be accurately applied to fibers (8,9). The methods, which A generalized drop length-height method is introduced here determine the contact angle by means of the direct observafor the determination of contact angle in the drop-on-fiber systems. tion of the formed meniscus using microscopy (10, 11), are This method overcomes some of the difficulties encountered in the associated with large subjective factors, since the liquid drop practice by applying the common maximum drop length-height surface changes steeply near the three-phase contact points method to determine the contact angle. Furthermore, with this (8). The contact angle can also be indirectly determined by new generalized method a large part of a drop profile can be using the Wilhelmy plate principle. The results obtained with used in the calculation, which reduces the statistical error of the this method lack often reproducibility (12, 13).
determination and improves the reliability and accuracy of the
Recently the method based on the determination of the obtained results. The method has been examined using both the theoretically simulated and the experimentally obtained drop pro-critical parameters of a drop profile (e.g. maximum drop files. The accuracy of the method has been estimated to be in order length, drop height, and the apparent contact angle of a drop of 0.5-1Њ for the drop profiles of usual experimental quality, which surface curve at its inflection point (8, 9)) received much can be obtained using common digital image processing hardware attention (2, 3, 8, 9, 12). Its principle is due to the Laplaceand software. ᭧ 1998 Academic Press
Young equation (in the absence of gravity effect), which Key Words: drop-on-fiber; contact angle; wetting of fibers; rules the profile of a liquid drop on a fiber. With this method method of contact angle measurement.
accurate measurement may be possible if the drops are small enough that the effect of gravity may be neglected and if the critical drop dimensions can be determined with enough pared to the original maximum drop length-height method.