Nanofabrication techniques typically rely on additive or subtractive methods in order to achieve nanostructured substrates. Additive manufacturing involves the building up of a three-dimensional object by direct-writing or printing of a digitally designed object. Subtractive manufacturing uses etching and other processes to remove solid material from a bulk sample. However, extension of these approaches to the nanoscale and in a high-throughput manner is challenging. This award supports an entirely different strategy for surface texturing at the nanoscale?monolithic nanofabrication?by first creating a thin layer on a thermo-polymer with plasma gases and then relieving the strain in the system. Since surface nanotextures form spontaneously across the entire surface upon compression, the technique is massively parallel. Key advantages of monolithic nanofabrication include simplicity and scalability especially since the polymer substrates (without nanopatterns) are already in use on shrink-wrapped buses. Large-area, hierarchical nanotextures in functional materials are important in a range of applications, including self-cleaning windows, water collection, photovoltaics, bio-fouling, and reduced friction and drag. This research is multi-disciplinary and involves the disciplines of manufacturing, mechanics, chemistry, and materials science. Products of monolithic nanofabrication will be integrated in nanopatterning modules for high school students within the NSF Materials World Network framework, in hands-on activities for public outreach events on nanomanufacturing, and in freshmen chemistry labs on polymers and surface hydrophobicity.
The development of monolithic nanofabrication will open new approaches to control disorder at the nanoscale and the microscale. Most large-area nanopatterning methods aim to produce periodic structures at ever smaller length scales. Well-ordered patterns are often not necessary, however, for an increasing range of applications. This work aims to manipulate local and long-range nanoscale disorder simultaneously on a single substrate thus making hierarchical nanotextures and hence enable unconventional applications. The major nanomanufacturing processing outcomes of this project are: (1) determining parameters to observe nano-fold and self-similar wrinkle formation; and (2) demonstrating how an all-chemical treatment of thermoplastics can generate a tunable mix of ordered and disordered nanopatterns. The major product outcomes include: (1) substrates with in-plane nanotextures with three or more wrinkle wavelengths; (2) nanotextured substrates with control over ordered and disordered regions; and (3) hierarchical nanotextures in functional materials. This platform is well-suited to extract the fundamental principles of how plasma gases react with soft materials to produce local nano-wrinkling. The scalability of the spontaneous texturing process and commercial availability of thermoplastics make monolithic nanofabrication a practical nanomanufacturing strategy.