Measuring the contact angle of water droplets on foliar surfaces

1988 ◽  
Vol 66 (12) ◽  
pp. 2599-2602 ◽  
Author(s):  
Richard L. Boyce ◽  
Graeme P. Berlyn
Keyword(s):  
Contact Angle ◽  
Contact Angles ◽  
Water Droplets ◽  
Projected Image ◽  
Novel Technique ◽  
Static Contact

We describe a novel technique for measuring static contact angles on foliar surfaces that uses a micromanipulator and a 35-mm camera equipped with a microlens, autobellows, focusing rail, and tripod. After placing droplets on foliage, the contact angle is photographed. Negatives are mounted as slides, and the contact angle is measured from the projected image. We suggest that this method has a number of advantages over those previously used.

Superhydrophobic Surfaces Properties for Anti-Icing

2011 ◽  
Author(s):  
Mohammad Amin Sarshar ◽  
Christopher Swarctz ◽  
Scott Hunter ◽  
John Simpson ◽  
Chang-Hwan Choi
Keyword(s):  
Contact Angle ◽  
Wind Tunnel ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Superhydrophobic Surfaces ◽  
Ice Formation ◽  
Flow Conditions ◽  
Water Droplets ◽  
Dynamic Flow ◽  
Static Contact

In this paper, the iceophobic properties of superhydrophobic surfaces are compared to those of uncoated aluminum and steel plate surfaces as investigated under dynamic flow conditions by using a closed loop low-temperature wind tunnel. Superhydrophobic surfaces were prepared at the Oak Ridge National Laboratory by coating aluminum and steel plates with nano-structured hydrophobic particles. The contact angle and contact angle hysteresis measured for these surfaces ranged from 165–170° and 1–8°, respectively. The superhydrophobic plates along with uncoated control ones were exposed to an air flow of 12 m/s and 20°F with micron-sized water droplets in the icing wind tunnel and the ice formation and accretion were probed by using high speed cameras for 90 seconds. Results show that the developed superhydrophobic coatings significantly delay the ice formation and accretion even with the impingement of accelerated super-cooled water droplets, but there is a time scale for this phenomenon which has a clear relation with contact angle hysteresis of the samples. Among the different superhydrophobic coating samples, the plate having the lowest contact angle hysteresis showed the most pronounced iceophobic effects, while the correlation between static contact angles and the iceophobic effects was not evident. The results suggest that the key parameter for designing iceophobic surfaces is to retain a low contact angle hysteresis, rather than to have only a low contact angle, which can result in more efficient anti-icing properties in dynamic flow conditions.

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

Biomimetics ◽  
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.

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

1998 ◽  
Vol 518 ◽  
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.

Modeling of Transport During Droplet Deposition and Spreading on Smooth and Microstructured Superhydrophilic Surfaces

2016 ◽  
Author(s):  
Jordan P. Mizerak ◽  
Van P. Carey
Keyword(s):  
Contact Angle ◽  
Contact Angles ◽  
Ansys Fluent ◽  
Effective Contact ◽  
Microstructured Surfaces ◽  
Static Contact ◽  
Droplet Behavior ◽  
Contact Line Pinning ◽  
The Impact ◽  
Superhydrophilic Surfaces

The dynamic behavior of impinging water droplets is studied in the context of varying surface morphologies on smooth and microstructured superhydrophilic surfaces. The goal of this study is to evaluate the capability of contact angle wall adhesion models to accurately produce spreading phenomena seen on a variety of surface types. We analyze macroscale droplet behavior, specifically spreading extent and impinging regime, in situations of varying microscale wetting character and surface morphology. Axisymmetric, volume of fluid (VOF) simulations with static contact angle wall adhesion are conducted in ANSYS Fluent. Simulations are performed on water for low Weber numbers (We<20) on surfaces with features of length scale 5–10μm. Advanced microstructured surfaces consisting of unique wetting characteristics and lengths on each face are also tested. Results show that while the contact angle wall adhesion model shows fair agreement for conventional surfaces, the model underestimates spreading by over 60% for surfaces exhibiting estimated contact angles below approximately 0.5°. Microstructured surfaces adapt the wetting behavior of smooth surfaces with higher effective contact angles based on contact line pinning on morphology features. The propensity of the model to produce Wenzel and Cassie-Baxter states is linked to the spreading radius, introducing an interdependency of microscale wetting and macroscale spreading behavior. Conclusions describing the impact of results on evaporative cooling are also discussed.

