Droplet Drying Patterns on Solid Substrates: From Hydrophilic to Superhydrophobic Contact to Levitating Drops

Abstract

This review is devoted to the simple process of drying a multicomponent droplet of a complex fluid which may contain salt or other inclusions. These processes provide a fascinating subject for study. The explanation of the rich variety of patterns formed is not only an academic challenge but also a problem of practical importance, as applications are growing in medical diagnosis and improvement of coating/printing technology. The fundamental scientific problem is the study of the mechanism of microand nanoparticle self-organization in open systems. The specific fundamental problems to be solved, related to this system, are the investigation of the mass transfer processes, the formation and evolution of phase fronts, and the identification of mechanisms of pattern formation. The drops of liquid containing dissolved substances and suspended particles are assumed to be drying on a horizontal solid insoluble smooth substrate. The chemical composition and macroscopic properties of the complex fluid, the concentration and nature of the salt, the surface energy of the substrate, and the interaction between the fluid and substrate which determines the wetting all affect the final morphology of the dried film. The range of our study encompasses the fully wetting case with zero contact angle between the fluid and substrate to the case where the drop is levitated in space, so there is no contact with a substrate and angle of contact can be considered as 180 ∘ .

Joint effect of advection, diffusion, and capillary attraction on the spatial structure of particle depositions from evaporating droplets

“…One of the most important and actively discussed problems is connected to studying structures of colloidal particles, which emerge on the surface of an evaporating sessile droplet and remain on the substrate after drying [6][7][8][9][10][11][12][13]. One of the examples is the effect of evaporative contact line deposition, the so-called coffee-ring effect [14][15][16].…”

Crystallographic features of oral fluid in young people with gingivitis

“…Some authors believe that this is due to the physicochemical characteristics of saliva (amount of protein, viscosity, pH) [8,13]. According to many studies, the very phenomenon of facies formation, as well as the diversity of its structure, is based on complex molecular and physical mechanisms [14][15][16]. The increase in the number of protein components and the decrease in the viscosity of the oral fluid causes a violation of the structure of the crystals, thickening of the main trunks and processes, as well as the formation of many irregular crystallization centers or their complete absence.…”

Nondestructive Characterization of Drying Processes of Colloidal Droplets and Latex Coats Using Optical Coherence Tomography

“…Drying of the colloidal droplets has been a subject of great interest since the 1980s [1]. Studies of a drying droplet, including changes of drying rate and contact angle, the progression of its shape, and final deposition pattern, can help us understand many interesting phenomena, such as coffee ring effects [2], electro-wetting effects [3], and Marangoni effects that are driven by surface tension gradients [4].…”