Systematic control of anisotropy and percolation in patchy particle gels

Patchy particle interactions enable the design of so-called ‘equilibrium gels’, a system where arrest is achieved without an underlying phase separation, resulting in structurally equilibrated gels which do not undergo coarsening-induced aging. We show that nanoparticle-incorporated supramolecular hydrogels - consisting of reversibly polymer-grafted metallic nanoparticles which are cross-linked with end-functionalized polymers – exhibit behaviour consistent with systems undergoing equilibrium arrest. We show that the interaction patchiness of this system can be controlled through the ratio of polymeric linkers to nanoparticles, thus resulting in a canonical system with tunable self-assembly, local structural anisotropy, and mechanical percolation thresholds. Moreover, we show that the addition of metal ions as a second competitive reversible cross-linking species results in the stabilization of locally anisotropic nanoparticle structures, thus resulting in a globally anisotropic structure and a dramatic reduction in the mechanical percolation threshold of the nanoparticle network in the hydrogel. These findings allow the systematic design of stable particle gels with tunable morphology and rigidity.