Chemistry Reference
In-Depth Information
100
µ
m
100
µ
m
Fig. 8.9
s
viscosity silicone oil submitted after shear rate step up to 6 per second. The right-hand
side micrograph shows the equivalent experiment for a physically cross-linked waxy maize
starch suspension droplet. The shear viscosity of both droplet fluids was 15 Pa
Left-hand side micrograph shows a HPMC droplet immersed in 200 Pa
·
s at 6 per
second. Note that the micrographs represent a snapshot from a time-dependent experiment.
·
HPMC droplet does not break up even though it becomes highly elon-
gated. On the contrary, the starch droplet disrupts under these conditions.
The ease of break-up for droplets of the granular starch system is evident
from Fig. 8.10. It shows the well-known Grace curve for shear-induced
droplet break-up of Newtonian droplets immersed in second immisci-
ble Newtonian fluid as well as experimental data obtained for the starch
droplets (Desse
et al
., 2009). The situation for the starch droplets is quite
complex, for example variation of the viscosity ratio
p
, see caption of
Fig. 8.10 for definition, in these experiments was achieved by changing
Ca*
100000
10000
1000
100
10
1
p
0.1
1E-05 0.0001 0.001
0.01
0.1
1
10
Fig. 8.10
Critical Capillary number as a function of viscosity ratio (defined as the viscos-
ity of the droplet fluid over the viscosity of the second immiscible fluid) for starch suspension
droplets (points, solid line added for guidance only) and for a Newtonian fluid. For p
larger than roughly 0.1, droplet break-up was not observed for the starch droplet system
investigated here. Error bars are smaller than the size of the points. (Desse et al., 2009).
Reproduced with permission.
