Capping Gold Nanoparticles with Stimuli-responsive Polymers to Cross Water−Oil Interfaces: In-Depth Insight to the Trans-Interfacial Activity of Nanoparticles

We present the results of an investigation of gold nanoparticles (NPs) capped with stimuli-responsive polymers, especially copolymers of di(ethylene glycol) methyl ether methacrylate (MEO2MA) and poly(ethylene glycol) methyl ether methacrylate (OEGMA) in biphasic water−toluene mixtures. Gold NPs capped with these copolymers spontaneously transferred across the water−toluene interface if salt was incorporated in aqueous dispersions of the gold NP/polymer composite materials. The fraction of NPs that transferred across the water−toluene interface dependeds on the chemical composition of the capping polymers and the diameter of the gold NPs but has little dependency on the ion valency of the salt included in the aqueous phase. Additionally, the van Oss−Chaudhury−Good model of surface energy was employed to provide insight into the importance of polymer surface energy on the trans-interfacial activity of the NP/polymer composite materials. The surface energy of copolymers of MEO2MA and OEGMA on model, planar substrates, and, consequently, on the trans-interfacial activity of NPs capped with those same copolymers, depended strongly on the methods used to fabricate the surface-grafted polymers.