Particle size effect on mechanical and thermal properties of SiO2 particulate polymer composites
Date
2012
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Publisher
University of Delaware
Abstract
The objective of this thesis is to investigate the effect of the particle size on mechanical and thermal properties of both micro- and nano sized SiO2 particulate composites over a wide range of particle volume fractions. In this study, spherically shaped 10μm and 20nm SiO2 particles, and diglycidyl ether of bisphenol A (DGEBA) are used as fillers and as matrix material, respectively. While 10μm SiO2 particles are dispersed in the epoxy through a direct shear mixing method, nano-composites are fabricated by using commercially available standard Nanopox F400 (nanoresins AG, Germany) with hardener (Albidur HE600) at desirable volume fractions up to 15vol%. All samples were examined for cure degree and particle dispersion quality by the use of differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) or transmission electron microscopy (TEM), respectively. The glass transition temperature of samples was identified by DSC and mechanical dynamic analysis (DMA). Using thermal mechanical analysis (TMA), the thermal stability of the samples was evaluated. This study also employs tensile and fracture testing to characterize the tensile properties including Young’s modulus (E), tensile toughness, and fracture toughness (KIC). In the test results, 20nm SiO2 particulate composites show greater Young’s modulus and fracture toughness than 10μm SiO2 particulate composites at the same volume fraction. Finally, a combined numerical/experimental approach is used to study the effects of the particle/matrix interphase on the Young’s modulus of SiO2 particulate nanocomposites having nanoparticle reinforcements of different sizes. Our experiments showed that the composite Young’s modulus increases with decreasing nanoparticle diameter at the same volume fraction, but our finite element (FE) model predictions did not match the expected trends when the interphase was not accounted for. The new models include an interphase region around the nanoparticle which results in an “effective particle volume fraction” that is larger than the actual particle volume fraction. The results from the models are compared with the experimental results and the new models are accurately fitted to the experimental results using the interphase thickness as a curve-fitting parameter. This is the first study on the use of combined numerical/experimental investigations of elastic stiffness characteristics to demonstrate the existence of a particle size-dependent “effective particle volume fraction” due to the particle/matrix interphase region in a particulate nanocomposite.