A novel approach to study the interactions between polymeric stabilized micron-sized oil droplets by optical tweezers

An Chen, Shao-Wei Li, Jian-Hong Xu

The well understanding of interaction forces between single dispersed droplets is crucial to the understanding of emulsion stabilization mechanism. Recently, many studies have reported the direct quantitative measurements of interaction forces between 20-200 μm single droplets coated polymers by atomic force microscope (AFM). These studies have revealed many important results about the relationship of the interaction forces and the droplet deformation. However, these studies of the quantitative relationship between the measured interaction forces and the separation distance of the front end of the droplet have rarely been reported. Optical tweezers instrument can make it possible to establish the quantitative relationship between the measured force and the separation distance of the front end of the droplet, which will make better understanding of the interaction mechanisms between droplets. Due to the differences of the measuring mechanism between atomic force microscopy (AFM) and optical tweezers, the theory model of AFM measurements cannot be fitted with the force measurement by optical tweezers. We have made an exhaustive comparison of the measuring differences between AFM and optical tweezers instrument in this work. Moreover, we built a numerical model to derive the repulsive pressure through the measured force curve in order to quantify the measured force of two micron-sized oil droplets coated polymers by optical tweezers. Furthermore, the novel method can be extended to other micron-sized emulsion systems, and these findings will be a vital progress on quantitative force measurements between micron-sized droplets.

DOI