Biomedical Engineering Reference
In-Depth Information
1st order, Ra = 17.6 nm
2nd order, Ra = 7.1 nm
3rd order, Ra = 6.1 nm
4th order, Ra = 5.8 nm
5th order, Ra = 4.5 nm
6th order, Ra = 4.1 nm
3.0
2.8
2.6
0.4475
Ra
Rq
0.4450
100
2.4
0.4425
2.2
2.0
0.4400
50
1.8
1.6
0.4375
1.4
1.2
0
0.4350
0
20
40
60
0
500
1000
1500
2000
2500
3000
1000
10000
100000
Distance (µm)
Image size (nm)
Size (pixels)
Fig. 7.3. Illustrations of the effects of scanning and data processing parameters on measured surface
roughness. Left: the effect of changing the area scanned (image size) on the measured roughness
values (
R
a
and
R
q
). In general smaller AFM scans show smaller values of roughness. Centre: the effect
of changing the number of pixels in the image (pixel resolution) on the roughness (
R
q
). In general,
there's a very weak relation between the pixel resolution and the roughness value. Reproduced with
permission from [415]. Right: effect of image processing (levelling algorithm) on roughness of line
scans on a femoral head implant replica (
R
a
). The higher the order of polynomial applied, the lower
the roughness [361]. Reproduced with the kind permission of Dr. James R. Smith, University of
Portsmouth, UK. (A colour version of this illustration can be found in the plate section.)
measurements of materials, AFM-based measurements have some unique advantages.
AFM-based nanoindentation was compared to measurements with a dedicated instrument
in Section 3.2.2. The main advantages of AFM are high force sensitivity (hence high
sensitivity to differences in sample stiffness, especially for compliant materials), and high
lateral resolution, which means that small features or domains can be selectively probed.
For these reasons, AFM-based nanoindentation has been widely applied in the physical
and materials sciences to probe mechanical properties of micro- and nanoparticles [186,
278], metals [417], silicon [418], and many other materials [419].
Polymers have been a particular focus of AFM nanoindentation studies [168, 181]. One
reason for this is that many composite polymeric materials exhibit nanoscale domains.
Examples include polymers with fillers or other added particulate materials, and block
copolymers. Measurement of the stiffness of such domains can help to understand their
contributions to the overall mechanical properties of the bulk materials. In some cases,
materials are added to a polymer specifically to change the mechanical properties, such as
adding stiffness, or increasing elasticity [420]. Furthermore, the nature of the interface
between the reinforcing material and the continuous polymer matrix are extremely
important for the mechanical properties of such materials. AFM-based nanoindentation
is ideal to probe the mechanical studies of nanoscale phases, as well as their interfaces.
Furthermore, measuring the resistance to mechanical probing of a polymer surface can
also help to identify individual phases in a composite material [158, 181]. An example of
this is illustrated in Figure 7.4. In this case, the material under study was a commercial
silicone paint, known to include both large (100-1000 nm) CaCO
3
filler particles, as well
as small (
10 nm) silica particles. Previous work had failed to detect Ca at the surface,
which led to the assumption that features seen at the surface, while of similar dimensions
to the CaCO
3
filler, had some other origin [421]. AFM-based nanoindentation measurements
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