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Figure 37 also provides shape information. Measurements of the radius of gyration (R
G
)
Or, in the form of a table:
Sample
M (g/mol) R
G
(nm)
1
M
1
R
G,1
2
M
2
R
G,2
3
M
3
R
G,3
.
.
.
.
.
.
R
G
(the radius of gyration) can be determined experimentally by light- or X-ray
scattering. The examples above refer to light scattering, where M and R
G
were obtained simultaneously in the same experiment.
2.2.2. Radius of gyration
(R
G
)
We first need to define the radius of gyration (R
G
). This term is a bit
misleading because we are not at all dealing with traditional gyration, like a
wheel spinning around an axis. Instead, R
G
tells us about how the mass is
distributed around the centre of mass. Consider a polymer having
i
monomers
of mass m
i
, each of distance r
i
from the centre of mass:
1
10
100
1 000
10 000
100 000
1 000 000
10 000 000
M (g/mol)
R
G
(nm)
Pullulan
Xanthan