Conformal and non-conformal surface modification of honeycomb-patterned porous films via tunable Cassie–Wenzel transition

RSC Advances ◽  
2016 ◽  
Vol 6 (57) ◽  
pp. 52131-52136 ◽  
Author(s):  
Qi-Zhi Zhong ◽  
Xiang Yu ◽  
Ming-Xu Cui ◽  
Ling-Shu Wan ◽  
Zhi-Kang Xu
Keyword(s):  
Surface Modification ◽  
Wetting Transition ◽  
Porous Films ◽  
Robust Approach ◽  
Cassie State ◽  
Wenzel State

We describe here a facile and robust approach to conformal and non-conformal surface modification by tuning the wetting transition between the Wenzel state and the Cassie state.

scholarly journals Dynamic Wetting Behavior of Vibrated Droplets on a Micropillared Surface

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Zhi-hai Jia ◽  
Wei Lei ◽  
Hui-nan Yang ◽  
Gang Wang
Keyword(s):  
Model Calculation ◽  
Water Droplet ◽  
Vertical Vibration ◽  
Wetting Transition ◽  
Compression Process ◽  
Dynamic Wetting ◽  
Wetting Behavior ◽  
Cassie State ◽  
Wenzel State

The dynamical wetting behavior has been observed under vertical vibration of a water droplet placed on a micropillared surface. The wetting transition takes place under the different processes. In compression process, the droplet is transited from Cassie state to Wenzel state. The droplet undergoes a Wenzel-Cassie wetting transition in restoring process and the droplet bounces off from the surface in bouncing process. Meanwhile, the wetting and dewetting models during vibration are proposed. The wetting transition is confirmed by the model calculation. This study has potential to be used to control the wetting state.

scholarly journals SURFACE EVOLVER SIMULATIONS OF DROPS ON MICROPOSTS

2012 ◽  
Vol 23 (08) ◽  
pp. 1240013 ◽  
Author(s):  
MATTHEW L. BLOW ◽  
JULIA M. YEOMANS
Keyword(s):  
Free Energy ◽  
Arbitrary Shape ◽  
Liquid Surface ◽  
Superhydrophobic Surfaces ◽  
Surface Evolver ◽  
Horizontal Section ◽  
Good Convergence ◽  
Cassie State ◽  
Wenzel State ◽  
Solid Liquid

An important feature in the design of superhydrophobic surfaces is their robustness against collapse from the Cassie–Baxter configuration to the Wenzel state. Upon such a transition a surface loses its properties of low adhesion and friction. We describe how to adapt the Surface Evolver algorithm to predict the parameters and mechanism of the collapse transition on posts of arbitrary shape. In particular, contributions to the free energy evaluated over the solid–liquid surface are reduced to line integrals to give good convergence. The algorithm is validated for straight, vertical and inclined, posts. Numerical results for curved posts with a horizontal section at their ends show that these are more efficient in stabilizing the Cassie state than straight posts, and identify whether the interface first depins from the post sides or the post tips.

Wetting Transition from the Cassie–Baxter State to the Wenzel State on Textured Polymer Surfaces

Langmuir ◽  
2014 ◽  
Vol 30 (8) ◽  
pp. 2061-2067 ◽  
Author(s):  
Daiki Murakami ◽  
Hiroshi Jinnai ◽  
Atsushi Takahara
Keyword(s):  
Polymer Surfaces ◽  
Wetting Transition ◽  
Wenzel State

Evaporation and Condensation on Two-Tier Superhydrophobic Surfaces

2008 ◽  
Author(s):  
Chuan-Hua Chen ◽  
Qingjun Cai ◽  
Chung-Lung Chen
Keyword(s):  
Superhydrophobic Surfaces ◽  
Enhance Heat Transfer ◽  
Evaporation And Condensation ◽  
Cassie State ◽  
Wenzel State ◽  
Change Behavior ◽  
Lotus Leaves ◽  
First Time ◽  
Short Carbon ◽  
Nanoscale Roughness

