scholarly journals The Possibility of Changing the Wettability of Material Surface by Adjusting Gravity

Research ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-11 ◽  
Author(s):  
Yong-Ming Liu ◽  
Zi-Qing Wu ◽  
Sheng Bao ◽  
Wei-Hong Guo ◽  
Da-Wei Li ◽  
...  
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Contact Region ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Angle Measurement ◽  
Measured Parameter ◽  
Material Surface ◽  
Vapor Interface ◽  
Liquid Vapor

The contact angle, as a vital measured parameter of wettability of material surface, has long been in dispute whether it is affected by gravity. Herein, we measured the advancing and receding contact angles on extremely low contact angle hysteresis surfaces under different gravities (1-8G) and found that both of them decrease with the increase of the gravity. The underlying mechanism is revealed to be the contact angle hysteresis and the deformation of the liquid-vapor interface away from the solid surface caused by gradient distribution of the hydrostatic pressure. The real contact angle is not affected by gravity and cannot measured by an optical method. The measured apparent contact angles are angles of inclination of the liquid-vapor interface away from the solid surface. Furthermore, a new equation is proposed based on the balance of forces acting on the three-phase contact region, which quantitatively reveals the relation of the apparent contact angle with the interfacial tensions and gravity. This finding can provide new horizons for solving the debate on whether gravity affects the contact angle and may be useful for the accurate measurement of the contact angle and the development of a new contact angle measurement system.

Examining Liquid Hydrogen Wettability Using Neutron Imaging

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Vinaykumar Konduru ◽  
Kishan Bellur ◽  
Ezequiel F. Médici ◽  
Jeffrey S. Allen ◽  
Chang Kyoung Choi ◽  
...  
Keyword(s):  
Contact Angle ◽  
Cone Angle ◽  
Neutron Cross Section ◽  
Liquid Hydrogen ◽  
Contact Angles ◽  
Neutron Imaging ◽  
Test Cell ◽  
Clear Understanding ◽  
Vapor Interface ◽  
Liquid Vapor

The control of propellant boil-off is essential in long-term space missions. However, a clear understanding of propellant cryogenic condensation/evaporation in microgravity is lacking. One of the key factors in designing such systems is the location of liquid surfaces and the relation to wettability. The BT-2 Neutron Imaging Facility located at the National Institute of Standards and Technology (NIST), Gaithersburg, MD, is used to image evaporation and condensation of hydrogenated propellants inside of an aluminum 6061 container. Liquid hydrogen has larger neutron cross-section area than the aluminum, allowing the visualization of the liquid-vapor interface. The test cell has a conical section that enables determination of a contact angle with enhanced accuracy. If the contact angle is equal to the angle of the cone, a flat liquid-vapor interface is expected. The test cell has the cone angle of 10o and a flat interface was not observed. Using the Laplace-Young equation to fit the interface, the contact angle for hydrogen and aluminum was between 0° and 4°. The theoretical Laplace curves with contact angles of 2o and 10o are plotted on the liquid-vapor interface. The of 2o curve is a closer fit as compared to the 10o curve. The uncertainty arises from resolution limits of the neutron imaging setup and edge detection. More details on the neutron imaging mechanism and relevant physics can be found from the authors' other publication of Cryogenics, 74, pp131-137, 2016: doi:10.1016/j.cryogenics.2015.10.016.

Numerical Modeling of Liquid Drop Spreading Behavior on Inclined Surfaces

2009 ◽  
Author(s):  
Young-Gil Park ◽  
Anthony M. Jacobi
Keyword(s):  
Solid Surface ◽  
Liquid Drop ◽  
Numerical Study ◽  
Contact Angle Hysteresis ◽  
Contact Angles ◽  
Quasi Equilibrium ◽  
Liquid Drops ◽  
Spreading Behavior ◽  
Inclined Surfaces ◽  
Liquid Vapor

A numerical study was conducted on the spreading behavior of liquid drops on flat solid surfaces. The model predicts the shape of liquid-vapor interface under static equilibrium using an unstructured surface grid composed of triangular elements. Incremental movement of base contour, i.e. solid-liquid-vapor contact line, is also captured such that the constrained boundary conditions, i.e. advancing and receding contact angles, can be satisfied. The numerical model is applied to a common experiment that studies the behavior of liquid drops on inclined surfaces, where the shape of the drops change in response to an alteration of total volume or gravitational direction. On a heterogeneous surface that has contact angle hysteresis, the shape of the base contour on the solid surface is not determined uniquely but rather dependent upon history. This study demonstrates such dependence by comparing the spreading of a liquid drop on a solid surface with different quasi-equilibrium paths.

