2.3 Characterisation Techniques
53
In this study, a Bruker Dimension Fastscan AFM system was employed to measure
peak force quantitative nanomechanical properties and acquire single force–distance
curve under the ambient condition. Moreover, RTESPA 525A probes with a nominal
spring constant of 200 N/m, a nominal tip radius of 8 nm and a nominal resonant
frequency of 525 kHz were utilised for the direct measurement of corresponding
nanomechanical properties of PVA bionanocomposite films. Before each measurement, it was confirmed that the deflection sensitivity was calibrated by obtaining a
force curve based on the stiff sapphire-12 surface. Later on, a thermal tuning method
[14] was applied to determine the spring constant, which was considered as one of
the most accurate methods for detecting the spring constant by measuring cantilever
mechanical responses to thermal agitation via the Brownian motion of encompassing
fluid molecules. AFM imaging analysis was undertaken with the TESPA probe at
the nominal spring constant of 40 N/m with a tip radius of 8 nm. The image scan
rate was kept at 2 Hz with a digital pixel resolution by 256 × 256. AFM topographic
images were the first-order flattened via Flatten command in Burker Nanoscope 1.5
software, which was used to remove unwanted features resulting from the vertical
(Z) scanner such as noise, bow and tilt.
2.4 Summary
• PVA with the hydrolysis degree of 99.99% was selected as a water-soluble
biopolymer with three different types of nanofillers. BCs were chosen because
of their 3D irregular shape and porous structures for the absorption of PVA
molecules. Additionally, Cloisite 30B clays were employed due to their 1D
platelet-like shape with a relatively large interlayer spacing as well as functional
groups to facilitate the close interaction with PVA molecular chains. HNTs have
been chosen in that such nanofillers possess 2D tubular structures with alumina
and silica groups on HNT surfaces, which assists in the good bonding between
HNTs and PVA matrices in PVA/HNT bionanocomposites.
• Solvent casting method was used in manufacturing PVA bionanocomposites. The
combination process of magnetic stirring, mechanical mixing and ultrasonication
is essential for the fabrication of PVA bionanocomposites. The only exception is
that no chemical solvent apart from water was used, and such bionanocomposite
films were kept in a silica gel-containing desiccator to avoid the moisture effect.
• SEM, XRD and FTIR analyses were carried out to investigate morphological
structures of PVA bionanocomposites films. Conventional tensile tests were
performed to determine their bulk mechanical properties, while nanomechanical
features were evaluated by PFQNM.
• Thermal stability and thermal properties of all bionanocomposites were determined via TGA and DSC, respectively.
53
In this study, a Bruker Dimension Fastscan AFM system was employed to measure
peak force quantitative nanomechanical properties and acquire single force–distance
curve under the ambient condition. Moreover, RTESPA 525A probes with a nominal
spring constant of 200 N/m, a nominal tip radius of 8 nm and a nominal resonant
frequency of 525 kHz were utilised for the direct measurement of corresponding
nanomechanical properties of PVA bionanocomposite films. Before each measurement, it was confirmed that the deflection sensitivity was calibrated by obtaining a
force curve based on the stiff sapphire-12 surface. Later on, a thermal tuning method
[14] was applied to determine the spring constant, which was considered as one of
the most accurate methods for detecting the spring constant by measuring cantilever
mechanical responses to thermal agitation via the Brownian motion of encompassing
fluid molecules. AFM imaging analysis was undertaken with the TESPA probe at
the nominal spring constant of 40 N/m with a tip radius of 8 nm. The image scan
rate was kept at 2 Hz with a digital pixel resolution by 256 × 256. AFM topographic
images were the first-order flattened via Flatten command in Burker Nanoscope 1.5
software, which was used to remove unwanted features resulting from the vertical
(Z) scanner such as noise, bow and tilt.
2.4 Summary
• PVA with the hydrolysis degree of 99.99% was selected as a water-soluble
biopolymer with three different types of nanofillers. BCs were chosen because
of their 3D irregular shape and porous structures for the absorption of PVA
molecules. Additionally, Cloisite 30B clays were employed due to their 1D
platelet-like shape with a relatively large interlayer spacing as well as functional
groups to facilitate the close interaction with PVA molecular chains. HNTs have
been chosen in that such nanofillers possess 2D tubular structures with alumina
and silica groups on HNT surfaces, which assists in the good bonding between
HNTs and PVA matrices in PVA/HNT bionanocomposites.
• Solvent casting method was used in manufacturing PVA bionanocomposites. The
combination process of magnetic stirring, mechanical mixing and ultrasonication
is essential for the fabrication of PVA bionanocomposites. The only exception is
that no chemical solvent apart from water was used, and such bionanocomposite
films were kept in a silica gel-containing desiccator to avoid the moisture effect.
• SEM, XRD and FTIR analyses were carried out to investigate morphological
structures of PVA bionanocomposites films. Conventional tensile tests were
performed to determine their bulk mechanical properties, while nanomechanical
features were evaluated by PFQNM.
• Thermal stability and thermal properties of all bionanocomposites were determined via TGA and DSC, respectively.