Gold Nanoparticle Adsorption in a Weak Polyelectrolyte Brush with Varying Molecular Weight

Current separation technologies struggle with selective adsorption of molecules and nanosized particles. Weak polyelectrolyte (PE) brushes, like poly(2-vinylpyridine) (P2VP), offer improved precision due to their stimuli-responsivity. We studied how environmental pH and P2VP brush molecular weight (10 and 53 kg/mol) affect gold nanoparticle (AuNP) (10- and 20-nm diameter) adsorption using quartz crystal microbalance with dissipation (QCM-D). Here, QCM-D measured the adsorption kinetics and areal number densities for each diameter of AuNP at either pH = 4.0 or pH = 6.2 to the P2VP brushes. At pH = 4.0, the swollen brushes promote greater AuNP adsorption compared to the collapsed brush state at pH = 6.2. Overall, higher molecular weight brushes significantly enhance AuNP uptake. Normalization of the QCM-D areal number densities by the 2-D random closed packing (RCP) maximums for each AuNP diameter provides insights into the preferential adsorption of 10-nm AuNPs at higher pH. The QCM-D dissipation change (∆D) values indicate 10 kg/mol P2VP brushes adsorb AuNPs predominantly near-surface, while 53 kg/mol P2VP brushes form multilayers of AuNPs. This study highlights the role of pH and brush molecular weight in nanoparticle adsorption, providing insights for designing smart surfaces in sensing and filtration applications.