This paper studies the impact and wicking dynamics of blood droplets on textile surfaces.
This study on blood droplet impact and wicking on textile surfaces provides fundamentally important perspectives for the application of bloodstain pattern analysis (BPA). Energy balance analysis is conducted for modeling the maximum spread factor. The dynamics of water droplet retraction after reaching the maximum spread are investigated on different surfaces. Distinct droplet retraction modes are classified, and the characteristics in different modes are compared accordingly. Similarity behavior during droplet retraction process is revealed. The paper includes a systematic parametric study of the influence of droplet impact velocity, fabric type, and droplet impact angle on blood droplet impact and wicking dynamics on fabrics. Considerable differences are observed among different types of fabrics. Blood droplet splashing characteristics are compared among these fabrics as well. Distinct bloodstain shapes are observed for blood droplet impact on fabrics with different impact angles. The more acute the impact angle, the larger aspect ratio the bloodstain will present. The subsequent wicking renders the aspect ratio to be smaller than that right after the inclined impact. A new approach for a quantitative analysis of bloodstain shapes on fabrics is also proposed, the successful generation of single micro blood droplet is reported, and the formation of micro droplets and micro droplet impact dynamics are investigated. Optimal operating range is identified for the stable generation of single blood droplet in the droplet-on-demand (DoD) mode. Micro blood droplet impact dynamics is compared with that of micro water droplets and millimeter-sized blood droplets. Effects of surface wettabilities on micro droplet impacts are revealed. The micro bloodstains formed by micro droplet impact on glass and plain-woven fabric are briefly discussed. Droplet impact and wicking are the essential process in many industrial, agricultural, and automotive applications. An improved understanding of the dynamics in these two processes will benefit those droplet-related technological applications.