Dynamic contact angles and contact angle hysteresis on laser-textured aluminum alloy surfaces

Superhydrophobic materials have been extensively studied because of their wonderful array of properties and applications. In this study, normal and superhydrophobic surface of silk fabric have been prepared via deposition of different shapes of PTFE nanostructure using magnetron sputter coating. The effects of PTFE sputter coating on surface morphology and surface chemical properties were characterized using atomic force microscopy (AFM) and ATR-FTIR (attenuated total reflection-Fourier transform infrared spectroscopy). The wettability of the fabric was characterized through measuring the surface contact angle by drop shape analysis apparatus and dynamic contact angle by Wilhelmy technique. As evaluated by water contact angle measurements, all the treatments resulted in a significant enhancement in the hydrophobicity of silk fabric, while larger sputtering pressures brought bigger PTFE nanoparticles, which led to higher contact angles. The results have also revealed that alternant working pressures, could bring gradient nanostructures which generated both high contact angle and less contact angle hysteresis.

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Anisotropic Wetting Characteristics of Biomimetic Rice Leaf Surface with Asymmetric Asperities

Journal of Nanoscience and Nanotechnology ◽

10.1166/jnn.2020.17570 ◽

2020 ◽

Vol 20 (7) ◽

pp. 4331-4335

Author(s):

Mu-Yeon Jang ◽

Jeong-Woo Park ◽

Seung-Yub Baek ◽

Tae-Wan Kim

Keyword(s):

Contact Angle ◽

Leaf Surface ◽

Contact Angle Hysteresis ◽

Dynamic Contact ◽

Contact Angles ◽

Droplet Flow ◽

Biomimetic Surfaces ◽

Rice Leaf ◽

The Difference ◽

Inclined Angle

Rice leaf surface has known as having functional performances such as self cleaning and antifouling as well as directional flowing due to a unique micro structure with groove. In this study, we investigated the effects of asymmetrical cone protrusions on the surface of droplet flow through the contact angle and contact angle hysteresis of the droplet. First, static and dynamic contact angles of droplet on the rice leaf are measured. We found that the rice leaf surface has a directional flow characteristic through the difference of the contact angle hysteresis with flow directions. We also fabricated the rice leaf-like surfaces with asymmetric asperities along microgrooves using rapid prototyping technique and evaluated anisotropic wettability properties for the produced biomimetic surfaces. The experimental results show that the direction of the micro asperity tip relative to the droplet flow and its inclined angle has a very important influence on the anisotropic flow. This research can help to clarify the anisotropic wettability by the surface structure.

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Biomimetic Approach for the Elaboration of Highly Hydrophobic Surfaces: Study of the Links between Morphology and Wettability

Biomimetics ◽

10.3390/biomimetics6020038 ◽

2021 ◽

Vol 6 (2) ◽

pp. 38

Author(s):

Quentin Legrand ◽

Stephane Benayoun ◽

Stephane Valette

Keyword(s):

Contact Angle ◽

Ginkgo Biloba ◽

Contact Angle Hysteresis ◽

Contact Angles ◽

Textured Surfaces ◽

Replication Process ◽

Wetting Behavior ◽

Static Contact ◽

Biomimetic Approach ◽

Highly Hydrophobic

This investigation of morphology-wetting links was performed using a biomimetic approach. Three natural leaves’ surfaces were studied: two bamboo varieties and Ginkgo Biloba. Multiscale surface topographies were analyzed by SEM observations, FFT, and Gaussian filtering. A PDMS replicating protocol of natural surfaces was proposed in order to study the purely morphological contribution to wetting. High static contact angles, close to 135∘, were measured on PDMS replicated surfaces. Compared to flat PDMS, the increase in static contact angle due to purely morphological contribution was around 20∘. Such an increase in contact angle was obtained despite loss of the nanometric scale during the replication process. Moreover, a significant decrease of the hysteresis contact angle was measured on PDMS replicas. The value of the contact angle hysteresis moved from 40∘ for flat PDMS to less than 10∘ for textured replicated surfaces. The wetting behavior of multiscale textured surfaces was then studied in the frame of the Wenzel and Cassie–Baxter models. Whereas the classical laws made it possible to describe the wetting behavior of the ginkgo biloba replications, a hierarchical model was developed to depict the wetting behavior of both bamboo species.

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The Surface Modification with Fluorocarbon Thin Films for the Prevention of Stiction in Mems

MRS Proceedings ◽

10.1557/proc-518-143 ◽

1998 ◽

Vol 518 ◽

Cited By ~ 5

Author(s):

Sang-Ho Lee ◽

Myong-Jong Kwon ◽

Jin-Goo Park ◽

Yong-Kweon Kim ◽

Hyung-Jae Shin

Keyword(s):

Contact Angle ◽

Contact Angle Hysteresis ◽

Contact Angles ◽

Fluorocarbon Films ◽

Perfluorodecanoic Acid ◽

Large Hysteresis ◽

Static Contact ◽

Receding Contact ◽

Highly Hydrophobic ◽

Receding Contact Angle

AbstractHighly hydrophobic fluorocarbon films were prepared by the vapor phase (VP) deposition method in a vacuum chamber using both liquid (3M's FC40, FC722) and solid sources (perfluorodecanoic acid (CF3(CF2)8COOH), perfluorododecane (C12F26)) on Al, Si and oxide coated wafers. The highest static contact angles of water were measured on films deposited on aluminum substrate. But relatively lower contact angles were obtained on the films on Si and oxide wafers. The advancing and receding contact angle analysis using a captive drop method showed a large contact angle hysteresis (ΔH) on the VP deposited fluorocarbon films. AFM study showed poor film coverage on the surface with large hysteresis. FTIR-ATR analysis positively revealed the stretching band of CF2 groups on the VP deposited substrates. The thermal stability of films was measured at 150°C in air and nitrogen atmospheres as a function of time. The rapid decrease of contact angles was observed on VP deposited FC and PFDA films in air. However, no decrease of contact angle on them was observed in N2.

