pH-Dependence of Gold Nanoparticle Adsorption to a Weak Polyelectrolyte Brush*

The ability to tailor nanoparticle adsorption onto surfaces is limited by the understanding of particle-surface interactions and dynamics. Here, we expand upon recent work investigating the pH-mediated size-selectivity of gold nanoparticles (Au NPs) adsorption to poly(2-vinylpyridine) (P2VP) brushes fabricated from diblock copolymer. Now, end-grafted P2VP brushes with molecular weights of 10 and 53 kg/mol are investigated. With increasing brush molecular weight, the brush heights increased and the grafting density decreased. We used AFM to characterize the brush out-of-plane surface structure and in situ ellipsometry to measure the film thicknesses as a function of pH. At pH=4.0 and pH=6.2, we monitored the adsorption of 10- and 20-nm citrate-functionalized Au NPs onto these brushes. We measured the kinetics of Au NP adsorption using QCM-D and imaged NP packing with SEM. Combining these techniques, we found a size-selective pH-mediated response of NP adsorption in these homopolymer P2VP brushes. While grafting density influences adsorption behavior, the ratio of brush height to Au NP diameter controls the adsorption behavior in this system. These findings of selective adsorption allow for enhanced design of separation membrane technologies for nanoscale particles and molecules.