Why do surfaces stick? Sticking occurs when molecules of a substance (generally, a semi-solid) have a stronger attraction (adhesion) to a surface than to each other (cohesion). Conversely, if molecules within a substance have greater affinity for each other (cohesion) than the surface (adhesion), non stick will occur.

Non stick (release) is not the same as lubrication. But release does relate to how a surface ‘wets’. Wetting is defined as the ability of a liquid to spread across a surface. If a surface is easily wetted, the surface is described as hydrophilic (water-attracting). If the surface is not easily wetted, the surface is described as hydrophobic (water-repelling). The poorer the wetting, the better the release coatings.

How then do we estimate the likelihood of release? We do so by measuring a liquid’s wetting force at the coated surface. Surfaces are considered ‘wettable’ when contact angles are less than 90 degrees (sticking). Surfaces are considered ‘non wettable’ when greater than 90 degrees (release).

Surface energy across an interface or the surface tension at the interface is a measure of energy required to form a unit area of new surface at the interface. Polar liquids like water have values of 73 dynes per cm at 20 degrees Centigrade, while Teflon, PTFE, PFA, FEP, or Silicone are typically 20 dynes per cm, or less.

So, what makes good release? Besides the fact that its interface must reject the other surface. A good non stick coating must cause the two surfaces in intimate contact to separate easily, smoothly, and cleanly.

Unfortunately, there is no single, universal type of release agent for all sticking applications. What works well with some products can perform poorly with others. Temperature, time, pressure, materials, material phase, permeability, and area of contact are some considerations.

Ideally, a non stick coating should have considerable tensile strength, so it is not easily abraded by constant contact. The release product should be chemically resistant so it does not break down in the presence of the sticking compound. And it should have heat and stress resistance so it does not decompose or tear apart. In addition, they should adhere to the substrate and be non-transferrable, so that they do not interfere with other, secondary finishing operations.