Structure-property relationships in exfoliated polyisoprene/clay nanocomposites

Structure-property relationships in exfoliated polyisoprene (PI)/clay nanocomposites have been studied as a function of the clay concentration with rheometry, X-ray diffraction, small-angle X-ray scattering, and transmission electron microscopy. The results presented here indicate that the interlayer spacing of layered silicates increases from 2 to at least approximately 14 nm because of the penetration of polymer molecules into the spacing between the silicate layers. The average aspect ratio (width/thickness) of the dispersed nanoplates is also estimated to be at least approximately 80. Additionally, the storage modulus of the nanocomposite exhibits frequency-independent pseudo-solidlike behavior above the percolation threshold [volume fraction of clay at the percolation threshold (phi(p)) - 0.02] and shows large enhancements (up to approximately six orders of magnitude) in comparison with the storage modulus of PI when the volume fraction of clay (phi) is greater than phi(p). For the shear-aligned PI/clay nanocomposites, an increase in the storage modulus with shear alignment is observed at phi < φ(p), whereas a decrease in the storage modulus is observed for φ > phi(p). (C) 2004 Wiley Periodicals, Inc.