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Estimation of interphase thickness of epoxy-based nanocomposites

Recent literature attributes the improvement often seen in the properties of nanocomposites to the interphase layer between the polymer matrix and the filler material. However, an understanding of the interphase in nanocomposites is still elusive. The present work aims at estimating the interphase thickness of epoxy based nanocomposites. For experimental studies, epoxy resin is used as the base polymer, and aluminium oxide (Al2O3) particles with an average size of 50 nm are used as fillers. The nanocomposites are characterized in terms of space charge density, conductivity, permittivity, and breakdown strength. All properties are measured for different nanofiller loadings (0.5 vol. % to 2 vol. %). The experimental findings reveal a correlation between interphase volume fraction and change in dielectric properties. It is assumed that the greatest change in property is achieved at that filler loading where the interphase volume fraction is maximized, provided adequate dispersion is achieved at all filler loadings. An approximate interphase thickness is estimated for epoxy alumina nanocomposites by using experimental results in conjunction with a simulation model. Accuracy of the estimated interphase thickness is seen to be dependent on the scatter in particle size and the uniformity of particle dispersion in the polymer matrix.