Salt-Induced Liquid–Liquid Phase Separation and Interfacial Crystal Formation in Poly(<i>N</i>-isopropylacrylamide)-Capped Gold Nanoparticles

We report on the dynamic response of aqueous solution containing poly(N-isopropylacrylamide)-capped gold (pNIPAM-capped Au) nanoparticles to introduction NaCl. The addition NaCl increases density and prompts liquid–liquid phase separation process, confining polymer a lower-density salt-deficient phase. As pNIPAM-occupied becomes excluded from higher-density NaCl-rich bulk solution, pNIPAM-capped Au follow reside surface formed pNIPAM-filled globes at interface between pNIPAM-containing exhibiting hexagonal packing with interparticle distance ∼23 nm. Driven by minimization hydrophobic interactions, buoyant Au-decorated globular assemblies filled pNIPAM escape air/water interface, collapse form planar crystalline domains different sizes, depending concentration. At low concentrations, produces an interfacial two-dimensional (2D) lattice 25–27 increase in concentration leads formation smaller escaping to, collapsing yielding domains.