1. Nanoscale Assembly of Complex Structures via Harnessing of an Elastic Instability Shu Yang (University of Pennsylvania) DMR 0548070 We exploited elastic instability triggered by the swelling of an elastic polymer membrane from poly(dimethylsiloxane) (PDMS) with a regular pattern of perforations. When exposed to an organic solvent, the pores elliptically deformed and elastic interactions between them generated a long-range orientational order of their axes and transformed the circular hole array into a "diamond plate" pattern with more then ten times size reduction. Theoretical modeling allows us to understand these effects quantitatively and rational design new motifs by varying the specific characteristics of the PDMS membranes. By adding nanoparticles to the solvent, we created a “nano-ink” which various nanoparticle patterns can be printed onto other substrates. The structural anisotropy of the resulting films may be useful for generation of anisotropic magnetic, photonic, phononic and surface plasmonic properties. Convective assembly of Fe 3 O 4 nanoparticles in toluene on the PDMS membrane with a square lattice of holes (D =1 μm, P =2 μm, and H = 9 μm). a-c, Schematic illustration of the self-assembly process. SEM of the original (d) and deformed (e) PDMS membranes. f, SEM of the nanoparticle pattern lifted off from the deformed PDMS membrane. Inset: higher magnification of an individual elliptical nanoparticle deposit, 78 nm wide by 2.3 mm long. References: Zhang, Y. Matsumoto, E. A., Peter, A., Lin, P., Kamien, R. D., and Yang, S., Nano Lett., 2008, 8, 1192. Ford, J. and Yang, S., Chem. Mater., 2007, 19, 5570. Lin, P. and Yang, S., Appl. Phys. Lett. 2007, 90, 241903.

2. Nanoscale Assembly of Complex Structures via Harnessing of an Elastic Instability Shu Yang (University of Pennsylvania) DMR 0548070 Education at Graduate and Undergraduate Levels: Two Ph.D. students and one international exchange undergraduate student from ETH Zürich, Switzerland were involved in nanofabrication, and grafting of polymer brushes on patterned surface. The PI delivered a seminar to the Undergraduate Materials Engineering Research Society at Penn, engaging their interests in soft materials The PI served as Faculty panelist at the Penn Graduate Women in Science (PGWISE) at Penn Engineering school to encourage women graduate students and postdocs pursuing faculty positions Outreach for pre-K-12 Education: One high school student did independent study on polymer directed synthesis of inorganic nanoparticles in the PI’s lab. Her work received honorable mention at the Delaware Valley Science Fair. The PI and her students demonstrated color changing of energy beads under the ultraviolet light at the Penn Children Center. The beads appeared white indoor, and changed instantly to a rainbow of color outside in the sun light. The students were taught how to protect themselves from the sun’s damage using sunscreen, sunglasses and medicine bottles. After the demonstration, the students were given sun print papers so that they could bring home to print various objects by sun light.