Correlation between contact line pinning and contact angle. Contact angle is generally attributed to surface roughness, surface heterogeneity, solution impurities adsorbing on the surface, or. Contact angle is defined geometrically as the angle formed by a liquid at the threephase boundary where a liquid, gas and solid intersect. Hydrodynamics and mechanism of hydrophobic foam column. Contact angle hysteresis, wettability and optical studies. Pdf contact angle hysteresis is an important physical phenomenon. Barteu department of chemistry, university of michigan, ann arbor, michigan received october 24, 1952 introduction many investigators have measured the contact angles of water on. Analysis of wetting and contact angle hysteresis on. Abstract contact angle hysteresis is an important physical phenomenon. The contact angle is calculated from the forces of interaction, sample geometry and liquid surface tension. The contact angle hysteresis, the variation of the dynamic angle, and the convex nanobending at the advancing contact line all vanished on the absolutely smooth surfaces.
However, in practice a dynamic phenomenon of contact angle hysteresis is often observed, ranging from the advancing contact angle to the receding contact angle. The effect of liquid structure on contact angle hysteresis. Comparison of contact angle hysteresis of different probe. Further, we find that both contactangle hysteresis and steepening of the contact angle with increasing contactline speed are dissipative effects. This hysteresis occurs due to the wide range of metastable states which can be observed as the liquid meniscus scans the surface of a solid at the solidliquidvapor interface. That this is an appropriate way of viewing hysteresis is. The results of this study highlight the critical role of chemical or mechanical hysteresis and the need to reduce this retentive force for minimizing power requirements in microfluidic devices. Nanoparticles modulate contact angle hysteresis in electrowetting sumit kumar1, pawan kumar2, sunandodasgupta1, 3 and suman chakraborty1, 2 1advanced technology development centre, indian institute of technology kharagpur, india 2department of mechanical engineering, indian institute of technology kharagpur, india 3department of chemical engineering, indian institute of technology. We also consider an extension of the classical theory of capillarity, in which the introduction of a dissipation mechanism can explain and predict the hysteresis of the contact angle. The relationships between contact angle, contact angle hysteresis, adhesion, and marine biofouling were studied. Pdf a model for contact angle hysteresis semantic scholar. The contact angle is the angle, conventionally measured through the liquid, where a liquidvapor interface meets a solid surface. That hysteresis can be quantified as an activation energy by the changes in interfacial area is argued. Pdf transparent, flexible, superomniphobic surfaces with.
Correlation between contact line pinning and contact angle hysteresis on heterogeneous surfaces. The model describes the steady motion of a twodimensional droplet driven by thermocapillary stresses including contact angle hysteresis. Understanding contact angle hysteresis on an ambient. To clarify further, contact angle hysteresis specifies a threshold resistance force to initial movement, and dynamic contact angle hysteresis refers to the resistance at a particular sliding speed. Abstract pdf 706 kb 2017 a dynamic theory for contact angle hysteresis on chemically rough boundary. Dynamic contact angle paper testing surface properties. Transparent, flexible, superomniphobic surfaces with ultra. The first method is referred to as the tilting base method. The phenomenon of contact angle hysteresis is not well understood, and is often explained in terms of curvature or line tension effects.
The theoretically predicted minimum in the curve of receding contact angle vs. Contact angle hysteresis, wetting mit opencourseware. The study of contact angles and contactangle hysteresis in the region of low contact angles is not easy owing to difficulties of technique. The receding angle which occurs on dewetting is usually smaller than the advancing angle. The heights of the energy barriers between metastable states of a drop are seen to be of utmost importance in determining the magnitude of contact angle hysteresis. It is predicted that the contact angle of one fluid region will be affected by a second fluid region in the sarne systern. It is omnipresent in nature and also plays a crucial role in various industrial. Contact angle and contact angle hysteresis measurements using the capillary bridge technique. The stainless steel aisi 304l sheet about 1 mm thick and. Contact angle hysteresis is an indication of the tendency of a droplet to bounce and bead when dropped on the surface, and the ability of a droplet to roll off the surface easily.
The lowest water contact angle hysteresis h w was obtained for reference variant owithout sandblastingwhere only degreasing treatment was used h w 3. Although the mechanism governing contact angle hysteresis remains an open topic, we can circumvent this. We apply thermodynamics in an analysis of this topic. Transparent, flexible, superomniphobic surfaces with ultralow contact angle hysteresis.
