Surfactant-driven flow transitions in evaporating droplets

Abstract

An evaporating droplet is a dynamic system in which flow is spontaneously generated to minimize the surface energy, dragging particles to the borders and ultimately resulting in the so-called "coffee-stain effect". The situation becomes more complex at the droplet's surface, where surface tension gradients of different nature can compete with each other yielding different scenarios. With careful experiments and with the aid of 3D particle tracking techniques, we are able to show that different types of surfactants turn the droplet's surface either rigid or elastic, which alters the evaporating fluid flow, either enhancing the classical coffee-stain effect or leading to a total flow inversion. Our measurements lead to unprecedented and detailed measurements of the surface tension difference along an evaporating droplet's surface with good temporal and spatial resolution.

arXiv commentAccepted for publication in Soft Matter (RSC)

References in corpus (5)

• Order-to-disorder transition in ring-shaped colloidal stains
• The Marangoni flow of soluble amphiphiles
• Stokes flow near the contact line of an evaporating drop
• Avalanche of particles in evaporating coffee drops
• Surfactant-induced rigidity of interfaces: a unified approach to free and dip-coated films

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• Evaporation of a sessile colloidal water-glycerol droplet: Marangoni ring formation
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• Evaporation of dilute sodium dodecyl sulfate droplets on a hydrophobic substrate
• Recent Developments on Colloidal Deposits Obtained by Evaporation of Sessile Droplets on a Solid Surface
• Evaporating sessile droplets: solutal Marangoni effects overwhelm thermal Marangoni flow
• Solutal Marangoni flow as the cause of ring stains from drying salty colloidal drops
• Marangoni-driven freezing dynamics of supercooled binary droplets