Bioinspired Superhydrophobic Papillae with Tunable Adhesive Force and Ultralarge Liquid Capacity for Microdroplet Manipulation

Abstract

Template‐free, highly efficient, and large‐area construction of complex multiscale architectures is still a great challenge for microfabrications. Inspired by the hierarchical micropapillae on the superhydrophobic surface of natural rose petals, here, a facile 3D shrinking method is reported to build a graphene oxide (GO) papillae array. Circular GO speckles with a gradient of thickness are deposited on an inflated latex balloon through the water‐evaporation‐driven assembly of GO nanosheets, which then shrink into hierarchical papillae under compressive stresses upon deflation. The fluoroalkylsilane modified GO papillae array exhibits a combined performance of strong superhydrophobicity (CA > 170°), tunable adhesive force (39.2–129.4 µN), and ultralarge liquid capacity (25 µL). The wetting states (Wenzel, Cassie‐I, and Cassie‐Baxter), the adhesive forces, and the liquid capacities all can be tuned by varying the buckling topography (microwrinkle or microfold), the papillae number (3, 4, 6, or 7), and the array arrangement (triangle, square, or hexagon). For one single papillae, the highest adhesive force and the highest liquid capacity incresed to a record breaking value of 26.5 µN and 4.2 µL, respectively, which are promising for programmable manipulations of microdroplets and relevant for multistep microreactions.

Bioinspired Multiscale Wrinkling Patterns on Curved Substrates: An Overview

“…More and more building blocks such as metal coatings, low-dimensional materials, and semiconductors were used to fabricate functional wrinkled structures on curved substrates, and meanwhile a number of novel topographies such as wrinkled architectures, highly compressed self-contact creases, highly convoluted interlocked structures, largearea crack-free crumpled films, and wrinkled hollow structures have been achieved by controlling parameters like the core-shell modulus ratio, substrates curvature, shell thickness, and deformation models. These wrinkled morphologies with special properties remarkably extend the applications of structured curved surfaces to superelastic electronics, bionic actuators, controllable adhesion, chemical protection, artificial vascular, and inflatable devices [53][54][55][56][57][58][59][60][61][62][63][64].…”

“…Therefore, surface wrinkling of thin stiff shells on hollow soft substrates will be the center of this section. Compared with solid core-shell systems, the expansion and contraction of hollow soft spheres and cylindrical tubes composed of elastic walls can be induced by inflation and deflation, and the contractioninduced compressive stress in the shells can be regulated by varying the pressure difference [54,55,61,157,199]. For hollow core-shell systems with thick walls (≥ 10 mm), directly pumping the air from the cavity is an efficient way to generate homogeneous compression in the shell, and sufficiently large compressive stress is able to trigger surface instability.…”

“…White precipitate White precipitate disappears Though the above-mentioned 1D and 2D wrinkling patterns on planar substrates have presented novel wetting properties, the fabrication of textured 3D architectures on curved substrates is critical for applications such as super-slippery surface [225,226], microdroplet manipulation [54], and water harvest [227]. Hierarchical 3D architectures consisting of tunable microstructures enable powerful control over the adhesion to liquids [54]. For example, periodic hierarchical papillae enable the rose petal high adhesion to water under superhydrophobic state (Petal Effect) [18].…”

Bioinspired Design of Graphene‐Based Materials

“…To achieve this, an effective strategy is to use graphene and GO structures to create a rough surface. For instance, both flower-like graphene nanosheets on silicone nanocone arrays [51] and wrinkled GO papillae arrays on latex [52] have been demonstrated for lossless droplet manipulation (for example, on tweezers and gloves: Figure 2g) thanks to their high roughness and adhesive nanoedges.…”

Effect of Tier Surface Structure on Non‐wetting Materials and Robust Superamphiphobic Surface

“…Materials with non‐wettability including superhydrophobicity and superamphiphobicity have a large application in various areas, such as self‐cleaning, chemical shielding, chemical reactions, oil‐water separation, heat transfer, liquid transport, self‐assembly, anti‐freezing and icephobicity . The excellent water repellent surface inspired by lotus leaf can be achieved by the laser processing technology, electrodeposition, sol−gel process and hydrothermal method with low surface energy chemical modifications.…”