Aggregation-dispersion Transition Of Nanoparticles In Ring Polymer Melts And Danamics Of Complex Vesicles In Shear Flow

Nanoparticle/polymer nanocomposites has been widely adopted in science and technology due to its unique optical, electrical and mechanical properties. While nanoparticle (NP)dispersion is believed to critically affect properties, efforts have been made to optimize NP dispersion. One way to improve miscibility is to functionalize the NP surface with compositions of polymer chains which shares identical chemistry with free polymers. Another way to tailor dispersion is to enhance polymer-NP interactions.Since ring polymers endure unique topological structure, ring polymers manifest themselves on a variety of properties against linear polymers. In Chapter 2, we find that in NP/ring polymer nanocomposites, an aggregation-dispersion transition occurs when the bending rigidity of ring polymers increases. The effective interactions between NPs have reversed from short-range attractive to repulsive. We further study the behaviors of ring polymers in the vicinity of NPs. For flexible ring polymers, polymers exhibit a radial distribution around NPs.While for semiflexible ring polymers, NPs are wrapped around by ring polymers, which cause high monomer density around NPs and act as a perfect barrier to avoid NP aggregation. Our study has given new access to tailor dispersion in NP/polymer nanocoposites.Dynamics of vesicles in flow have caused numerious attentions due to its high resemblence with biological process. Researches have found that a clean vesicle exhibits three motion types in shear flow: tumbling, trembling and tank-treading. Real vesicles in biological systems are always decorated with macromolecules, such as glycocalys, proteins. Some cells are even decorated with flagella. Besides, vesicle-vesicle interactions, such as electrostatics or collision,can affect the dynamics of vesicles in shear flow. Our investigations into the dynamics of these complex vesicles in shear flow may help explore new vesicle motion types, which give us a better understanding of some biological process. In chapter 3, we have investigated dynamics of a 2D vesicle grafted with polymers or small vesicles in shear flow. Besides the three motion types mentioned above, a novel tank-treading-translating transition is found when the size of grafting polymers or grafting vesicles is large enough. Moreover, grafting position as well as the number of grafting vesicles may also affect the tank-treading-translating transition.The dynamics of a single vesicle in shear flow is regarded as the basis for the description of dilute multi-vesicle suspensions without interactions. As for semi-dilute or non-dilute vesicle suspensions, the vesicle-vesicle interactions, such as collsion, have proved to have significant effects on the orientations of vesicles as well as the rheology of suspensions. In chapter 4, we have simulated the dynamics of two attractive 3D vesicles suspended in shear flow. We find that elastic vesicles mainly exhibit four motion types: coupled tumbling, coupled trembling,collision/rotation mixture, and separated tank-treading. The dynamics of vesicles are determined by the competition between the shear flow and the attractive interactions of the two vesicles.Furthermore, the dynamics of rigid vesicles are relatively simple.In chapter 5, we have studied the self-assembly behaviors of nanoplates with various shapes on elastic shells. We find that only on shells with moderate bending energy,nanoparticles can form ordered structures on shell surface. The aggregation strutures mainly depend on the shape as well as the number of nanoplates. Meanwhile, by varying the number as well as the length of nanorods, the elastic shell may deform into various shapes, such as sphere,tricorn, ellipsoid, pillow-like or irregular shape.