Uptake of anionic gold nanoparticles by cationic microgel particles in dispersion: The effect of pH

The interactions of negatively charged gold nanoparticles with positively charged poly(2-vinylpyridine) microgel particles, initially in either their collapsed (pH 6) or swollen (pH 3) states, have been studied in aqueous dispersion. When the gold nanoparticles are mixed with the collapsed microgel particles, at pH 6, they adsorb around the surface of the microgel particles, having no appreciable affect on the size or structure of the microgel particles. However, this uptake of the anionic nanoparticles onto the surface of the microgel particles does lead to a reversal of the surface charge of the latter. When the gold nanoparticles are mixed with swollen cationic microgel particles at pH 3, the anionic gold nanoparticles are initially taken up into the interior of the cationic polymer network, due to electrostatic attraction. Addition of further gold particles leads to the (irreversible) collapse and reversal of sign of the microgel particles. The amount of gold particles absorbed into the interior of the microgel particles is found to decrease with increasing cross-linker content of the P2VP particles.