scholarly journals Comparison of contact angle measurement methods of liquids on metal alloys

2016 ◽  
Vol 71 (1) ◽  
pp. 89 ◽  
Author(s):  
Konrad Terpiłowski ◽  
Lucyna Hołysz ◽  
Diana Rymuszka ◽  
Robert Banach
Keyword(s):  
Contact Angle ◽  
Contact Angle Hysteresis ◽  
Contact Angle Measurement ◽  
Contact Angles ◽  
Angle Measurement ◽  
Measurement Methods ◽  
Metal Alloys ◽  
Sessile Droplet ◽  
Immersion Method ◽  
Basic Approach

<p>The paper presents the studies of metal wettability using two methods: the sessile droplet and immersion ones. Based on the measured contact angles, there was calculated apparent surface free energy from the acidic–basic approach and the contact angle hysteresis. The advancing contact angles measured using the immersion method exhibit a little higher values than those measured by the sessile droplet method. The application of the immersion method leads to obtaining higher contact angle hysteresis. Both methods give different values of contact angles but they can be applied independently for estimation of metal surface wettability.</p>

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.

scholarly journals Is contact angle a cause or an effect? – A cautionary tale

2020 ◽  
Vol 146 ◽  
pp. 03004
Author(s):  
Douglas Ruth
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Contact Angles ◽  
Two Dimensions ◽  
Experimental Results ◽  
Flow In Porous Media ◽  
Two Dimensional ◽  
Wide Range ◽  
Fluid Drop ◽  
Surrounding Fluid

The most influential parameter on the behavior of two-component flow in porous media is “wettability”. When wettability is being characterized, the most frequently used parameter is the “contact angle”. When a fluid-drop is placed on a solid surface, in the presence of a second, surrounding fluid, the fluid-fluid surface contacts the solid-surface at an angle that is typically measured through the fluid-drop. If this angle is less than 90°, the fluid in the drop is said to “wet” the surface. If this angle is greater than 90°, the surrounding fluid is said to “wet” the surface. This definition is universally accepted and appears to be scientifically justifiable, at least for a static situation where the solid surface is horizontal. Recently, this concept has been extended to characterize wettability in non-static situations using high-resolution, two-dimensional digital images of multi-component systems. Using simple thought experiments and published experimental results, many of them decades old, it will be demonstrated that contact angles are not primary parameters – their values depend on many other parameters. Using these arguments, it will be demonstrated that contact angles are not the cause of wettability behavior but the effect of wettability behavior and other parameters. The result of this is that the contact angle cannot be used as a primary indicator of wettability except in very restricted situations. Furthermore, it will be demonstrated that even for the simple case of a capillary interface in a vertical tube, attempting to use simply a two-dimensional image to determine the contact angle can result in a wide range of measured values. This observation is consistent with some published experimental results. It follows that contact angles measured in two-dimensions cannot be trusted to provide accurate values and these values should not be used to characterize the wettability of the system.

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.

Macroscopic Wetting Behavior and a Method for Measuring Contact Angles

1990 ◽  
Vol 112 (3) ◽  
pp. 289-295 ◽  
Author(s):  
K. Katoh ◽  
H. Fujita ◽  
H. Sasaki
Keyword(s):  
Contact Angle ◽  
Solid Surface ◽  
Liquid Surface ◽  
Contact Angles ◽  
Critical Height ◽  
Solid Cone ◽  
Wetting Behavior ◽  
Conventional View ◽  
The Subject ◽  
Thermodynamic Instability

Macroscopic wetting behavior is investigated theoretically from a thermodynamic viewpoint. The axisymmetric liquid meniscus formed under a conical solid surface is chosen as the subject of the theoretical analysis. Using the meniscus configuration obtained by the Laplace equation, the total free energy of the system is calculated. In the case of the half vertical angle of the cone φ = 90 deg (horizontal plate), the system shows thermodynamic instability when the meniscus attaches to the solid surface at the contact angle. This result, unlike the conventional view, agrees well with the practical wetting behavior observed in this study. On the other hand, when 0 deg < φ < 90 deg, the system shows thermodynamic stability at the contact angle. However, when the solid cone is held at a position higher than the critical height from a stationary liquid surface, the system becomes unstable. It is possible to measure the contact angle easily using this unstable phenomenon.

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