Adhesive–adherent interfaces probed with grazing-incidence small-angle neutron scattering

The inner structure of a pressure-sensitive adhesive (PSA) is investigated at the surface as well as at the buried adhesive–adherent interface. Time-of-flight grazing-incidence small-angle neutron scattering (TOF-GISANS) is used to obtain depth-resolved structural information about the statistical copolymer poly(ethylhexylacrylate-stat-d-methylmethacrylate), which represents a well studied model PSA comprising 80% ethylhexylacrylate and 20% deuterated methylmethacrylate. Small and rare defects of around 40 nm in lateral size are found at the surface, while in the probed film volume a very low concentration of smaller structures of between 25 and 37 nm is found. Acidic and basic cleaning procedures are applied to the silicon adherent to alter the surface chemistry. At the buried interface of the adhesive and adherent no lateral structures are resolvable, irrespective of the surface treatment. The absence of dominant lateral structures shows that the statistical copolymer does not phase separate on a length scale that is of interest for applications. Furthermore, the findings prove the suitability of this kind of sample system for reflectivity measurements and demonstrate the suitability of TOF-GISANS for nondestructive investigations of buried interfaces in adhesion science.