A wetting agent is a surface-active molecule used to reduce the surface tension of water. The high surface tension of water is problematic in many applications where spreading and penetration of water is required. These include for example paints and other coating formulations, detergents, pesticides, and others.
The main purpose of the wetting agent is to reduce the surface tension of water. Pure water has very high surface tension of 72.8 mN/m (at 20 °C). The high surface tension of water causes problems in many industrial processes where water-based solutions are used as the solution is not able to wet the surface it is applied to. Wetting agents are commonly used to reduce the surface tension of water and thus help the water-based solutions to spread.
Wetting agents are utilized in many different products. In coating industry, wetting agents help the fluid phase to wet pigment particles during the pigment dispersion process. They also help to reduce the surface tension of the coating so that it properly wets the substrate upon application. In pesticides, wetting agents help the solution to spread on the leaf surface thus increasing their efficiency. The waxy surface of many insects, fungi, and plants makes it difficult for most water-based pesticides solution to penetrate to their target.
Wetting agents belong to a class of surfactants. Surfactants are surface active which make them prone to adsorb at air-liquid or liquid-liquid interfaces. They help to reduce the surface tension by penetrating in between the water molecules and thus reducing the cohesion between them.
As the main purpose of the wetting agent is to reduce the surface tension of the water, the surface tension measurements are routinely done. The surface tension measurement will show how much the wetting agent is able to reduce the surface tension but also how much of the wetting agent should be used.
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Surface tension can be measured with force tensiometer using Du Noüy ring or Wilhelmy plate. Or with optical tensiometer using the pendant drop method.
Du Noüy method utilizes the interaction of a platinum ring with the surface of the liquid.
Surface tension of blood is an important characteristic when protective materials are being evaluated.
A basic requirement of any coating is that it should form a uniform, defect-free surface. Surface and interfacial tensions play a key role in that.
Surfactants are used in many industrial fields. Characterization of surfactants is thus important to optimize their performance and the products they are applied to. Surface and interfacial tension measurements offer versatile method to study the properties and behavior of the surfactant solution.
A term surfactant comes from the word surface active agent. At the interface, they align themselves so that the hydrophobic part is in the air and hydrophilic part is in water. This will cause the decrease in surface or interfacial tensions.