Biomedical Engineering Reference
In-Depth Information
0.5
0.4
0.3
F
x
(
μ
)
0.2
0.1
0.0
0.1
0.2
0.3
μ
0.4
0.5
0.6
(Å
-1
)
2.18
An example of a Kratky plot (from polyisobytlene dissolved in
benzene-
d
6
at
θ
-solvent conditions. Solid line is by the curve calculated
for the polymer chain in the bulk using Monte Carlo methods. (Source:
Reprinted with permission from Ref. 56. Copyright 1983. American
Chemical Society.)
conformational relaxation processes are slow compared to the timescale
of deformation.
54
In experiments with drawing stretching of polystyrene
57
and polypropylene
58
fi laments, it was found that molecular deformation, as
determined by the ratio of the
R
g
parallel to the draw direction to that in
the undeformed sample, was equal to the macroscopic deformation, con-
sistent with the hypothesis that molecules are deformed affi nely and that
the melt is incompressible (Fig. 2.19). The results also showed that a single
chain is long enough to traverse several lamellae - 136 nm in polypropylene
that could span about eleven lamellae. Non-affi ne deformation has been
observed at high elongations (>3) and in crosslinked networks.
2.7.2 Polymer mixtures
Another signifi cant application of SANS is in the investigation of the mis-
cibility characteristics of polymer blends. Methods such as thermal analysis,
mechanical measurements and light scattering demonstrate macroscopic
segregation, whereas SANS can probe the thermodynamics of polymer-
polymer interactions at the molecular level. This is done by deuterating one
of the components in a blend.
53