Effect of contact angle hysteresis on thermocapillary. Figure 3 pictures the force exerted on the substrate on advancing and on. Contact angle hysteresis explained american chemical society. Similarly, the contact angle hysteresis for the halogenated benzenes decreases n the order chlorobenzene bromobenzene iodobenzene. The wellknown young equation describes the balance at the threephase contact of solidliquid and gas. The equations of wenzel and of cassie and baxter are discussed in relation to the model. Dynamic contact angle hysteresis in liquid bridges arxiv. There are two common methods for measuring this range of contact angles. To clarify this, starting from the basic definition of contact angle hysteresis, we introduce the formalism and models for implementing contact angle hysteresis into relevant physical phenomena. For weak heterogeneities, we expect no hysteresis, but the contact line becomes wiggly. Characterization of grafted polyethylene by contact.
A view of contact angle hysteresis from the perspectives of the threephase contact line and of the kinetics of contact line motion is given. Contact angle hysteresis, wetting of textured solids figure 15. The theoretical result that the contact angle hysteresis on a textured surface is a function of the equilibrium static contact angle. A given system of solid, liquid, and vapor at a given temperature and pressure has a unique equilibrium contact angle.
Contact angle hysteresis cah is one of the most important and classic elements of wetting of liquid droplets in systems from centimeter to. This article is published with open access at abstract advancing and receding contact angles of. In sharp contrast, the solids that made of atoms, even at atomic roughness, could bring significant deviation from the equilibrium angle and the convex nanobending at. Wetting on rough surfaces and contact angle hysteresis. Contact angle hysteresis at smooth and rough surfaces. Contact angle effect has been well investigated but not complete due to interfacial wettability consisting of both static behavior contact angle and dynamic behavior contact angle hysteresis. One criterion for deciding between dynamic and static contact angle is the technical wetting process observed. It quantifies the wettability of a solid surface by a liquid via the young equation. Utilizing dynamic tensiometry to quantify contact angle.
The phenomenon of contact angle hysteresis a great interest in surface energy is contact angle hysteresis. The hysteresis generally decreases with decreasing of the contact angles. Dynamic contact angles and hysteresis under electrowetting. We discuss the behavior of a liquid partially wetting a solid surface, when the contact angle at equilibrium. The theoretical wettability behavior of an idealized, rough surface agrees well with that of real surfaces. Contact angle hysteresis at smooth and rough surfaces behrooz raeesi1, norman r. This can be due to the simultaneous increase of roughness factor r f and the static apparent contact angle as ba value decreases and ha increases. As the roughness increases, the energy barrier will also. The effect of roughness on the wettability of an idealized sinusoidal surface has been studied with a digital computer. Once a drop is dispensed on the surface with the surface level, the. We investigate the dependence of hysteresis on texture parameters, evaluate the current model, propose a modification, and show that the two modelscurrent and proposedare useful bounds on the hysteresis of the surface. When a liquid comes in contact with a solid surface, the system can either adopt the fully wetted wenzel state22 or yield a composite liquidair interface, which is known as the cassiebaxter state.
Pinning of a contact line retreating from left to right due to surface impurities. Contact angle of and surface roughness are correlated by wenzels equation 16 by. The equilibrium shape of a liquid drop l surrounded by vapor v and placed over a flat solid surface s is a spherical cap. Here, methods of adjusting contact angle hysteresis cah were proposed, and then, the cah effect on the hydrodynamics was investigated. To clarify this, starting from the basic definition of contact angle hysteresis, we introduce the. Contact angle hysteresis advances in chemistry acs. Contact angle hysteresis is defined as the difference between advancing and receding contact angles. When a liquid drop is placed on a solid, it spreads. To measure the contact angle hysteresis, the advancing and receding angles in liquid bridges are extracted for different types of liquids under various cyclic. Contact angle hysteresis, adhesion, and marine biofouling. The solid is assumed to be either flat, but chemically heterogeneous this in turn modulating the interfacial tensions, or rough. Contact angle hysteresis an overview sciencedirect topics. Contact angle hysteresis is an important physical phenomenon. It is omnipresent in nature and also plays a crucial role in various industrial processes.
Fluids 27, 032107 2015 desorption phenomena and macroscopic flowinduced viscous dissipation. Thus, other experimental parameters such as the equilibrium contact angle. Wetting on rough surfaces and contact angle hysteresis numdam. Contact angle hysteresis and interacting surface defects. This difference, referred to as hysteresis, is used as a measure of the roughness of the solid. Two possible choices of boundary conditions, needed to recover youngs law for the contact angle, are presented. Dynamic contact angle measurements on superhydrophobic. The model is based on the balance between released capillary energy and dissipation asso. Despite its relevance, there is a lack of consensus on how to incorporate a description of contact angle hysteresis into physical models. The role of the substrate roughness in contact angle. Arguments are made that advancing and receding are discrete events that have different activation energies. Determination of an empirical relation between contact. Understanding contact angle hysteresis on an ambient solid.
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