Impinging blood droplets on different wettable surfaces: Impact phenomena,contact line motion,post-impact oscillation and dried stains |
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| Affiliation: | 1. School of Physics, University of Electronic Science and Technology of China, Chengdu 610054, China;2. Department of Radiology, Chengdu Seventh People’s Hospital, Chengdu 610000, China;1. Centre for Forensic Science, Department of Applied Sciences, Faculty of Health & Life Sciences, Northumbria University, Ellison Building, NE1 8ST Newcastle Upon Tyne, United Kingdom;2. Northumbria Sport, Northumbria University, NE1 8ST Newcastle Upon Tyne, United Kingdom;3. King’s Forensics, Department of Analytical, Environmental & Forensic Sciences, King’s College London, SE1 9NH London, United Kingdom;1. University of Texas Southwestern, 1801 Inwood Rd, Dallas, TX 75390-9132, USA;2. Friendly Foot Care, PC, 50 W. 94th Place, Crown Point, IN, USA;3. Former Research Scholar, Department of Anthropology, Panjab University, 160014, Chandigarh, India;4. Department of Forensic Medicine & Toxicology, Medical College Building, All India Institute of Medical Sciences, Jodhpur, Rajasthan 342005, India;5. Department of Anthropology, Panjab University, Chandigarh, India;1. Hacettepe University, Institute of Sciences, Division of Forensic Science, Ankara, Turkiye;2. Hacettepe University, Department of Chemistry, Ankara, Turkiye;3. Üsküdar University, Forensic Science Department, Istanbul, Turkiye;1. Department of Pathology, King George’s Medical University, Lucknow, India;2. Department of Prosthodontics, King George’s Medical University, Lucknow, India;3. Department of Pathology, Dr. Ram Manohar Lohiya Institute of Medical Sciences, Lucknow, India;4. Department of Forensic Medicine and Toxicology, King George’s Medical University, Lucknow, India;5. Department of Biochemistry, King George’s Medical University, Lucknow, India;1. Formerly of Forensic Science Service Ltd, 109 Lambeth Road, London SE1 7LP, United Kingdom;2. Cellmark Forensic Services, Unit B1, Buckshaw Link, Ordnance Road, Buckshaw Village, Chorley, Lancashire PR7 7EL, United Kingdom;3. Formerly of Forensic Science Northern Ireland, 151 Belfast Road, Carrickfergus, Co. Antrim BT38 8PL, Northern Ireland;4. Formerly of Key Forensic Services, 207C Cavendish Place, Birchwood Park, Warrington WA3 6WU, United Kingdom;5. SPA Forensic Services, Aberdeen, Nelson Street, Aberdeen AB24 5EQ, United Kingdom;6. Formerly of Cellmark Forensic Services, 16 Blacklands Way, Abingdon Business Park, Abingdon, Oxfordshire OX14 1DY, United Kingdom;7. Formerly of Eurofins Forensic Services, Building 3, Drayton Manor Business Park, Tamworth, Staffordshire B78 3GL, United Kingdom;8. Department of Justice and Equality, Forensic Science Ireland, Garda Headquarters, Phoenix Park, Dublin 8, Ireland |
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| Abstract: | Understanding the underlying hydrodynamics of impinging blood droplets and finding out the physical parameters determining the bloodstain characteristics are of great importance in blood related forensic investigations. In this work, the impact of non-Newtonian blood droplets on solid surfaces ranging from lyophilic to superlyophobic was systematically investigated and compared to that of Newtonian droplets with a similar dynamic shear viscosity. We show that impinging blood droplets behave as low-viscosity Newtonian droplets in the short-time spreading, which is dominated by capillary and inertial forces, but their non-Newtonian viscoelasticity would notably affect the droplet retraction and post-impact oscillation occurring in large timescales. Whereas the strong liquid–solid adhesion and the non-Newtonian elongational viscosity hinder droplet recoiling and thus alter the impact phenomena on lyophobic and superlyophobic surfaces, the shear and elongational viscosities are coupled to result in higher damping coefficients of oscillating blood droplets after deposition, in comparison to that of impinging Newtonian droplets. The size of the dried bloodstain was found to be different from both the maximum spreading radius of the droplet that can reach during impact and the final radius of the deposited droplet after oscillation, and their correlations are highly dependent on the impact velocity and surface wettability. Moreover, the morphologic characteristics of the bloodstains would also be changed by varying either the impact velocity or the surface wettability. We envision that these findings can not only find applications in the bloodstain pattern analysis, but also provide useful information for medical diagnosis based on blood droplet test. |
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| Keywords: | Bloodstain pattern analysis Forensic investigation Droplet impact Surface wettability |
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