(517a) Monte Carlo Simulations of the Assembly of Copolymer Functionalized Nanoparticles

Functionalizing nanoparticles with copolymer ligands is an attractive method to tailor the assembly of the nanoparticles. We use Monte Carlo simulation to demonstrate how monomer sequence (e.g. alternating or diblock) in the grafted copolymers is a tuning parameter to control assembly of nanoparticles, and the shapes, sizes and structure of the assembled nanoclusters. We first perform a single molecule study to understand the effect of various molecular parameters, such as monomer sequence, molecular weight, monomer interactions of the grafted copolymer and particle size on the conformations of the grafted copolymer chains. Our results show that monomer sequence, particle diameter, and grafting density dictate whether a) the grafted chains aggregate to bring attractive monomers from multiple grafted chains together (interchain and intrachain monomer aggregation) if the enthalpy gained by doing so offsets the entropic loss caused by the stretching of the chains or b) each grafted chain folds onto itself to bring its attractive monomers together (purely intrachain monomer aggregation) if the entropic loss from interchain aggregation cannot be overcome by the enthalpic gain [1]. This single molecule study is followed by simulations of assembly of multiple (AB) copolymer grafted spherical nanoparticles in an implicit small molecule solvent [2]. Our results show that alternating sequence produces relatively large isotropic clusters when either A-A or B-B monomers are attractive in the presence of negligible A-B repulsions, but smaller clusters or particle dispersions in the presence of strong A-B repulsions. Diblock sequence produces nanoclusters that are smaller and more compact when the block closer to the surface (A-A) is attractive and larger, loosely held together clusters when outer block (B-B) is attractive in the presence of both strong and negligible (A-B) repulsions. Additionally, diblock copolymer grafted particles tend to assemble into anisotropic shapes despite the isotropic grafting of the copolymer chains on the particle surface. In the dilute concentration regime we show that the structure within a cluster is primarily governed by the copolymer functionalization imparting a “valency” to the nanoparticle “atom” [2]. In this talk we will present results from these simulations of a single copolymer grafted nanoparticle and of the assembly of multiple copolymer grafted nanoparticles.

1. A. Seifpour, P. Spicer, N. Nair, A. Jayaraman. ‘Effect of monomer sequences on conformations of copolymers grafted on spherical nanoparticles: A Monte Carlo simulation study.’ J. Chem. Phys. 132 164901 (2010)
2. T. Martin, A. Seifpour, and A. Jayaraman. ‘Assembly of Copolymer Functionalized Nanoparticles: A Monte Carlo simulation study.’ Soft Matter (2011) (in press)