Formation of Ordered Mesoporous Materials under Slow Aggregation Conditions

Abstract

We present dissipative particle dynamics (DPD) simulations of a mesostructured diblock A5B5 copolymer system in a medium of aggregating nanoparticles. A soft potential model for reaction-limited cluster aggregation of nanoparticles, suitable for use in DPD, which has the character of a strong glass forming liquid, is also presented. The simulations model the process of aggregation in the slow limit, where the copolymer mesophase formation and nanoparticle aggregation occur together from an initially homogeneous system, rather than the fast limit, where nanoparticle aggregation occurs rapidly around an existing copolymer mesophase. The resulting phase diagram shows that, for a strong enough aggregation potential, nanoparticle aggregation is associated with demixing between a homogeneous aggregated nanoparticle phase and a lamellar copolymer phase. For weaker aggregation, the phase behavior is similar to that seen for a nonaggregating system. The observed demixing is relatively insensitive to the nanoparticle selectivity between the copolymer constituents.