To function well, it should have good adhesion to a surface and good cohesion, or internal strength. For good adhesion, it is important that the adhesive can readily flow out on the surface. The degree, or freeness, of the flow often determines the intensity of adhesion. Degree of flow depends on the difference between the surface energy of the material and the surface energy of the adhesive. Mechanisms for adhesion include both mechanical adhesion and specific adhesion.
Mechanical adhesion occurs when the adhesive flows into the texture of the substrate.
Specific adhesion includes electrostatic forces, van der Waals forces and acid-base interactions that take place between the adhesive and the substrate. In the case of acrylic pressure-sensitive adhesives, the intensity of the bond typically increases over time. This growing degree of 'stickiness' occurs because of the long time it takes for the adhesive to flow onto and into the surface texture, and for the adhesive polymer to align with the surface to create the interactions.