Modeling the interfacial properties of Poly(Ethylene oxide-Co-Propylene oxide) polymers at water-toluene interface

Understanding how the structure of demulsifiers affects its interfacial properties is essential to developing new demulsifiers with desired properties. Modeling is an important tool to methodically study the effect of polymer architecture on its microscopic structure and macroscopic properties. Here modified interfacial Statistical Associating Fluid Theory (iSAFT) was used to study the interfacial properties of additives at water-toluene interface. The density profile, surface adsorption and interfacial tension (IFT) was predicted for different architectures of poly (ethylene oxide-co-propylene oxide) (PEO-PPO) at the interface. The predicted IFT was validated against experimental data (for Pluronics, Tetronics and Poloxamer) and the theory was found to be in good agreement with experiments. The effect of molecular weight, branching, PEO:PPO ratio and ordering of the PEO and PPO blocks was studied. It was found that IFT was lowest for high molecular weight and highly branched polymers and the IFT curve went through a minima with varying PEO:PPO ratio. The hydrophilic PEO block on the outside and hydrophobic PPO block as the inside block led to more interfacial adsorption and lowering of IFT compared to the reverse polymer (PPO outside and PEO inside).