Emulsions, Microemulsions, and Lyotropic Liquid Crystals - Surface and Colloid Chemistry: Principles and Applications - page 210

FIGure 9.6 Stable emulsion formation by polymers. Polymer molecules adsorb (on solid
particles) and penetrate (on liquid drops).
will strongly attract positively charged ions in the surrounding bulk aqueous phase.
At a close distance from the surface of a drop, the distribution of the charges will be
changing very much. While at a very large distance there will be electrical neutral-
ity, there will be an equal number of positive and negative charges.
Electrostatic repulsion exists between the two negatively charged drops, and
strong repulsion would be exhibited even at large distances (many times the size
of the particle). The shape of the EDL curve will be dependent on the negative and
positive charge distribution. It is easily seen that, if the concentration of counterions
increases, the magnitude of EDL will decrease, and this will reduce the maximum of
the total potential curve. The stability of emulsions can thus be increased by decreas-
ing the counterion concentration.
Another important emulsion stabilization is achieved by using polymers. The
large polymer molecules adsorbed on solid particles (Figure 9.6) will exhibit repul-
sion at the surface of the particles. The charged polymers also will give additional
charge-charge repulsion. Polymers are used in many pharmaceutical, cosmetics,
and other systems (milk). Obviously, the choice of a suitable polymer is specific to
each system.
9.5.3.6.1 Advanced Emulsion Technology
As is already obvious, emulsion technology is a state-of-art system and mostly pro-
tected by patents (Johnson, 1979; Sjoblom et al., 2008; Friberg, 1976). In the follow-
ing text, some examples are given that can serve as useful basic information.
9.5.3.6.1.1 Nanoemulsion Technology The low-energy emulsification method
(Emulsion Inversion Point [EIP]) has been used to prepare O/W nanoemulsions
in the water/potassium oleate-oleic acid-C12E10/hexadecane ionic system. This
method had not been used practically in ionic systems up until now. The result-
ing droplet sizes, much smaller than those obtained with high-energy emulsifica-
tion methods, depend on the composition (formulation variables) and preparation
variables (addition and mixing rate). Phase diagrams, rheology measurements, and
experimental designs applied to nanoemulsion droplet sizes obtained were combined
to study the formation of these nanoemulsions. To obtain nanosize droplets, it was