Characterization of Mechanical Properties of Polymer Nanocomposites with Spherical Inhomogeneities

Goudarzi, Taha | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40433 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Naghdabadi, Reza; Bagheri, Reza
  7. Abstract:
  8. The improved properties of nanocomposites are not achievable with conventional composites. Scale effect is one the most important parameters in the physical and mechanical properties of polymeric nanocomposites. One of the physical phenomena, which can be related to the scale effect, is the very large interface between the nanoparticles and the polymeric matrices. Motional behavior and conformation of polymeric chains change near the nanoparticles surfaces. Due to high interface of the nanoparticles with the polymeric matrices the amount of these types of changes in the polymeric chains are so large that can change the physical and mechanical properties of polymeric nanocomposites. In this thesis to investigate the effect of this high interfacial area on the mechanical properties of epoxy-silica nanocomposites some nanocomposite specimens with small weight fraction of hydrophobic and hydrophilic silica nanoparticles and Epon 828 epoxy resin have been synthesized and tested. To get a better dispersion an ultrasonic apparatus has been used in the synthesis process. The specimens having ultrasonic in their synthesis process showed a better mechanical properties than the other specimens and the pure resin. By the way, more improved properties can still be achieved with a better dispersion. To model this size-dependent behavior of the nanocomposites with micromechanical schemes (i.e. generalized self-consisted method (GSCM)), Gurtin and Murdoch theory of surface elasticity has been used which assumes that there is some free energy in the interface of the inclusions and the matrix phase. This energy results in a surface stress which induces a traction jump across the interface. The amount of this jump is related to the surface Lame constants and the size of the inclusion. In this regard, we can obtain some size dependent moduli which can be used for investigation of the size dependency of moduli in polymeric nanocomposites containing spherical/cylindrical inhomogeneities. For the case of spherical inclusions the shear modulus of an isotropic effective medium has been derived as an answer of a nonlinear system of 8 equations with 8 unknowns which is new to literature. A closed-form expression for the transverse shear modulus of a transversely isotropic nanoporous material is derived. With the help of the derived modulus a size-dependant yield function for such nanoporous materials is presented. Using the surface moduli available in literature, the obtained shear modulus for an isotropic nanoporous material showed drastic discrepancies in comparison with the classical results. The size-dependent yield function for a nanoporous material containing cylindrical nanovoids with the help of the surface moduli showed improvements up to 40% for void radius of 1 nm, in comparison with the classical results. Also, with the help of the effective moduli for an isotropic nanocomposite, a method for modeling Young modulus of epoxy-silica nanocomposites is proposed and verified by literature data. Finally, using the proposed method the achievable improvement in Young modulus of the synthesized epoxy-silica nanocomposites determined to be up to 35% for weight fraction of 0.02 which is in good accordance with the experimental results of the thesis.
  9. Keywords:
  10. Surface Effect ; Three Phase Model ; Epoxy Silica Nanocomposite ; Surface Elasticity ; Micromechanical Modeling

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