The debonding of a model pressure-sensitive adhesive (PSA) poly-n-buthylacrylate is investigated by a combination of the mechanical tack test, optical microscopy and in situ ultra-small-angle X-ray scattering. From the mechanical test, macroscopic values such as forcedistance curves are determined. The force-distance curve exhibits the typical non-linear behavior. With microscopy the macroscopic cavitation structure is observed. Scattering addresses the structure of the PSA on a microscopic level for the first time. As a new feature, a sub-structure of the usual optically resolvable macroscopic fibrils between the PSA surface and the probe punch is detected. The sub-structure exists over a large distance between the PSA and the probe surface and remains constant in diameter. This behavior of the sub-structure as well as the dependence of the force plateau on the film thickness are compared with theoretical predictions.

Polymer blend films consisting of a tacky and a non-adhesive component are promising candidates for low tack applications. Immiscibility of both components results in a phase separation process yielding a tacky matrix with glassy objects embedded. The influence of the blending ratio of the components poly-n-butylacrylate (PnBA) and polystyrene (PS) is addressed. The mechanical information resulting from the tack test shows the possibility to vary the bonding strength of the PSA blend over a wide range. The macroscopic and microscopic structural characterization with optical microscopy and ultra small angle X-ray scattering shows that the blend PnBA:PS exhibits similarities to common filler systems as well as deviates regarding installed structures. Due to the large domain size on a microscopic level, only the tacky component, PnBA, defines the adhesive behavior. The non-adhesive component limits the contact area between the adhesive and the substrate.

Cover:The picture on the cover shows an in-situ characterisation of a pressure sensitive adhesive film with the mechanical tack test and synchrotron radiation based ultra small angle scattering. This combination allows to tailor the adhesive properties and to understand the de-bonding mechanism. Further details can be found in the article by P. Müller-Buschbaum,* T. Ittner, E. Maurer, V. Körstgens, and W. Petry on page 825.

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