High-resolution TEM analysis of flatten carbon nanotube packing in nanocomposites

• Observation of CNT packing in the epoxy composite with high mechanical properties.
• Cryo-microtoming of carbon nanotube composite for TEM observation.
• Different type of CNT stacking was configured with high-resolution TEM.
• Development of 3D printed fixture for efficient sample collection.

Due to the nanoscale size of carbon nanotubes (CNTs), observing the CNT/CNT and CNT/resin interactions in nanocomposites requires a high resolution transmission electron microscope (TEM) analysis. This research focuses on developing a protocol to provide an effective and reliable approach to obtain ultra-thin (<25 nm) cross sections of CNT/polymer nanocomposites for TEM analysis. Improvements were achieved by studying the relationships between chosen microtome cutting parameters, sample characteristics, and TEM image quality. A cutting protocol was established so that ultra-thin cross sections can be achieved by different microtome operators. In addition, a custom made tool was utilized to aid in the sample collection process. The 3D printed tool made it possible to view both the cut sample and TEM grid under the same optical view, ensuring that the cut sample was successfully transported to the TEM grid.Two CNT nanocomposite samples made with different resins were studied for both microtome cutting and TEM analysis and it revealed the alignment direction of the nanotubes and numerous stacks of CNT bundles. In addition, there was visible flattening of CNT packing into dumbbell shapes similar to results obtain in CNT yarn materials. TEM for the 3-layer CNT BP/BMI nanocomposite revealed uniform cutting in the resin areas. However, when the diamond knife reached graphite crystalline regions, the nanotubes either became deformed into a cone-like structure, were cut thicker than the resin, or folded over onto itself. This is most likely due to the high mechanical properties of CNT in response to the stress of cutting.