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110
ratio’ of a polymer. C
∞
is a stiffness parameter reflecting chain stiffening due to
two structural properties, namely the fixed bond angles and hindered rotation
around linkages. Quantitatively, C
∞
expresses quantitatively the increase in
average end-to-end distance (<r
2
>
0.5
) of an otherwise randomly coiled
polymer. We could determine C
∞
from M-R
G
data using the theory of random
coils (RC), provided the chains were long enough to satisfy random coil
criteria.
The table below shows C
∞
data for a range of polysaccharides (and double-
stranded DNA).
Polymer
Solvent
Stiffness parameters
C
∞
Persistence
length
estimates (nm)
Dextran
Water
1.8
0.7
Pullulan
Water
4.3
1.3
Amylose
DMSO
5
Barley 1,3/1,4
β-glucans
Water
13-14
3.5-3.8
Hyaluronan
Water, I =
0.15 M
27
7
Chitosans
(F
A
= 0-0.65)
pH 4.5, I = 0.1
M
19-30
5.1-7.6
Alginates
Water, I =
0.17 M
55
15
Carboxymethy
l cellulose
Water, I = 0.1
M
115
12-16
DNA
Water, I = 0.2
M
45
Xanthan
Water, I = 0.1
M
480
120
Scleroglucan 0.1 M NaOH
150
In recent years another stiffness parameter has been much used in the
literature. It is called the persistence length (symbol: q or L
p
). The persistence
length is connected to an (abstract) alternative model for polymer chains
called the wormlike chain model (WC).
In contrast to the RC model, the WC model is not restricted to long chains, but
is valid all the way from short rod-like chains (rigid rod limit) and across the