Evaporation Induced Spontaneous Micro‐Vortexes through Engineering of the Marangoni Flow

Abstract

Vortex flow fields are widely used to manipulate objects at the microscale in microfluidics. Previous approaches to produce the vortex flow field mainly focused on inertia flows. It remains a challenge to create vortexes in Stokes flow regime. Here we reported an evaporation induced spontaneous vortex flow system in Stokes flow regime by engineering Marangoni flow in a micro‐structured microfluidic chip. The Marangoni flow is created by nonuniform evaporation of surfactant solution. Various vortexes are constructed by folding the air–water interface via microstructures. Patterns of vortexes are programmable by designing the geometry of the microstructures and are predictable using numerical simulations. Moreover, rotation of micro‐objects and enrichment of micro‐particles using vortex flow is demonstrated. This approach to create vortexes will provide a promising platform for various microfluidic applications such as biological analysis, chemical synthesis, and nanomaterial assembly.

Orientation-Controlled Ultralong Assembly of Janus Particles Induced by Bubble-Driven Instant Quasi-1D Interfaces

“…Therefore, the hydrophilic substrate is beneficial for the Janus-1/SDS configuration and adverse for the Janus-2/CTAB configuration. On the other hand, as previously reported, 40 the surfactant can induce Marangoni flow and suppress the coffee ring effect, which also plays a vital role in the actual assembly (Figure 2e,f). As shown in Figure S14, the coffee ring effect overcrowded the particles at edges and caused the disordered aggregation (Figure S13) at low surfactant concentration, which is competitive for interfacial patterning.…”

Mechanomaterials: A Rational Deployment of Forces and Geometries in Programming Functional Materials

“…[95] Alternatively, methods that interfere with the evaporation-driven capillary flow can also disturb the transportation of feeding materials to the contact line. General strategies include inducing additional flows inside the liquid (e.g., Marangoni flow, [96] electro-osmotic flow, substrate vibrations, surface acoustic waves), manipulating interactive forces between the feeding materials (e.g., tuning inter-particle Optical and SEM images of the Ag nanoparticles coffee-ring arrays through capillary assembly in a transparent electrode (a1). Reproduced with permission.…”

Marangoni Flow Manipulated Concentric Assembly of Cellulose Nanocrystals

“…Marangoni effect, directing flow from regions with low surface tension to high surface tension area, can regulate this capillary flow and generate a recirculating flow, [33] in which temperature and surfactant concentration are the crucial factors to modulate the surface tension gradient to influence the Marangoni effect. [34,35] Marangoni flow is able to initiate an additional mass transfer for solute in the droplet, thus stimulate the assembly behavior, [36,37] contributing to new optical/ electrical properties. [38] Herein, a novel negative spherulite-like concentric assembling behavior of carboxyl modified cellulose nanocrystals (M-CNCs) was obtained, ascribing to synergistic interactions of Marangoni effect and capillary follow during the evaporation of sessile M-CNCs droplet.…”