Chemistry Reference
In-Depth Information
However, once formed, these structures are incredibly robust and due to
their interfacial rheology are resistant to Ostwald ripening even when
the air cells are micron sized.
10.3.4
Sheared gels (fluid gels)
So having considered how to rebuild structures using water or air in
emulsions and multiple emulsions, are there alternative routes which do
not require the use of 'emulsions'? An example of how oil droplets in
an emulsion product can be replaced using the design rules established
from a microstructural approach is the development of sheared gels,
for example agar, carrageenan, alginate, etc. (Norton
et al
., 1999). So
what happens when you take a gelling biopolymer and shear it during
the gelation process? The result is gel particles, which if the shear is
sufficient are spherical (Gabriele
et al
., 2009). Each particle has the
same rheology as the bulk gel from which they were produced.
It has been shown how the particles and rheological parameters de-
pend on the processing conditions and how different sheared gels can
be produced (Wolf
et al
., 2000). An example of the ongoing work in the
field has recently been published (Gabriele
et al.
, 2010). In this work,
it was shown how the rate of cooling at a set shear rate in the process
influences the sheared gel obtained (Fig. 10.13). This figure gives a good
example of how these sorts of material behave. As can be seen, agarose
Fig. 10.13
Stress/shear rate curves of 1% agarose sheared gels produced at a constant
shear rate, but with different cooling profiles (adapted from Gabriele et al., 2010).
