Wrinkling Instability and Adhesion of a Highly Bendable Gallium Oxide Nanofilm Encapsulating a Liquid-Gallium Droplet

Abstract

The wrinkling and interfacial adhesion mechanics of a gallium-oxide nanofilm encapsulating a liquid-gallium droplet are presented. The native oxide nanofilm provides mechanical stability by preventing the flow of the liquid metal. We show how a crumpled oxide skin a few nanometers thick behaves akin to a highly bendable elastic nanofilm under ambient conditions. Upon compression, a wrinkling instability emerges at the contact interface to relieve the applied stress. As the load is further increased, radial wrinkles evolve, and, eventually, the oxide nanofilm ruptures. The observed wrinkling closely resembles the instability experienced by nanofilms under axisymmetric loading, thus providing further insights into the behaviors of elastic nanofilms. Moreover, the mechanical attributes of the oxide skin enable high surface conformation by exhibiting liquid-like behavior. We measured an adhesion energy of 0.238 ± 0.008 J m between a liquid-gallium droplet and smooth flat glass, which is close to the measurements of thin-sheet nanomaterials such as graphene on silicon dioxide.

Thermal Effects on the Crystallization Kinetics, and Interfacial Adhesion of Single‐Crystal Phase‐Change Gallium

“…After curing at room temperature for 30 min, the two parts were strongly bonded. As previously reported in, 1.75 mm diameter post was replicated using double molding approach to fabricate a holder for a hemispherical droplet cap of 1.75 mm used in the crystallization study in Figure 1b.…”

“…The load cell was mounted to a high‐precision piezo motion stage (LPS‐65 2″, Physik Instrumente GmbH & Co. KG) in the vertical z direction, with a resolution of 5 nm and maximum velocity of 10 mm s −1 . A long‐ranged motor stage (M‐605 2DD, Physik Instrumente GmbH & Co. KG) was used in y direction with 1 µm resolution and high maximum velocity up to 50 mm s −1 …”

“…The device was lowered gently on to the substrate surface at a constant speed of 200 µm s −1 , attaining a compression load of 10 mN. The supercooled Ga droplet conformed to the substrate forming circular and radial wrinkles at the interface . The wrinkling instability emerged at the interface to relieve the applied compressive stress.…”

Highly Stretchable Bilayer Lattice Structures That Elongate via In‐Plane Deformation

“…Integration of such stretchable structures into electronic devices usually relies on intricate device designs (such as patterned substrate) with prereserved spaces to accommodate the out‐of‐plane features, increasing the complexity of the fabrication process . More importantly, surfaces with these out‐of‐plane features are uneven and nonsmooth, which gives rise to high surface roughness, poor adhesion, and low optical transmittance …”

“…Integration of such stretchable structures into electronic devices usually relies on intricate device designs (such as patterned substrate) with prereserved spaces to accommodate the out-of-plane features, increasing the complexity of the fabrication process. [4] More importantly, surfaces with these out-of-plane features are uneven and nonsmooth, which gives rise to high surface roughness, [21] poor adhesion, [22] and low optical transmittance. [23] The advent of modern additive manufacturing techniques such as 3D printing offers rapid prototyping and demonstrate potent capability in printing a broad range of materials into complex structures, thereby opening new opportunities to manufacture novel engineering structures.…”