Disk-Ring Deposition in Drying a Sessile Nanofluid Droplet with Enhanced Marangoni Effect and Particle Surface Adsorption

Abstract

The present study is to explore the central particle deposition from drying a sessile nanofluid droplet experimentally and theoretically. Normally, a pinned colloidal droplet dries into a coffee-ring pattern as a result of moving the particles to a three-phase line by the radial direction capillary flow. However, the strong evaporation can generate the nonuniform temperature at the evaporating droplet interface and the droplet periphery temperature is higher than that close to the droplet centerline. The induced Marangoni flow would reversibly transport the particles at the periphery toward the centerline. We have thus designed the experiments to increase the droplet evaporation rate in vacuum conditions and accordingly to enhance the Marangoni effect. We have observed distinguishable disk deposition inside the outer coffee ring. A three-dimensional diffusion-limited cluster–cluster aggregation Monte Carlo model has been developed to simulate the deposition process. With modeling the Marangoni effect, particle adsorption at the liquid–air interface and particle aggregation behaviors, the formation of the disk pattern inside a coffee ring has been simulated. The qualitative agreement has been found in the comparison of local deposition distribution between the related experiment and simulation.

Implications of the Coffee-Ring Effect on Virus Infectivity

“…This phenomenon, known as the “coffee-ring effect”, , reflects the balance between capillary and Marangoni flows in a drying droplet . Capillary flows deposit particles at the water–surface contact line, whereas Marangoni flows transport particles from the periphery to the center . These different convection and deposition processes dominate at different evaporation stages and collectively give rise to the final deposition pattern. , Past studies have shown that the coffee-ring effect is affected by surface hydrophobicity, pH, droplet chemical composition, as well as particle morphology .…”

Evaporation of a Sessile Colloidal Water–Glycerol Droplet: Marangoni Ring Formation

“…Including colloidal interactions along with hydrodynamics in simulations can also help us to further understand the process. 31 , 66 , 74 , 75 …”

“…Particle-laden droplets evaporating at very low pressures also show an inner ring. 31 In all these cases, the thermal Marangoni flow transports the particles along the liquid–air interface away from the contact line and toward the inner ring. Similarly, when the droplet contains surfactants 11 , 24 or surfactant-like polymers, 32 the solutal Marangoni flow transports the particles along the liquid air interface and toward the inner ring.…”

Droplet-based microfluidic synthesis of nanogels for controlled drug delivery: tailoring nanomaterial properties via pneumatically actuated flow-focusing junction

“…62 Moreover, during sample preparation for AFM, the formation of colloidal nano-agglomerates can occur, due to the variation of the surface tension gradient during evaporation of the laid droplet (Marangoni effect). [63][64][65] In particular, the presence of colloidal clusters was more noticeable in the AFM image of NG_2.…”