Inscribing wettability gradients onto polymer substrates with different stiffness using corona discharge in point-to-plane geometry

We use direct current (DC) corona discharge to create wettability gradients on polymer surfaces. The inhomogeneous current density distribution due to a point-to-plane arrangement induces local changes of the wettability of polymer surfaces, resulting in macroscopic wettability gradients. We found that condensation of water vapor on the surface allows a more precise characterization of the wettability gradient than macroscopic contact angle measurements. Condensation experiments allow characterizing different zones with different wettability. The wettability pattern depends on the stiffness of the substrate. We conjecture that Coulomb interactions influence the spatial distribution of wettability. Indirect measurements of the electrostatic surface potential after exposure support this assumption. (C) 2015 Elsevier B.V. All rights reserved.