Effect of Surfactant on the Drying Patterns of Graphite Nanofluid Droplets

We investigate the effect of surfactant on the formation of nanoparticle aggregates that resulted from evaporation of sessile nanofluid droplets theoretically and experimentally. A Monte Carlo model is developed to explain the transition from the coffee-ring pattern to the uniform deposition in drying the pinned sessile nanofluid droplets. The model applies the diffusion limited cluster–cluster aggregation approach coupled with the biased random walk of nanoparticles. The experiments show that the addition of surfactant in nanofluids helps the formation of a coffee ring instead of the uniform domain coverage. The simulations suggest an explanation of this transition by controlling the sticking probability parameter between the particles. The simulated results statistically agree with the experimental observation of the finally dried graphite nanoparticle structures from the pinned nanofluid droplets

Evaporation-Induced Branched Structures from Sessile Nanofluid Droplets

We investigate the formation of branched nanoparticle aggregates resulting from the evaporation of sessile nanofluid droplets of the copper water-based nanofluids experimentally. Both symmetric and asymmetric drying patterns were found as the sessile droplet evaporated. A kinetic Monte Carlo (KMC) approach is developed to explain the drying process in a circular domain, representing the top view of a drying sessile droplet. It is found that the lattice-gas-based Monte Carlo model can describe the nanoparticle self-assembly into a solid highly branched aggregate. While the chemical potential function is coupled to the nondimensional spherical droplet size during evaporation, the results reveal that the fingering contact line instabilities can emerge under a given condition and force the formation of a branched nanoparticle structure. The pattern comparison shows that the simulation results have a qualitative agreement with the experiments. The parameter study shows that the model parameters, such as domain diameter, chemical potential distribution, particle interaction energy, and so on, have significant influence on the resulting patterns

Evaporation-Induced Branched Structures from Sessile Nanofluid Droplets

We investigate the formation of branched nanoparticle aggregates resulting from the evaporation of sessile nanofluid droplets of the copper water-based nanofluids experimentally. Both symmetric and asymmetric drying patterns were found as the sessile droplet evaporated. A kinetic Monte Carlo (KMC) approach is developed to explain the drying process in a circular domain, representing the top view of a drying sessile droplet. It is found that the lattice-gas-based Monte Carlo model can describe the nanoparticle self-assembly into a solid highly branched aggregate. While the chemical potential function is coupled to the nondimensional spherical droplet size during evaporation, the results reveal that the fingering contact line instabilities can emerge under a given condition and force the formation of a branched nanoparticle structure. The pattern comparison shows that the simulation results have a qualitative agreement with the experiments. The parameter study shows that the model parameters, such as domain diameter, chemical potential distribution, particle interaction energy, and so on, have significant influence on the resulting patterns

Evaporation-Induced Branched Structures from Sessile Nanofluid Droplets

We investigate the formation of branched nanoparticle aggregates resulting from the evaporation of sessile nanofluid droplets of the copper water-based nanofluids experimentally. Both symmetric and asymmetric drying patterns were found as the sessile droplet evaporated. A kinetic Monte Carlo (KMC) approach is developed to explain the drying process in a circular domain, representing the top view of a drying sessile droplet. It is found that the lattice-gas-based Monte Carlo model can describe the nanoparticle self-assembly into a solid highly branched aggregate. While the chemical potential function is coupled to the nondimensional spherical droplet size during evaporation, the results reveal that the fingering contact line instabilities can emerge under a given condition and force the formation of a branched nanoparticle structure. The pattern comparison shows that the simulation results have a qualitative agreement with the experiments. The parameter study shows that the model parameters, such as domain diameter, chemical potential distribution, particle interaction energy, and so on, have significant influence on the resulting patterns

Elimination of the Coffee-Ring Effect by Promoting Particle Adsorption and Long-Range Interaction

A Monte Carlo model has been developed to investigate the transition from the coffee-ring deposition to the uniform coverage in drying pinned sessile colloidal droplets. The model applies the diffusion-limited aggregation (DLA) approach coupled with the biased random walk (BRW) to simulate the particle migration and agglomeration during the droplet drying process. It is shown that the simultaneous presence of the particle adsorption, long-range attraction, and circulatory motion processes is important for the transition from the coffee-ring effect to the uniform deposition of finally dried particles. The absence of one of the specified factors favors the coffee-ring deposition near the droplet boundary. The strong outward capillary flow on the latest evaporation stage can easily destroy the entire particle pre-ordering at the early drying stages. The formation of a robust particle structure is required to resist the outward flow and alter the coffee-ring effect

