The Wicking Kinetics of Liquid Droplets into Yarns

The wicking kinetics of liquid droplets into yarns is studied using a computerized imaging system. A new method is suggested for characterizing the yarn structure by monitoring droplet absorption. The method is based on the comparative analysis of the time needed for droplet disappearance as a function of droplet volume for various yarns. A mathematical model is developed to describe the wicking kinetics. We show that for wetting liquids, the time of droplet absorption T _w is a linear function of the initial droplet volume squared V ₀ ². For a given liquid-yarn pair, the slope of this relationship provides important information about the yarn properties. The linear relationship between T _w and V₀ ² is verified by experimental data for a typical spin finish. The model predicts that droplet wicking can occur even if the advancing contact angle θ_a is slightly greater than 90°. However, for nonwetting liquids, the relationship between T _w and V ₀ ² is nonlinear, and a criterion for droplet wicking into nonwetted yarns is obtained.