(245b) Ordering of Nanoparticles Mediated by End-Functionalized Triblock Copolymers

Using molecular dynamics simulations we show that triblock copolymers, designed to have specific affinity for nanoparticles at the chain ends, can successfully mediate assembly of nanoparticle/copolymer composites. In this talk, we will present a detailed investigation of the phase diagram of these nanocomposites as a function of both nanoparticle size and concentration. We find a rich phase diagram with a number of distinct ordered structures. Next to phases such as hexagons or gyroids, regularly observed in copolymer solutions and melts, we find a novel square columnar phase of two interpenetrating line-lattices of micellar cylinders and aligned nanoparticles. We argue that this phase is a realization of the packing problem of binary mixtures of disks. Using theory of minimal and constant mean curvature surfaces we study nanoparticle and copolymer density profiles and develop qualitative understanding of origin and stability of ordered structures. Further, based on the analysis of stretching of copolymers we argue that nanoparticles help stabilize gyroid order and drastically widen the region of phase diagram occupied by gyroids. We also propose experimental realizations of our model calculation. Our study suggests that combining nanoparticles with functionalized block copolymers can provide a simple and efficient tool for assembling novel materials with nanometer scale resolution.

Reference: Rastko Sknepnek, Joshua A. Anderson, Monica H. Lamm, Joerg Schmalian, and Alex Travesset: ``Nanoparticle Ordering via Functionalized Block Copolymers in Solution'', ACS Nano, 2008, submitted.