Biomedical Engineering Reference
In-Depth Information
0.1-10 nm
b
b
a
c
a
10-100 nm
1-100
μ
m
mm
2.1
Schematic of the hierarchical structure in crystallizable polymers.
and intramolecular interactions. Information at these length scales
often relates to the chemical structure of the polymer. The structure in
between these two extremes, at 10-100 nm length scales, provides infor-
mation about the mesoscale structures that are often present in polymers.
Analysis of the structure at each of these three length scales is necessary
to understand how the changes in chemical composition lead to changes
at sub-nm (molecular) length scales, are propagated through the meso-
scale structures, then onto the microscopic length scales, and fi nally man-
ifest as the changes in material properties. In this section, we focus on the
characterization of nanoscale and mesoscale structures, and the signifi -
cance of these measurements.
Unlike the microscopic techniques in the previous chapter, the tech-
niques described here do not directly lead to a molecular image. Rather, the
techniques described in this chapter make use of the result of interactions
between radiation and the bulk materials, the scattering of light, X-ray and
neutron radiations, to deduce the structure. These techniques often provide
a parameter that can be related to physical characteristics of the structure,
such as the orientation parameter, that relates to how well the molecules
are aligned, and a size parameter, that relates to the physical dimension of
the object. Clever use of the techniques has made it possible to construct a
model that can be related on the one hand to the chemical structure of the
material, and on the other to the macroscopic images obtained using micro-
scopic techniques.
