Adsorption Dynamics and Equilibrium of PEO-PDMS Block Polymers to Oil/Water Interfaces

Adsorption of block copolymer surfactants to air/water interfaces has been studied in detail for several decades, but little data exist on their adsorption to oil/water interfaces. We have characterized the dynamic and equilibrium adsorption behavior of several oil-soluble polyethylene oxide-b-polydimethylsiloxane surfactants to oil/water interfaces using a microtensiometer platform. This platform allows the accurate determination of the initial stages of adsorption with minimal convection, allowing for precise determination of the adsorption mechanism for given solution conditions. These surfactants are quite surface active—surface activity has been seen for solution concentrations as low as 10-8 mol/L. Adsorption dynamics are strongly influenced by the curvature of the interface (a tunable parameter of the microtensiometer platform), allowing us to vary adsorption timescales over a wide range. The influence of surfactant architecture (block size, block ratio) and solution properties (concentration, solvent viscosity) on adsorption dynamics and equilibrium will be discussed. Studies of surfactant desorption will provide insight in designing appropriate experiments for studying the interfacial mechanics of these interfaces.