(4ab) Fabrication and Evaluation of Omniphobic Surfaces for Liquid Repellency and Reduced Ice Adhesion

Currently I am a postdoctoral associate advised by Dr. Joseph M. Mabry (Edwards Air Force Base), Professor Gareth H. McKinley (MIT Mechanical Engineering), and Professor Robert E. Cohen (MIT Chemical Engineering). Following the conclusion of my postdoctoral tenure, I hope to begin a tenure track faculty position in a Chemical Engineering or Materials Science and Engineering Department. My research program as a faculty member will focus on the fabrication of polymeric materials, including block polymers, nanocomposites, and coatings, and the evaluation of their structure-property relationships. Core experimental competencies of my laboratory will include polymer synthesis, structural characterization (e.g., small-angle X-ray scattering), surface characterization (e.g., contact angle measurements, electron microscopy), and dynamic measurements (e.g., rheology).

Our research team investigates the fundamentals of solid-liquid and solid-solid interactions and uses the principles elucidated from these studies (and those of other groups) to design and fabricate surfaces with desired wettability and adhesion characteristics. My research has largely involved omniphobic surfaces that resist wetting by all liquids and adhere poorly to other solids. In this poster I will highlight two of these specific projects:

Relationships between Water Wettability and Ice Adhesion

Reports describing superhydrophobic surfaces that resist wetting by water droplets have appeared with increasing frequency in the literature over the past twenty years. Typically this liquid repellency is imparted using a combination of surface texture and low-energy organic coatings. The fundamentals of ice adhesion have, relative to their water wettability counterparts, received relatively little attention in the literature, and it is not widely understood which attributes must be tuned to design icephobic surfaces. Here we probe the relationships between advancing/receding water contact angles and the strength of ice adhesion to more than 20 nominally smooth (Wenzel roughness < 1.01) test coatings with a broad range of wettabilities. Contact angles are measured using a commercial goniometer while the shear strengths of ice adhesion are evaluated with a home-built laboratory-scale apparatus. We find that high receding water contact angles correlate strongly with reduced ice adhesion. We believe that these results allow us to estimate the maximum reduction in ice adhesion strength that is attainable by coating smooth surfaces with known low energy coatings. Current efforts are focused on examining the adhesion of ice and other freezing/vitrifying liquids to surfaces with a variety of surface textures and liquid wettabilities.

Towards Robust Hydrophobic and Oleophobic Surfaces

Sustenance of metastable composite (solid-liquid-air) interfaces is critical to achieving the high contact angles and low contact angle hystereses that are characteristic of a strong repellency of low surface tensions liquids. Unfortunately many such surfaces described in the literature are of limited utility in applications due to poor mechanical properties, optical opacity, expensive fabrication procedures, and/or non-robust repellency against low surface tension liquids (e.g., oils). Here we describe the development of a replica molding process used to prepare mechanically robust crosslinked elastomeric substrates comprised of perfluoropolyethers or polysiloxanes that are characterized by submicron re-entrant surface texture. Some of these crosslinkable materials are available commercially, while others are prepared in our laboratory. Essential steps in this protocol include the preparation of a master mold using photolithographic techniques, filling the mold and subsequently curing the crosslinkable oligomers, and releasing the elastomeric replica from the template. Substrates with a range of reentrant texture feature sizes and spacings are prepared and the wettabilities of these surfaces are probed using a variety of high (e.g., water) and low (e.g., hexane) surface tension liquids.