Temperature and anion responsive self-assembly of ionic liquid block copolymers coating gold nanoparticles

In this paper, double hydrophilic ionic liquid block copolymers (ILBCs), poly poly[1-methyl-3-(2-methacryloyloxy propylimidazolium bromine)]-block-(N-isopropylacrylamide) (PMMPImB-b-PNIPAAm) was first synthesized by reversible addition-fragmentation chain transfer (RAFT) and then attached on the surface of gold nanoparticles (Au NPs) via a strong gold-sulfur bonding for preparing hybrid nanoparticles (PMMPImB-b-PNIPAAm-@-Au NPs). The hybrid NPs had a three layers micelle-like structure, including a gold core, thermo-responsive inner shell and anion responsive outer corona. The self-assembling behavior of thermal- and anion-response from shell and corona were respectively investigated by change of temperature and addition of (CF₃SO₂)₂N^-. The results showed the hybrid NPs retained a stable dispersion beyond the lower critical solution temperature (LCST) because of the space or electrostatic protecting by outer PMMPImB. However, with increasing concentration of (CF₃SO₂)₂N^-, the micellization of self-assembling PMMPImB-b-PNIPAAm-@-Au NPs was induced to form micellar structure containing the core with hydrophobic PMMPImB-(CF₃SO₂)₂N^- surrounded by composite shell of Au NPs-PNIPAAm via the anion-responsive properties of ILBCs. These results indicated that the block copolymers protected plasmonic nanoparticles remain self-assembling properties of block copolymers when phase transition from outer corona polymer.