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30.3.2 Selective Adsorption of OSA-Starch
To study the molar mass distribution of adsorbed and non-adsorbed OSA-
starch, an emulsion with a volatile oil phase (cyclohexane) was prepared with
OSA-starch B27-21. In this way the oil phase could be eliminated by flushing
with N
2
after emulsification. The molar mass and rms radii distributions could
then be determined by asymmetrical flow-field flow fractionation coupled to
multi-angle light scattering with refractive index detection (AsFlFFF-MALS-
RI). This is a technique that enables us to characterize very large macromol-
ecules such as the OSA-starch.
22-24
The relative molar mass distributions in the
upper and lower phase, after emulsion separation, are shown in Figure 5. We
can see that the high molar mass components are selectively adsorbed as they
are only detected in the upper phase. Consequently, the lower molar mass
components are found at higher levels in the lower phase. The concentration of
OSA-starch was determined gravimetrically in the whole emulsion, in the lower
a
0.15
0.10
0.05
b
0.15
0.10
0.05
0.00
5
6
7
8
9
log M
Figure 5 Molar mass distribution of OSA-starch in (a) upper phase and (b) lower phase.
The relative mass concentration of OSA-starch (C
rel
) is plotted against the
logarithm of the molar mass M. The upper phase contained not only the
dispersed phase but some aqueous phase as well
(Redrawn from Ref. 25).
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