Droplet formation and contact angles of liquids on mammalian hair fibres

The wetting by a liquid drop of a model mammalian hair fibre is compared with that of a smooth cylindrical fibre. (B. J. Carroll, J. Collodid Interface Sci., 1976, 57, 488). The model considered has a series of axially symmertrical serrations regularly spaced along the fibre length and these are shown to play an important role in the wetting behaviour of the system, principally through their ability to act as points of ‘hingeing’ for the three-phase contact lines at the two ends of the liquid drop. It is shown that the apparent contact angles in the system can in certain cases be related to the true contact angle and to the geometry of the fibre asperities. It should thus be possible to estimate empirically the true system contact angle and experimental results are presented in support of this conclusion.