Ramé-hart Glossary. Ramé-hart Glossary of Surface Science Terms Absorption describes the behavior of a liquid the permeates a solid surface. Adhesion (also called dispersive or adsorptive adhesion) describes the force that holds dissimilar molecules together. (See image under Wettability section.) In surface science the Work of Adhesion is the interactive force between the liquid and solid phases and we use the Young-Dupree equation as follows: In surface science, the term "adhesion" almost always refers to dispersive adhesion.
Adsorption describes the adhesion of a liquid (such as in a sessile drop) to a solid surface. Advancing and Receding Contact Angles are typically measured using a tilting base option. As the solid is tilted from 0° to 90°, the uphill angle (or receding angle) decreases while the downhill angle (or advancing angle) increases. The video below shows an example of advancing and receding contact angles using the tilt method. Dewetting can be the result of evaporation or absorption.
Science buddies. Please ensure you have JavaScript enabled in your browser. If you leave JavaScript disabled, you will only access a portion of the content we are providing. <a href="/science-fair-projects/javascript_help.php">Here's how. </a> Abstract Have you ever wondered why a water strider can walk on water? Objective Investigate how a small raft made from a clear plastic sheet can be propelled by water surface tension. Credits Author: David Chung Editors: Andrew Olson, Justin Spahn, and Teisha Rowland, Ph.D., Science Buddies Share your story with Science Buddies! I Did This Project! Last edit date: 2013-02-09 Introduction If you have ever blown up a balloon, you know it is pretty easy to blow up without becoming out of breath when it is made of soft, stretchy rubber. Liquids also experience surface tension. What can lower the surface tension of water? Terms and Concepts Resistance Surface tension Molecule Cohesive forces Polar molecules Hydrophilic Surfactants Questions Bibliography Materials and Equipment.
Hydrophobic effect. A droplet of water forms a spherical shape, minimizing contact with the hydrophobic leaf. The hydrophobic effect is the observed tendency of nonpolar substances to aggregate in aqueous solution and exclude water molecules.[1][2] The name, literally meaning "water-fearing," describes the segregation and apparent repulsion between water and nonpolar substances. The hydrophobic effect explains the separation of a mixture of oil and water into its two components, and the beading of water on nonpolar surfaces such as waxy leaves. At the molecular level, the hydrophobic effect is important in driving protein folding,[3][4] formation of lipid bilayers and micelles, insertion of membrane proteins into the nonpolar lipid environment and protein-small molecule interactions.[5] Substances for which this effect is observed are known as hydrophobes.
Amphiphiles[edit] Amphiphiles are molecules that have both hydrophobic and hydrophilic domains. Folding of macromolecules[edit] Protein purification[edit] Superhydrophobe. A drop on a Lotus surface. Superhydrophobic surfaces are highly hydrophobic, i.e., extremely difficult to wet. The contact angles of a water droplet exceeds 150° and the roll-off angle/contact angle hysteresis is less than 10°.[1] This is also referred to as the Lotus effect, after the superhydrophobic leaves of the lotus plant. Theory[edit] A liquid droplet rests on a solid surface and is surrounded by gas. The contact angle, θC, is the angle formed by a liquid at the three phase boundary where the liquid, gas, and solid intersect.
A droplet resting on a solid surface and surrounded by a gas forms a characteristic contact angle θ. If the solid surface is rough, and the liquid is in intimate contact with the solid asperities, the droplet is in the Wenzel state. Where = Interfacial tension between the solid and gas = Interfacial tension between the solid and liquid = Interfacial tension between the liquid and gas θ can be measured using a contact angle goniometer. = φ(cos θ + 1) – 1 M. Web.ornl.gov/adm/partnerships/events/bridging_gap/presentations/Superhydrophobic_Materials.pdf. Superhydrophobicity, Learn from the Lotus Leaf. Mengnan Qu1, Jinmei He1 and Junyan Zhang2 1. Introduction As early as the eleventh century, the Song dynasty of China, one scholar named Zhou Dunyi (1017–1073), had planted the lotus all over the poll in his home and wrote an article named Ode to A Lotus Flower.
From then on, in the East Asian countries and regions, especially the ancient China, the lotus flower and its leaves are frequently compared to one’s noble spirit and purity because of “live in the silt but not sullied”. This sentence displays an interesting phenomenon to us: the lotus’ flowers and leaves unfold and stayed immaculacy by the pollution even when emerging from mud and muddy waters. In addition to the leaves of plants, a number of insects, their wings also have the ability to resists water to spread on their surfaces. Figure 1. a) An almost ballshaped water droplet on a non-wettable plant leaf (Blossey, 2003). Figure 2. The non-wetting leg of a water strider. 2.
