Spontaneous uptake of droplets into non-wetting capillaries

The equilibrium state of a droplet deposited on chemically heterogeneous surfaces is studied by using many-body dissipative particle dynamics. The length ratio covers 2 orders from 0.01 to 1 and allows a systematical inspection of the changes of the droplet shape, contact angle, and aspect ratio with this parameter. Moreover, a new parameter, global aspect ratio, is introduced to better characterize the distortion of the droplet. It is found that the droplet shape at the equilibrium stage strongly lies on the deposition position when the length ratio is beyond 0.1. Additionally, the lateral displacement is observed when depositing the droplet on the border of two stripes at large length ratios (over 0.1). On the other hand, the Cassie area fraction also has a significant effect on the wetting behaviors. When the droplet is driven by a body force with a 45° inclined angle to the stripes, the moving direction could be strictly in line with the force direction, deviating from the force direction, or totally in line with the stripes, depending on the length ratio.

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“…Some applications of this boundary condition can be found in previous work. 39,40 2.3. Substrates Modeling.…”

Section: Methodsmentioning

confidence: 99%

“…It has been proved that this boundary condition is effective in keeping the liquid/solid interface properties and preventing the penetration. Some applications of this boundary condition can be found in previous work. , …”

Section: Methodsmentioning

confidence: 99%

Anisotropic Wetting of Droplets on Stripe-Patterned Chemically Heterogeneous Surfaces: Effect of Length Ratio and Deposition Position

et al. 2018

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“…As a mesh-free and coarse-graining numerical approach, dissipative particle dynamics , (DPD) is designed to address problems at the mesoscale. More details of the theoretical aspects and applications of DPD can be found in some recent reviews. − Many-body DPD (MDPD) is one of the variants of the original DPD and has been intensively employed to simulate the fluid system with liquid/vapor interfaces; thus, it is especially suitable for the simulation of wetting phenomena. − MDPD inherits the main interaction scheme from original DPD, so it still satisfies the fluctuation–dissipation theorem. However, the conservative force is modified from a pure repulsive interaction to a force-loop interaction, and thus, the free liquid/vapor interface can be mimicked.…”

Section: Methodsmentioning

confidence: 99%

Droplet Sliding: The Numerical Observation of Multiple Contact Angle Hysteresis

et al. 2019

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Droplets sliding on surfaces always exhibit an advancing and a receding contact angle. When exerting different driving forces on the droplet to force it to slide at different velocities, the droplet would alter its shape to adapt to the new motion. Hence, different advancing/receding contact angles are likely to be observed, leading to the multiple contact angle hysteresis on a given surface. To verify this hypothesis, many-body dissipative particle dynamics is employed to perform the sliding simulation on both chemically homogeneous and heterogeneous surfaces. By ensuring the droplet sliding in uniform motions under different driving forces, the advancing/receding contact angles are recorded for analysis. Simulation results show that, for homogeneous surfaces, a larger driving force can result in both larger advancing contact angle and smaller receding contact angle, while for heterogeneous surfaces, increasing the driving force only results in smaller receding contact angles. For both cases, multiple contact angle hysteresis can be observed. These observations are contrary to the currently prevailing opinion, which believes that the contact angle hysteresis should be unique on given surfaces. Our findings would advance the understanding of wetting phenomena and possibly inspire new guidance for the design of functional interfaces.

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“…With the development of computer simulation, molecular dynamics (MD) simulations that can capture the microscale details of the lubrication process provide a reliable methodology for studying the microcapillary imbibition process. Many researchers adopted MD to study the fluid flow in the micropores. − To ensure the applicability of the L–W equation at the microscale, the dynamic contact angle, , inertia term, and effective viscosity were incorporated in the L–W equation to describe the fluid imbibition process. According to ref , the inertial terms can be ignored for pores with a small radius due to the dominant viscous forces.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulations of Lubricant Recycling in Porous Polyimide Retainers of Bearing

Chen

Zhu

et al. 2021

Langmuir

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Porous polyimide (PI) materials are one of important bearing retainer materials in space applications due to the storage and continuous supply of a lubricant through the porous structure. Understanding the lubricant recycling process in porous polyimide retainers is of vital importance to improve lubricant supply performance of bearing. In this work, through molecular dynamic simulations, coarse-grained models are built to study lubricant recycling processes on porous and solid surfaces. A spontaneous imbibition behavior is observed when the lubricant is present on the porous surface. The dynamic change in the contact angle in this process and the deviation of the effective radius from the volumetric radius because of the molecular structure of polyimide causes the classical Lucas–Washburn (L–W) equation fail to describe the process. By fitting dynamic contact angle and effective radius, a modified L–W equation is developed, which well predicts the process of imbibition. Furthermore, it is found that the lubricants between the porous polyimide surface and the solid surface are recycled by extrusion, and spontaneous imbibition does not occur. In this case, the accumulation of lubricant pressure and weak interfacial interaction between the lubricant and the solid surface are also the main factors that promote lubricant recycling.

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Spontaneous uptake of droplets into non-wetting capillaries

Cited by 19 publications

References 22 publications

Anisotropic Wetting of Droplets on Stripe-Patterned Chemically Heterogeneous Surfaces: Effect of Length Ratio and Deposition Position

Anisotropic Wetting of Droplets on Stripe-Patterned Chemically Heterogeneous Surfaces: Effect of Length Ratio and Deposition Position

Droplet Sliding: The Numerical Observation of Multiple Contact Angle Hysteresis

Molecular Dynamics Simulations of Lubricant Recycling in Porous Polyimide Retainers of Bearing

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