Biomedical Engineering Reference
In-Depth Information
0.010
0.008
0.006
0.004
0.002
0
0
0.5
1.0
1.5
2.0
m
−
1
)
q
(
μ
Figure 10.5
Change of light scattering profile I(q) versus time for a ternary solution of 4.2% gelatin, 4.2%
dextran and water quenched to T = 21°C at 126 s (
□
), 378 s (
Δ
), 560 s (
◊
), 1160 s (
○
) and 1382 s (+).
From Tromp et al.(
1995
) © 1995 American Chemical Society.
quench. Subsequently, phase separation above the gelation temperature proceeded via
formation of large gelatin-rich spheres that grew by coalescence. For the gelling system
the morphology was
'
frozen
'
after about 20 min, when it was still a
ne network.
10.4.1.2
Gelatin
maltodextrin
Another example of segregative phase separation and gelation is provided by aqueous
gelatin
-
maltodextrin mixtures quenched to various end temperatures (Lorén et al.,
2001
,
2002
). The co-system, maltodextrin, represents one of a series of commercially degraded
starches. The authors determined the time evolution of the bicontinuous microstructures
by confocal laser scanning microscopy (CLSM) of a
-
fluorescently labelled maltodextrin,
and the growth of the bicontinuous microstructures was quanti
ed by Fourier image
analysis. The mixtures were quenched from 60°C to various end temperatures both above
and below the gelatin gelation temperature, and the gelatin concentration was chosen so
the continuous phase was gelatin-rich. Measurements showed that the mixture phase
separated through SD at all temperatures. The authors noted that the time of residence in
the region where phase separation competes with gel formation was of critical impor-
tance in in
uencing the morphology of the resulting system, gelation of the continuous
phase having a strong in
uence on the structure evolution. Phase separation
finally
'
'
became trapped kinetically (
) by gelation (Lorén et al.,
2002
).
A series of six CLSM micrographs of the ternary solution recorded at various times
during a temperature quench is shown in
Figure 10.6
. The series of micrographs clearly
show the mottled pattern attributed to the SD phase separation mechanism. The onset of
phase separation is shown in micrograph (a) as
pinned
fluctuations in concentration with a
characteristic wavelength, i.e. a characteristic distance between the maltodextrin
domains (bright phase). The micrograph series also shows that the distance between
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