Self-Assembled Liquid Particles: How to Modulate their Internal Structure - Food Colloids: Self-Assembly and Material Science - page 78

(a) (b)

10

10

76 ° C

76°C

58 ° C

58°C

1

39°C

1

39°C

25°C

25°C

0 1 2 3 4

0 1 2 3 4

q (nm -1 )

q (nm -1 )

Figure 8 Scattering curves of two dispersions with (a) d ¼ 84 and (b) d ¼ 47.6. These
samples were measured while heating at 25, 39, 58, and 761C (thin lines) and
while cooling at 58, 39, and 251C (thick lines). Curves are shifted vertically by a
constant arbitrary factor for better visibility

particle internal structure that occur during heating/cooling processes, we
carried out an SAXS investigation on two aqueous dispersions (with d ¼ 84
and 47.6). The scattering curves of these two dispersions, which are presented in
Figure 8 as a function of temperature (from 25 to 761C), reveal the structural
reversibility of the confined structures. In both samples, the peaks shift in their
dependence on temperature, and for d ¼ 84 there is an additionally observed
reversible transition of the type H 2 2

L 2 . We note that, for each investigated
temperature, the scattering curves are identical and are not dependent on
whether the sample temperature was reached by heating or cooling. This
indicates that the internal self-assembly structure in all of the samples contain-
ing oil, at a certain temperature, is independent of the thermal history: that is,
heating or cooling to the required temperature leads to the same structure. This
fact is clear evidence that the formed structures in the kinetically stabilized
particles, in analogy to those in the nondispersed TC-rich bulk phases, are
thermodynamic equilibrium structures.
Thus, when adding n-tetradecane to the MLO + water + F127 system at
constant temperature the internal self-assembly structure of the kinetically
stabilized particles transforms from Pn3m (cubosomes) to H 2 (hexosomes),
andthentoaW/O(L 2 ) microemulsion phase (EME). To our knowledge, this
isthefirsttimethattheformationofstable EME systems has been properly
described and proven to exist at room temperature. It thereafter becomes
possible to form a W/O microemulsion-in-water emulsion system, which is
different from the well-known double emulsion (emulsion-in-emulsion
system) because the kinetically stabilized internal W/O emulsion in the double
emulsion system is replaced by the thermodynamically stable W/O micro-
emulsion as the 'inner' emulsion in the EME. Stable EMEs are superior to
double emulsion systems, since they consist of stabilized droplets in an
aqueous continuous phase, which contain in the inner part an entrapped
equilibrium self-assembled structure.