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Dynamic covalent cross-links impart hydrogels with viscoelastic and self-healing properties, motivating applications as biomimetic cell scaffolds and injectable materials. The long bond lifetime results in complex rheological behavior including shear thickening. We hypothesized that this behavior applies broadly across dynamic covalent hydrogels and can be engineered through reaction rate constants. Thus, we synthesized multiarm poly(ethylene glycol) (PEG) hydrogels with conjugate addition, boronate ester, or terpyridine-zinc cross-links, which tune bond dissociation kinetics and hydrogel relaxation times over four orders of magnitude. All formulations exhibited shear thickening, with the onset dictated by the relaxation time. Although multiple mechanisms may underlie this behavior, chain stretching is hypothesized to contribute to shear thickening, as the cross-linking concentration remained constant under shear and networks with more defects correlated with increased shear thickening. These molecular and structural drivers of shear thickening apply across dilute dynamic covalent tetra-PEG hydrogels, clarifying their suitability for applications under shear. 

Controlling the structure and function of colloidal gels requires a detailed understanding of how the various components govern network formation and aging. In particular, molecular additives like salts are widely used to tune interparticle interactions, yet their influence on gelation pathways in complex systems such as colloidal nanocrystal gels remains inadequately understood. Here, we investigate how noncoordinating salts modulate the evolution of gels formed using chemically linked tin-doped indium oxide nanocrystals. Through combined structural, dynamic, and kinetic analyses, we demonstrate that increasing salt concentration accelerates gelation. When rescaled by salt-dependent characteristic times, the evolution collapses onto universal trajectories, revealing a time-salt superposition principle. The universality extends across length scales, suggesting a consistent salt-dependent mechanism that controls both local structuring and macroscopic network formation. This observed salt modulation of structure and dynamics provides a predictive basis for controlling the kinetics of nonequilibrium nanocrystal gel assembly, enhancing the rational design of functional nanomaterials with tunable properties. 

Abstract Colloidal nanocrystal gels offer tunable optical properties governed by both the nature of the building blocks and their spatial arrangement. When assembled via reversible molecular linkers, their phase behavior and structure are primarily dictated by bond strength and lability. However, precise control over these interactions remains a significant synthetic challenge and is often system‐specific. Here, we present a simple, broadly tunable linking strategy that modulates nanocrystal phase behavior and assembly structure by leveraging competitive metal–ligand equilibria. We achieve programmable control over gelation temperature and network structure by tuning competitive metal–terpyridine and metal–halide equilibria in terpyridine‐functionalized tin‐doped indium oxide (ITO) nanocrystals, governed by metal and halide identity, concentration, and temperature, enabling wide‐range infrared optical modulation. Combined kinetic Monte Carlo and optical simulations reveal that weaker, more labile links facilitate particle crawling, leading to denser gel structures with enhanced plasmon coupling. This strategy eliminates the need for complex ligand or linker design and establishes competitive coordination chemistry as a versatile platform for engineering dynamic, stimuli‐responsive colloidal assemblies. 

Gelation offers a powerful strategy to assemble plasmonic nanocrystal networks incorporating both the distinctive optical properties of constituent building blocks and customizable collective properties. Beyond what a single-component assembly can offer, the characteristics of nanocrystal networks can be tuned in a broader range when two or more components are intimately combined. Here, we demonstrate mixed nanocrystal gel networks using thermoresponsive metal–terpyridine links that enable rapid gel assembly and disassembly with thermal cycling. Plasmonic indium oxide nanocrystals with different sizes, doping concentrations, and shapes are reliably intermixed in linked gel assemblies, exhibiting collective infrared absorption that reflects the contributions of each component while also deviating systematically from a linear combination of the spectra for single-component gels. We extend a many-bodied, mutual polarization method to simulate the optical response of mixed nanocrystal gels, reproducing the experimental trends with no free parameters and revealing that spectral deviations originate from cross-coupling between nanocrystals with distinct plasmonic properties. Our thermoreversible linking strategy directs the assembly of mixed nanocrystal gels with continuously tunable far- and near-field optical properties that are distinct from those of the building blocks or mixed close-packed structures.