Correlative Raman spectroscopy and scanning electron microscopy of thermosetting carbon nanotube composite microstructures

Abstract

In recent years carbon nanotubes (CNT) have attracted significant research into their processing, properties and applications due to their extraordinary mechanical [1], electrical [2] and thermal properties [3]. Incorporating CNTs into polymer matrices to produce composite materials is one strategy to harness the potential of these materials. The development of a powder based processing route for thermosetting nanocomposites allows the manufacture of materials with high loading fractions (up to 20wt%) of CNTs [4]. Typically, nanocomposites with randomly dispersed CNTs show a decline in strength and plateau in elastic modulus beyond a few volume percent CNTs, as well as severe embrittlement [5, 6]. However, in recent work, the highest strength and modulus of the powder‐based composites increased up to the highest loading [4]. Differential interference contrast (DIC) optical reflective microscopy of these nanocomposites have revealed a texture with domains on the length scale of the original powder particles, suggesting the migration of resin out of the nanocomposite particles to fill voids at particle interfaces. Raman spectroscopy combined with scanning electron microscopy is a powerful tool to identify the presence of epoxy rich regions and variations in CNT density. The correlated chemical and morphological analysis provides insight into the unique microstructure of the nanocomposite not possible by elemental analysis methods, such as EDS. Using correlated Raman and SEM techniques, the relationship between CNT loading on the “grain size” is quantified and calibrated resulting in an enhanced understanding of how the microstructure affects the macro mechanical properties of the nanocomposite.