Test Methods

Shear Strength—The shear strength of adhesive bonds was determined using single lap-shear specimens, 25-mm wide, with an overlap of 10 mm. All substrates were cleaned with isopropyl or ethyl alcohol prior to any further treatment. The bonded specimens were tested in an Instron mechanical tester at a rate of 10 mm/min. Five specimens were tested per experimental point.

Peel Strength—The peel strength was determined using 180° peel specimens, which were prepared in accordance with ASTM C794 [23] but modified by CSIRO [24,25], by reducing the sealant thickness from the recommended 1.6 mm to 0.2 mm to provide greater stress concentration at the substrate/sealant interface. When inherent adhesion problems are present, this modified procedure favors ad­hesive delamination rather than cohesive failure within the relatively weak sili­cone sealants. The specimens were tested in an Instron mechanical tester at the rate of 10 mm/min. Two peel specimens were tested per experimental point.

XPS Analysis—XPS analyses were performed on a VG Escalab MkII spec­trometer[28] equipped with an AlKa source, non-monochromatized, at a power of 150 W. Samples were exposed to irradiation for less than 30 min to avoid

substantial decomposition of the polymer surfaces in the analysis beam. Spec­tra were recorded at the normal emission of the photoelectron relative to the surface plane of the samples (0°). The spectrometer did not provide for charge neutralization. Elements present were identified from survey spectra, and the atomic concentrations were estimated from integrated peak intensities and pub­lished sensitivity factors [26]. Components of the C1s signal were estimated by curve fitting using Gaussian-Lorentzian line shapes and a nonlinear back­ground substration. The binding energy scale was calibrated using a value of 285.0 eV for the CH2 component as an internal reference. The random error in the quantitative analysis of elemental compositions is between 5 % and 10 % in the present cases.