Following the Synthesis of Metal Nanoparticles within pH-Responsive Microgel Particles by SAXS

Abstract

pH-responsive poly(2-(diethylamino)ethyl methacrylate), PDEA, microgels have been utilized as nanoreactors for the formation of metal nanoparticles. The PDEA microgels exhibit reversible swelling properties in water as a function of the solution pH; at low pH, the microgel particles are swollen. while an increase of the pH leads to hydrophobic latex particles. Metal nanoparticles were synthesized within the microgel particles by the incorporation of the appropriate metal precursor followed by metal reduction. Two synthetic routes have been utilized for the preparation of the nanoparticles and are compared herein: in the first method, the K 2 PtCl 6 precursor was added to the hydrophilic swollen microgel particles at low pH (method A) followed by metal reduction and increase of the pH by the addition of base, while in the second method, H 2 PtCl 6 was added to the hydrophobic latex particles at high pH and next the metal salt was reduced in situ using NaBH 4 (method B). The structure of the hybrid systems was investigated by small-angle X-ray scattering (SAXS) during the three steps of the metal nanoparticle synthesis: the original microgel dispersion in water of the appropriate pH, the metal-loaded polymer matrices, and the metal nanoparticle-containing microgels after reduction. The pH-responsive character of the microgels as well as the metal incorporation was confirmed by the scattering profiles. Following metal reduction, Pt nanoparticles are formed with a radius of about 1 nm for both methods. The scattering profiles acquired both before and after reduction for the two methods exhibit differences which are attributed to the spatial distribution of the platinic anions and the Pt nanoparticles.