Time: Thursday & Friday, September 22nd & 23rd, 2:00 p.m.
Location: Aggarwal Lecture Hall, Room 130
Polymer Engineering Academic Center
250 South Forge Street, Akron, OH 44325-0301
Lectures Are Free And Open To The Public
A decade-long collaboration with colleague Professor Michael F. Rubner of the Department of Materials Science and Engineering at MIT has focused on novel and useful surface/thin-film phenomena that are observed in nature. We have employed a simple and elegant water-based layer-by-layer assembly technique to provide conformal multifunctional coatings on a wide variety of substrates. Proper selection of nanoparticles and macromolecules and precise control of processing conditions have enabled us to develop materials that mimic some fascinating natural phenomena: fog harvesting by desert beetles, broadband antireflection of the moth eye, and the brilliant structural colors found in hummingbird and butterfly wings. We have also brought our methodologies to the biotic/abiotic interface where we assemble payload-containing 'backpack' structures on living immune cells for possible use in in-vivo imaging, therapies and bottom-up tissue engineering.
Superhydrophobic surfaces that display water contact angles greater than 150° with low contact angle hysteresis are becoming commonplace in the materials community. Microscopic pockets of air trapped beneath the high surface tension (γlv = 72mN/m) water droplets lead to a composite solid-liquid-air interface in thermodynamic equilibrium. Previous experimental and theoretical work suggests that it should not be possible to form similar fully-equilibrated composite interfaces with drops of low surface tension liquids such as alcohols or alkanes (e.g. pentane: γlv = 16 mN/m). In this lecture I will discuss novel surfaces that possess the required combination of re-entrant topographical texture and surface chemistry to support strongly metastable composite solid-liquid-air interfaces for any liquid. Quantitative design parameters will be introduced to guide the development of these novel omniphobic surfaces. For a given feature size R, two independent design parameters [surface chemistry as revealed in the equilibrium contact angle θ, and texture spacing, embodied in the dimensionless spacing ratio D*= (R+D)/R] can be used to develop surfaces with desirably large values of apparent contact angle (θ*) and robustness of the metastable composite interface. Most revealing is the scaling of the composite interface robustness which indicates clearly why, in the consideration of self-similar arrangements of topographical surface features, 'smaller is better' for producing surfaces that resist wetting by low energy liquids. Examples that have been realized to date include lithographically fabricated features in silicon, randomly deposited fiber mats, dip-coated textiles and wire meshes.
Robert E. Cohen was born and raised in Oil City, Pennsylvania, an environment that led to an early interest in the discipline of Chemical Engineering. He studied at Cornell (BS), Caltech (MS and PhD) and Oxford University (Postdoc) prior to joining the MIT faculty in 1973. He is the founding Director of MIT's Program in Polymer Science and Technology and the architect of MIT's unique Doctoral Program in Chemical Engineering Practice. Currently he is the St. Laurent Professor of Chemical Engineering. He has directed the DuPont/MIT Alliance since its inception in 2000. His publications reflect interests in polymer structure/property relations. Based on patents produced in his laboratory, he co-founded MatTek Corporation (http://www.mattek.com) in 1985. He is a fellow of the American Institute of Chemical Engineers, the American Physical Society and the Materials Research Society. In 2010 he was elected to the National Academy of Engineering. Bob and his wife Jane live in the Jamaica Plain section of the city of Boston. They have two children: Genevieve, a kindergarten teacher in San Diego CA, and Eliot who works in information technology in Boston.