Strain-stiffening
is one of the characteristic properties of biological
hydrogels and extracellular matrices, where the stiffness increases
upon increased deformation. Whereas strain-stiffening is ubiquitous
in protein-based materials, it has been less observed for polysaccharide
and synthetic polymer gels. Here we show that agarose, that is, a
common linear polysaccharide, forms helical fibrillar bundles upon
cooling from aqueous solution. The hydrogels with these semiflexible
fibrils show pronounced strain-stiffening. However, to reveal strain-stiffening,
suppressing wall slippage turned as untrivial. Upon exploring different
sample preparation techniques and rheological architectures, the cross-hatched
parallel plate geometries and in situ gelation in the rheometer successfully
prevented the slippage and resolved the strain-stiffening behavior.
Combining with microscopy, we conclude that strain-stiffening is due
to the semiflexible nature of the agarose fibrils and their geometrical
connectivity, which is below the central-force isostatic critical
connectivity. The biocompatibility and the observed strain-stiffening
suggest the potential of agarose hydrogels in biomedical applications.
Biological high-performance composites inspire to create new tough, strong, and stiff structural materials. We show a brittle-to-ductile transition in a self-assembled nacre-inspired poly(vinyl alcohol)/nanoclay composite based on a hydration-induced glass-to-rubber transition in the 2D-nanoconfined poly(vinyl alcohol) layers. The findings open routes to design dissipative toughening mechanisms to combine stiffness and strength in nanocomposites.
Even though nanocomposites have provided a plethora of routes to increase stiffness and strength, achieving increased toughness with suppressed catastrophic crack growth has remained more challenging. Inspired by the concepts of mechanically excellent natural nanomaterials, one-component nanocomposites were fabricated involving reinforcing colloidal nanorod cores with polymeric grafts containing supramolecular binding units. The concept is based on mechanically strong native cellulose nanocrystals (CNC) grafted with glassy polymethacrylate polymers, with side chains that contain 2-ureido-4[1H]-pyrimidone (UPy) pendant groups. The interdigitation of the grafts and the ensuing UPy hydrogen bonds bind the nanocomposite network together. Under stress, UPy groups act as sacrificial bonds: simultaneously providing adhesion between the CNCs while allowing them to first orient and then gradually slide past each other, thus dissipating fracture energy. We propose that this architecture involving supramolecular binding units within side chains of polymer grafts attached to colloidal reinforcements opens generic approaches for tough nanocomposites.
Even though nanocomposites have provided a plethora of routes to increase stiffness and strength, achieving increased toughness with suppressed catastrophic crack growth has remained more challenging. Inspired by the concepts of mechanically excellent natural nanomaterials, one‐component nanocomposites were fabricated involving reinforcing colloidal nanorod cores with polymeric grafts containing supramolecular binding units. The concept is based on mechanically strong native cellulose nanocrystals (CNC) grafted with glassy polymethacrylate polymers, with side chains that contain 2‐ureido‐4[1H]‐pyrimidone (UPy) pendant groups. The interdigitation of the grafts and the ensuing UPy hydrogen bonds bind the nanocomposite network together. Under stress, UPy groups act as sacrificial bonds: simultaneously providing adhesion between the CNCs while allowing them to first orient and then gradually slide past each other, thus dissipating fracture energy. We propose that this architecture involving supramolecular binding units within side chains of polymer grafts attached to colloidal reinforcements opens generic approaches for tough nanocomposites.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.