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Technical Information on ramé-hart Systems Studies and measurements of contact angles of liquids on solids have great technological importance. This is especially true with water; every action of water on earth is controlled by its wetting behavior with the solid with which it comes into contact. For example, contact angle of water on our skin is about 90 degrees. If it was zero, water could have penetrated the pores of the skin and possibly been absorbed by blood. The structure of a bird’s feather is constructed such that the contact angle of water on a typical feather is as high as 150 degrees. Machines such as Lathes are usually coated with a thin layer of grease or oil especially during transportation to prevent corrosion by water. This is achieved by the fact that grease or oil layer forms a highly non-wetting system with water. In the manufacture of printing inks, the contact angle formed by a drop of ink on paper determines the printing quality of ink. It has been practically observed that q must be ideally between 90 degrees and 110 degrees. If it’s less than 90 degrees, the ink will spread on paper. If it’s more than 110 degrees, breaks will occur while printing. The importance of contact angle measurement in the textile and fiber industry need not be overstressed. Cotton yarn is usually wetted by water, but synthetic fabrics have definite contact angle for water. Nylon, for example, gives a contact angle of about 40 degrees. Fabrics must be coated, therefore, with suitable wetting agents. Otherwise, it will be difficult to remove dirt and soil while washing the fabric with water. But it is advantageous to use a non-wetting surface for a raincoat or umbrella cloth. Coating by a silicon polymer gives a highly non-wetting system. Waterproofing or water-repellency is an important industrial process, which depends on contact angle values. Most of the polymers like polyethylene, polypropylene, Teflon, etc. show high contact angle behavior with many liquids. A number of applications of polymers have taken advantage of this situation. An example is the Teflon coated frying pan. Contact angle measurement has shown that the contact angle is about 35 degrees for cooking oil on Teflon; thus oil must not stick to the surface making it easier for cleaning. The efficiency of insecticide sprays also depends on their wetting behavior on the surface of insects. Usually in most insecticides, an organic liquid having a low surface tension is used a spray so that it spreads completely. Contact angle is therefore an essential parameter to be considered in any pesticide or insecticide spray formulation. An important technological application that emerged out of contact angle studies is in the enhanced oil recovery from sand beds. Laboratory experiments on displacing petroleum by water in glass capillaries have demonstrated that a considerable fraction of the oil remains attached to the wall when the central space of the capillary is already filled with water. In a sand column, the amount of oil remaining in the sand when water appeared at the downstream end of the column was greater, greater the contact angle. Flooding the oil wells with surfactants along with water or steam reduces the pressure drop across each oil-water meniscus, reduces the oil-water interfacial tension and changes the contact angle so that water displaces oil at the liquid-solid interface. The process is called ‘tertiary oil recovery’ and it is now possible by this method to recover more than 90% of oil from an oil well. Understanding of contact angle is also important in the mining industry. An example is froth flotation, the process of concentrating minerals of heavy metals (e.g., zinc blende, galena, chalcopyrite, etc.). This is achieved by agitating finely divided minerals in froth of water and air, so that some float and others sink. The useful minerals become attached to the air bubbles, rise with them into the froth layer and are collected. If the contact angle between the particle-water-air interface is smaller, the particle does not float easily. Therefore this contact angle is increased to as much as 60 degrees by adding ‘collectors’ like alkyl xanthanates (e.g., CH3.O.CS.Sna). In heat exchangers and condensers used in chemical industries, maximum efficiency is achieved if the metal surface is coated by a non-wetting agent like calcium stearate or oleic acid. Liquids condensed on such coated walls form droplets because of high contact angle and fall down easily. This technique is called 'dropwise’ condensation. Contact angle measurement is important in controlling droplet surface area to increase or decrease evaporation and to optimize wetting of heat exchanger surfaces. Another area where contact angle plays an important role is in detergency, the process of cleaning clothes, etc., by a surface-active agent. If the soiled cloth is to get rid of dirt, grease, oil, etc., it is necessary