1 Supporting Information Thermal Gradient Enabled XPS Analysis of PDMS Elastomer Adhesion to Polycarbonate Dongchan Ahn*, Nick E. Shephard, Patricia A. Olney, Christopher S. McMillan Dow Corning Corporation, 2200 W. Salzburg Road, Midland, Michigan 48686-0994. * Corresponding author: e-mail d.ahn@dowcorning.com ; Fax 989-496-4654. 1. Details and Characterization of Thermal Gradient Curing Method The mixed PDMS elastomer formulations (MSA and MSA + IEA) were spread onto a 25 x 76 mm polycarbonate (PC) substrate, which was supported by the bottom plate of the aluminum thermal gradient press. A peel sample was constructed by sandwiching a layer of the test formulation between the PC substrate and Al foil, which was adhered to the top plate of the press using a spray mount adhesive. Bondline thickness was controlled by using two copper wire spacers, placed at each end of the substrate, to give a 0.041 inch bondline. The sample was then cured under the linear gradient, ranging from approximately 50° C to 150° C over the length of the substrate. At the end of the curing cycle the substrate was removed from the press, carefully ensuring the Al foil also released from the top plate. The foil was cut to size along the outer edge of the substrate. The edges of the sample were cut away with a sharp razor, leaving a 0.50 inch wide peeling strip in the center of the sample. An interfacial crack was initiated by manually peeling back the strip a few millimeters from the low temperature end of the substrate. The interfacial crack was then allowed to propagate by attaching a 1500 g weight to the cold end of the peel strip at a 90° peeling angle until it was arrested by a transition to cohesive failure (CF). Measuring from the hot end, the distance to the point of onset of cohesive