Coarse-grained molecular dynamics study of block copolymer/nanoparticle composites under elongational flow.

Symmetric diblock copolymer/nanoparticle (NP) systems under planar elongational flow have been modeled and simulated using coarse-grained nonequilibrium molecular dynamics. The aim of our present study is to understand how the dispersion of NPs in a block copolymer system is influenced by elongational flow and how the presence of NPs changes the rheology and flow-induced morphology transition in block copolymers. We consider two different kinds of spherical NPs categorized with respect to their interaction potential with the polymeric blocks: (1) selective NPs that show a preference toward one of the blocks of a model diblock copolymer and (2) nonselective NPs that show equal attraction toward both blocks. For unrestricted simulation times during elongational flow, spatially and temporally periodic boundary conditions devised by Kraynik and Reinelt [Int. J. Multiphase Flow 18, 1045 (1992)] have been implemented. Our results show that the concentration peak of both selective NPs at the center of the preferred domain and nonselective NPs at the domain interface becomes broader with increasing elongation rate, suggesting that elongational flow can be used as another parameter to control nanocomposite self-assembly. In addition, our results reveal that the onset of flow-induced transition from lamellar to disordered morphology is greatly influenced by particle-particle and particle-polymer interactions.