Chemistry Reference
In-Depth Information
be controlled by changing the concentration and type of hydrogelator, the
concentration of the dispersed phase, and/or the temperature. This allows a
wide range of tuning parameters, resulting in a rather broad regime of visco-
elastic properties. In most of the observations related to entrapment of ISA-
somes in hydrogels, the nanostructures and sizes of ISAsomes are quite
thermoreversible, and they equilibrate rapidly; on the contrary, bulk LC phases
undergo slow transitions that are more often metastable, especially in the
cooling direction.
The preparation of ISAsomes by the shearing technique can be diffi cult,
primarily due to the large difference in viscosities of the components (oil phase
and water phase). It has been observed that the addition of hydrogelator MC
to the aqueous phase affords more comparable viscosities, which facilitates
mixing at high temperature. This, in turn, leads to stable ISAsome solutions at
room temperature (unpublished results). A further advantage of hydrogel
formation in ISAsome systems is the possibility of controlling (more specifi -
cally, reducing) the rate of interparticle material transfer, as shown by our
results. In addition, we have investigated the arrested dynamics of ISAsomes
in such hydrogel networks by multispeckle DLS (data not shown) (Iglesias
et al., in preparation).
ISAsome-hydrogel systems can be dried into thin fi lms of variable charac-
teristics (Fig. 6.14a) (Kulkarni et al., 2011a). Films were formed from ISAsome-
loaded KC and MC gels upon drying at low or high temperature, respectively.
The fi lm thickness was found to increase with the amount of ISAsome loading.
Due to dehydration, the dried hydrogel network becomes compact and thereby
immobilizes the ISAsomes (Fig. 6.14b). The ISAsomes can, however, be remo-
bilized upon rehydration of such fi lms. The ISAsome - loaded fi lms were trans-
parent (less transparent for increased loading) and became turbid upon
rehydration, as shown in Figure 6.14c. Details of rehydration and ISAsome
restoration are explained in the following discussion.
During the drying of the loaded fi lm, the ISAsomes also lose their water,
and the original H
2
nanostructure is converted into L
2
(Fig. 6.15 a). Never-
theless, the original nanostructure (H
2
) is restored upon rehydration of the
fi lm. Using time-resolved SAXS, we were able to track the nanostructural
changes in the ISAsome system upon partial hydration (equal amount of
water added to the dried material) of a loaded KC fi lm. The ISAsomes
rapidly (
300 s) take up the water and regain their original H
2
nanostruc-
ture, which is then stabilized (900 s) (Fig. 6.15b). Partially hydrated fi lm is
essentially thermoreversible, as shown in Figure 6.15c. The size of the ISA-
somes remains practically the same upon loading into the hydrogel network
and subsequent drying into fi lm form, as indicated by DLS measurements
performed on the diluted (1000
<
) mixtures of ISAsomes, resolubilized
loaded gel and resolubilized loaded dry fi lm (Fig. 6.15d). Solid fi lms contain-
ing ISAsomes are promising systems for the handling and storage of ISA-
somes, as well as for potential materials science applications that require
functional surfaces.
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