Chemistry Reference
In-Depth Information
9
6
3
0
-3
-6
0
50
100
Time / min
Figure 10 The quantity ln[(1/
f
) - 1]/T
abs
versus time for data in Figure 9. Lines are
straight line fits to the data points. Symbols are as for Figure 9. (The data at
the beginning and end of the crystallization process have been omitted for
simplicity.)
in previous work,
14
this melting is in the surface layer, but in the case of PGE
it is far deeper than that observed with the other surfactants (see Figure 5).
Label 3 in Figure 6 indicates the point where information was lost because of
increased attenuation of the sound, but this is far less pronounced than for the
case of the other surfactants. Label 4 indicates that the melted material is
different to that at the same temperature on the cooling cycle. The starting
temperature of 401C was chosen to ensure that whatever phase formed during
melting was completely melted before the beginning of another experimental
cycle. We note finally that a phase transition is apparent in the cooling liquid
just below 101C. Other workers have seen evidence of such a transition in PGE
emulsions; e.g., Sonada et al.
7
noted a rotator-triclinic transition around this
temperature, but this effect appears far larger in the case of PGE than the other
surfactants. Higami et al.
9
reported phase transitions on cooling at 8 and 21C.
However, the large amount of PGE present relative to the oil (a 4:1 ratio) does
lead us to question the nature of such 'emulsions'.
Our Tween-stabilized emulsions behave here in a manner consistent with
all our previous work.
24-26,14-15,17
On the other hand, the two Caflon-stabilized
emulsions (Figures 7 and 8) show significant differences between each
Search WWH ::
Custom Search