pH-Controllable Coating of Silver Nanoparticles with PMMA-b-PDMAEMA Oligomers: A Molecular Dynamics Simulation Study

Silver nanoparticles (AgNPs) coated with pH-responsive polymers have become a very appealing "smart" nanocarrier for targeted drug delivery. To get a better understanding of the structure of hybrid organic/inorganic nanomaterials, we studied pH-controllable coating of AgNPs by a block copolymer, poly(methyl methacrylate)-block-poly(2-(N,N-dimethylamino)ethyl methacrylate) (PMMA-b-PDMAEMA), by using atomistic molecular dynamics simulations. PMMA-b-PDMAEMA contains a poorly water-soluble nonionic PMMA chain and a pH-responsive PDMAEMA moiety capable of switching its conformation upon altering pH. We found that the adsorption of a series of PMMA20-b-PDMAEMA20 oligomers onto AgNPs is crucially dependent on the protonation degree (α) of PDMAEMA, which is defined as a ratio of the numbers of protonated/total N,N-dimethylamino moieties. The tightly bound polymeric structure was formed around the nanoparticle at α = 0, whereas the loose coating was observed upon PDMAEMA protonation at α = 1. At partially protonated PDMAEMA (α = 0.5), the polymer chains segregate and collapse onto the nanoparticle. In the protonated forms (α = 0.5 and 1.0), PMMA-b-PDMAEMA adsorption onto AgNPs occurs primarily through the hydrophobic PMMA block so that the protonated positively charged PDMAEMA segment favors residing in an aqueous solution. Our results demonstrate that the pH-controllable behavior of PMMA-b-PDMAEMA coating opens up the opportunity for its use as a "smart" polymeric shell for AgNPs.