Physics of contact angle measurement

Contact angles can be of great value; however, making meaningful contact an gle measurements and interpreting those measurements is complex. For years, researchers have addressed a wide variety of issues concerning contact ang les. Some questions have been qualitatively answered; others remain open. I n this paper, we focus on three issues which are particularly important for the measurement and use of contact angles. the appropriate definitions and use of macroscopic and microscopic contact angles, a brief survey of the l ength scales relevant to phenomena controlling contact angles, and the role of vibrations in determining contact angles. We emphasize contact angle is sues relevant to heterogeneous surfaces, specifically, ambient surfaces pre valent in nature and industry. (C) 1999 Elsevier Science B.V. All rights re served.