Designing Hierarchical Three-dimensional Surfaces by Controlling Strain

Mechanical instabilities such as wrinkles, buckles, and folds exist in nature and can span orders of magnitude in length scales, from kilometers to nanometers. While most work has aimed to eliminate such disorders, this proposal seeks to manipulate features into hierarchical nanostructure architectures using a bottom-up self-assembly approach. Moreover, efforts devoted to structuring materials have focused primarily on making periodic structures at ever smaller length scales with the ultimate goal of massively scaling their production. However, ordered patterns are increasingly unnecessary for a growing range of applications, from anti-biofouling coatings to omniphobic surfaces. The ability to manipulate strain in new materials systems over multiple length scales can open prospects for hierarchical substrates and unconventional applications. In our proposed work, we aim to determine the processing conditions necessary to achieve new classes of hierarchical structures with a precision < 10 nm by tuning the plasma gases (single and in combinations) used to form the top skin layer, by testing and discovering new functional skin layers, by modeling and visualizing the strain-relief process, and by manipulating global and local compressive strain in 1D and 2D. We anticipate that these unconventional 3D architectures—that can also be formed in a diverse range of multi-functional materials—will enable new solutions to key applications and facilitate new prospects for high-performance nanoscale material assemblies. Also, we propose to manipulate local and long-range nanoscale disorder within a single substrate and to determine mechanisms responsible for the formation of hierarchical, multi-scale structures. Specifically, we will chemically treat thermoplastic substrates with plasma gases and relieve strain to spontaneously produce hierarchical nanotextures over large areas. We anticipate that processes involved as well as products—controlled hierarchical nanostructures—will be significant for basic and technological research. Major processing outcomes include: (1) design principles of memory-based processing to produce hierarchical nanotextured materials; (2) mechanism by which “soft” skin layers on viscoelastic materials can result in high-aspect ratio surface patterns with controlled hierarchy; and (3) conditions to realize hierarchical structures with adjacent orthogonal chemical patterns that can be modulated by external triggers. Major product outcomes include: (1) large-area 3D nanotextured surfaces with exquisitely controlled ordered and disordered regions; (2) hybrid, hierarchical nanotextured structures with unique chemical, optical, and physical properties; and (3) multi-generational architectures that can be realized in a materials-general framework.