3.1. Separation time vs water content
The data in Fig. 3 shows that the separation times decrease with
increasing heating time for all water contents from 5% to 30%. Separation
times converge when heating times were >120 s despite
significant differences in the separation time for untreated emulsions.
For example, the emulsion containing 5% water took
10,000 s to separate whereas the 70/30 emulsion took 4000 s.
The difference between the separation times for the four untreated
emulsions is likely to arise from the different sizes of water droplets
present in each emulsion. This results from the constant stirring
speed and constant stirring time when making the
emulsions. From an energy balance standpoint the energy imparted
by the stirrer creates surface area within the emulsions
due to the shear force created, the rest is lost as heat. The same
stirring conditions are expected to yield the same total droplet surface
area within the emulsion, so for a smaller water volume the
droplet diameter must be smaller to give the same surface area
as that for a larger water volume. The trends shown in Fig. 3 follow
this hypothesis; the 95/5 emulsion contains the smallest droplets
and takes the longest to separate whereas the 70/30 emulsion will
have the largest droplets and will separate in the shortest time.
Despite the differences in separation time of untreated emulsions,
the data in Fig. 3 shows that the separation time of all four
emulsions is comparable after >120 s of microwave heating. There
are several possible mechanisms contributing to this behaviour: