Liquid transport on soft surfaces such as human tissues, gels, or soft plastics occurs in nature, medical technologies, and industrial processes. Both the fluid and the surface may move and their motion is coupled. This coupling makes prediction of the motion difficult and leads to new phenomena. In this work, liquid motion on soft substrates will be investigated by both theory and experiments through four research problems. The first research thrust relates to the surface-tension driven wave motion in liquids on soft solids, and is relevant to technologies such as inkjet printing and microfluidics. The second area involves the motion of a drop on a soft surface due to gradients in the stiffness of the surface, and is relevant to the motion of cancer cells in human tissues. The third investigation involves splashing of liquids on soft surfaces, and could impact forensic analysis and the aerosol delivery of drugs to neonates. The final objective involves the spreading of liquids on deformable viscoelastic solids, and is applicable to the manufacture of flexible electronics and the design of biomedical devices. The research is integrated with undergraduate education through long-term, focused projects and undergraduate summer research experiences, and with graduate education through curriculum development and graduate student research and mentoring activities.
The interaction of soft substrates with fluid interfaces is common to many biological, medical, and industrial processes; flexible electronics are manufactured using immersion lithography, ultrasonic waves are used for medical imaging of soft tissue interfaces, aerosol drug delivery for neonates suffering from respiratory distress syndrome as well as adults being treated for asthma and COPD relies upon droplet deposition on biological tissue, and forensic analysis interprets complex blood splat patterns. Describing these substrate deformations has led to the development of the field of elastocapillarity, in which elastic stresses are coupled to surface tension (capillarity). The aim of this CAREER award is to advance the field of elastocapillary fluid mechanics through carefully-selected theoretical and experimental studies of four canonical problems that focus on the dynamic coupling between the elastic and fluid fields: elastocapillary waves, droplet durotaxis, spreading on compliant substrates, and drop impact. Theoretical models will describe capillary instabilities in soft solids, Marangoni-driven flows that arise from gradients in substrate elasticity (durotaxis), and contact-line dynamics during spreading on compliant substrates. Table-top experiments on drop impact will be designed to facilitate undergraduate learning through research. Elastocapillarity is a new, interdisciplinary field that encompasses a wide range of traditional disciplines, such as fluid mechanics, solid mechanics, and mathematics. The lack of a well-developed course curriculum and a continuously evolving subject matter requires innovative strategies to educate students in this emerging interdisciplinary field, broadly categorized as "learning through research", which incorporate focused long-term Creative Inquiry projects and summer research opportunities. Delivering educational content via targeted extended research projects can serve as a template for other emerging scientific fields. Targeted mentoring through the graduate research and professional development seminar series will improve research culture and help place under-represented students in academic/scientific careers.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
