ABSTRACT
Pressure sensitive adhesives (PSAs) share the properties of liquid and solid materials [1,2]. Liquid-like behavior of PSAs plays an important role at the stage of establishment of proper adhesive contact. This behavior provides easy wetting of the surface of substrate that is necessary to form a strong adhesive bond under application of slight pressure over a short period of time (few seconds). Solid-like behavior of the PSAs is of principal importance at the stage of adhesive bond failure when the material resists to applied detaching force, dissipating and storing a great amount of mechanical energy. In other words, the solid-like behavior is needed to impart the strength to the adhesive bond. In this way, the PSAs are liquids being subjected to shear deformation under compressive stress, and solids (incapable to flow, with elastic modulus below 1 MPa [3]) as the material is stretched under tensile debonding stress. Since these soft materials are not able to flow, very large tensile deformations accompany the failure of adhesive bond. From rheological point of view, PSAs can be defined as viscoelastic polymer liquids with a pronounced yield stress [4]. At molecular level, the pressure sensitive adhesion results from a specific balance between high energy of intermolecular cohesion and a large free volume [5,6]. The large free volume is the consequence of low glass transition temperature (Tg) of the PSAs, which generally falls below -40 °C [7]. The high cohesive energy is a necessary condition of solid-like behavior of the PSAs.
