The impact and freezing of water droplets on solid surfaces is a problem not only of intense fundamental interest but also a practical one, posing severe challenges to the uninterrupted operation of equipment and machinery exposed to the environment. Over the past few years, surfaces that retard ice formation (a.k.a. icephobic surfaces) have attracted increased attention, with superhydrophobic surfaces suggested as a possible solution. Despite some limited work in this area, the impact of droplets on surfaces, which is a common mechanism of ice-formation in the environment, lacks a thorough fundamental understanding.
Preliminary work on delayed freezing of inkjet generated supercooled water microdroplets accumulating one-after-the-other on various surfaces -including superhydrophobic coatings- revealed that the effect of surface roughness in this problem might be equally as important as surface energy (i.e. wettability). The work will examine the impact and freezing of supercooled-water droplets on surfaces with controlled micro-to-nanoscale texture, prescribed wettability (ranging from hydrophobic to superhydrophobic) and self-cleaning ability. Freezing delays will be quantified by means of high spatial and temporal resolution instrumentation; the measured freezing delays will be used to evaluate the icephobic potential of each surface. The effects of wettability (contact angle), self-cleaning ability (droplet roll-off tilt angle), droplet impact parameters (diameter, velocity, incidence angle) and droplet/surface temperature difference on droplet bounce, freezing and ice/frost accumulation will be analyzed. In addition to the above passive means of delaying ice formation, localized heat input will be examined as an active method to reduce ice formation/build-up by using superhydrophobic, electrically-conducting, nanoparticle-filled, polymer-based, composite coatings developed in the PI?s laboratory. These novel coatings feature well-controlled micro/nanotexture, tunable wettability (contact angle), self-cleaning ability (contact angle hysteresis), and favorable electrical properties.
Intellectual Merit: The work is believed to be highly transformative. It addresses a fundamental problem that has not yet been investigated thoroughly, although it is of high relevance to icephobicity as it pertains to practical applications. The proposed study takes advantage of recent developments on super-repellent polymer composite coatings that feature well-controlled micro/nanotexture, tunable wettability, self-cleaning ability and electrical properties, all necessary tools for the proposed investigation. The problem involves rich phenomena in fluid physics and heat transport, non-equilibrium phase change, and super-repellent multifunctional materials.
Broader Impacts: The proposed program will enrich the science base for icephobic surface design, and if successful, has the potential to guide development of icephobic surfaces with superior properties. The research will advance discovery and fundamental understanding, while promoting teaching, training, and learning by means of a parallel education/outreach component. The PI will partner with a local minority-serving high school to expose these students and their teachers to the exciting world of nanoscience by involving them in cutting-edge research pursued in a university laboratory. Graduate and undergraduate students who will be involved in the research will serve as mentors to the high school students.
