Abstract

The inherent biocompatibility of Span and Tween surfactants makes them an important class of nonionic
emulsifiers that are employed extensively in emulsion and foam stabilization. The adsorption of Span-
Tween blend at water/oil surface of emulsion has been investigated using a population balance model
for the first time. Destability of emulsion was modeled by considering sedimentation, coalescence and
interfacial coalescence terms in population balance equation (PBE). The terms of coalescence efficiency
and interfacial coalescence time were considered as a function of surface coverage of droplets by
surfactant molecules. The surface coverage at different surfactant concentrations was determined by
minimization of difference between the model predictions and experimental average droplet sizes. After
optimization, the surface coverage outputs were fitted with different adsorption isotherms to evaluate
the adsorption behavior of Span-Tween surfactants blend at water/oil surface. The results show that
Freundlich isotherm can predict the adsorption behavior of closer to the experimental observation.
Moreover, fitted parameters imply the favorable adsorption of Span-Tween blend at water/oil interface.