Light-Fueled Beating Coffee-Ring Deposition for Droplet Evaporative Crystallization

Abstract

Condensed deposition favors biochemical analysis, bioassays, and clinical diagnosis, but the existing strategies may suffer from low resolution, inaccurate control, cross-contamination, or miscellaneous apparatus. Herein, we propose a noncontact light strategy to enable the condensed deposition for droplet evaporative crystallization, in which the photothermal effect of a focused infrared laser is employed to induce intense evaporation. Due to the localized heating effect, not only can the droplet evaporative crystallization on the hydrophobic substrate be promoted, but also the resultant intensified Marangoni flow enables the movement of the early-formed crystals, preventing the pinning of the triple-phase contact line. Synergy of the Marangoni flow and nonuniform evaporation makes the solutes tend to accumulate near the focused light beam region, which facilitates the condensed deposition. More importantly, this light strategy not only enables condensed deposition on the hydrophobic surface with low hysteresis, but also works successfully on the hydrophilic substrate with high hysteresis via adjusting input laser power. It is demonstrated that the light strategy proposed in the present study has great potential for relevant applications.

Surfactant Control of Coffee Ring Formation in Carbon Nanotube Suspensions

“…All of the patterns classified as coffee ring in this study had some form of nanoparticle deposition within the ring. While this is a common observation, − it is worth noting that, at lower DTAB concentrations, where larger central features are present, these were differentiated from combined patterns (consisting of a dot-like central deposit with an additional coffee ring feature) due to the nature of the inner deposits. In the case of a dot-like feature, one singular central deposit is observed and the intermediate zone between the ring and the inner deposits remains clear .…”

“…These results are of particular interest, because undesired self-assembly in evaporating complex droplets often creates unwanted effects and many existing methods for mitigating these effects are either costly or too complex. Some recent examples include applying a magnetic field in the evaporation of an iron oxide solution on PDMS, 70 heating to high temperatures (between 130 and 250 °C) for a variety of inkjet inks, 71 irradiating with infrared laser beams for calcium sulfate suspensions on hydrophobic PDMS and hydrophilic polydopamine substrates, 57 and exposure to air flow for polytetrafluoroethylene on both glass and silicon wafer substrates. 72 Although these methods offer effective CRE suppression, they are complicated to use and generally require the utilization of costly specialized equipment.…”

Control of the Drying Patterns for Complex Colloidal Solutions and Their Applications

“…Several studies have also demonstrated various methods to control the final deposition pattern of an evaporating droplet without modification of its composition. It can be achieved by altering the dynamics of internal flow using external factors such as vapor source [ 101 , 102 , 103 , 104 , 105 , 106 ], atmospheric drying condition [ 73 , 74 , 75 , 76 ], the temperature of substrate [ 77 , 78 , 79 , 80 , 81 , 82 ], SAW or magnetic field [ 52 , 135 , 136 ]. These factors help to obtain uniform or spot-like dried patterns of colloidal droplets.…”

“…Another strategy to achieve uniform deposits is utilizing a light source to actuate Marangoni flow in the droplet [ 136 ]. The light source rapidly converts light energy into heat and induces a nonuniform temperature distribution along the droplet surface.…”

“…( b ) Evaporative crystallization process of the light-induced droplet and final deposition patterns under the light-induced, plate-heating-induced, and natural evaporation on the (i) hydrophobic and (ii) hydrophilic surfaces (reproduced with permission from ref. [ 136 ]. Copyright 2021 American Chemical Society).…”