The wicking kinetics of liquid droplets into yarns

The wicking kinetics of liquid droplets into yams 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-o(2). For a given liquid-yam pair, the slope of this relationship provides important information about the yam properties. The linear relationship between T-w, and V-o(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 theta (a) is slightly greater than 90 degrees. However, for nonwetting liquids, the relationship between T-w and V-o(2) is nonlinear, and a criterion for droplet wicking into nonwetted yams is obtained.