Tunable hierarchical nano-micro-structures by harnessing localized instabilities
Changyong Cao (Duke University), Xuanhe Zhao (Duke University), Qinghua Qin (Australian National University)
Soft Materials and Structures
Mon 2:40 - 4:00
Barus-Holley 158
Surface patterns with hierarchical structures have been intensively studied in the past decade due to their intriguing phenomena and promising applications resulted from the hierarchical features across multiple length scales. In this paper, we fabricate tunable three-level hierarchical nano-micro-structures by harnessing localized instabilities. The mechanism and formation process of such hierarchical patterns are investigated both theoretically and experimentally. Localized ridges and crumpling patterns formed under highly prestretched substrate (>200%) are studied in detail. The effects of film thickness, materials properties of film and substrate, and prestrain levels on the localized ridges of nanofilms attached on compliant substrates are investigated and further verified by numerical simulations. The morphology evolutions of prestretched bilayer system, under uniaxial relaxation and sequential/simultaneous biaxial relaxation, are also investigated. Buckle induced delamination is found between the nanofilm and compliant substrates. Experimental results show that the obtained hierarchical structures are high-surface-area, reversible and easily tunable by controlling prestrain levels mechanically and controlling the thickness of nanofilm. Such desired properties greatly expand its potential applications such as superhydrophobic coatings and cell patterning.