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Abstract

School of Energy and Chemical Engineering (Chemical Engineering)Nowadays, there has been demand for advanced composite materials due to their outstanding characteristics in wide ranges of academic and industrial fields. Composite materials usually possess improved properties not being observed in pure material itself. Particularly, polymer composite materials composed of constituents based on polymer matrix have been widely researched due to their highly enhanced capabilities (e.g., elasticity, flexibility, conductivity, hardness, stretchable, scalable, and so on) in various fields. Polymers, which are composed of structural repeat units with covalent bonds, have been gradually becoming essential and indispensable materials in the recent world owing to their high flexibility, elasticity, ease of processing, low cost, light weight, and other unique properties. Therefore, to utilize polymers more effectively for advanced composite materials, many fundamental studies have been researched to discover fundamental reasons (i.e., molecular origins) for their intrinsic characteristics corresponding to the polymer physics and rheology. Recent experimental techniques offer some microscopic information. Nevertheless, it is still challenging issue to conduct a full atomic level analysis through only experimental approach. As such, depending on the rapid increase in computing power, multi-scale computer simulation methods have been developed to reveal the fundamental origin for some unique phenomena observed at the macroscopic level. Therefore, we conducted a detailed numerical analysis on rheological and mechanical properties of polymeric materials via mainly nonequilibrium molecular dynamics (NEMD) simulations and finite-element-method (FEM) simulations (Abaqus CAE and COMSOL Multiphysics). In this dissertation, we first present comprehensive analysis on the shear rheology of polymers for various molecular architectures (linear, ring, and short-chain branched) in the bulk and confined systems using atomistic NEMD simulations. In comparison to bulk polymeric system, the interfacial chain dynamics near the boundary solid walls in the confined system are interesting. Detailed molecular-level analysis of the individual chain motions for various molecular architectures are carried out to characterize the intrinsic molecular mechanisms for interfacial chains in three characteristic flow regimes (weak, intermediate, and strong) regarding to the interfacial slip behavior (i.e., degree of slip). Based on fundamental studies for polymers, we additionally modeled and analyzed polymer nanocomposites to fabricate versatile sensor devices using FEM simulations collaborated with experimental approach. Through a precise modeling in consideration to (particularly) mechanical properties, we found the most optimized construction of the nanostructured polymeric materials with highly improved sensing performances (ultrahigh sensitivity, linear sensing capability, and broad sensing range). Finally, we demonstrated highly sensitive triboelectric, ferroelectric, mechanochromic, and piezoresistive sensors with a proper physical (fundamental) mechanism to improve sensing ability.ope