22
With SEC-LS coupled with an on-line viscometer in the triple-detector configuration,
additional precision can be gained in determining molecular sizes, and thus providing
meaningful information of polymer branching and conformational differences.
10,11
The coupling of a viscometer and a light scattering detector in one SEC instrument
greatly improves the precision and dynamic range of SEC for polymer conformation studies.
The SEC-Viscometry-LS results are insensitive to typical adverse variations of SEC
experimental conditions, such as flowrate inconsistency, band broadening, column deterioration,
non-SEC retention effect, moderate sample overloading, etc.
In the SEC-Viscometry-LS experiment, the molecular size at every elution volume can
be calculated in addition to the molecular weight value. For the hydrodynamic radius of the
molecule (
R
h
):
[A.2-11]
[ ]
R
M
h
=
3
4
0 025
1 3
π
η
.
For linear flexible chain polymers, this can be related to the radius of gyration, using the Flory-
Fox and Ptitsyn-Eizner equations,
12,13
where,
[A.2-12]
[ ]
3
1
2
1
6
1
Φ
=
M
R
g
η
[A.2-13]
(
)
Φ =
×
−
+
2 55 10 1 2 63
2 86
21
2
.
.
.
ε
ε
[A.2-14]
ε
=
−
2
1
3
a
where
a
is the exponent of the Mark-Houwink equation:
[A.2-15]
[ ]
η
=
KM
a
SEC-VISCOMETRY-RALLS/LALLS
In this triple detector method, the angular dissymmetry in the scattered intensity is
accounted for by using the combined measurements of intrinsic viscosity at 90° light scattering
intensity (RALLS: Right Angle Laser Light Scattering-
Figure 6
) to determine both molecular
size and the molecular weight. Size determination of small polymer molecules is possible with
this new method, even when there is no observable multi-angle LS dissymmetry.
10
M. A. Haney, C. Jackson, and W. W. Yau, Water’s International GPC Symposium Proceedings, 1991.
11
C. Jackson, H. G. Barth, and W. W. Yau, Water’s International GPC Symposium Proceedings, 1991.
12
T. G. Fox and P. J. Flory, J. American Chemical Society,
73
, 1904 (1951).
13
O. B. Ptitsyn, and Y. E. Eizner, Sov. Phys., Tech. Phys. 4, 1020 (1960).