Environment-sensitive stabilisation of silver nanoparticles in aqueous solutions

We describe the preparation and characterisation of inorganic-organic hybrid block copolymer silver nanoparticles via the preparation of spherical multi-responsive polymeric micelles of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP₃₈-b-PEO₂₁₁ and poly(acrylic acid)-block-poly(isopropyl acrylamide), PAA₅₅-b-PNIPAAm₈₈ in the presence of AgNO₃. Hence, the P2MVP and PAA segments were employed to fix Ag⁺ ions within the micellar core (25 °C) or shell (60 °C), while the PEO segments ensured spontaneous reduction of Ag⁺ ions into metallic Ag, as well as colloidal stabilisation. Spherical and elongated composite core-shell(-corona) nanoparticles (CNPs) were formed containing several small, spherical silver nanoparticles within the micellar core or shell. As the co-assembly of the oppositely charged copolymers into micelles is electrostatically driven, the CNPs can be destabilised by, for example, addition of simple salts, i.e., the CNPs are stimuli responsive. CNP size and morphology control can be achieved via the preparation protocol. For example, heating to 60 °C, i.e., above the PNIPAAm LCST, results in core-shell-corona CNPs with the Ag-NPs situated in the aggregate shell.