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97
M R
G
(nm)
10000
5
50000
8.6
250000
14.6
1
10
100
1000 10000 100000 1000000
M (g/mol)
R
G
(nm)
Figure 40. Data for a polymer shaped like a solid shere.
2.2.4. The R
G
-‐M
relationships
for
rigid
rods.
A rod is even simpler: M
∝
L, and
G
1
R
L 0.289L
12
=
=
(see chapter 6.4.1 in
textbook for strict mathematical proof),
therefore:
log log
.
G
G
R M
R M const
∝
=
+
If we plot log R
G
as a function of log M should for a rod obtain a straight line
with slope 1.0.
In fact, xanthan (see Figure 5) behaves like a stiff rod when the molecular
weight is below 10
6
g/mol (Da). The slope of the dotted line in Fig. 5 is in fact
1.0.