The proposed research is based on an interdisciplinary effort that involves polymer surface chemistry, interface manipulation, and advanced nano-/microfabrication techniques. Through the interplay of surface roughness at the micro- and nano- scales at specific locations on a topographically structured surface, a quantitative understanding of surface properties will evolve and test the incompletely understood basic theories. Specifically, the PI plans to: 1) design new chemical routes to selectively graft polymer brushes only on the tip of the nanopatterned surface; 2) develop novel synthetic and fabrication strategies to spatially control the grafting density, (relative) chain length, composition, architecture, and location of polymer brushes on the silicon and polymer nanostructures, 3) synthesize a variety of responsive brushes with increasing complexity, to systematically investigate their structure and function in collapsed and extended states on a patterned substrate; 4) quantitatively relate molecular parameters to the driving forces for the surface wettability and transition in response to a small temperature change.
Nature offers excellent examples of hierarchical architectures with multi-faceted functions. For example, animal fur pulls the tips of the fibers together while keeping them separated closer to the skin, allowing for the sheeting of water off the fur. The geckos foot is self-cleaning, dry adhesive on the tips of the foot toes. Inspired by the unique natural designs, this proposal aims to develop novel synthetic approaches that will spatially control and switch the surface/interfacial properties in three dimensions. It will not only provide important scientific insights of how to manipulate surface wettability and adhesion, but also will impact a diverse range of technologies, including microfluidics, controlled assembly and material synthesis, cell engineering, and soft robotics. Students at all levels will be exposed to a diverse range of topics in chemistry, materials science and engineering, and nanotechnology through new training and outreach opportunities, including an annual research retreat, a new course development, and industrial internships at Bell Laboratories, Lucent Technologies.
Control of interfacial properties is of great importance for both fundamental materials research and practical applications. Nature offers excellent examples of hierarchical architectures with spatially controlled wetting and adhesion properties. For example, animal fur pulls the tips of the fibers together while keeping them separated closer to the skin, allowing for the "sheeting" of water off the fur. The gecko’s foot is self-cleaning, dry adhesive on the tips of the foot toes. Inspired by the unique natural designs, we have fabricated high aspect ratio (HAR) polymer pillar arrays and developed novel approaches to functionalize the surface of HAR pillars selectively. In turn, we study the surface properties and their dynamic tuning as a function of surface topography, chemistry and environmental change. Due to their mechanical compliance and large surface area, the HAR micropillars are susceptible to deformation by surface forces, such as adhesive and capillary forces. We have developed systematic understanding of these forces and test the incompletely understood theories, leading to the development of new methods to fabricate hierarchical HAR micropillar arrays. The new insights into the HAR polymer pillar stability and clustering allow us to develop new methods of fabrication hierarchical HAR micropillar array and to harness these forces towards controlled assembly and actuation of micropillar arrays for novel applications (e.g. ultrathin whiteness and tunable optical display). The study supported by NSF grant not only provides important scientific insights of how to manipulate surface wettability and adhesion, but also will impact a diverse range of technologies, including microfluidics, controlled assembly and material synthesis, cell engineering, and soft robotics. Our results have been presented in numerous conferences (ACS, APS, MRS and Gordon Research Conference) and invited seminars. Two invited reviews were published in Acc. Chem. Res. and Adv. Funct. Mater., respectively. Students at all levels and postdocs involved in the project have been exposed to a diverse range of topics in chemistry, materials science and engineering, and nanotechnology through new training and outreach opportunities, including REU activities, science demonstrations at K-12 level, a new course development, senior design projects, industrial internship, and new collaborations with Industry.
