Anisotropic hydrogel based on bilayers: color, strength, toughness, and fatigue resistance

Abstract

In this highlight, we introduce a novel anisotropic hydrogel with a perfect 1D photonic crystal structure based on the uni-axial alignment of lamellar bilayers. The gel was synthesized in a one-pot polymerization from a precursor solution containing polymerizable surfactant (dodecyl glyceryl itaconate: DGI), acrylamide, and cross-linker. By applying shear flow to the precursor solution, lamellar bilayers of self-assembled DGI were aligned in one direction parallel to the substrate surface. The polymerized lamellar bilayers were stacked periodically and entrapped in the polyacrylamide matrix to give a hydrogel with 1D photonic crystal structure. This hydrogel, containing 94-95 wt% water and 1.0-1.5 wt% bilayer molecules, shows perfect one-dimensional swelling, strong anisotropy in the elastic modulus, and magnificent structural color by multilayer interference according to Bragg's law of diffraction.Owing to the softness and large deformability, the color of the gel can be reversibly tuned by both compressive and tensile mechanical stimuli over the entire wavelength range of visible color. The single-domain lamellar bilayer not only diffract light, but also serves as reversible sacrificial bonds that dissociates upon deformation, exhibiting large hysteresis as an energy dissipation mechanism, which gives the gel high tensile strength and fatigue resistance. Both the molecular dissociation and lipid-like mobile nature of DGI molecules in the bilayers dramatically enhance the resistance against crack propagation by the formation of extra-ordinary blunting, which gives the gel an extraordinarily high toughness.3

Lamellar–micelle transition in a hydrogel induced by polyethylene glycol grafting

“…As have been revealed in our previous paper, the stratified lamellar bilayers not only diffract light to exhibit magnificent structural color but also serve as reversible sacrificial bonds to dissipate energy and toughen the hydrogel dramatically [20,21]. The structure transition of the bilayers from continuous phase to discontinuous phase should also substantially influence the mechanical strength of the hydrogel.…”

“…Recently, we have successfully developed stable lamellar bilayer structure of macroscopic giant size in a soft, dilute polymer network of hydrogel system [19][20][21]. The sheet-like lamellar structure, of thousands bilayer membranes stacking in single domain, is formed from self-assembly of a lipid-like polymeric surfactant, poly(dodecyl glyceryl itaconate) (PDGI).…”

Bottom-up and top-down manipulations for multi-order photonic crystallinity in a graphene-oxide colloid

“…4 However, color reflection throughout the entire visible spectrum was recently obtained from photonic crystals in a well-prepared nematic GO dispersion. 5 Structural coloration has also been demonstrated in other colloidal systems such as in the swollen lamellar mesophase of plate-like particles with or without a supporting polymer network or surfactants, [6][7][8] the columnar phase of regularly sized plate-like particles [8][9][10] and the steric packing assembly of silica or polymer spheres or cubes. [11][12][13] Nonetheless, color reflection in the GO dispersion is quite unexpected, considering that GO particles are highly polydisperse, irregularly shaped, curved in solution, 14,15 and two orders of magnitude thinner than the photonic band-gap.…”

Bioinspired Nanocomposite Hydrogels with Highly Ordered Structures

“…[30][31][32] The other feature is the ordered hierarchical structures that range in scale from the molecular to the macroscopic. [13,[33][34][35] Such unique hierarchical structures endow living organisms with anisotropic mechanical toughness and functionality, thereby adapting them for complicated use in external environments.…”