Self-Assembly of Gradient Concentric Rings via Solvent Evaporation from a Capillary Bridge

Abstract

A drop of solution containing nonvolatile solute is allowed to evaporate from a sphere-on-flat geometry. Left behind is a striking pattern of gradient concentric rings with unprecedented regularity. The center-to-center distance between adjacent rings, lambda(C-C), and the height of the ring, h(d), are strongly affected by the concentration of the solution and the properties of the solvent. The nature of the formation of regular gradient ring patterns during the course of irreversible solvent evaporation is revealed through theoretical calculations based on the mass conservation of the solution.

Dynamical Model for the Formation of Patterned Deposits at Receding Contact Lines

“…The model incorporates wettability, capillarity, evaporation, convective transport of the solution and diffusion of the solute and has been derived employing a long-wave approximation. We find that a strong nonlinear dependence of viscosity (i.e., the front mobility) on concentration triggers, in an intricate interaction with evaporation and diffusion, the deposition of periodic and aperiodic line patterns as observed in experiments for many different materials and settings [2,[5][6][7][8][9][10][11]30]. We believe that the model explains a basic mechanism for the formation of regular line patterns.…”

“…Although most studies agree that the patterns result from a stick-slip motion of the contact line caused by pinning/depinning events [2,6,11,16] no dynamical model of the periodic deposition process ex-…”

“…We believe that the model explains a basic mechanism for the formation of regular line patterns. They result from a self-organised cycle of deposition-caused pinning-depinning events that is experimentally often described as a stick-slip motion [6,10,11]. In the future the basic dynamical model should be extended to study the influence of other important effects on the deposition.…”

“…Other observed structures include crack [3] and chevron [4] patterns. Recently it has been shown that evaporating polymer solutions [5][6][7] and (nano)particle suspensions [8-10] may be used to fabricate strikingly regular stripe patterns, where the deposited stripes are parallel to the receding contact line and have typical distances ranging from 10-100µm. The goal is to use this effect as a non-lithographic technique for covering large areas with regular arrays of small-scale structures, such as, e.g., concentric gold rings with potential uses as resonators in advanced optical communications systems [11].…”

Concentric rings of polystyrene and titanium dioxide nanoparticles patterned by alternating current signal guided coffee ring effect

“…Nonetheless, neither DC nor AC signal was used to manipulate the self-assembly process of nanoparticles into regular patterns during the droplet drying process. Previous efforts towards patterning of nanoparticles through the coffee ring effect include using confined environments and sphere on a substrate to form gradient concentric ring patterns 19 or spiral patterns 20 from polymer solutions in a repetitive "stick-slip" manner.…”