Different surfactants give different results, as illustrated in Figure
11.11. Plateau values are obtained at high surfactant concentrations.
Emulsification was in the regime TI, and according to Eq. (11.11) the
droplet size obtained should be proportional tog0.6. This roughly agrees
with the plateau values ofd 32 obtained, though not precisely. Moreover, the
shapes of the curves show clear differences. Some factors causing such
differences have been identified, but a full explanation cannot yet be given.
11.4.1 Droplet Breakup
The first question is, What is theeffective interfacial tensionduring droplet
deformation and breakup? This depends on surface loadG, which depends
on the adsorption rate of the surfactant. Actually, this rate can be very high,
since surfactant is not transported by diffusion but by convection. This
would imply thatGcan be fairly high. However, every breakup event occurs
FIGURE11.11 Specific droplet surface areaA(and average droplet sized 32 )asa
function of total surfactant concentrationc, obtained at approximately constant
emulsification conditions for various surfactants; PVA¼poly(vinyl alcohol); also for
soy protein a plateau value ofAis reached, at about 20 kg?m^3. Approximate
plateau values for the interfacial tensiongare 3, 10, and 20 mN?m^1 for the
nonionic, caseinate, and PVA, respectively.