(181z) Calculation of Vapor-Liquid Coexistence of Grafted Nanoparticles

It is well known that the aggregation/dispersion of nanoparticles can have a significant impact on the properties of the system. One approach to control the aggregation is to graft polymers to the surface of the nanoparticles. The resulting behavior is therefore dictated by contributions from both the nanoparticle and polymer interactions and significant changes to the properties can be achieved by tuning these interactions.  In this work we use molecular dynamics (MD) simulations to calculate the vapor-liquid coexistence of grafted nanospheres under a wide range of conditions.  We use a coarse-grained model, generic enough to be applicable to a wide range of systems, but with parameters informed by recent studies of the interactions between silica nanoparticles [1] and the interactions between alkane chains known to accurately reproduce phase equilibria [2]. NVT MD simulations are performed using the GPU-enabled HOOMD-Blue [3-4] package, where vapor-liquid equilibrium is calculated using the quench dynamics technique. Vapor-Liquid coexistence is examined as a function of nanosphere interaction strengths, grafting density and grafting length. We find that the critical temperature increases with nanoparticle-nanoparticle interaction strength relative to a pure polymer system.  We also observe that the critical temperature is relatively unaffected by polymer length for low grafting densities.

References:

1. C.K. Lee and C.C. Hua, J. Chem. Phys. 132, 224904 (2010)

2. M.G. Martin and J.I. Siepmann, J. Phys. Chem. B 102 (1998)

3. J. A. Anderson, C. D. Lorenz, and A. Travesset, Journal of Computational Physics 227(10): 5342-5359

4.  http://codeblue.umich.edu/hoomd-blue