A pH-Dependent Phase\nSeparation Drives Polyamine-Mediated\nSilicification from Undersaturated Solutions

Silica polymerization from its soluble monomers is fundamental\nto many chemical processes. Although industrial methods require harsh\nconditions and concentrated precursors, biological silica precipitation\noccurs under ambient conditions from dilute solutions. The hallmark\nof biosilica is the presence of amine-rich organic macromolecules,\nbut their functional role remains elusive. Here, we show a pH-dependent\nstimulatory effect of such polyamines on silica polymerization. Notably,\nthis process is decoupled from the saturation degree, allowing the\nsynthesis of polymer–silica hybrid products with controlled\nnetwork morphologies from undersaturated solutions. The data suggest\na two-step phase separation process. First, an associative liquid–liquid\nphase separation forms a micrometer-size dense phase. Second, silica\nundergoes a liquid-to-solid transition in the supersaturated condensates\nto form a bicontinuous silica structure. This study can inspire “soft\nchemistry” routes to design organic–inorganic nanomaterials\nwith regulatory principles optimized by evolution.