Static contact angle algorithm of hydrophilicity and its application in silicone rubber hydrophobicity detection

To improve accuracy of calculating the static contact angle of hydrophilic materials, we proposed a static contact angle algorithm considering globule volume and hydrophobicity. The globule edge curve was generated by the Young-Laplace equation, in the meantime, noise was superimposed to the curve to simulate the error of edge extraction, thereby, we studied the influences of the globule volume and contact angle on circle fitting algorithm and ellipse fitting algorithm. When the contact angle is not more than 90°, the globule volume less than 200 μL, and contact line shorter than 1 cm, we studied the influence of noise content on accuracy of the two algorithms. The results indicate that, the influence of noise on the ellipse fitting algorithm is more remarkable than that on the circle fitting algorithm, and the larger contact angle, the smaller influence. The error of the circle fitting algorithm will increase obviously with the increase of the globule volume, and the ellipse fitting algorithm will increase slightly. If the contact angle is less than 15°, the circle fitting algorithm should be selected to calculate the contact angle. If the contact angle is larger than 15° and less than 70°, in the meantime, the globule volume is less than 7 μ L, the circle fitting algorithm should be selected. If the contact angle is larger than 15° and less than 70°, in the meantime, the globule volume is larger than 7 μL, the ellipse fitting algorithm should be selected. If the contact angle is larger than 70° and less than 90°, the ellipse fitting algorithm should be selected. Finally, the proposed contact angle algorithm was used to calculate the static contact angle of silicone rubber samples with different hydrophobicities, and the conclusion was verified by the experiment. If the silicone rubber material is hydrophilic, the accuracy of the static contact angle measurement can be improved by using the proposed method.