Particle-Size and Chain-Length Effects On Forces Between Functionalized Silica Nanoparticles

To prevent the flocculation and phase separation of nanoparticles in solution during industrial processing, nanoparticles are often functionalized with short chain surfactants. Here we present fully-atomistic molecular dynamics simulations which characterize how these functional coatings affect the interactions between nanoparticles and with the surrounding solvent. In particular, we examine the behavior of silica nanoparticles coated with poly(ethylene oxide) oligomers in water.

We have shown in previous work that the hydrodynamic behavior of the functionalized nanoparticles is different than uncoated particles [Lane et al., Phys. Rev. E (2009)]: the force oscillation observed for uncoated particles is not observed for functionalized nanoparticles. However, in equilibrium systems, the thermal energy of the particles is insufficient to permit significant depletion of water molecules between the nanoparticles. In the present work, we extend the results of our previous study to determine the effects of particle sizes (5-20 nm) and chain lengths (6-100 repeat units) on the equilibrium interactions between nanoparticles. While particle size plays a dominant role in controlling the long-range interaction between particles, the effects of the functionalized groups are observed primarily in the short-range interactions.

This work is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.