The physical properties of thin polymer films are critical for the development of numerous technologies, ranging from alternative energy sources to ?smart? coatings. In the thin film regime, the size scale of individual molecules is commensurate with the film?s thickness; therefore, the inter-molecular and intra-molecular mechanisms that define a material property are influenced by surface properties. Recent efforts in the polymer scientific community have focused on the impact of confinement on properties such as the glass transition temperature and elastic modulus, but relatively little is known on the impact of geometric confinement on properties related to non-linear deformation. The proposed research will use novel methods to fold and crumple thin polymer films, while quantifying the energy focusing and strain localizing processes involved in these non-linear mechanics. The specific research plan includes three primary efforts: 1) the folding and crumpling of homogenous, thin polymer films; 2) the folding and crumpling of nanostructured polymer films; and 3) the characterization of crumpled surface properties. These efforts will be distinguished from recent research on crumpling by studying films with molecular-scale thickness and combining crumpling mechanics with the properties of pre-patterned substrates to control long-range order in crumpled sheet morphologies. Additionally, the energy focusing processes of folding will be used to assemble nanoscale components, including tailored inorganic nanoparticles. The fundamental knowledge of folding and crumpling gained through this research not only will provide insight into materials properties at molecular length scales, but also will lead to advanced concepts for controlling the morphology and structure of thin polymer films for advanced applications.
NON-TECHNICAL SUMMARY The proposed research is focused on developing novel methods to fold and crumple ultra-thin polymer films, which are only a few molecules thick. The results of this research will have broad impact, from providing new knowledge of how molecular assemblies respond to mechanical stress at the nanometer length scale to developing robust strategies for patterning surfaces in future applications, such as alternative energy source technologies. In addition to the research funded by this program, the research team will introduce an innovative program to involve high school students from diverse backgrounds in the creative aspects of scientific research. This program, the Materials Challenges Competition (MCC), will build upon existing programs that are common in undergraduate engineering disciplines (e.g. the solar powered vehicle competition) to initiate a materials competition among high school teams from the Western Massachusetts region. The implementation of this program will provide opportunities for students and the general public in Western Massachusetts to realize the importance of materials research in answering current technological challenges.
Although wrinkles and folds are commonly observed in both natural and synthetic materials, we know relatively little about how they form. What we do know is that Nature uses them often in the processes of growth as well as function. Therefore, we hypothesize that further knowledge will lead to significant technological gains. In particular, fundamental knowledge of wrinkles and folds, especially ones that are more than 50 times smaller than a human hair, will allow us to both exploit and prevent their formation for a wide range of technologies, including lightweight, flexible electronics and responsive surfaces for tissue engineering. In this project, we studied how wrinkles grow and when they change into a fold. From our research on this topic, we have been able to develop ways to distinguish between folds and wrinkles, to understand how materials properties control the formation of folds, to demonstrate that molecular-scale changes in thickness can cause a film to fold before it wrinkles, and to develop ways to suppress the formation of folds and allow for wrinkles to grow very tall. These advances are significant in the development of the next generation of materials that follow Nature in becoming both increasingly responsive and sustainable and form the intellectual merit of this proposal. Beyond these research advances, the PI and graduate student researchers broaden the impact of their research and knowledge gained by disseminating these results in several written publications, in presentations given around the world, and in the support of a high school level research program that the PI initiated. This high school level research program invites teams of 3-4 high school students to conduct year-long research projects mentored by the PI’s research group. The teams attend monthly group meetings at the University of Massachusetts Amherst and attend a seminar given by a visiting scientist in the field of polymer science. This program has had a large impact on influencing a very high percentage of the participants to continue to pursue undergraduate degrees in science and engineering fields.
