Pinning-Free Evaporation of Sessile Droplets of Water from Solid Surfaces

Abstract

Contact-line pinning is a fundamental limitation to the motion of contact lines of liquids on solid surfaces. When a sessile droplet evaporates, contact-line pinning typically results in either a stick–slip evaporation mode, where the contact line pins and depins from the surface in an uncontrolled manner, or a constant contact-area mode with a pinned contact line. Pinning prevents the observation of the quasi-equilibrium constant contact-angle mode of evaporation, which has never been observed for sessile droplets of water directly resting on a smooth, nontextured, solid surface. Here, we report the evaporation of a sessile droplet from a flat glass substrate treated with a smooth, slippery, omni-phobic covalently attached liquid-like coating. Our characterization of the surfaces shows high contact line mobility with an extremely low contact-angle hysteresis of ∼1° and reveals a step change in the value of the contact angle from 101° to 105° between a relative humidity (RH) of 30 and 40%, in a manner reminiscent of the transition observed in a type V adsorption isotherm. We observe the evaporation of small sessile droplets in a chamber held at a constant temperature, T = (25.0 ± 0.1) °C and at constant RH across the range RH = 10–70%. In all cases, a constant contact-angle mode of evaporation is observed for most of the evaporation time. Furthermore, we analyze the evaporation sequences using the Picknett and Bexon ideal constant contact-angle mode for diffusion-limited evaporation. The resulting estimate for the diffusion coefficient, D E, of water vapor in air of D E = (2.44 ± 0.48) × 10–5 m2 s–1 is accurate to within 2% of the value reported in the literature, thus validating the constant contact-angle mode of the diffusion-limited evaporation model.

Surficial Marangoni Flow‐Induced Growth of Ultrathin 2D Molecular Crystals on Target Substrates

“…Considered that Dif-TES-ADT has very good solubility in toluene and toluene evaporated mush faster than DMF, the underlying fluid should be the antisolvent DMF. [31,32] Compared with DMF, toluene as the good solvent had a lower boiling point than that of DMF, so it would first evaporate at the interface. The formed crystal was floating on the top of the fluid at first, and then the underlying fluid evaporated as well, the crystal was finally landed on the substrate (Figure 3aiv).…”

“…Since the mixed solvent had a good wettability on the substrate with a low contact angle of ≈2.1° (Figure S8, Supporting Information), the contact line was strongly pinned by the substrate, which would maintain the shape of the liquid film at the beginning of the crystal growth process. Solvents evaporate much faster at the liquid/air interface than that at other areas . Compared with DMF, toluene as the good solvent had a lower boiling point than that of DMF, so it would first evaporate at the interface.…”

Double-sided slippery liquid-infused porous materials using conformable mesh

“…The liquid lubricant layer thus eliminates the contact line pinning normally associated with sessile droplets on solid surfaces, leading to high drop mobility and remarkably low contact angle hysteresis 4 . In addition to superhydrophobicity and SLIPS, the only other materials method, of which we are aware, to eliminate contact line pinning is to use a Slippery, Omniphobic, Covalently Attached Liquid (SOCAL) surface 5,6 .…”

Interfacial Strategies for Smart Slippery Surfaces

“…With a small correction for the presence of the lubricant skirt from the wetting ridge, the constant contact angle model of evaporation provided excellent estimates of the diffusion coefficient of the vapor [83] . Most recently, we implemented the SOCAL method on a glass substrate (the fifth slippery surface strategy) and reported the evaporation of water droplets over a wide range of relative humidity (10% -70%) [84] . On these liquid-like surfaces droplets adopted perfect spherical cap shapes and contact lines were completely mobile with contact angle hysteresis of ~1˚.…”

“…On these liquid-like surfaces droplets adopted perfect spherical cap shapes and contact lines were completely mobile with contact angle hysteresis of ~1˚. The evaporation of sessile droplets was described by the constant contact angle model of diffusion limited evaporation and provided excellent estimates of the diffusion coefficient [84] . Fig.…”