Basic HTML Version
105
can calculate n for each sample, since we usually know the molecular weight
of the monomer (M
0
)
34
such that n = M
i
/M
0
(see also Section 2.1.3)
We also need to determine <r
2
> from the corresponding R
G
data. This is
easily achieved using the relations from Chapter 2.1. (remember: valid only
for random coils, n
→∞
):
R
G
2
=
1
6
r
2
r
2
=
α
2
C
∞
nl
2
=
1
6
α
2
C
∞
nl
2
In a
θ
-solvent
α
=1, hence:
r
2
=
C
∞
nl
2
R
G
2
=
1
6
C
∞
nl
2
We thus obtain a set of experimental and calculated data:
Observed
experimentally
Calculated
from M
Observed
experimentally
Calculated
from R
G
Further
calculated
M
1
n
1
R
G,1
<r
1
2
>
<r
1
2
>/l
2
M
2
n
2
R
G,2
<r
2
2
>
<r
2
2
>/l
2
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
M
i
n
i
R
G,i
<r
i
2
>
<r
i
2
>/l
2
Since <r
2
> = C
∞
nl
2
⇒
then <r
2
>/l
2
= C
∞
n
A plot of <r
2
>/l
2
versus
n should therefore be linear and give C
∞
as the slope.
Alternatively a plot of <r
2
>/nl
2
versus
n should give a horizontal line equal to
C
∞
.
Below (next page) is given an example, where M
0
= 162 g/mol and l = 0.5 nm
(typical for
β
-1,4-liked glucans):
34
For cellulose, M
0
= 162 since glucose is C
6
H
12
O
6
(M = 180) and a molecule of water (M =
18) is split of in forming the glycosidic bond