Date of Award

August 2020

Document Type


Degree Name

Master of Science (MS)


Mechanical Engineering

Committee Member

Joshua Bostwick

Committee Member

John R Saylor

Committee Member

Xin Zhao


Drop impact onto elastic substrates is important in applications such as spray coating, bioprinting, forensic analysis, and aerosol drug delivery. The dynamics of impact are complex and include a sequence of events that cause a drop to splash or deposit, form a corrugated leading edge with a well-defined number of spines that may or may not pinchoff into satellite drops during spreading, and finally retraction of the main drop to an equilibrium configuration. Careful experiments are performed to quantify droplet impact on soft gel substrates made of either PDMS silicone or gelatin hydrogels of varying elastic modulus. High-speed photography and image processing quantify the splash dynamics. The splash threshold, as defined by the Weber number, increases as the substrate elasticity decreases making it harder to splash on soft substrates. For relatively stiff substrates, the spreading factor agrees with previously literature but there is systematic deviation for the softest substrates indicating that elasticity plays a crucial role in the spreading dynamics. Surprisingly, the retraction dynamics on soft substrates do not show any correlation with the impact velocity for water, but show a complex behavior when using ethanol as the working liquid which can be attributed to the different wetting properties. The reported results agree well with existing literature for most cases and provides new insights for gels with small elasticity.



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