Influence of molecular features on the tackiness of acrylic polymer melts

The effects of molecular weight and acrylic acid content on the adhesive properties of a series of monodisperse poly(n-butyl acrylate) materials have been investigated. The short-time adhesion, or "tackiness", of these model pressure-sensitive adhesives was quantified by performing probe-tack experiments. These experiments consist of a bonding phase, where a flat punch is brought into contact with a PnBA layer, and a subsequent debonding phase, where the probe is pulled away from the surface. The debonding process was separated into three distinct deformation mechanisms: (1) the appearance of cavities throughout the adhesive layer; (2) lateral growth of these cavities within the plane of the adhesive layer; (3) the formation and eventual failure of a fibrillar structure as the adhesive is extended in the direction of the applied tensile load. Cavitation depends primarily on the elastic character of the adhesive, but the lateral cavity growth and extensional mechanisms are strongly affected by the ability of the adhesive to flow during the time scale of the experiment. The nature of these processes was determined by an effective Deborah number, defined as the terminal relaxation time of the polymer multiplied by the initial strain rate imposed during the debonding process.