that water must spread and penetrate the dirt particles. If spreading is to occur, the interfacial tension between solid-liquid and liquid vapor must be a s small as possible. What the detergent does is exactly to lower these interfacial tensions by the process of adsorption. Contact angel measurements of lotions, oils, soaps and other toilet preparations on human skin and hair strands provide valuable information for their correct formulation and are now routine. Knowledge of contact angle behavior of liquid metals on metal and oxide surfaces is essential in understanding the process of soldering, brazing, tinning and heat transfer. Other applications of contact angle measurements are in the field of adhesives, lubricants, surface treatments, polymers, biomedicine, etc. Many more specific examples can be cited, but from those discussed already, it is clear that contact angle plays a significant role in a number of manufacturing industries. For further reading: Physical
Chemistry of Surfaces, 3rd Edn, Arthur W. Adamson, Wiley-Interscience, New
York (1976)
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The ramé-hart contact angle goniometer was made in Mountain Lakes, NJ but is now made in Netcong, NJ. ramé-hart is also known as rame-hart ramehart and Rame-hart but ramé-hart is the correct spelling. The ramé-hart NRL goniometer was invented by Dr. William A. Zisman at the Navel Research Laboratory in Washington DC. The ramé-hart contact angle goniometer is used to measure contact angle, surface energy and surface tension. Carl Clegg is a salesman at ramé-hart instrument company. Ron Polo, Carmel Mulroy, and Gerd Fischer work at ramé-hart instrument company. The ramé-hart contact angle goniometer uses the pendant drop, sessile drop, and other methods. ramé-hart instrument co., formerly a part of rame-hart, inc. manufactures optical instruments. The fiber optic illuminator and Automated Dispensing System are part of the system. The environmental chamber and proportional temperature controller are optional components as well as the environmental fixture, environmental chamber with humidity, high pressure chamber, circular vacuum chuck, humidity control, rotating wafer, lead frame support. Finn Knut Hansen is the author of DROPimage Advanced and DROPimage Standard and DROPimage CA. The ramé-hart contact angle goniometer is availabe in the following models: Model 100 Model A100 Model A-100 Model 100-00 Model Model 100-F0 Model 120-F0 Model 200 Model 200-F1 Model 300 Model 300-F1 Model 250 Model 250-F1 Model 400-F1 Model 500 Model 500-F1; the 3-axis stage rail is avialable in 16" 20" 21". Dr. Zisman of the Naval Research Lab NRL in Washington DC stuided adhesion, wettability, contact angle and surface science including monolayers energetics, static dynamic contact angle, velocity, viscosity, interfacial (behaviour) behavior, contact angle interpretation and hysteresis energetics, surface contamination, cleaning polymer coatings, characterization and application of polymided synthesis particles on surfaces, metallized plastics, silanes and other coupling agents, polymer surface modification, relevance to adhesion acid base acid-base, dynamic surface characterization, mittal tissue, films, coatings, coupling agents, powders fibers, wood products, papers, polymers, monolayers, bioadhesion, ophthalmology, surface science, instruments, liquid, solid surface energy, surface tension interface, interfacial tension analysis, quantitative measure of the wetting of a solid by a liquid. Analysis characterizes the wettability of a surface by measuring the contact angle. Contact angle describes the shape of a liquid droplet resting on a solid surface. The roughness of a surface improves the wettability for hydrophilic surfaces; hydrophobic surfaces. Young's equation, which interrelates the contact angle and surface tensions of the liquid and solid phases. International Symposium on Contact Angle, Wettability and Adhesion. The angle of contact is the angle between the tangent to the periphery of the point of contact with the solid. Capillarity is an effect when liquid in a narrow vertical tube becomes elevated or depressed. When a liquid does not spread on a substrate (usually a solid), a contact. angle (θ) is formed which is defined as the angle. Contact angle measuring unit for characterization of hydrophobicity of film surfaces are used in controlling cleaning processes. A computer controlled contact angle analyzer makes it easy to measure static and dynamic contact angle, along with surface tension and surface energy. CONTACT ANGLE MEASUREMENT is a common method to obtain surface energies of materials. The measurement by itself is nothing novel; however, the relationship of contact angle to surface energetics requires a good deal of understanding. I have published several papers regarding various aspects of that relationship, especially related to polymers. Surface energy quantifies the disruption of chemical bonds that