Controlling the Morphology of Ring-Like Deposits by Varying the Pinning Time of Driven Receding Contact Lines

Abstract

The variety of morphologies observed in the particle deposits produced by solvent evaporation may be ruled to a large extent by contact line dynamics and in particular, by self-pinning events described by the contact line. If the number of particles in the suspension bulk increases, more particles should be transported toward the contact line during evaporation. Increasing times of contact line pinning should lead to the same effect than particle concentration. In this work, we investigated the different ring-like deposits obtained at driven receding contact lines by varying separately nanoparticle concentration and pinning time. We used a recent methodology based on "shrinking" sessile drops to mimic the contact line dynamics of freely evaporating drops. Unlike drying drops, with this methodology the particle concentration in the drop bulk is assumed to remain mostly constant during the entire process. We concluded that no nanoparticle deposit is formed if the pinning time is reduced below a critical value for a given substrate-particle system. However, an increase of pinning time enables the ring formation even at low particle concentrations.

A review on suppression and utilization of the coffee-ring effect

“…If CAH is high, during when the contact angle decreases to the receding angle, typically a few seconds depending upon the rate of evaporation, solutes can accumulate at the contact line. Such accumulation produces ringlike deposits only if the duration of pinning is above a critical value for a given substrate-solute system [72]. On the other hand, short pinning time even with high initial solute concentration can minimize CRE producing smaller inner rings [73].…”

Surfactant-driven flow transitions in evaporating droplets

“…Larger correlations have recently been described on other factors not explored in this study as the wettability of the substrate, the particle-substrate adherence, or the particle electrical charge. [23][24][25]38] The most efficient way to avoid coffee-ring patterns in an evaporating drop is by making the contact line mobile, and therefore eliminate its self-pinning. This occurs naturally on hydrophobic substrates and using particles with low adhesion.…”

Calculation of the heat flux near the liquid–gas–solid contact line

“…Insufficient understanding of transfer processes in the zone of three-phase contact line holds back the studies of several phenomena, such as boiling, cavitation, rivulet flows, destruction of liquid films, spreading and evaporation of droplets, droplet condensation, etc. [1][2][3][4]. The thickness of liquid in this zone with the length of about several microns, often called the microregion, decreases from 1 − 3 μm to 10 − 20 nm (the adsorbed film).…”