Development, characterization and multifunctional performance of polymer matrix/silicon nitride nanocomposites
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Date
2025-01-22
Authors
Διάφας, Νικόλαος
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Abstract
Polymer matrix-inorganic/ceramic nano-inclusion composites are a class of materials that has attracted worldwide scientific interest in the last decades. In this thesis, the development and characterization of multifunctional nanocomposite systems with parameter the content of the reinforcing phase was carried out. Epoxy resin was used as the matrix, while Si3N4 nanoparticles were used as the reinforcing phase. Initially, the morphological and structural characterization of all nanocomposite systems was carried out using XRD (X-ray Diffraction) and SEM (Scanning Electron Microscopy) techniques. Through the study of XRD patterns and SEM images, the fine dispersion of the nanoparticles as well as the successful incorporation of the nanoparticles into the polymer matrix was determined.
Then, the thermomechanical characteristics of the nanocomposite specimens were studied using dynamic mechanical analysis and tensile testing. Through dynamic mechanical analysis, the following quantities were determined: storage modulus, loss modulus and loss tangent/damping coefficient tanδ as a function of temperature. Furthermore, the study of nanocomposites by this technique indicated the variation of glass transition temperature, as well as the increased values of storage modulus as a function of increasing filler content. Through tensile testing, static mechanical properties of the nanocomposites such as elastic modulus, maximum stress, yield strength, fracture stress and toughness were studied and determined.
In addition, the dielectric response of all epoxy resin/Si3N4 nanocomposite systems was investigated over a wide range of frequencies and temperatures by broadband dielectric spectroscopy (BDS). The results indicated the presence of three relaxation mechanisms, referring to (a) the transition from the glassy to elastomeric phase of the polymer matrix (𝛼-mode), (b) the rearrangement of the polar side groups of the main chain (𝛽-mode), and (c) the interfacial polarization (IP) between the heterogeneous components of the nanocomposites. Furthermore, it was found that the AC conductivity follows the universal AC conductivity law (AC universality law). All the nanocomposite systems exhibited improved dielectric properties, which are mainly attributed to the heterogeneity of the epoxy resin/nanoparticle system as well as the extended interface created between the individual components.
Finally, charging and discharging experiments were performed under DC electric field conditions for all nanocomposites, to calculate the respective stored and recovered energies, as well as their coefficient of energy efficiency. From these experimental results, it was determined that these nanocomposites have energy storage and recovery capability and that the addition of Si3N4 NPs enhances this property.
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Keywords
Nanocomposites, Epoxy resin, Silicon nitride, Dielectric properties, Thermomechanical behavior, Multifunctionality, Nanodielectrics, Energy storing/retrieving, Energy efficiency coefficient