Modification of Steel Surfaces with Nanometer Films of Al2O3 and TiO2 Decreases Interfacial Adhesion to Polymers: Implications for Demolding Shape-Engineered Polymer Products

Abstract

Alumina (Al2O3) and titanium dioxide (TiO2) thin films were deposited by the atomic layer deposition technique on steel substrates used in the polymer injection molding industry. The modified steel surfaces were systematically characterized by SEM, EDS, AFM, XPS, and OCA. Surface energy values were obtained to predict the demolding behavior of modified steel surfaces when in contact with different polymers. The lowest surface energy was obtained using Al2O3 and H2O as an oxygen source on 1.2311 steel (1.2311-Al-H), representing a 30% decrease when compared to 1.2311 bare ground steel. Results were confirmed by the simulation of polymer–mold interaction. The produced polycarbonate surface presents defects with an average diameter of 0.5 μm that result from mimicking of the Al2O3 textured surface (contrasting with the defects with a diameter of 1.85 μm using bare 1.2311 steel). The best compromise between surface energy and roughness was obtained using the TiO2-H2O film (1.2311-Ti-H). The modified steel with TiO2 ALD coating produced the smoothest polymeric surface. The modification of steel surfaces with nanometer films of Al2O3 and TiO2 decreased the interfacial adhesion to polymers, which had implications for demolding shape-engineered polymers, a requirement for high-aspect-ratio parts.