Self-Assembly of Ditethered Nanospheres and Comparison with Triblock Copolymer Mesophases
Christopher R. Iacovella, Chemical Engineering, University of Michigan, 2350 Hayward Street, 3440 G.G. Brown, Ann Arbor, MI 48109 and Sharon C. Glotzer, Chemical Engineering and Materials Science and Engineering, University of Michigan, 2300 Hayward Street, Ann Arbor, MI 48109.
Linear and star triblock copolymers are known to self assemble into a wide array of complex morphologies. The use of polymer-tethered nanoparticles is a unique method to control the self-assembly of nanoparticles into phases reminiscent of these and other block copolymers. Here we present the results of Brownian dynamics simulations used to investigate the phase behavior of nanospheres functionalized with two tethers to form building blocks whose geometries are analogous to ABC triblock copolymers. In this analogy, the nanoparticle plays the role of the middle "block". We investigate the phase behavior under melt conditions as a function of both nanoparticle diameter and dihedral angle, the angle separating the two tethers. We find a variety of phases that resemble those of linear and star triblock copolymers, including the alternating diamond, alternating gyroid, and alternating orthorhombic tricontinuous lattices, tetragonal and [8,8,4] columnar phases, and a unique phase of NaCl ordered spherical micelles. We additionally explore the phase behavior (i) as a function of block fraction under melt conditions and show evidence of a transition from tricontinuous to lamellar structures, and (ii) as a function of volume fraction under selective solvent conditions for which we find the double gyroid, hexagonally packed cylinder, and BCC ordered micelle phases. We discuss under what conditions ditethered nanoparticles do and do not behave as more traditional triblock copolymers.