Interaction between coated graphite nanoparticles by molecular simulation

We present and discuss here simulation results for a realistic model of chain molecules anchored on selected nanoparticles. The nanoparticles are taken to be composed of graphite, and the anchored molecules are C₁₂ alkane chains. The main goal is to investigate the effect of the anchored chains on the mediated forces between the coated nanoparticles. We also examine the structure of the anchored chains. The grafting density (the surface density of grafted chains) is identified as a key parameter that drastically affects the chain adsorption and the effective force between nanoparticles. At low grafting densities, the chains are basically adsorbed on the surfaces, while at high grafting densities the chains form brushes. The effect of the temperature on these mediated forces is also investigated following the same procedure. At low grafting densities the force depends weakly on the temperature, indicating a prevalence of energy over entropy. At high grafting densities the conformation of the brushes has a direct impact on the force, which is seen to be clearly temperature dependent. This has strong implications in practical applications, since the possibility to control a colloidal dispersion by means of the temperature is here shown to depend on the grafting density. These results serve both as a source of baseline results useful for comparison and as a stepping stone toward future work with systems that are more involved to simulate.