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

Fluids ◽  
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.

Investigation of Pool Boiling Critical Heat Flux Enhancement on a Modified Surface Through the Dynamic Wetting of Water Droplets

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Ho Seon Ahn ◽  
Joonwon Kim ◽  
Moo Hwan Kim
Keyword(s):  
Surface Tension ◽  
Heat Flux ◽  
Contact Angle ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Water Layer ◽  
Contact Angles ◽  
Water Droplets ◽  
Dynamic Wetting ◽  
Modified Surface

Dynamic wetting behaviors of water droplet on the modified surface were investigated experimentally. Dynamic contact angles were measured as a characterization method to explain the extraordinary pool boiling critical heat flux (CHF) enhancement on the zirconium surface by anodic oxidation modification. The sample surface is rectangular zirconium alloy plates (20 × 25 × 0.7 mm), and 12 μl of deionized water droplets were fallen from 40 mm of height over the surface. Dynamic wetting movement of water on the surface showed different characteristics depending on static contact angle (49.3 deg–0 deg) and surface temperature (120 °C–280 °C). Compared with bare surface, wettable and spreading surface had no-receding contact angle jump and seemed stable evaporating meniscus of liquid droplet in dynamic wetting condition on hot surface. This phenomenon could be explained by the interaction between the evaporation recoil and the surface tension forces. The surface tension force increased by micro/nanostructure of the modified zirconium surface suppresses the vapor recoil force by evaporation which makes the water layer unstable on the heated surface. Thus, such increased surface force could sustain the water layer stable in pool boiling CHF condition so that the extraordinary CHF enhancement could be possible.

Temperature-Dependent Wettability of Water on a Nickel Surface at Pressurized Condition: A Molecular Dynamics Study

2019 ◽  
Author(s):  
Dong-Lei Zeng ◽  
Biao Feng ◽  
Jia-Wen Song ◽  
Li-Wu Fan
Keyword(s):  
Contact Angle ◽  
Hydrogen Bonds ◽  
Average Energy ◽  
Contact Angles ◽  
Nickel Surface ◽  
Free Energies ◽  
Water Droplets ◽  
Temperature Dependent ◽  
Interfacial Free Energies ◽  
Solid Liquid

Abstract Temperature-dependent wettability of water droplets on a metal surface in a pressurized environment is of great theoretical and practical significance. In this paper, molecular dynamic simulation is used to study this problem by relating the temperature-dependent apparent contact angles to the changes in solid-liquid and solid-vapor interfacial free energies and hydrogen bonds in the nano-sized water droplets with increasing the temperature. The temperature range of interest is set from 298 K to 538 K in a 20 K interval under a constant pressure of 7 MPa. The results show that the contact angle in general decreases with raising the temperature and decreasing trend can be divided into two sections with different slopes. The contact angle drops slowly when the temperature is below 458 K as a critical point. Beyond this point, the contact angle shows a much steeper decrease. The difference between solid-vapor and solid-liquid interfacial free energies is found to decrease slightly with temperature. Combining with that the surface tension drops with increasing the temperature, a decreasing trend of the contact angle is expected according to the Young’s equation. As the temperature increases, the number and average energy of the hydrogen bonds both decrease, and the hydrogen bonds tend to aggregate at the bottom of the nano-droplets.

