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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 44: Wetting, Fluidics and Liquids at Interfaces and Surfaces II (joint session CPP/DY)

CPP 44.6: Talk

Thursday, March 30, 2023, 10:45–11:00, MER 02

How droplets dry on stretched soft substrates — •Binyu Zhao, Yixuan Du, and Günter K. Auernhammer — Leibniz Institute of Polymer Research Dresden, Dresden 01069, Germany

Droplets evaporation on solid substrates is a ubiquitous phenomenon and relevant in many natural and industrial processes. Well known are the coffee-ring. Many studies have succeeded in promoting, suppressing or even reversing the formation of coffee-ring by using non-spherical particles, surfactants, patterned substrates, and so on.

Here, we show that a uniaxial stretching of soft substrates strongly controls the dynamics of droplet evaporation and particle deposition through controlling the contact line motion. Water droplet evaporates with an elongated non-circular contact line on the stretched substrates and switches the elongation direction during evaporation. The contact line evolution depends on the orientation of the contact line relative to the stretching direction. When nanoparticles are added into the liquid, the circular deposition pattern, i.e., the so-called coffee-ring, becomes elongated along the direction perpendicular to the stretching direction. Particularly, such non-circular deposition pattern exhibits periodic height gradients along its rim. The finer structure of the pattern can be controlled by applying different stretching ratios to the soft substrate and thus are correlated to the anisotropic surface stresses near the contact line. The findings broaden our understanding of droplet wetting and evaporation on soft and anisotropic substrates, and open the way to reshaping the coffee-ring to allow anisotropic, non-circular patterning.