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79
The intrinsic viscosity of pectins: Role of branching
The following figure is taken from the literature
24
:
The dotted points (
•
) are experimental data for intrinsic viscosity [
η
]
(measured at an ionic strength of 0.1 M) and weight-average molecular weight
(M
w
, obtained by light scattering) for different fractions of pectin from
sunflower.
Note that the data follow the Mark-Houwink equation for M
w
between 10
4
and
10
5
(g/mol). The authors found that [
η
] = 0.0955 M
w
0.73
. This is within the
range 0.5-0.8 which is expected for random coils in
θ
-solvents or good
solvents, respectively.
For M
w
> 100.000 the curve deviate from the expected straight line. This is
attributed to branching. Adding long branches tend to increase the molecular
weight, but not the specific
25
hydrodynamic volume of the equivalent sphere:
24 Anger, H. and Berth, G. (1985). Carbohydrate Polymers 6 (1986) 193-202.
25 Specific => per gram, not per molecule