Influence of the Molecular Weight of Poly (Ethylene Glycol) on the Aqueous Dispersion State of Magnetic Nanoparticles: Experiments and Monte Carlo Simulation

Abstract

Here, we used experiments and Monte Carlo simulations (MC) to identify appropriate poly (ethylene) glycol (PEG) polymer molecular weight (Mw) as the coating agent for iron oxide nanoparticles (IONPs) resulting in individual particles in water. IONPs coated with PEG Mw’s ranging from 1500 to 6000 Da showed highly stable dispersions for more than a year. Transmission electron microscopy (TEM) results of the dispersions revealed that particles coated with lower PEG Mw were aggregated, which shifted to individual form with increasing PEG Mw used for coating. We find that this transformation is due to increased PEG layer shell thickness (from 1.47 to 6.46 nm) with increasing PEG Mw (from 1500 to 6000 Da), which imparted sufficient repulsive steric forces to overcome the attractive van der Waals and magnetic forces. To predict appropriate PEG Mw resulting individual IONPs in water, the number density distribution of different PEG Mw coated particles was determined using MC simulation which employs interparticle potentials between the interacting particles as a function of their interparticle distance. The predictions gave very good agreement with our’s and others’ experimental data. Thus, the study helps to identify a suitable polymer Mw as a coating agent, resulting in individual nanoparticle dispersion.