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(a)
(b)
Figure 2.32. Stress-strain relations of the nematic networks (
σ
∗
≡
σ/Nk
B
T
) for var-
ious temperatures (a) (From Warner & Wang, 1991); and experimental stress-strain
relations of the nematic networks (b) (Modified from Schatzle
et al
., 1989.)
Disagreement between classical network theory and experimental data
occurs. The entanglement effect was thought to be responsible for the devia-
tion. According to the classical network theory, the stress-strain rela-
tionship should follow Equation 2.139. The plot of the reduced force,
σ
∗
/
(
λ
2
−
1
/λ
), against the reciprocal strain, 1
/λ
, should be constant,
i.e.
,
unity. But experiments show that the reduced force is a function of the
extension ratio
λ
. Figure 2.33 shows the typical experimental data of PDMS
