Understanding the Physical Phenomena of Functionalized Nanomaterials in Nanoscale System Based on the Intermolecular Interaction via Multiscale Simulation

Abstract

Nanomaterials can be applied to biosensors, solar cells, drug delivery, and carriers of heat and electrons, and the range of potential applications have become more diverse. With the increasing number of fields for the application of nanomaterials, it is essential to understand their physical phenomena and characteristics. The performance of nanomaterials is determined by the type, size and chemical characteristics of materials and the environment. Therefore, more detailed information on the molecular interactions between nanomaterials and other organic materials is required to achieve suitable designs for each application. In this study, the molecular behavior and physical phenomena of nanomaterials (e.g., inorganic nanoparticles, polymers, proteins, and carbon-based particles) were investigated using multiscale simulation methods, including coarse-grained molecular dynamics (CGMD), all-atom molecular dynamics (AAMD) and density functional theory (DFT) calculation. In chapter 1, molecular interactions and physical phenomena in biological, solar cells, and fluid systems are introduced. The background of representative studies is described and the multiscale computational approach is shown along with detailed explanations of each method. In chapter 2, the dimerization of gold nanoparticles (Au-NP) with amphiphilic polymer brush is studied using the dissipative particle dynamics (DPD) method. Dimer Au-NP nanoparticles with a size less than 10 nm have high surface plasmon resonance intensity and low steric effect for efficient bio-labeling. We theoretically studied the self-assembly of monomer and dimer Au-NP’s by considering influential factors such as the Au-NP size, polymer thickness, and gap distance between dimer Au-NP’s. Larger Au-NP’s are obtained when the amounts of each polymer (i.e., PEG and PMMA) are roughly identical, and the distance between Au-NP’s in the dimer is shorter when the amount of PMMA is reduced within the condition of dimerization. In chapter 3, isomer effects on the hole-transporting efficiency in the perovskite solar cells (PSCs) and on the self-assembly of cancer-targeting amphiphilic peptides are investigated. First, two fluorinated isomeric analogs of well-known hole-transporting material (HTM) Spiro-OMeTAD are developed and applied to PSCs. To understand the structure-property relationship induced by the constitutional isomerism, we performed theoretical analyses and revealed that meta-fluorinated HTMs are packed more tightly than ortho-fluorinated HTMs. Second, we performed CGMD simulations to observe the self-assembly of peptides containing both L- and D-isomers and found that the racemate assemblies form a bundle of fibrils and more effectively destroy the cancer cell membrane than enantiomer assemblies of fiber. In chapter 4, the heat transfer mechanism of graphene flakes (GFs) in nanofluids is investigated using a nanopipe simulation system. The temperature and velocity profile of nanofluids are similar to those shown in the results of macroscale, while GFs do not follow the pipe flow and form a dense layer of nanoparticles near the pipe wall. GFs flow mainly near the pipe wall and perform the role as heat carriers from the pipe to fluids. The dense layer is maintained in a thermally fully developed region, and enhances the heat transfer ability of the fluids. Finally, we found that functional groups with fluids that are more miscible are more effective at improving the heat transfer ability, forming a thicker dense layer of particles. The findings reported herein, which include the theoretical interpretation of various physical phenomena of nanomaterials, are promising for drug delivery systems, solar cells, and fuel cell systems, especially using proteins and biomass such as cellulose and biodegradable polymers.