Understanding the drying behavior of polymer-coated particle dispersions using optical tweezers

After spilling coffee, a tell-tale circular stain is left by the drying droplet. This universal phenomenon, known as the coffee ring effect, is observed independent of the dispersed material. However, for many technological processes (e.g., coating and ink-jet printing) a uniform particle deposition is required and the coffee ring effect is a major drawback. In preliminary work, I found that the coffee ring effect can be avoided by coating the dispersed particles with surface-active polymers, which leads to a homogeneous particle film independent of the dispersed material type, shape and liquid. The aim of the project ""CoffeeRings"" is to provide a fundamental understanding on how the physio-chemical properties of the polymer coating affect the interactions of the particles and the drying behavior of the respective particle dispersion.I will receive hands-on training on optical tweezers by the hosting group to fundamentally determine and systematically quantify the changes induced by the polymer coating throughout all stages of the drying process with single-particle resolution. In WP1, I will synthesize a series of model particles with a defined polymer coating and adjust polymer type, grafting density and chain length. In WP2, I will use optical tweezers to measure their interaction potential in bulk liquid, their adsorption rate to liquid interfaces, and their interaction potential when confined at liquid interfaces, which will mimic the involved interactions within drying dispersion droplets. In WP3, I will investigate the drying behavior of the particle dispersions and combine the macroscopic drying manifestations with the microscopic interactions determined in WP2.The successful realization of this project will improve the compositions of particlepolymersolvent mixtures to obtain reliable, homogeneous deposits, which will stimulate technological advances coating and ink-jet printing processes.""