Quantized wrinkles and fracture of stiff membranes on soft films

Abstract

Stiff membranes on soft substrates may wrinkle and fold during compression1-11, but the strong post-buckling nonlinearity3,12 and the propensity of overall bending of these systems4,9,11 under large compression make the intriguing morphological evolution ill-controlled and less understood. Here, we present a simple peeling strategy that controllably makes stiff nanomembranes on soft microfilms wrinkled, then folded with a preset period, and ultimately fractured into regular ribbons. The fold and fracture periods exhibit a quantized, stepped dependence on the microfilm thickness, with the period doubled per step. The controlled wrinkle-to-fold-to-fractures transitions can be quantified by both computations and a scaling law, showing generality to different forms of compressive loading. This quantized wrinkle evolution deepens our understanding of complex behaviors of such natural and artificial systems as cerebral cortexes, skins, and coating materials, and opens a way to advanced manufacturing by fracturing large-area nanomembranes into uniformly shaped microflakes.

Buckling‐Pattern‐Based Characterization of Stiff Membrane on Soft Film

“…Here, the values of t m and λ 0 were determined from experimental measurements; the E s and μ s of the PDMS layer are set to 1.8 MPa and 0.48, respectively. [26] Despite some fluctuations, we can see that the calculated moduli are independent of t m , with an average value of 34.6 GPa. This result is less than that of the SiO 2 film (75 GPa) but much larger than the modulus of the PDMS film (1.8 MPa).…”

“…However, in a bilayer film with a constant stiff layer thickness (t m ), the intrinsic periodic length λ 0 of the wrinkling instability threshold remains as constant. This is because λ 0 is proportional to the thickness of the stiff membrane t m and independent of the thickness of the soft film t s , if the thickness contrast of the soft film to the stiff membrane is sufficiently large, expressed as follows [25,26]…”

Periodic fracture behaviour of nanomembranes

“…2b) with the increase of the local curvature of the bending region. 31 Membrane fracture occurs completely at the crease bottom as the local curvature further increases (iii, Fig. 2b).…”

Buckling Behavior of Few-Layer Graphene on Soft Substrate

“…The surface perimeter of the wrinkle is equal to the intrinsic periodic length, λ 0 (µm), of the wrinkling instability threshold in the stiff and soft bilayer system. If the thickness contrast of the soft film to the stiff membrane is sufficiently large, λ 0 is proportional to the thickness of the stiff membrane, t m , and independent of the thickness of the soft film, t s , expressed as follows [22,23]…”