A simple method for measuring the superhydrophobic contact angle with high accuracy

Yi-Lin Hung; Yao-Yuan Chang; Meng-Jiy Wang; Shi-Yow Lin
June 2010
Review of Scientific Instruments;Jun2010, Vol. 81 Issue 6, p065105
Academic Journal
A modified selected-plane method for contact angle (θ) measurement is proposed in this study that avoids the difficulty of finding the real contact point and image-distortion effects adjacent to the contact point. This method is particularly suitable for superhydrophobic surfaces. The sessile-drop method coupled with the tangent line is the most popular method to find the contact angle in literature, but it entails unavoidable errors in determining the air-solid base line due to the smoothness problem and substrate tilting. In addition, the tangent-line technique requires finding the actual contact point. The measurement error due to the base line problem becomes more profound for superhydrophobic surfaces. A larger θ deviation results from a more superhydrophobic surface with a fixed base line error. The proposed modified selected-plane method requires only four data points (droplet apex, droplet height, and two interfacial loci close to the air-solid interface), avoiding the problem of the sessile-drop-tangent method in finding the contact point and saving the trouble of the sessile-drop-fitting method for best fitting of the numerous edge points with the theoretical profile. A careful error analysis was performed, and a user-friendly program was provided in this work. This method resulted in an accurate θ measurement and a method that was much improved over the classical selected plane and the sessile-drop-tangent methods. The θ difference between this method and the sessile-drop-fitting method was found to be less than three degrees.


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