Structure of Solvent-free Grafted Nanoparticles: Molecular Dynamics and Density-functional Theory

The structure of solvent-free oligomer-grafted nanoparticles has been investigated using molecular dynamics simulations and density-functional theory. At low temperatures and moderate to high oligomer lengths, the qualitative features of the core particle pair probability, structure factor, and the oligomer brush configuration obtained from the simulations can be explained by a density-functional theory that incorporates the configurational entropy of the space-filling oligomers. In particular, the structure factor at small wave numbers attains a value much smaller than the corresponding hardsphere suspension, the first peak of the pair distribution function is enhanced due to entropic attractions among the particles, and the oligomer brush expands with decreasing particle volume fraction to fill the interstitial space. At higher temperatures, the simulations reveal effects that differ from the theory and are likely caused by steric repulsions of the expanded corona chains.The authors would like to thank Professor Fernando Escobedo for suggesting the simulation model used in this work and for helpful discussions. This publication is based on work supported in part by Award No. KUS-C1-018-02, made by King Abdullah University of Science and Technology (KAUST). Additional support was provided by Grant No. DE-SC-0002128 from the (U.S.) Department of Energy (DOE), Office of Basic Energy Sciences and Grant No. CBET-1033155 from National Science Foundation (NSF)