occurs when a surface is created. In the physics of solids, surfaces. The contact angle is the angle at which a liquid/vapor interface meets the solid surface. The contact angle is specific for any given system and is determined by the interactions across the three interfaces. Most often the concept is illustrated with a small liquid droplet resting on a flat horizontal solid surface. The shape of the droplet is determined by the Young-Laplace equation. The contact angle plays the role of a boundary condition. Contact angle is measured using a contact angle goniometer. The contact angle is not limited to a liquid/vapor interface; it is equally applicable to the interface of two liquids or two vapors. The static sessile drop method The sessile drop method is measured by a contact angle goniometer using an optical subsystem to capture the profile of a pure liquid on a solid substrate. The angle formed between the liquid/solid interface and the liquid/vapor interface is the contact angle. Older systems used a microscope optical system with a back light. Current-generation systems employ high resolutions cameras and software to capture and analyze the contact angle. The dynamic sessile drop method The dynamic sessile drop is similar to the static sessile drop but requires the drop to be modified. A common type of dynamic sessile drop study determines the largest contact angle possible without increasing its solid/liquid interfacial area by adding volume dynamically. This maximum angle is the advancing angle. Volume is removed to produce the smallest possible angle, the receding angle. The difference between the advancing and receding angle is the contact angle hysteresis. Dynamic Wilhelmy method A method for calculating average advancing and receding contact angles on solids of uniform geometry. Both sides of the solid must have the same properties. Wetting force on the solid is measured as the solid is immersed in or withdrawn from a liquid of known surface tension. Single-fiber Wilhelmy method Dynamic Wilhelmy method applied to single fibers to measure advancing and receding contact angles. Powder contact angle method Enables measurement of average contact angle and sorption speed for powders and other porous materials. Change of weight as a function of time is measured. The dynamic contact angles of water on these surfaces are carefully measured and found to be consistent with the theoretical predictions of the Cassie model and the Wenzel model. When a water drop is at the Wenzel state, its contact angle hysteresis increases along with an increase in the surface roughness. While the surface roughness is further raised beyond its transition roughness (from the Wenzel state to the Cassie state), the contact angle hysteresis (or receding contact angle) discontinuously drops (or jumps) to a lower (or higher) value. In surface science, an instrument generally called a contact angle goniometer is used to measure the contact angle at which a liquid/vapor interface meets a solid surface. The first contact angle goniometer was designed by Dr. William Zisman of the United States Naval Research Laboratory in Washington, DC and manufactured by ramé-hart of Mountain Lakes, NJ. This tool is used not only for contact angle and surface energy applications, but also to measure surface tension using pendant drop, sessile drop, and other methods. The original manual contact angle goniometer used an eyepiece with microscope. The current generation of contact angle instruments uses cameras and software to capture and analyze the drop shape and are better suited for dynamic and advanced studies. Surface energy is most commonly quantified using a contact angle goniometer and a number of different methods. Thomas Young described surface energy as the interaction between the forces of cohesion and the forces of adhesion which, in turn, dictate if wetting occurs. If wetting occurs, the drop will spread out flat. In most cases, however, the drop will bead to some extent and by measuring the contact angle formed where the drop makes contact with the solid the surface energies of the system can be measured. Young also developed the well-regarded Young's Modulus which is used to measure the stiffness of a material as well as Young's Equation which defines the balances of forces caused by a wet drop on a dry surface. If the surface is hydrophobic then the contact angle of a drop of water will be larger. Hydrophilicity is indicated by smaller contact angles and higher surface energy. Water has high surface energy by nature; it's polar and forms hydrogen bonds. In the case of "dry wetting", one can use the Young-Dupree equation which is expressed by the work of adhesion. This method accounts for the surface pressure of the liquid vapor which can be significant. Pierre-Gilles De Gennes, a Nobel Prize Laureate in Physics, describes wet and dry wetting and how the difference between the two relates to whether or not the vapor is saturated .
