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Static and Hydrodynamic Interaction Forces between Pluronic Stabilized Emulsion Droplets Measured Using Afm

Raymond R. Dagastine1, Tam T. Chau1, Derek Y.C. Chan2, Geoff W. Stevens1, and Franz Grieser3. (1) Department of Chemical and Biomolecular Engineering, University of Melbourne, Parkville, 3010, Australia, (2) Department of Mathematics and Statistics, University of Melbourne, Parkville, 3010, Australia, (3) School of Chemistry, University of Melbourne, Parkville, 3010, Australia

Pluronics, (PEO-PPO-PEO) tri-block co-polymers, are commonly used in a wide range of applications ranging from emulsion stabilization to drug delivery due to their low toxicity and cost. Understanding the behaviour of adsorbed Pluronics layers at the oil-water interface and their effect on interactions on the nanometer scale is crucial in controlling emulsion stability. However, measurements of interfacial forces at deformable interfaces are uncommon due experimental challenges. In this work, we have employed a recently developed method using atomic force microscopy (AFM)1, 2 to study the static and hydrodynamic interactions between oil droplets in aqueous solution stabilized by a series of Pluronic co-polymers. Both electrostatic double layer and steric forces were observed in combination with pronounced hydrodynamic drainage forces. The effect of stabilizer length from changes in both polymer molecular weight and solvent quantity on both surface forces and hydrodynamic drainage will be discussed.

1. Dagastine, R. R.; Stevens, G. W.; Chan, D. Y. C.; Grieser, F., Forces between two oil drops in aqueous solution measured by AFM. J. Colloid Interface Sci. 2004, 273, (1), 339-342.

2. Carnie, S. L.; Chan, D. Y. C.; Lewis, C.; Manica, R.; Dagastine, R. R., Measurement of Dynamical Forces between Deformable Drops Using the Atomic Force Microscope. I. Theory. Langmuir 2005, 21, (7), 2912-2922.