(272e) Self Assembly of Nanoparticle-Polymer-Nanoparticle Triblocks

Self assembly has emerged as an important tool in the formation of ordered structures at the nanoscale, allowing, for example, to spatially organize particles of multiple species. The influence of a polymer connector in the self assembly of nanoparticles of two different species is studied using Monte Carlo simulations. Nanoparticles A and B are connected by a polymer chain of variable length. The size of the nanoparticles is greater than the size of the beads used to model the polymer chain. Continuum Monte Carlo simulations in an isothermal isobaric ensemble were carried out varying connector length and nanoparticle size. The phase behavior for each system was mapped out as a function of temperature and pressure (hence concentration). Using cut-and-shifted Lennard-Jones potentials, like species interactions are made to be attractive while unlike species interactions are made to be repulsive. This work complements a previous study by Iacovella et. al.¹ who investigated phase behavior of nanospheres with a polymer tether. Our results show that the presence of the second nanoparticle alters the phase diagram significantly. When two nanoparticles A and B are connected by a chain of eight beads (each bead being one half the diameter of a nanoparticle), the polymers form microsegregated cylinders and spheres which are surrounded by a shell of nanoparticles. Spherical micelles of polymer chains were formed when the chain length was decreased to four and two beads. Clustering of like nanoparticles was observed in the shell surrounding the polymer cylinders/spheres. Well ordered structures can be formed of either nanoparticles (if polymer is eluted) or polymer (if the nanoparticles are eluted). The phase behavior of the nanoparticle-polymer-nanoparticle system is compared with the phase behavior of triblock copolymer systems. The influence of nanoparticle geometry on the phase behavior of the triblocks is also studied using cuboid shaped nanoparticles.

¹ Iacovella et. al., Langmuir, 2005, 21, 9488.