Estimation of the Interphase Thickness in Epoxy Based Nanocomposites

Ref ISH2015_363 • 2015

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Summary

Recent research has established that the introduction of nano-sized fillers into polymers often results in enhanced dielectric properties over the neat polymer. Often, the large improvement in properties is widely attributed to the properties of the interphase layer between the polymer matrix and filler material. However this interphase is yet to be identified and understood. An understanding of the interphase is of supreme importance in order to tailor and design dielectric properties through introduction of nano-sized fillers. The present work aims at estimating the interphase thickness in epoxy based nano-composites. The epoxy resin (LY 556) is used as the base polymer, and aluminum oxide (Al2O3) particles with an average size of 50 nm are used as fillers. Both as-received as well as surface modified particles are used. The nano-composites are characterized in terms of space charge density, conductivity, permittivity, and breakdown strength. The Pulsed Electro Acoustic (PEA) system from TechImp, Italy is used for space charge measurements. Polarization-depolarization current measurements are made with a Keithley (6517A) electrometer. Permittivity is measured using HAMEG (HM8118) programmable LCR meter. The properties are measured for different nano-filler loadings (0.5 vol. % to 2 vol. %). It is ensured that all samples are free from agglomeration, and dispersion is uniform. The dispersion of nanoparticles in the base polymer is examined using Field Emission Scanning Electron Microscopy (FESEM), and then quantified using a method devised in the author's laboratory. The experimental findings reveal a correlation between interphase volume fraction and improvement in dielectric properties. It is assumed that the best improvement in property is achieved at that filler loading where the interphase volume is maximised, provided adequate dispersion is achieved at all filler loadings. An approximate interphase thickness in the epoxy alumina nano-composites is estimated using the interphase volume model.