Controlled Surfaces through Self-assembly and Patterning

Cornell University, Ithaca NY

Investigators

Abstract

The proposed studies are aimed at developing a fundamental understanding of the way in which the self-assembly of fluoropolymers can be harnessed to form periodic nm-length scale polymer structures, controlled by a variety of thermal and optical methods. In the proposed research we will synthesize and study the surface and bulk properties of semifluorinated (SF) LC-coil block copolymers in which the SF group I a monodendron. The surface will be probed with a variety of techniques, but in particular scanning force microscopy (SFM) and near edge X-ray absorption fine structure (NEXAFS) measurements will be used to examine surface topography and composition. A particular focus of the proposed research derives from our recent observation that polymers with SF monodendron side groups are capable of forming not only low energy surfaces, but may spontaneously organize into arrays with periodic organization on the 20 nm length scale that can span regions approaching millimeter dimensions. The SF monodendrons will be produced with selected alkyl to fluorinated segment ratios, arm number and end group in order to test the model predicting surface curvature. A photoactive azobenzene group will also be used in mondendron synthesis to both alter the packing structure and take advantage of its photo-optical properties. By combining the known trans-cis isomerization behavior of the azobenzene chromophore, we also plan to use photoprocessing to direct long-range organization of these surface structures. In the production of small-scale patterns needed for nanotechnology, there is no convenient process for building structures or modifying surfaces in the 10 to 50 nm length regimes. Structures that appear homogeneous over micron length scales can be extremely heterogeneous at these smaller dimensions, thus making issues such as the control of surface energy and composition extremely important. Fluoropolymers are ideal materials for exploring many of these factors in surface and interface design. The low surface energy of fluoropolymers has attracted interest in such diverse surface control applications as the prevention of protein binding to biomedical surfaces, as environmentally friendly fouling resistant marine coatings and for self-cleaning architectural materials. The unusual transparency of fluoropolymers at short optical wavelengths has lead to their study as next generation photoresists for microelectronics manufacture while their low dielectric constant and refractive index has made their use in microelectronics and communications widespread. This program will harness self-pattern surfaces. There exist immense possibilities for applications in biotechnology, information science and advanced materials if patterning at these length scales can be harnessed while simultaneously controlling surface composition.