Figure 3. Figure 4. 3. 3.1. 3.2. Figure 5. Figure 6. 3.3. Contact angle. Cloth, treated to be hydrophobic, shows a high contact angle. The contact angle is the angle, conventionally measured through the liquid, where a liquid/vapor interface meets a solid surface. It quantifies the wettability of a solid surface by a liquid via the Young equation. A given system of solid, liquid, and vapor at a given temperature and pressure has a unique equilibrium contact angle. However, in practice contact angle hysteresis is observed, ranging from the so-called advancing (maximal) contact angle to the receding (minimal) contact angle. The equilibrium contact is within those values, and can be calculated from them.
Thermodynamics[edit] Schematic of a liquid drop showing the quantities in Young's equation. The shape of a liquid/vapor interface is determined by the Young–Laplace equation, with the contact angle playing the role of a boundary condition via Young's Equation. , the solid–liquid interfacial energy by , then the equilibrium contact angle where Hysteresis[edit] . And. Hydrophobicity clasification guide. Tensiometers. Force tensiometers Measurement principle: When a solid touches the surface of a liquid, the liquid tends to be drawn up in a meniscus. The force exerted by the meniscus is measured by a microbalance using a Du Noüy ring or a Wilhelmy plate, in either push or pull mode. The microbalance reading is used to calculate surface tension using a selection of software models. Force tensiometry is an accurate technique to measure the static surface tension and interfacial tension of liquids.
These direct measurements allow the determination of dynamic contact angle, surface free energy, powder wettability, absorption, cleanliness, surface heterogeneity and density. It is also widely used for measuring critical micelle concentration of surfactants and the only method to determine the absorption and contact angle of packed powders and fiber beds. Click here to contact us Sigma 700/701 provide outstanding versatility with full computer control and a high level of automation. Optical tensiometers. Neverwet. Scotchgard. Pond Skater (Gerridae. The pond skater is a delicate water-based insect commonly found on still bodies of water across the Northern Hemisphere. There are around 500 different species of pond skater that are known by a variety of different names including water striders, water bugs, magic bugs, skaters, skimmers, water scooters, water skaters, water skeeters, water skimmers, water skippers and Jesus bugs. The pond skater is most commonly found across Europe where they live on the surface of ponds, slow streams, marshes, and other quiet waters, in all parts of the continent.
Pond skaters are most well known for their ability to "walk on water", where pond skaters use surface tension to delicately walk on the surface of the water. Pond skaters float on the surface of the water sensing vibrations and ripples in the water with sensitive hairs on their legs and bodies. The long legs of the pond skater mean that they are very agile on the surface of the water and can jump to evade a predator or to catch an insect .
Properties of water. Water (H 2O) is the most abundant compound on Earth's surface, covering 70 percent of the planet. In nature, water exists in liquid, solid, and gaseous states. It is in dynamic equilibrium between the liquid and gas states at standard temperature and pressure. At room temperature, it is a tasteless and odorless liquid, nearly colorless with a hint of blue. Many substances dissolve in water and it is commonly referred to as the universal solvent. Because of this, water in nature and in use is rarely pure and some properties may vary from those of the pure substance. However, there are also many compounds that are essentially, if not completely, insoluble in water. Forms of water[edit] Vienna Standard Mean Ocean Water is the current international standard for water isotopes. Heavy water is water with a higher-than-average deuterium content, up to 100%.
Physics and chemistry[edit] 2 H 2O(l) H 3O+(aq) + OH−(aq) Percentage of elements in water by mass: 11.1% hydrogen, 88.9% oxygen. [edit] [edit] Electronegativity. This electrostatic potential map shows how the oxygen atom has a more negative charge (red) than the positive (blue) hydrogen atoms of a water molecule . The most commonly used method of calculation is that originally proposed by Linus Pauling. This gives a dimensionless quantity, commonly referred to as the Pauling scale, on a relative scale running from around 0.7 to 3.98 (hydrogen = 2.20). When other methods of calculation are used, it is conventional (although not obligatory) to quote the results on a scale that covers the same range of numerical values: this is known as an electronegativity in Pauling units. The opposite of electronegativity is electropositivity: a measure of an element's ability to donate electrons.
