(144b) Examination of the Aggregation Behavior of Polymer Grafted Nanoparticles Using Molecular Simulation and Theory

Authors: 
Haley, J. D., Vanderbilt University
Iacovella, C. R., Vanderbilt University
McCabe, C., Vanderbilt University
Cummings, P. T., Oak Ridge National Laboratory

The aggregation and dispersion of nanoparticles can have a significant impact on the characteristics of a system, enhancing the physical, electrical, or optical properties [1]. Understanding what controls the aggregation/dispersion of nanoparticles is important to the predictable self-assembly of nanomaterials and how to effectively control and tune their targeted properties [2]. For polymer tethered nanoparticles (TNPs), a convenient and informative approach to explore aggregation vs. dispersion is to study the strong connection between the vapor-liquid equilibrium (VLE) and the grafting architecture of the TNP. Here, molecular simulations and the hetero - statistical associating fluid theory for potentials of variable range (hetero-SAFT-VR) [3,4] are used to examine this behavior, coupling the detailed structural understanding gleaned from simulation with the efficiency of SAFT for thermodynamic properties.   It is observed from both simulation and hetero-SAFT-VR calculations that for low grafting densities, the coexistence region shrinks with increasing graft length, with a reduction in both the critical density and temperature, the latter of which is the opposite of what is seen for pure polymers; for higher grafting densities, increased chain length results in an increase in critical temperature, related to screening effects.  Simulations and SAFT predictions were also used to investigate the effects of chain length polydispersity on the behavior of the TNP systems, finding minimal changes to the aggregation behavior.  The solubility of the TNPs in a carbon dioxide solvent was also investigated, to determine how TNP architectures can be used to tune dissolution.

References:

1. Hore, M. and Composto, R., Current Opinion in Chemical Engineering, 2013. 2(1):95

2. Whitesides, G.M. and Grzybowski, B.,  Science, 2002. 295(5564):2418

3. Peng ,Y. and McCabe, C., Molecular Physics, 2007. 105(2): 261

4. McCabe, C., Gil-Villegas, A., Jackson, G., and Del Rio, F., Molecular Physics, 1999. 97(4): 551

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