Piling-to-buckling transition in the drying process of polymer solution drop on substrate having a large contact angle

Abstract

We studied the drying process of polymer solution drops placed on a substrate having a large contact angle with the drop. The drying process takes place in three stages. First, the droplet evaporates keeping the contact line fixed. Second, the droplet shrinks uniformly with receding contact line. Finally the contact line is pinned again, and the droplet starts to be deformed. The shape of the final polymer deposit changes from concave dot, to flat dot, and then to concave dot again with the increase of the initial polymer concentration. This shape change is caused by the gradual transition from the solute piling mechanism proposed by Deegan to the crust buckling mechanism proposed by de Gennes and Pauchard.

Modeling the elastic deformation of polymer crusts formed by sessile droplet evaporation

“…However, most of the literature is for shells of uniform thickness [16,17,18,19] or specific, engineered non-uniformities [20]; those with a thickness profile similar to that expected for evaporating droplets have not been investigated. Furthermore, the rich array of deformed shell profiles observed in experiments [3,4,5,6,7] has not, to the best of our knowledge, been systematically quantified as a function of the shell parameters, even for uniform shells.…”

“…For sessile (i.e. pinned contact line) droplets on a wetting substrate, the effect is compounded by the outward radial flow of solvent during evaporation which, for low-concentration solutions, leads to enhanced solute deposition near the pinned line [6,11,12,13,14]. For the higher concentrations where crust formation occurs, this outward flow suggests that the thickness of the crust will vary nonuniformly over the surface of the droplet, being thicker near the outer contact line and thinner near the centre or apex.…”

“…Of concern here is the formation of a glassy 'crust' that can appear on the liquid-vapour interface of evaporation polymer [3,4,5,6,7] or colloid [7,8,9] solutions. Such crusts are believed to produce roughened surface profiles after drying of thin films [10].…”

Combing and self-assembly phenomena in dry films of Taxol-stabilized microtubules

“…1c). Contrary to the reticulation, however, the difference between the central and outer area of the dried films is a phenomenon that is of a very general nature and is mostly due to two phenomena: (1) the omnipresence of the outward capillary flow, and (2) the formation of a solid crust due to salt crystallization, the presence of which has been shown to influence the final shape of the dried deposit [39].…”

Dynamics of Drying Process of Polymer Solution Droplets: Analysis of Polymer Transport and Control of Film Profiles

“…Several approaches have been proposed to suppress the outward flow and to obtain a flat film, such as to control the initial contact angle of the droplet 20,21) , to control the substrate temperature 22) , and to use a mixed solvent. 23) For practical applications, the method that can be applied universally independent of the component in the droplet is desired.…”