Investigation of surface energy for organic light emitting polymers and indium tin oxide

The contact angles on the thin films of poly(2-methoxy-5-(2'-ethyl-hexyloxy )-p-phenylenevinylene) (MEH-PPV) and indium tin oxide (ITO) were measured b y the sessile-drop technique. The surface energies of the films were calcul ated using the 2-liquid geometric mean and 3-liquid Lifshitz-van der Waals acid-base(LWAB) approaches. The overall total surface energies (gamma(S)) o f MEH-PPV and the as-received ITO were 26.4 and 25.8 mJ/m(2), respectively. Both approaches yielded almost the same surface energies. The surface ener gies were mainly contributed to by dispersion interactions or Lifshitz-van der Waals (LW) interactions for both MEH-PPV and ITO. The changes in the co ntact angles and surface energies of the ITO films, due to different solven t cleaning processes and argon plasma treatments, were analyzed. Experiment al results revealed that the total surface energy of the ITO films increase d after various cleaning processes. In comparison with different solvents u sed in this study, we found that methanol is an effective solvent for ITO c leaning, as a higher surface energy was observed. ITO films treated with ar gon plasma showed the highest surface energy. This work demonstrated that c ontact angle measurement is a useful method to diagnose the cleaning effect on ITO films. (C) 2000 Elsevier Science S.A. All rights reserved.