Superhydrophobic surfaces exhibit large contact angle and small hysteresis which promote liquid transport and enhance heat transfer. Here, liquid-vapor phase change behavior is reported on superhydrophobic surfaces with short carbon nanotubes deposited on micromachined posts, a two-tier texture mimicking the surface structure of lotus leaves. Compared to one-tier microtexture which energetically favors the Wenzel state, the two-tier texture with nanoscale roughness favors the Cassie state, the desired superhydrophobic state. During droplet evaporation, the two-tier texture delays the transition from Cassie to Wenzel state. Using two-tier texture with hexadeconethiol coating, continuous dropwise condensation was demonstrated for the first time on engineered superhydrophobic surfaces.

scholarly journals Wetting Transitions of Liquid Gallium Film on Nanopillar-Decorated Graphene Surfaces

Molecules ◽  
2018 ◽  
Vol 23 (10) ◽  
pp. 2407 ◽  
Author(s):  
Junjun Wang ◽  
Tao Li ◽  
Yifan Li ◽  
Yunrui Duan ◽  
Yanyan Jiang ◽  
...  
Keyword(s):  
Metal Droplet ◽  
Adhesion Energy ◽  
Wetting Transition ◽  
Liquid Gallium ◽  
Patterned Surfaces ◽  
Final State ◽  
Wetting Transitions ◽  
Graphene Surface ◽  
Wenzel State ◽  
Wetting Model

Molecular dynamics (MD) simulation has been employed to study the wetting transitions of liquid gallium droplet on the graphene surfaces, which are decorated with three types of carbon nanopillars, and to explore the effect of the surface roughness and morphology on the wettability of liquid Ga. The simulation results showed that, at the beginning, the Ga film looks like an upside-down dish on the rough surface, different from that on the smooth graphene surface, and its size is crucial to the final state of liquid. Ga droplets exhibit a Cassie–Baxter (CB) state, a Wenzel state, a Mixed Wetting state, and a dewetting state on the patterned surfaces by changing distribution and the morphology of nanopillars. Top morphology of nanopillars has a direct impact on the wetting transition of liquid Ga. There are three transition states for the two types of carbon nanotube (CNT) substrates and two for the carbon nanocone (CNC) one. Furthermore, we have found that the substrates show high or low adhesion to the Ga droplet with the variation of their roughness and top morphology. With the roughness decreasing, the adhesion energy of the substrate decreases. With the same roughness, the CNC/graphene surface has the lowest adhesion energy, followed by CNT/graphene and capped CNT/graphene surfaces. Our findings provide not only valid support to previous works but also reveal new theories on the wetting model of the metal droplet on the rough substrates.

Cassie–Baxter to Wenzel state wetting transition: a 2D numerical simulation

RSC Advances ◽  
2013 ◽  
Vol 3 (46) ◽  
pp. 24530 ◽  
Author(s):  
Daisiane M. Lopes ◽  
Stella M. M. Ramos ◽  
Luciana R. de Oliveira ◽  
José C. M. Mombach
Keyword(s):  
Numerical Simulation ◽  
Wetting Transition ◽  
Wenzel State ◽  
2D Numerical Simulation

Analysis of Gas Diffusion-Induced Cassie to Wenzel State Transition on a Structured Surface

2016 ◽  
Author(s):  
Jonah Kadoko ◽  
Georgios Karamanis ◽  
Toby Kirk ◽  
Marc Hodes
Keyword(s):  
Concentration Field ◽  
Gas Diffusion ◽  
Dimensional Solution ◽  
One Dimensional ◽  
Gas Concentration ◽  
Structured Surface ◽  
Cassie State ◽  
Wenzel State ◽  
The Times ◽  
Quiescent Liquid

We provide an approximate and one-dimensional solution for transient diffusion of gas between parallel ridges into a degassed and quiescent liquid suspended in the Cassie state above a parallel-ridge type structured surface. At time equal to zero, the liquid and gas are at the same pressure; therefore, the meniscus formed between ridges is flat. The analysis provides the transient gas concentration field in the liquid. It also computes the times when the triple contact line begins to move down the ridges and that when the meniscus contacts the bottom substrate compromising the Cassie state.

scholarly journals Spontaneous recovery of superhydrophobicity on nanotextured surfaces

