Exploiting Supramolecular Interactions from Polymeric Colloids for Strong Anisotropic Adhesion between Solid Surfaces

Abstract

Adhesion occurs by covalent bonding, as in reactive structural adhesives, or through noncovalent interactions, which are nearly ubiquitous in nature. A classic example of the latter is gecko feet, where hierarchical features enhance friction across the contact area. Biomimicry of such structured adhesion is regularly achieved by top‐down lithography, which allows for direction‐dependent detachment. However, bottom‐up approaches remain elusive given the scarcity of building blocks that yield strong, cohesive, self‐assembly across multiple length scales. Herein, an exception is introduced, namely, aqueous dispersions of cellulose nanocrystals (CNCs) that form superstructured, adherent layers between solid surfaces upon confined evaporation‐induced self‐assembly (C‐EISA). The inherently strong CNCs (EA > 140 GPa) align into rigid, nematically ordered lamellae across multiple length scales as a result of the stresses associated with confined evaporation. This long‐range order produces remarkable anisotropic adhesive strength when comparing in‐plane (≈7 MPa) and out‐of‐plane (≤0.08 MPa) directions. These adhesive attributes, resulting from self‐assembly, substantially outperform previous biomimetic adhesives obtained by top‐down microfabrication (dry adhesives, friction driven), and represent a unique fluid (aqueous)‐based system with significant anisotropy of adhesion. By using C‐EISA, new emergent properties will be closely tied with the nature of colloids and their hierarchical assemblies.

Nanocellulose: Recent Fundamental Advances and Emerging Biological and Biomimicking Applications

“…Through this process, CNCs become aligned, thus providing anisotropic adhesion, offering strong gluing of a wealth of materials (Figure 10b). [ 273 ] Finally, CNFs also afford gluing, as manifested upon gluing several types of particles within a strong network (Figure 10c,d). [ 274 ] The above literature examples were discussed mainly in the context of gel‐like glues.…”

“…Reproduced with permission. [ 273 ] Copyright 2020, Wiley‐VCH. c) CNF allows high cohesion between particles upon their gluing.…”

Plant Nanomaterials and Inspiration from Nature: Water Interactions and Hierarchically Structured Hydrogels

“…[ 203 ] In another report, capillary forces as obtained under confinement between two substrates, were shown to induce alignments in gelled dispersions undergoing evaporation. [ 204 ] The different processes reported to align nanocelluloses hints at the necessity of adapting processes, for future large‐scale operations, to the specific building blocks (e.g., nanocrystals or nanofibrils) in order to tether the opto‐mechanical properties of the obtained materials.…”

Chitin–amyloid synergism and their use as sustainable structural adhesives

“…S3 †). The more diluted suspension failed at an average ultimate load of 236 AE 44 N, while the more concentrated one failed at 496 AE 75 N. Similarly to the observations made for cellulose nanocrystals, 23 the relationship between areal density and strength was not linear. Furthermore, the impacts of solution volume and concentration are expected to affect the areal density and the time before gelation happens, provided homogeneous wetting occurs within the curing bond.…”

“…289 AE 67 N, or 1.45 AE 0.4 MPa. Compared to CNCs previously tested using a similar setup, ChNCs reached roughly equivalent ultimate loads, as 1.1 mg of CNCs at 0.41 mg cm À2 failed at 269 AE 99 N. 23 A more detailed comparison with recent biocolloidal adhesive performance is herein presented in Section 3.4.…”