Coffee-stain growth dynamics on dry and wet surfaces

Abstract

The drying of a drop containing particles often results in the accumulation of the particles at the contact line. In this work, we investigate the drying of an aqueous colloidal drop surrounded by a hydrogel that is also evaporating. We combine theoretical and experimental studies to understand how the surrounding vapor concentration affects the particle deposit during the constant radius evaporation mode. In addition to the common case of evaporation on an otherwise dry surface, we show that in a configuration where liquid is evaporating from a flat surface around the drop, the singularity of the evaporative flux at the contact line is suppressed and the drop evaporation is homogeneous. For both conditions, we derive the velocity field and we establish the temporal evolution of the number of particles accumulated at the contact line. We predict the growth dynamics of the stain and the drying timescales. Thus, dry and wet conditions are compared with experimental results and we highlight that only the dynamics is modified by the evaporation conditions, not the final accumulation at the contact line.

References in corpus (6)

• The NumPy array: a structure for efficient numerical computation
• scikit-image: Image processing in Python
• Controlled uniform coating from the interplay of Marangoni flows and surface-adsorbed macromolecules
• Tuning the receding contact angle on hydrogels by addition of particles
• Mechanical tuning of the evaporation rate of liquid on crossed fibers
• Homogeneous deposition of particles by absorption on hydrogels

Cited by in corpus (3)

• Natural convection above circular disks of evaporating liquids
• Contact-line deposits from multiple evaporating droplets
• Simultaneous evaporation and imbibition of a droplet on a flooded porous substrate