Ceramic interface properties evaluation based on contact angle measurement Cristina Vladuta a, ⁎ , Luminita Andronic a , Maria Visa b , Anca Duta a a Transilvania University of Brasov, Centre: Product Design for Sustainable Development Eroilor 29, 500036 Brasov, Romania b College for Natural Sciences, Armoniei 6, 500189, Brasov, Romania Available online 29 August 2007 Abstract The ceramic interface properties and morphology were estimated based on contact angle measurements. The contact angle, θ, was measured using different liquids (glycerol, NaCl 3.5% solution, oleic acid and ultra pure water) with known surface tensions. Correlations of the contact angle with the chemical bonds and morphology of thin films are presented. The thin films, deposited via Spray Pyrolysis Deposition (SPD) are TiO 2 (dense, porous) and WO 3 (dense, porous) films. The interface properties of the ceramic layers were explained using the topography images obtained with Atomic Force Microscopy (AFM), and by measuring the contact angles and surface tensions. The contact angles method is sensitive at high θ values. The experiments indicated that the recommended testing liquid is pure water, both for TiO 2 and WO 3 thin films, allowing a clear difference between dense and porous surfaces. The measurements were done at the initial moment of the contact drop-sample and with 1 s step up to 30 min. The presented results can be further used in optimizing the layer-by-layer deposition of thin films. © 2007 Elsevier B.V. All rights reserved. Keywords: Ceramics; Contact angle; Surface tension; Surface roughness 1. Introduction Thin films of TiO 2 and WO 3 are part of the multi-layered structures used in novel optoelectronic devices like dye- sensitized and solid state solar cells [1], and photo electro- chemical cells, PECC, [2]. In developing layer-by-layer deposition for the multi-layered structures, the surface proper- ties (surface energy, wettability) play an important role and are correlated with the surface morphology and polarity. The contact angle is a surface property, a consequence of intermolecular interactions. There is a growing interest, in the recent years, in modifying surface properties of polymer films, inorganic oxides, and other solid substrates, [3]. Information obtained from contact angle measurements for a wide range of solid substrates (e.g. polymer surface, glass, ceramics, etc), has proved vital to the formulation of adhesives, composites, and biocompatible materials, and in generating fundamental understanding of solid–solid and solid–liquid intermolecular interactions (e.g., van-der Waals, acid/base type interactions and electrostatic interactions) [4]. Many studies, [5], showed that contact angle is strongly dependent on the liquid and surface nature and solid/liquid contact time. For a flat smooth surface, the contact angle θ is defined by the equilibrium condition of three interfacial tensions: solid–liquid,σ SL , solid–vapor, σ SV , and liquid– vapor, σ LV , which are related through Young's equation: r LV cosh ¼ r SV À r SL ð1Þ Eq. (1) contains only two quantities experimentally measur- able, θ and the liquid–vapor surface tension σ LV . There are different approaches on how to introduce additional relations needed to evaluate the surface energy of the solid, σ SV , [6,7]. This paper uses the Fowkes approach, describing wetting and adhesion processes in conjunction with contact angles for many systems: r LV 1 þ cosh ð Þ¼ 2 r p LV r p SV   1 2 þ r d LV r d SV   1 2 h i ð2Þ where σ LV P , σ LV d , σ SV P , σ SV d are polar (p) and dispersed (d) components of the liquid- and solid-surface energies, [6,7]. Available online at www.sciencedirect.com Surface & Coatings Technology 202 (2008) 2448 – 2452 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. Fax: +40 268 475597. E-mail addresses: c.vladuta@unitbv.ro (C. Vladuta), a.duta@unitbv.ro (A. Duta). 0257-8972/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2007.08.033