To estimate adhesion at polymer-solid interfaces, model substrates with varying -NH2 density on Al2O3 were prepared by a self-assembly of mixed amine terminated silanes (AS) and methyl terminated silanes (MS). The density of -NH2 groups on Al2O3 was varied by changing the mol.% of AS and MS in solution. The model surfaces were characterized by means of X-ray photoelectron spectroscopy (XPS), contact angle measurements, atomic force microscopy (AFM), and mechanical tests with polymers. The analysis of the competitive coadsorption kinetic model showed that MS adsorbed two times faster than AS on aluminum surfaces. The surface energetics of Al2O3 was controlled by the mixed silane treatments from hydrophobic and low energetic to hydrophilic and high energetic surfaces.