Chain length dependent stabilization of charged nanoplatelet dispersions by inorganic polyphosphates

The increasing demand for accessible phosphorus sources, essential for plant growth, is placing growing pressure on both industry and academia. Here, we investigate nanoplatelets as carriers for phosphate species, using Laponite® as a model system for sprayable phosphorus formulations. We examine how phosphate species chain length (1, 2, 3, 14, 60, and 130 monomers) governs dispersion stability and interparticle assembly of nanoplatelet dispersions at 1 wt%. A combination of cryogenic transmission electron microscopy (cryo-TEM), ³¹P magic-angle spinning NMR, small-angle X-ray scattering (SAXS), light scattering, and coarse-grained molecular dynamics simulations reveals that electrostatic interactions between anionic phosphate species and the anisotropically charged platelet surfaces dictate structural evolution. Short-chain phosphate species (1-3 monomers) enhance charge screening, increasing compressibility and promoting clustering. In contrast, longer-chain polyphosphates ( ≥  14 monomers) preferentially associate with the positively charged platelet rims, suppressing dense rim-face aggregation while still permitting open, weakly connected structures, thereby stabilizing the dispersions against compact flocculation. Cryo-TEM directly visualizes this transition in assembly behavior as chain length increases. These results establish a molecular-level understanding of how multivalent polyelectrolytes regulate anisotropic colloidal interactions and demonstrate that chain length provides a direct handle for tuning nanoplatelet dispersion stability. The findings offer general design principles for stable nanoplatelet-polyphosphate formulations with controllable aggregation and phosphate release characteristics.