Chemistry Reference
In-Depth Information
Table 4.1 Predicted dependence of the Raman band shift rates with both
strain and stress for the different models of fi ber structure
Band shift
Uniform stress
Uniform strain
d
d
f
Δν
ε
Independent of
E
f
∝
E
f
d
d
Δν
σ
Independent of
E
f
1
E
f
∝
f
It is therefore predicted that in the situation where there is a uniform
strain in the fi ber, d
f
should be proportional to the reciprocal of
the fi ber modulus, 1/
E
f
. If the band shift is measured as function of
strain, then using Equation 4.3 and since the strain is uniform,
Δ
ν
/d
σ
d
d
Δν
ε
σ
==
d
d
f
E
.
(4.8)
r
f
r
Hence since
E
r
is constant, then d
f
is constant. Table 4.1 summa-
rizes these predictions for Raman band shifts in the cases of uniform
stress and uniform strain.
Δ
ν
/d
ε
4.3 RAMAN SPECTROSCOPY AND MOLECULAR
DEFORMATION
Before laser sources became available, because the Raman effect is
very weak [13,14], infrared spectroscopy of polymers was far more
popular as a technique for the characterization of polymers [15 - 19] .
Even in these early stages of development, however, Raman spectra
were reported from polymeric materials such as polystyrene [20] . Until
the development of laser technology, and particularly the emergence
of new optical rejection fi lters [21] for enhancing Raman Stokes and
anti-Stokes spectral peaks and the microscope or microprobe systems
for high spatial resolution [22], detailed studies of polymers were not
possible. Interest then began into using vibrational spectroscopy to
follow local changes in the structure of polymer fi bers. Further interest
in the use of Raman spectroscopy to characterize polymers has
increased with the development of polymers with conjugated back-
bones which undergo resonance Raman scattering and give strong, very
well - defi ned spectra. After the initial studies into the characterization
of static samples, people began to use these techniques to understand
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