The Crucial Role of Charge in Thermoresponsive-Polymer-Assisted Reversible Dis/Assembly of Gold Nanoparticles

20 Apr 2018

Dynamic control of the spacing between Au nanoparticles using nano-architectures incorporating the thermo-responsive polymer poly(N-isopropylacrylamide) (PNIPAM) has the capability to induce strong color changes from the plasmon shifts. PNIPAM self-assembles on the surface of Au nanoparticles regardless of its terminal group. However in many cases, the collapse of this PNIPAM coating at elevated temperatures fails to cause a color change, due to electrostatic and steric repulsion between the Au nanoparticles. We uncover here how tuning the charge repulsion between the nanoparticles is crucial to achieve large, reversible shifts of the plasmon resonances. Using NH2 terminal groups of the PNIPAM is most effective, compared to SH, COOH and H terminations, due to their synergistic role in citrate stripping and charge neutralization. This detailed understanding of the Au-PNIPAM system is vital to enable temperature-responsive plasmonic systems with large tuning ranges, suitable for applications such as plasmonic actuators, displays, and Raman switches.