One-dimensional assembly of polymeric ionic liquid capped gold nanoparticles driven by electrostatic dipole interaction

Abstract

In this paper, a bottom-up method for preparing a one-dimensional plasmonic nanostructure is described using a gold nanoparticle capping agent poly[1-methyl 3-(2-methacryloyloxy propylimidazolium bromine)] (PMMPImB-@-Au NPs) as a building block. The core–shell particles were prepared via a “grafting-to” approach, and the structures were confirmed by dynamic light scattering, UV/vis spectroscopy, transmission electron microscopy and thermogravimetric analysis. The development of new plasmonic coupling absorption in the higher-wavelength region and TEM analysis clearly reveal that the PMMPImB-@-Au NPs form chain-like assemblies after the addition of HPO₄²⁻. The effects of different anion valences and polymer chain lengths, the structure of gold cores that have been removed and the change in the particle surface potentials were investigated to determine the mechanism of assembly. The results indicate that some divalent and polyvalent anions, such as HPO₄²⁻, SO₄²⁻, CO₃²⁻, PO₄³⁻ and P₂O₇⁴⁻, can serve as a molecular bridge for electrostatic coupling with two imidazolium groups from adjacent particles, and electrostatic dipole interaction is the major driving force for the self-assembly of PMMPImB-@-Au NPs with chain-like arrays.