2016 ◽  
Vol 113 (20) ◽  
pp. 5508-5513 ◽  
Author(s):  
Suruchi Prakash ◽  
Erte Xi ◽  
Amish J. Patel
Keyword(s):  
Surface Texture ◽  
Hydrophobic Surface ◽  
Water Repellency ◽  
Density Fluctuations ◽  
Enhanced Sampling ◽  
Ambient Conditions ◽  
Elevated Pressures ◽  
Cassie State ◽  
Wenzel State ◽  
Phase Change Heat Transfer

Rough or textured hydrophobic surfaces are dubbed “superhydrophobic” due to their numerous desirable properties, such as water repellency and interfacial slip. Superhydrophobicity stems from an aversion of water for the hydrophobic surface texture, so that a water droplet in the superhydrophobic “Cassie state” contacts only the tips of the rough surface. However, superhydrophobicity is remarkably fragile and can break down due to the wetting of the surface texture to yield the “Wenzel state” under various conditions, such as elevated pressures or droplet impact. Moreover, due to large energetic barriers that impede the reverse transition (dewetting), this breakdown in superhydrophobicity is widely believed to be irreversible. Using molecular simulations in conjunction with enhanced sampling techniques, here we show that on surfaces with nanoscale texture, water density fluctuations can lead to a reduction in the free energetic barriers to dewetting by circumventing the classical dewetting pathways. In particular, the fluctuation-mediated dewetting pathway involves a number of transitions between distinct dewetted morphologies, with each transition lowering the resistance to dewetting. Importantly, an understanding of the mechanistic pathways to dewetting and their dependence on pressure allows us to augment the surface texture design, so that the barriers to dewetting are eliminated altogether and the Wenzel state becomes unstable at ambient conditions. Such robust surfaces, which defy classical expectations and can spontaneously recover their superhydrophobicity, could have widespread importance, from underwater operation to phase-change heat transfer applications.

Stability Analysis of Cassie-Baxter State Under Pressure Driven Flow

2010 ◽  
Author(s):  
Tae Jin Kim ◽  
Carlos H. Hidrovo
Keyword(s):  
Liquid Layer ◽  
Friction Reduction ◽  
Wetting Transition ◽  
Textured Surface ◽  
Microchannel Flow ◽  
Flow Conditions ◽  
Cassie State ◽  
The Stability ◽  
Gas Layer ◽  
Micro Cavity

The Cassie-Baxter state is a phenomenon in which a liquid rests on top of a textured surface with a gas layer trapped underneath the liquid layer. This gas layer introduces an effective shear free boundary that induces slip at the liquid-gas interface, allowing for friction reduction in liquid channel flows. Multiple studies have shown that different surface configurations result in different friction reduction characteristics, and most work is aimed at controlling the roughness factor and its shape in order to achieve an increased slip flow. This paper investigates the effects that different texturing geometries have on the stability of the Cassie state under pressurized microchannel flow conditions. To test the stability effects associated with the pressurized microchannel flow conditions, microfluidic channels with microstructures on the side walls were designed and fabricated. The microstructures were designed to induce the Cassie state with a liquid-air interface forming between the texturing trenches. The air trapped within the microstructure is treated as an ideal gas, with the compressibility induced pressure rise acting as a restrictive force against the Wenzel wetting transition. The model was validated against experimental flow data obtained using microchannel samples with microtextured boundaries. The microchannels were fabricated in PDMS (poly-dimethylsiloxane) using soft lithography and were baked on a hot plate to ensure the hydrophobicity of the microtexture. Pressure versus flow rate data was obtained using a constant gravitational pressure head setup and a flow meter. The liquid-gas interface layer in the microchannel was visualized using bright field microscopy that allowed measurement of the liquid penetration depth into the microtexturing throughout the microhannel. The experimental results indicate that air trapped in the pockets created by micro-cavity structures prevented the liquid layer from completely filling the void. As expected, the pressure drop in the micro-cavity textured channel showed a considerable decrease compared to that in the flat surfaced channel. These results also suggest that micro-cavities can maintain the Cassie state of a liquid meniscus, resting on top of the surface, in larger pressure ranges than open spaced micro-pillars arrays.

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