the stiffness and adhesion of nanocomposites along with corresponding acquired dimensions [193, 194]. The use of PFQNM
greatly supports the measurement of material elastic properties based on tip–sample
force curves and the acquisition of topographic images simultaneously. Moreover,
other critical properties, consisting of tip–surface adhesion and surface deformation,
can also be obtained by overcoming the difficulty associated with lateral forces. Such
a technique is believed not only to sophisticatedly distinguish between nanofillers,
nanointerphases and polymer matrices, but also to accurately quantify dimensions
and nanomechanical properties of interphase.
Nanomechcanical properties of PVA and PVA nanocomposites are completely
different from those of their bulk material counterparts. It is worth noting that average
elastic modulus of bulk PVA films is approximately 2.064 GPa at a macroscopic level
[168], which is far less in magnitude when compared with local nanophase such as 9.9
GPa for PVA/10 wt% poly(acrylic acid) (PAA) blends [195]. Moreovere, in case of
PVA-PAA-based nanocomposites reinforced with 10 wt% CNCs [195], their average
interphase elastic modulus was found to vary from 12.8 GPa at the interface of CNCs
to 9.9 GPa in PVA-PPA matrices. On the contrary, PVA nanocomposites reinforced
with 10 wt% CNCs possessed the highest elastic modulus only 1.9 GPa in their bulk
properties [196]. Such a modulus-variation phenomenon between nanomechanical
1 Introduction to PVA-Based Bionanocomposite Films
interphase thickness based on molecular dynamic (MD) simulations, which implied
that the interphase thickness appeared to be relatively insensitive to nanoparticle
diameters and contents. Li et al. [183] reported that the volume fraction of interphases
could be size independent by using a modified hierarchical multi-interphase model
(MHMM). However, the interphase thickness might be influenced by the reinforcing
efficiency of nanoparticles when their lengths were over 40 nm. On the contrary, Gu
et al. [184] and other co-workers [185, 186] inferred that the interphase thickness
could be non-constant in nanocomposites systems. So far, nanointerphase properties
and features have not been explicitly quantified in a systematic manner by means of
direct topography of nanomechanical characterisation. As a matter of fact, nanomechanical techniques using tip–sample interactions such as atomic force microscopy
(AFM) [187], nanoindentation and nanoscratch tests [188, 189] are vital as effective
and relatively straightforward approaches to determine nanomechanical properties
of interphase. In addition, interphase dimensions and sizes can be clearly specified
due to their distinct mechanical properties from those of bulk materials. The interphase width of glass fibres coated with coupling agents was previously determined to
be around several microns [188, 190]. Nonetheless, a quantitative analysis of interphase dimensions associated with nanomechanical properties still undergoes limited
lateral resolutions and positioning capability of indenter probe used in nanoindentation and nanoscratch techniques. In particular, interphase regions of thermosetting
polymer/glass fibre composites are much thinner than those of individual fibre and
matrix components [191]. Plastic deformation usually takes place under a high fraction of applied load, thus resulting in an increase in the minimum allowable distance
between tow indentation spots, as well as the reduction of lateral resolutions of such
tests [190, 192]. The peak force quantitative nanomechanical mapping (PFQNM)
becomes a relatively new and powerful technique to quantitatively measure nanomechanical properties of materials such as the stiffness and adhesion of nanocomposites along with corresponding acquired dimensions [193, 194]. The use of PFQNM
greatly supports the measurement of material elastic properties based on tip–sample
force curves and the acquisition of topographic images simultaneously. Moreover,
other critical properties, consisting of tip–surface adhesion and surface deformation,
can also be obtained by overcoming the difficulty associated with lateral forces. Such
a technique is believed not only to sophisticatedly distinguish between nanofillers,
nanointerphases and polymer matrices, but also to accurately quantify dimensions
and nanomechanical properties of interphase.
Nanomechcanical properties of PVA and PVA nanocomposites are completely
different from those of their bulk material counterparts. It is worth noting that average
elastic modulus of bulk PVA films is approximately 2.064 GPa at a macroscopic level
[168], which is far less in magnitude when compared with local nanophase such as 9.9
GPa for PVA/10 wt% poly(acrylic acid) (PAA) blends [195]. Moreovere, in case of
PVA-PAA-based nanocomposites reinforced with 10 wt% CNCs [195], their average
interphase elastic modulus was found to vary from 12.8 GPa at the interface of CNCs
to 9.9 GPa in PVA-PPA matrices. On the contrary, PVA nanocomposites reinforced
with 10 wt% CNCs possessed the highest elastic modulus only 1.9 GPa in their bulk
properties [196]. Such a modulus-variation phenomenon between nanomechanical