Chemistry Reference
In-Depth Information
reactions, where direct mixing of the reactants may cause rapid reaction or
even explosion.
6.5 ISA
SOMES
EMBEDDED IN THERMOREVERSIBLE
POLYMERIC GELS AND FILMS
The basis for all our systems is the nanostructured liquid crystalline phase,
which is oil continuous and has a high viscosity that is fi xed for a given LC
phase and temperature. LC phases converted into ISAsomes are water-
continuous dispersions. It is possible to increase the viscosity of these disper-
sions by adding a certain type of hydrogelling agent. In this section we describe
the embedding of ISAsomes in hydrogel networks and their further immobi-
lization by dehydration of the hydrogels to give dry fi lms.
Two different hydrogelling agents, namely,
- carrageenan (KC) and meth-
ylcellulose (MC), (Tomsic et al., 2008) have been exploited for this purpose.
KC is a linear sulfated polysaccharide extracted from red seaweed; whereas
MC is a hydrophobically modifi ed form of cellulose that does not occur in
nature. The structural units of MC and KC are shown in Figure 6.11. Both of
these polymers form thermoreversible hydrogels in aqueous medium, with or
without the addition of salts. KC forms a viscous gel at room temperature,
while MC undergoes a sol-gel transition at elevated temperature. Due to the
fact that the two polymers have independent gelling mechanisms, it was also
possible to obtain a mixed (double) gel system containing a 1 : 1 mixture of
these gelling agents. The resulting system is a gel at lower and higher tempera-
ture with a narrow window consisting of the sol state (Tomsic et al., 2008). This
narrow window facilitates the homogeneous incorporation of colloidal ISA-
somes. This property could be potentially utilized to release gel-embedded
functional material at specifi c sites under fl uid (sol) conditions.
Guillot et al. (2009b) and Tomsic et al. (2009) have performed systematic
studies on aqueous systems of the two hydrogelators (KC and MC) and their
mixtures for incorporating various ISAsomes. Investigations focused on the
changes as a function of hydrogelator concentration, type of ISAsome nano-
κ
Figure 6.11
Hydrogelling agents. Structural representation of (a) KC and (b) MC
building blocks.
Search WWH ::
Custom Search