Authors: Manos Anyfantakis, Zheng Geng, Mathieu Morel , Sergii Rudiuk, and Damien Baigl, Langmuir 2015
Evaporation of colloidal droplets containing suspended particles on a solid substrate is a non-equilibrium process. Flow patterns inside an evaporating sessile drop induces variety of particle ordering in the final deposition pattern. Owing to in-homogenous evaporative flux along the drop surface, and compensating capillary flow towards the immobile contact line through the bulk of the drop, ring like depositions are observed on drying drops of colloidal suspensions. These non-uniform ring-like deposits are known as 'coffee-rings'. A competitive Maragoni flow generated by surface tension gradients along the drop surface, opposing the radially outward capillary flow inside the drop, often reverses and/or suppresses the coffee-ring formation in sessile drops. During the talk, we will briefly talk about the the different strategies to suppress undesirable coffee-ring formation in drying drops of colloidal suspensions. Effect of surfactants on the colloidal morphologies generated by drying of sessile drops will be discussed further. Role of a charged surfactant on modifying the surface properties of the particle, and the particle - interface interaction will be the key focus. Different classes of surfactants inducing spatially homogeneous and in-homogeneous deposition of colloidal particles and the underlying mechanisms will be further explored.
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