Cohesive Energy
Physical properties measure the cohesive energy at the interface of a liquid, determining its ability to wet a solid surface. The surface tension of a liquid must be overcome by repellent finishes on textile fibres to prevent absorption and staining. It governs how easily water, oil, or chemical finishes can penetrate fabric structures.
Wetting Chemistry
Repellent finishes create a low-energy surface on textile fibres that is lower than that of the liquid applied. Since surface tension forces droplets to minimize their surface area, liquids on treated fabrics form spheres instead of spreading. This prevents the liquid from wetting the yarn and soaking into the fabric.
Chemical Treatment
Fluorochemicals are the most effective treatments because they lower the surface energy of fibres to a level below that of most oils and water. When surface tension is lower than the fabric surface energy, wetting occurs, but if it is higher, the liquid is repelled. This principle is why C6 fluorocarbons are used to resist hydrocarbons like oil and grease, which have very low surface tension values compared to water.
It is the fundamental physics used to design protective garments for industrial and outdoor applications.
Test Liquids
Laboratory test methods like AATCC 118 use a series of liquids with different values of this property to grade the performance of textile treatments. By testing a fabric’s resistance to liquids of decreasing surface tension, technicians can determine the precise performance level of the finish. This measurement ensures the fabric meets commercial standards before shipping.