Molecular Simulation of the Contact Angle of Water Droplet on a Platinum Surface

2005 ◽  
Author(s):  
Bo Shi ◽  
Shashank Sinha ◽  
Vijay K. Dhir
Keyword(s):  
Contact Angle ◽  
Molecular Simulation ◽  
Simulation Study ◽  
Water Droplet ◽  
Solid Wall ◽  
Contact Angles ◽  
Water Droplets ◽  
Platinum Surface

This paper presents a molecular simulation study of the contact angles of water droplets on a platinum surface for a range of temperatures. SPC/E and Z-P model are used for the water-water and water-platinum potentials, respectively. The results show that the contact angle decreases with the increase of system temperatures and increases when the potential decreases. When the temperature is high enough, the contact angles drop to zero degrees. The results were compared with the argon-virtual solid wall and water-Aluminum results, a similar trend was found.

Spreading-Droplet Simulation With Surface Tension Model Using Inter-Particle Force in Particle Method

2013 ◽  
Author(s):  
Eiji Ishii ◽  
Taisuke Sugii
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Dynamic Contact Angle ◽  
Particle Method ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Particle Methods ◽  
Static Contact ◽  
Particle Force ◽  
Surface Tension Model

Predicting the spreading behavior of droplets on a wall is important for designing micro/nano devices used for reagent dispensation in micro-electro-mechanical systems, printing processes of ink-jet printers, and condensation of droplets on a wall during spray forming in atomizers. Particle methods are useful for simulating the behavior of many droplets generated by micro/nano devices in practical computational time; the motion of each droplet is simulated using a group of particles, and no particles are assigned in the gas region if interactions between the droplets and gas are weak. Furthermore, liquid-gas interfaces obtained from the particle method remain sharp by using the Lagrangian description. However, conventional surface tension models used in the particle methods are used for predicting the static contact angle at a three-phase interface, not for predicting the dynamic contact angle. The dynamic contact angle defines the shape of a spreading droplet on a wall. We previously developed a surface tension model using inter-particle force in the particle method; the static contact angle of droplets on the wall was verified at various contact angles, and the heights of droplets agreed well with those obtained theoretically. In this study, we applied our surface tension model to the simulation of a spreading droplet on a wall. The simulated dynamic contact angles for some Weber numbers were compared with those measured by Šikalo et al, and they agreed well. Our surface tension model was useful for simulating droplet motion under static and dynamic conditions.

scholarly journals Preparation of Parabolic Superhydrophobic Material for Oil-Water Separation

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1914 ◽  
Author(s):  
Xiaoying Qiao ◽  
Chunyan Yang ◽  
Qian Zhang ◽  
Shengke Yang ◽  
Yangyang Chen ◽  
...  
Keyword(s):  
Contact Angle ◽  
Carbon Tetrachloride ◽  
Separation Efficiency ◽  
Contact Angles ◽  
Engine Oil ◽  
Water Droplets ◽  
Water Separation ◽  
Oil Water Separation ◽  
Oil Water ◽  
Copper Mesh

In order to prepare parabolic superhydrophobic materials, copper meshes were used as the substrate and ultrasonic etching and oxidative corrosion were carried out with FeCl3 solution and H2O2 solution, respectively, and then the surface was modified with stearic acid (SA). The topological structure and surface wettability of the prepared mesh were characterized by fluorescence microscope, scanning electron microscopy and contact angle measurement. Finally, the as-prepared copper meshes were applied to oil-water separation. The results showed that the micro-nano-mastoid structure on the surface of the copper mesh was flaky bulges, forming a rough structure similar to a paraboloid. When the oxidative corrosion time of H2O2 was 1 min, it is more beneficial to increase the hydrophobicity of the surface of the copper mesh and increase the contact angle of water droplets on the surface of the membrane. Additionally, based on superhydrophobic materials of the parabolic copper mesh, the static contact angles of the water droplets, engine oil and carbon tetrachloride with the surface were approximately 153.6°, 5° and 0.1°, respectively and the sliding angle of the water droplets with the surface were approximately 4.9°. The parabolic membrane was applied to discuss the separation efficiency of different oils with deionized water and the separation efficiency was obtained as benzene > carbon tetrachloride > oil > machine oil. Therefore, based on the research, the parabolic superhydrophobic material has good efficiency of oil-water separation.

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