Evaporation-Induced Branched Structures from Sessile Nanofluid Droplets

We investigate the formation of branched nanoparticle aggregates resulting from the evaporation of sessile nanofluid droplets of the copper water-based nanofluids experimentally. Both symmetric and asymmetric drying patterns were found as the sessile droplet evaporated. A kinetic Monte Carlo (KMC) approach is developed to explain the drying process in a circular domain, representing the top view of a drying sessile droplet. It is found that the lattice-gas-based Monte Carlo model can describe the nanoparticle self-assembly into a solid highly branched aggregate. While the chemical potential function is coupled to the nondimensional spherical droplet size during evaporation, the results reveal that the fingering contact line instabilities can emerge under a given condition and force the formation of a branched nanoparticle structure. The pattern comparison shows that the simulation results have a qualitative agreement with the experiments. The parameter study shows that the model parameters, such as domain diameter, chemical potential distribution, particle interaction energy, and so on, have significant influence on the resulting patterns

Elimination of the Coffee-Ring Effect by Promoting Particle Adsorption and Long-Range Interaction

A Monte Carlo model has been developed to investigate the transition from the coffee-ring deposition to the uniform coverage in drying pinned sessile colloidal droplets. The model applies the diffusion-limited aggregation (DLA) approach coupled with the biased random walk (BRW) to simulate the particle migration and agglomeration during the droplet drying process. It is shown that the simultaneous presence of the particle adsorption, long-range attraction, and circulatory motion processes is important for the transition from the coffee-ring effect to the uniform deposition of finally dried particles. The absence of one of the specified factors favors the coffee-ring deposition near the droplet boundary. The strong outward capillary flow on the latest evaporation stage can easily destroy the entire particle pre-ordering at the early drying stages. The formation of a robust particle structure is required to resist the outward flow and alter the coffee-ring effect

Elimination of the Coffee-Ring Effect by Promoting Particle Adsorption and Long-Range Interaction

A Monte Carlo model has been developed to investigate the transition from the coffee-ring deposition to the uniform coverage in drying pinned sessile colloidal droplets. The model applies the diffusion-limited aggregation (DLA) approach coupled with the biased random walk (BRW) to simulate the particle migration and agglomeration during the droplet drying process. It is shown that the simultaneous presence of the particle adsorption, long-range attraction, and circulatory motion processes is important for the transition from the coffee-ring effect to the uniform deposition of finally dried particles. The absence of one of the specified factors favors the coffee-ring deposition near the droplet boundary. The strong outward capillary flow on the latest evaporation stage can easily destroy the entire particle pre-ordering at the early drying stages. The formation of a robust particle structure is required to resist the outward flow and alter the coffee-ring effect

Elimination of the Coffee-Ring Effect by Promoting Particle Adsorption and Long-Range Interaction

A Monte Carlo model has been developed to investigate the transition from the coffee-ring deposition to the uniform coverage in drying pinned sessile colloidal droplets. The model applies the diffusion-limited aggregation (DLA) approach coupled with the biased random walk (BRW) to simulate the particle migration and agglomeration during the droplet drying process. It is shown that the simultaneous presence of the particle adsorption, long-range attraction, and circulatory motion processes is important for the transition from the coffee-ring effect to the uniform deposition of finally dried particles. The absence of one of the specified factors favors the coffee-ring deposition near the droplet boundary. The strong outward capillary flow on the latest evaporation stage can easily destroy the entire particle pre-ordering at the early drying stages. The formation of a robust particle structure is required to resist the outward flow and alter the coffee-ring effect

Octagon to Square Wetting Area Transition of Water–Ethanol Droplets on a Micropyramid Substrate by Increasing Ethanol Concentration

The wettability and evaporation of water–ethanol binary droplets on the substrate with micropyramid cavities are studied by controlling the initial ethanol concentrations. The droplets form octagonal initial wetting areas on the substrate. As the ethanol concentration increases, the side ratio of the initial wetting octagon increases from 1.5 at 0% ethanol concentration to 3.5 at 30% ethanol concentration. The increasing side ratio indicates that the wetting area transforms from an octagon to a square if we consider the octagon to be a square with its four corners cut. The droplets experience a pinning–depinning transition during evaporation. The pure water sessile droplet evaporation demonstrates three stages from the constant contact line (CCL) stage, and then the constant contact angle (CCA) stage, to the mixed stage. An additional mixed stage is found between the CCL and CCA stages in the evaporation of water–ethanol binary droplets due to the anisotropic depinning along the two different axes of symmetry of the octagonal wetting area. Droplet depinning occurs earlier on the patterned surface as the ethanol concentration increases