Measuring and modelling the adsorption kinetics of polydisperse PiBSA-based emulsifiers using dynamic interfacial tension measurements
Authors :- Sumit Tripathi, Su Nee Tan, Amitabh Bhattacharya, Rico F Tabor
Publication :- Colloids and Surfaces A: Physicochemical and Engineering Aspects (2021), 624, p.126728.
Adsorption kinetics of industrially relevant emulsifiers typically show complex behaviour that cannot be simply explained by conventional adsorption kinetics models. In this work, we seek to understand the complex adsorption behaviour of PiBSA (polyisobutenyl succinic anhydride) based emulsifiers and SMO (sorbitan monooleate), which have significant industry relevance as they are often used as the stabiliser in emulsion explosive formulations. We attempt to explain the dynamics of multiple adsorbing species in emulsion systems by using PiBSA based emulsifiers and SMO as a model. We measure dynamic interfacial tension at toluene–water and methylated canola oil (mc oil)–water interfaces using pendant drop tensiometry for different concentrations of four industrial-grade emulsifiers that have different head group chemistries. Using our experimental measurements of dynamic interfacial tension, we estimate the dynamic adsorbed amounts of these emulsifiers using the Gibbs isotherm and Langmuir-Szyszkowski equation. The observed adsorption kinetics of these emulsifier molecules deviate from a single-mode adsorption process, likely because of competition between the kinetically versus thermodynamically favoured molecules present in the emulsifier, and the total dynamic adsorbed amount thus depends on the competition between these faster-diffusing (kinetic) and slower-diffusing (thermodynamic) species. We demonstrate that the adsorption kinetics of all the four types of emulsifiers near their equilibrium adsorption states can be well approximated by the ‘two adsorbing species model’ discussed in our previous work (Tripathi and Tabor, 2016).