Ionic liquid induced sphere-to-ribbon transition in the block copolymer mediated synthesis of silver nanoparticles

Abstract

Spherical silver nanoparticles (AgNPs) with size ∼20 nm have been synthesized from an aqueous AgNO₃ solution using the amphiphilic block copolymer, Pluronic P123 (EO₂₀–PO₇₀–EO₂₀), under ambient conditions without the use of any other reducing agents. The size of the AgNPs was highly dependent on the size and geometry of the micelles of the block copolymer. The AgNPs synthesized from the block copolymer mediated synthesis were characterized by UV-Vis spectroscopy, Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS). The addition of an ionic liquid (IL), N-alkyl pyridinium dodecyl sulphate, C_nPyDs, where n = 4, 6, 8, prepared by modifying N-alkyl pyridinium chloride with an anionic surfactant, sodium dodecyl sulphate (SDS), induced a sphere-to-ribbon (cylindrical) transition of the AgNPs. We observed that the presence of ILs reduces the equilibrium time as well as acting as a shape directing agent. The micelles of P123 and ILs in aqueous solution were characterized by Small Angle Neutron Scattering (SANS) and DLS methods. The size and shape of the AgNPs correlate with the geometry of micelles of the amphiphilic block copolymer and ILs in aqueous solution.