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Numerical Bifurcation Analysis of a Film Flowing over a Patterned Surface through Enhanced Lubrication Theory

Fluids ◽

10.3390/fluids6110405 ◽

2021 ◽

Vol 6 (11) ◽

pp. 405

Author(s):

Nicola Suzzi ◽

Giulio Croce

Keyword(s):

Contact Angle ◽

Bifurcation Analysis ◽

Dynamic Contact Angle ◽

Flow Characteristics ◽

Dynamic Contact ◽

Contact Angles ◽

Inclined Plate ◽

Lubrication Equation ◽

Static Contact ◽

Numerical Bifurcation

The bifurcation analysis of a film falling down an hybrid surface is conducted via the numerical solution of the governing lubrication equation. Instability phenomena, that lead to film breakage and growth of fingers, are induced by multiple contamination spots. Contact angles up to 75∘ are investigated due to the full implementation of the free surface curvature, which replaces the small slope approximation, accurate for film slope lower than 30∘. The dynamic contact angle is first verified with the Hoffman–Voinov–Tanner law in case of a stable film down an inclined plate with uniform surface wettability. Then, contamination spots, characterized by an increased value of the static contact angle, are considered in order to induce film instability and several parametric computations are run, with different film patterns observed. The effects of the flow characteristics and of the hybrid pattern geometry are investigated and the corresponding bifurcation diagram with the number of observed rivulets is built. The long term evolution of induced film instabilities shows a complex behavior: different flow regimes can be observed at the same flow characteristics under slightly different hybrid configurations. This suggest the possibility of controlling the rivulet/film transition via a proper design of the surfaces, thus opening the way for relevant practical application.

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Contact Angles in Imaginary Number Space: A Novel Tool for Probing the Remaining Mysteries of Ultrahydrophilicity and Superhydrophilicity.

MRS Proceedings ◽

10.1557/opl.2014.352 ◽

2014 ◽

Vol 1648 ◽

Author(s):

Herbert P. Jennissen

Keyword(s):

Contact Angle ◽

Smooth Surface ◽

Dynamic Contact ◽

Contact Angles ◽

Lotus Effect ◽

Hydrophilic Surfaces ◽

Current Thinking ◽

New Development ◽

Minimal Contact ◽

Titanium Surfaces

ABSTRACTImaginary contact angles underlying hyperhydrophilicity and the Inverse Lotus Effect introduce a fundamental new development in the area of contact angles and wettability. Just as the Lotus Effect expanded hydrophobicity beyond the maximal contact angle of 119° on a smooth surface, the Inverse Lotus Effect expands hydrophilicity beyond the minimal contact angle of 0° on a smooth surface. Imaginary dynamic contact angles thus offer an exciting enhancement in tools and methodology for measuring the wettability on rough, highly hydrophilic surfaces. Contrary to current thinking, full or perfect wetting of rough surfaces is only little understood and cannot be predicted by classical equations. Therefore also the exact physical basis of imaginary dynamic contact angles remains to be elucidated. In this short treatise some aspects of the new field will be treated with examples derived from rough titanium surfaces employed in the medical field.

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Simulation of Spreading Dynamics of a EWOD Droplet With Dynamic Contact Angle and Contact Angle Hysteresis

ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 2 ◽

10.1115/mnhmt2009-18558 ◽

2009 ◽

Cited By ~ 2

Author(s):

Fangjun Hong ◽

Ping Cheng ◽

Zhen Sun ◽

Huiying Wu

Keyword(s):

Contact Angle ◽

Contact Line ◽

Low Voltage ◽

Contact Angle Hysteresis ◽

Dynamic Contact Angle ◽

Dynamic Contact ◽

Dielectric Surface ◽

Contact Radius ◽

Droplet Spreading ◽

Spreading Dynamics

In this paper, the electrowetting dynamics of a droplet on a dielectric surface was investigated numerically by a mathematical model including dynamic contact angle and contact angle hysteresis. The fluid flow is described by laminar N-S equation, the free surface of the droplet is modeled by the Volume of Fluid (VOF) method, and the electrowetting force is incorporated by exerting an electrical force on the cells at the contact line. The Kilster’s model that can deal with both receding and advancing contact angle is adopted. Numerical results indicate that there is overshooting and oscillation of contact radius in droplet spreading process before it ceases the movement when the excitation voltage is high; while the overshooting is not observed for low voltage. The explanation for the contact line overshooting and some special characteristics of variation of contact radius with time were also conducted.

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