In order to develop w/o/w emulsions characterized by two separate aqueous p
hases of different pH, a preliminary study was carried out to obtain a bett
er insight into the possible diffusion processes taking place between an in
ner acidic aqueous phase and an external phase of higher pH (pH approximate
to6). In fact, such systems could be of great interest for pharmaceutical
use. For this purpose, a model emulsion was formulated. The study of pH and
conductivity showed that acidic species transport take place between the t
wo aqueous compartments. The three main release mechanisms that might be re
sponsible for this passage across the oil phase were investigated: breakdow
n of oil globules, facilitated transport by surfactant micelles across the
oil phase or by Fickian diffusion. It appears that this last mechanism was
involved. In order to control this diffusion process, an alkaline species,
octadecylamine was introduced in the oil phase. This compound could form an
ion pair with the lactate ion at the interface of the external aqueous pha
se and the oil phase, thus, limiting the acidification of the external aque
ous phase. (C) 2001 Elsevier Science B.V. All rights reserved.