Biomimetic synthesis of silica nanospheres depends on the aggregation and phase separation of polyamines in aqueous solution

Long-chain polyamines extracted from the highly siliceous cell walls of diatoms are known to precipitate silica nanospheres from aqueous, silicic-acid containing solutions at near-neutral pH in vitro. The same is true for synthetic polyamines such as polyallylamine. In the present contribution we show that the microscopic phase separation of polyallylamine in aqueous solution is strictly correlated with the silica precipitation activity of polyallylamine/silicic acid solutions. Multivalent anions such as phosphate or sulfate efficiently induce this microscopic phase separation. At higher anion concentrations, macroscopic phase separation occurs. In contrast to the multivalent phosphate and sulfate ions, the monovalent chloride ions are much less efficient in polyallylamine aggregate formation.