Cholak I. Determination of the Physical Properties of Polymer and Composite Materials by Methods of Molecular Dynamics and Structural Mechanics

Cholak I. V. Determination of the Physical Properties of Polymer and Composite Materials by Methods of Molecular Dynamics and Structural Mechanics. – Qualifying scientific work on the rights of the manuscript. The dissertation is devoted to the determination of the physical and mechanical properties of polymer and composite materials using molecular dynamics (MD) methods and structural mechanics before their synthesis, which is necessary for predicting their effectiveness in solving specific tasks under conditions close to real-world operations. An analytical review of the current state of research on the physical and mechanical properties of polymeric and composite materials was conducted. The software and various force fields used for modeling polymers and polymer nanocomposite materials (PNCMs) by MD methods, the techniques for building molecular systems of polymers and composites, and the ways of equilibrating molecular models for further simulation of the materials’ physical and mechanical properties were considered. It was established that numerical modeling methods are powerful tools for minimizing the consumption of material resources and the time required for the development of new materials, particularly nanocomposites. Modeling processes in polymers and polymer nanocomposites before their synthesis using the mentioned methods allows studying the behavior of materials under conditions approximating real operational environments and determining the feasibility of their production at the design stage. The relationship between molecular dynamics and structural mechanics methods was considered through a multiscale approach to enhance modeling capabilities. It was found that the use of a multiscale approach helps to reduce the computational power required and extends the temporal and spatial boundaries of the systems under study. Using the LAMMPS software, MD modeling of the physical and mechanical properties of polyethylene was carried out. The results of verifying the polyethylene (PE) molecular model showed that the MD simulation data either matched or were close to the available literature data. Theoretical studies of the mechanical properties of polyethylene-carbon nanotube (PE-CNT) and PE-graphene nanocomposites were carried out using similar algorithms. Molecular dynamics modeling of the thermophysical properties of PE-CNT and PE-graphene nanocomposites was conducted, including thermal conductivity, specific isobaric heat capacity, the coefficient of linear thermal expansion (CLTE), and the glass transition temperature. Nonlinear two-parameter dependencies of the mechanical and thermophysical properties of PE-CNT and PE-graphene in the temperature range of (280–320) K and the filler volume fractions (0–2.0 %) and (0–1.5 %), respectively, were obtained. For the development of new nanocomposite materials, it is no longer necessary to perform complex and lengthy numerical experiments based on MD modeling. This set of properties is needed for modeling the thermo-elasto-plastic state of PE-CNT and PE-graphene nanocomposite products under operational conditions in a continuum approximation. Mathematical models were formulated, and corresponding numerical models were developed for the stress-strain state tasks for testing PE-CNT nanocomposite materials with functionalized CNT in an isotropic medium approximation. Research was conducted on the effective mechanical properties of PE-CNT nanocomposites with various volume fractions and random placement of functionalized CNTs of different lengths in the polymer matrix. Tools in the form of mathematical models, theoretical research methods for studying the physical and mechanical properties of polymeric materials by molecular dynamics and structural mechanics methods, and calculations for packaging that use polymer nanocomposite materials were developed. Recommendations were made for the use of polymer nanocomposite materials in industrial production and the packaging industry. The efficiency of using PE-CNT nanocomposites instead of PE in water supply pipes and containers for storing chemicals was determined using corresponding comparative stress-strain state calculations. The results of the dissertation were implemented into the educational process of the Department of Chemical, Polymer, and Silicate Engineering at Igor Sikorsky Kyiv Polytechnic Institute during the teaching of courses such as "Research and Engineering of Packaging Equipment", "Applied Problems of Continuum Mechanics", and "Scientific Work on the Topic of the Master's Thesis" for the specialty "131 – Applied Mechanics", with a focus on "Packaging Engineering and Packaging Equipment".