Rapid formation of uniformly layered materials by coupling reaction–diffusion processes with mechanical responsiveness

Abstract

Straightforward manufacturing pathways toward large-scale, uniformly layered composites may enable the next generation of materials with advanced optical, thermal, and mechanical properties. Reaction–diffusion systems are attractive candidates to this aim, but while layered composites theoretically could spontaneously arise from reaction–diffusion, in practice randomly oriented patches separated by defects form, yielding nonuniformly patterned materials. A propagating reaction front can prevent such nonuniform patterning, as is the case for Liesegang processes, in which diffusion drives a reaction front to produce layered precipitation patterns. However, while diffusion is crucial to control patterning, it slows down transport of reactants to the front and results in a steady increase of the band spacing as the front advances. Here, we circumvent these diffusive limitations by embedding the Liesegang process in mechanically responsive hydrogels. The coupling between a moving reaction front and hydrogel contraction induces the formation of a self-regulated transport channel that ballistically carries reactants toward the area where patterning occurs. This ensures rapid and uniform patterning. Specifically, large-scale ( > 5-cm) uniform banding patterns are produced with tunable band distance ( d = 60 to 160 µm) of silver dichromate crystals inside responsive gelatin–alginate hydrogels. The generality and applicability of our mechanoreaction–diffusion strategy are demonstrated by forming patterns of precipitates in significantly smaller microscopic banding patterns ( d = 10 to 30 µm) that act as self-organized diffraction gratings. By circumventing the inherent limitations of diffusion, our strategy unlocks the potential of reaction–diffusion processes for the manufacturing of uniformly layered materials.

Reaction–Diffusion Coupling Facilitates the Sequential Precipitation of Metal Ions from Battery Feedstock Solutions

“…The latter segment was characterized by two distinct regimes with oscillatory features of 0.02 and 0.4 cm in wavelengths, respectively (Figure S2), as evident by the line profiles (Figure E). These oscillations did not follow the spacing law for conventional Liesegang patterns but were rather similar to the equidistant precipitate bands found in a mechanically responsive gel system . The experiment with the mixed-salt solution produced a complex precipitate pattern that extended 6.3 cm, significantly farther than the single-salt experiments due to the larger total metal ion concentration (Figure F).…”

Modelling network formation in folded protein hydrogels by cluster aggregation kinetics

“…Such an approach, to explore reaction-and diffusion-limited cluster aggregation, has proved successful in other biological systems, including modelling bacteria to understand their morphology and behaviour and DNA-lipid complexes in gene delivery. This study on folded protein hydrogels sets the stage for future studies to exploit cluster aggregation to create more complex network architectures, including patterned systems [85][86][87] , which might be explored in applications.…”

Patterning Complex Line Motifs in Thin Films Using Immersion‐Controlled Reaction‐Diffusion

“…Numerical Model: The model was partially based on previous work, [37] with two significant changes: the model shown here was 2D instead of 1D and incorporates a moving contact line. The reaction-diffusion system modeled here was the periodic precipitation of silver dichromate in a gelatin hydrogel as a result of silver nitrate diffusing into the gel matrix and reacting with potassium dichromate to produce an insoluble salt (Equation 1 (3)…”

“…[36] To overcome such drawbacks, we recently have shown highly uniform banding patterns in bulk gels by employing a mechanochemical feedback loop that transports reagents non-diffusively through opening channels. [37] However, because mechanical opening of a transport channel is integral to the approach, this strategy only works for 3D materials, highlighting that entirely new principles need to be developed to achieve uniform largescale patterning of complex motifs in thin films. Overview of the R-DIP process.…”