Self-Assembled Liquid Particles: How to Modulate their Internal Structure - Food Colloids: Self-Assembly and Material Science - page 74

phase were preserved. Moreover, in all cases, a comparison of the temperature-
dependent lattice parameters of the internal phase in the dispersion with the
parameters of the nondispersed bulk phase with excess water gives identical
values. This good agreement clearly shows that the internal structure of the
dispersions at each temperature corresponds to the equilibrium structure of
MLO with excess water.
To prove that the temperature-induced structural changes are reversible, a
dispersion was measured at three different temperatures in a heating-cooling
cycle (Figure 4). At 251C the dispersed particles are ECP with an internal
structure of Pn3m; after heating to 581C they are transformed to EHP; and
upon further heating to 871C the transition to ELP takes place. On cooling the
dispersion back to 581C, we found an EHP again, and at 251C the initial ECP.
This means that, upon cooling the melted entrapped L 2 phase in the kinetically
stabilized droplets of our dispersions, the ELP recrystallizes back to the original
H 2 and finally to Pn3m at room temperature, i.e., a reversible structural
transformation. The respective scattering curves of the dispersion at 251C
(ECP) and 581C (EHP) coincide. This shows that the internal structure of the
dispersed droplets depends only on the current temperature, irrespective of
whether it was reached by heating or cooling. This proves that the internal
structure of the dispersed particles is a thermodynamic equilibrium structure.
In addition, the mean radius of these particles was determined by dynamic light
scattering to be

140 nm, with a rather polydisperse size-distribution width of

B

ca. 25%.
In summary, aqueous submicrometre-sized dispersions of the binary MLO
+ water system, which are stabilized by means of the polymer, possess a
distinct internal structure depending only on temperature and composition. We
have demonstrated that the internal structure of the particles can be tuned with

ELP

87 ° C

1

EHP

58 ° C

ECP

° C

25

0. 1

0 1 2 3

4

q (nm -1 )

Figure 4 Scattering curves of a dispersion, containing 8 wt.% MLO in a 1 wt.% F127
solution, measured in the heating direction at 25, 58, and 871C (thin lines) and
then in the cooling direction at 58 and 251C (thick lines)