Two-Dimensional Numerical Analysis of Gas Diffusion-Induced Cassie to Wenzel State Transition

We develop a two-dimensional model for the transient diffusion of gas from the cavities in ridge-type structured surfaces to a quiescent liquid suspended above them in the Cassie state to predict the location of the liquid vapor-interface (meniscus) as a function of time. The transient diffusion equation is numerically solved by a Chebyshev collocation (spectral) method coupled to the Young-Laplace equation and the ideal gas law. We capture the effects of variable meniscus curvature and, subsequently, when applicable, movement of triple contact lines. Results are presented for the evolution of the dissolved gas concentration field in the liquid and, when applicable, the time it takes for a meniscus to depin and that for longevity, i.e., the onset of the Cassie to Wenzel state transition. Two configurations are examined; viz., one where an impermeable membrane pressurizes the liquid above the ridges and one where hydrostatic pressure is considered and the top of the liquid is exposed to non-condensable gas.

Insights into the Self-Optimized Hydrophobicity of Cerium Oxide Surface under Impact Abrasive Wear

Cerium oxide (CeO2) is one of potential candidates of hydrophobic coatings servicing in harsh environments. In this letter, abraded CeO2 surface was prepared using sandblasting treatment to investigate the wetting mechanism under the condition of impact abrasive wear. The water contact angle (WCA) of the abraded surface increased from 62.8° to 93.7° after aging in ambient air for about 700 h. The hydrophobic self-optimisation mechanism of the abraded CeO2 surface is due to the hierarchical structure formed during impact abrasive wear and the surface adsorption of airborne hydrocarbon, resulting the wetting state changed from “Wenzel state” to “Cassie-Baxter State”.

Reversible electrowetting transitions on superhydrophobic surfaces

Electric field applied across the interface has been shown to enable transitions from Cassie to Wenzel state on superhydrophobic surfaces with miniature corrugations. Molecular Dynamics (MD) simulations manifest the possibility...

The upward tilt of honeycomb cells increases the carrying capacity of the comb and is not to prevent the outflow of honey

The cells of the combs of Apis mellifera are tilted upwards by approximately 13°. The literature says that this tilt serves to prevent the outflow of honey. We checked this by hanging empty honeycombs upside down into beehives. Honey was stored in these inverted honeycombs in the same way as in the normally oriented combs, and inverted combs were also well accepted for rearing the brood. We thus show that the benefit for the bees of the upward tilt of the cells is not to prevent leakage of honey. Honey is obviously in a Wenzel state on the hydrophobic, micro-structured cell walls. The associated wetting of the cell wall causes adhesion that prevents leakage. We propose that the benefit of the inclination of the cells is to direct about 10% of the weight of cell contents onto the midwall, thus increasing the carrying capacity of the comb.

Controlling wetting properties on nanostructure surfaces by the coupled effect of the structural parameter and roughness factor

Aims: The wetting properties of the nanostructure surface can be controlled by the structural parameter associate with roughness surface. Background: Increasing the roughness of hydrophobic surface can enhance the hydrophobicity of the surface. Objective: We chose copper material modified by fluorosilane as the substrate, and used Lammps software to establish four different shapes nanostructures, square pillar, cylinder, frustum and cone nanostructure respectively with pillar height and theoretical gap changing to study the influence of structural parameter and roughness factor on wetting properties of surfaces. Method: Molercular dynamic simulation Result: The structural parameter h/b can determine the wetting transition of the droplet on surfaces. With the same height and theoretical gap, the contact angle of the frustum and the cone surfaces is larger than that of the square pillar surfaces and cylinder surfaces due to the effect of wedge surface. Conclusion: (1)The values of the contact angle exhibit a strong dependence on roughness factor. The roughness factor will increase by this way of increasing height and decreasing gap, and the contact angle of droplet increase with the roughness factor increasing on the four surfaces. There exists the critical structural parameter h/b to determine the Cassie and Wenzel state transition of the droplet on various nanostructure surfaces.And the critical structural parameter values are 1.5, 1.5, 2.08 and 2.24 for the square pillar, cylinder, frustum and cone nanostructures respectively. Other: The wetting properties can be controlled by the structural parameter associate with the roughness factor. Increasing the pillar height and decreasing the gap of the nanostructure surfaces will make the structural parameters reach the standard of transition value h/b of the droplet state, and the droplet will change from Wenzel state to Cassie state.