Crystallization in Monodisperse Emulsions with Particles in Size Range 20–200 nm - Food Colloids: Self-Assembly and Material Science - page 405

1530

1500

1470

1440

1410

1380

-5 0 5 10 15 20 25 30 35 40

Temperature / degrees C

Figure 3 Sound velocity plotted against temperature for two heating/cooling cycles of the
130-nm emulsion sample (20 vol.% oil) containing Tween 20 (Tween 20 (1)).
A heating/cooling rate of B 11C min 1 was used, but during crystallization and
melting the rate was reduced to 0.0131C min 1 . All data acquired during the
experiment are recorded. The polynomial fits for the temperature dependence of
the velocity of sound in the liquid n-hexadecane emulsion and in the fully
crystallized n-hexadecane dispersion are shown as lines on the graph

(r 2 > 0.98)

shown in Figure 3 and the resultant analysis in terms of crystalline solids is
shown in Figure 4. The overall results are summarized in Table 1. Data in
Figure 3 are missing during the melting process between 13 and 17.41C. This is
due to attenuation of the sound wave arising from the freezing/melting proc-
ess. 15 This attenuation process is not normally seen during the crystallization
process because the undercooling creates a significant energy difference be-
tween the solid and liquid phases, which the thermal fluctuation (

300 nK) in
the acoustic field is unable to overcome. 15 At temperatures close to the melting
point, the energy difference between the liquid and crystalline phases is
very small and the thermal fluctuation in the acoustic field is sufficient to tip
the system from liquid to solid, and back again, creating an attenuation of the
propagating acoustic wave. We have observed this phenomenon in all our
experiments.
In Table 1 and Figures 4-8 are presented all our new experimental results
together with some earlier data. 24,25 Examination of Table 1 illustrates the general
features of

B

the data. First, the crystallization temperature does not vary