(393ai) Templating Nanoparticle Arrays Via Shear-Directed Assembly of Spherical and Worm-Like Block-Copolymer Micelles: A Coarse-Grained Molecular Dynamics Study

Spherical and worm-like block-copolymer micelles are known to attain long-range order under shear flow. Recently, these non-equilibrium structures have been exploited to template nanoparticles of diameters on order of the micelle diameter. However, the interplay between macroscopic variables and resulting mesostructure along with the shear-ordering mechanisms remains poorly understood.  We present results which elucidate this connection by employing coarse-grained molecular dynamics (CGMD) – affording direct observation at a molecular scale. Critically, our model preserves the hydrodynamic interactions by use of a dissipative particle dynamics (DPD) thermostat in an explicit, coarse-grained solvent. First, the effect of nanoparticles on the formation of spherical and worm-like micelles from self-assembling block copolymers has been investigated. The micelle-nanoparticle suspensions are subjected to simple and oscillatory shear of varying strain and frequency/rate, and the rheological response is compared to experiments of similar systems published in the literature. A relationship between the rheological response and the micelle-nanoparticle structure (and transitions) is also proposed. Finally, observed structures are quantified by structure and form factors for comparison to experimental results published using small-angle neutron scattering (SANS). These scattering patterns also differentiate between zig-zag and sliding mechanisms of the ordered nanoparticle sheets.