Electronegativities of the elements[edit] Methods of calculation[edit] Pauling electronegativity[edit] The difference in electronegativity between atoms A and B is given by: or sometimes, a more accurate fit This is an approximate equation, but holds with good accuracy. A. Wetting. Water beads on a fabric that has been made non-wetting by chemical treatment. Figure 1: Droplet of water on an ideal surface. Water droplet immersed in oil and resting on a brass surface Same fluids as above, but resting on a glass surface Wetting is the ability of a liquid to maintain contact with a solid surface , resulting from intermolecular interactions when the two are brought together. The degree of wetting (wettability) is determined by a force balance between adhesive and cohesive forces . Wetting is important in the bonding or adherence of two materials. Explanation [ edit ] Adhesive forces between a liquid and solid cause a liquid drop to spread across the surface .
Figure 2: Wetting of different fluids. The contact angle (θ), as seen in Figure 1, is the angle at which the liquid–vapor interface meets the solid–liquid interface. For water , a wettable surface may also be termed hydrophilic and a non-wettable surface hydrophobic . High-energy vs. low-energy surfaces [ edit ] . And. Marangoni effect. History[edit] Mechanism[edit] Tears of wine show clearly in the shadow of this glass of wine with a 13.5% alcohol content Since a liquid with a high surface tension pulls more strongly on the surrounding liquid than one with a low surface tension, the presence of a gradient in surface tension will naturally cause the liquid to flow away from regions of low surface tension. The surface tension gradient can be caused by concentration gradient or by a temperature gradient (surface tension is a function of temperature).
As an example, wine may exhibit a visible effect called "tears", as shown in the photograph. The Marangoni number, a dimensionless value, can be used to characterize the relative effects of surface tension and viscous forces. Significance to transport phenomena[edit] Under earth conditions, the effect of gravity causing density-driven convection in a system with a temperature gradient along a fluid/fluid interface is usually much stronger than the Marangoni effect. See also[edit] Surface tension. Surface tension has the dimension of force per unit length, or of energy per unit area.
The two are equivalent—but when referring to energy per unit of area, people use the term surface energy—which is a more general term in the sense that it applies also to solids and not just liquids. In materials science, surface tension is used for either surface stress or surface free energy. Causes[edit] Diagram of the forces on molecules of a liquid Surface tension preventing a paper clip from submerging. The cohesive forces among liquid molecules are responsible for the phenomenon of surface tension. In the bulk of the liquid, each molecule is pulled equally in every direction by neighboring liquid molecules, resulting in a net force of zero.
Surface tension is responsible for the shape of liquid droplets. Another way to view surface tension is in terms of energy. Effects of surface tension[edit] Water[edit] Several effects of surface tension can be seen with ordinary water: A. C. D. E. A. , with is by. Scientific Victorian. Surface energy. Contact angle measurements can be used to determine the surface energy of a material.
Here, a drop of water on glass. Surface energy quantifies the disruption of intermolecular bonds that occur when a surface is created. In the physics of solids , surfaces must be intrinsically less energetically favorable than the bulk of a material (the molecules on the surface have more energy compared with the molecules in the bulk of the material), otherwise there would be a driving force for surfaces to be created, removing the bulk of the material (see sublimation ).
The surface energy may therefore be defined as the excess energy at the surface of a material compared to the bulk. For a liquid, the surface tension (force per unit length) and the surface energy density are identical. Water has a surface energy density of 0.072 J/m 2 and a surface tension of 0.072 N/m; the units are equivalent. Cutting a solid body into pieces disrupts its bonds, and therefore consumes energy.
Where , and . . And. Surface tension. In materials science, surface tension is used for either surface stress or surface free energy. Causes[change | edit source] Diagram of the forces on molecules in liquid Surface tension prevents the paper clip from submerging. The cohesive forces among the liquid molecules cause surface tension. In the bulk of the liquid, each molecule is pulled equally in every direction by neighboring liquid molecules, resulting in a net force of zero. The molecules at the surface do not have other molecules on all sides of them and therefore are pulled inwards.
Surface tension is responsible for the shape of liquid droplets. Another way to view it is in terms of energy. As a result of surface area minimization, a surface will assume the smoothest shape it can. Effects in everyday life[change | edit source] Water[change | edit source] Studying water shows several effects of surface tension: A. C. D. E. A. Surfactants[change | edit source] Soap bubbles have very large surface areas with very little mass. Where. Web.mit.edu/1.63/www/Lec-notes/Surfacetension/Lecture3.pdf. Surface Tension.
Capillary surface.