ISS: Unmasking contact-line mobility for Inertial Spreading using Drop Vibration and Coalescence

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PI: Steen, PaulProposal Number: 1637960The proposed research is focused on the study of the behavior of drops pinned on a surface that vibrates. The proposal is about developing a theory to predict the drop oscillation modes and the mobilization of the drop, while conducting very careful experiments to verify the theoretical findings at microgravity conditions. The advantage of conducting experiments at the International Space Station (ISS) is to focus on cases that are affected by gravity. Results from this work can have applications on Earth in medical, manufacturing, industrial and agricultural processes. For example, one of these processes is immersion lithography - an important technique that has allowed for down-scaling in semiconductor chip manufacturing processes. Results for the proposed work could improve the process of inertial spreading, a fundamental component in immersion lithography, and reduce defects found on semiconductor manufacturing by 10% over current standards. This can potentially lead to cost savings on the order of 10% in the semiconductor industry, which is already worth several hundred billion dollars annually.Features of contact line motions that are small-scale and fast on Earth become larger and slower on the ISS, making them accessible to optical imaging there. ISS experiments are proposed to study inertial spreading. Inertial spreading is vitally important to manufacturing, coating and forming operations on Earth but challenging to study and has received less attention than viscous spreading. The experiments proposed will enable a contact line mobility parameter to be estimated. Two setups are envisioned. The first will periodically force the contact line motion of a substrate-attached drop using a mechanical shaker that drives plane normal oscillations. Using an electrowetting-based trigger, the second setup will induce a transient droplet-droplet coalescence event with consequent large sweeping by contact lines. Mobility is a material-like phenomenological parameter that captures out-of-equilibrium dynamical responses of a moving contact line. Once measured, the idea is that mobility can be used in predictions of inertial spreading in other situations. Shaker and sweeping experiments represent forced and transient contact line motions, respectively, and will demonstrate the utility of the mobility parameter. Predictions for mobile contact lines have received limited testing because contact line speeds are fast with small scale features of importance. The ISS will unmask these features and enable testing of a high-level theory of mobility of inertially-spreading contact lines. To the extent that the theory has rather striking parallels to the harmonic oscillator, to the Schroedinger equation and to the periodic table, educational impact to a broad group of students and public will accrue. Moreover, experiments can be phrased as a quest for "motion elements" using the metaphor with the periodic table of the chemical elements. The proposed education plan will teach graduate women to be competent technical leaders through the development of an outreach module that integrates the themes of the research conducted here to high school students. The long-term impact is to broaden the participation of women in STEM by developing their professional and mentoring skills, and empowering more women to pursue advanced career goals as postgraduates. A secondary impact is to continue to encourage young girls to pursue science and math in high school so that they are well-prepared and motivated to choose scientific majors in college.