| Nanoparticles/polymer nanocomposites are of major scientific and technological interest in diverse areas of colloid science, polymer science, nanomaterials, and biology. Self-assembly of nanoparticles/polymer nanocomposites is one of the most promising candidates for the development of novel materials with high macroscopic electrical, mechanical, optical, or thermodynamic performance as well as can help us to understand the structures of some concerned biomolecules and their corresponding biological function. In general, the self-assembly behavior of nanoparticles/polymer nanocomposites will be affected by various elements and the final morphology is determined by a complex interplay between entropy and enthalpy within the system. In this thesis, by employing molecular dynamics (MD) simulation and coarse-grained (CG) model, the self-assembly behaviors of nanoparticles/polymer nanocomposites under different conditions have been widely studied and many interesting phenomena and results are presented, the concerned elements including the molecular architecture of polymer system (such as long polymer chain, star polymer, polymer brush), the stiffness of polymer, the interaction between nanoparticles and polymer system, and the size and shape of nanoparticles (spherical nanoparticle, nanorod, nanoplate, binary nanoparticle, elastic shell and so on). The results presented here may be helpful for the construction of a set of universal strategies that can be used to guide and control the self-assembly behaviors of nanoparticles/polymer nanocomposites.In Chapter 2, we demonstrate that long semi-flexible polymer chains can serve as an effective soft elastic medium for manipulating the ordered structures of small numbers of building blocks, which can be easily controlled by the chain bending stiffness. For two spherical particles in a polymer-particle mixture, three types of local organization are identified:monomer level tight particle bridging, direct contact aggregation, and dispersion. For small numbers of spherical particles in a polymer-particle mixture, the ordered structures of particles, such as spherical and linear particle aggregations, depend mainly on chain bending stiffness. For non-spherical building blocks, the relative orientations of neighboring building blocks are also strongly affected by chain bending stiffness.In Chapter 3, the ordered structures of nanorods (NRs) in the semiflexible star polymer/NR mixtures are explored and the structures of small numbers of NRs can be well controlled by varying the stiffness of semiflexible star polymers. At a moderate binding energy between star polymers and NRs, four completely different structures of small numbers of NRs are observed, including that the side-to-side hexagonal aggregation structures of NRs for flexible star polymers, the partly parallel aggregation structures of NRs and the end-to-end contact parallel aggregation structures of NRs for semiflexible star polymers, and the partial dispersion of NRs for rigid star polymers. Helical conformations of semiflexible star polymers binding with NRs are responsible for the formation of the end-to-end contact parallel aggregation structures for small numbers of NRs.In Chapter 4, the aggregation behaviors and phase separation of binary nanoparticles immersed in semiflexible polymer brushes are explored and the conformations of the binary nanoparticle-brush mixtures are very sensitive to the size ratio of binary nanoparticle and the attractive interactions between the nanoparticles and polymer brushes. The phase separation of the binary nanoparticles is observed at a relatively strong attractive interaction under the effects of inter-nanoparticle depletion attractions provided by polymer brushes. Furthermore, the crystallization of small nanoparticles occurs at a strong interaction and a hexagonal close-packed-like (hcp-like) ordered structure is formed.In Chapter 5, we explored the spatial orientations and conformational transitions of nanorods (NRs) within semiflexible polymer brushes. The orientations of the NR clusters are controlled by the competition between the entropy cost for NRs infiltrated into the polymer brushes and the attractive energy between NRs and polymer brushes. By reducing the grafting density or enhancing the number of NRs, the NR cluster experiences an orientation transition from the vertical direction to the horizontal direction. The semiflexible polymer brushes are regarded as the soft confinements for the NRs, and the soft confinements can induce the formation of the NR aggregation under the effect of the depletion attractionsIn Chapter 6, the statistical properties and phase transitions of semiflexible polymers on a soft elastic shell are investigated. The phase diagram of adsorbed semiflexible polymers depends on the bending energy of the elastic shell and the binding energy between polymers and the elastic shell. The ordered regular pentagons of polymers are observed at a moderate adhesive strength and bending energy. At the same time, the shape of the soft elastic shell can be controlled easily by adjusting the chain length of adsorbed polymers. |
