Recent findings regarding the controversy surrounding asphaltene molecular weight coupled with increasing understanding of their molecular structure has enabled the understanding of asphaltene properties. It has been shown previously that larger ring systems require more alkane substituents to maintain a balance between ring stacking propensity vs steric repulsion. Here, stacking and its disruption in asphaltenes and aromatic ring systems are explored using highresolution transmission electron microscopy (HRTEM). It is shown that molecularly disparate asphaltenes exhibit stacking invariants. Solubility data herein suggests these stacking invariants naturally follow from the solubility classification of asphaltenes.

We present the first synthesis of double coaxial carbon nanotubes with nitrogen-doped and boron-doped multiwalls by the template technique with two-step chemical vapor deposition. X-ray photoelectron spectra confirm the coaxial formation of different-doped structures. The electrical conductance and oxygen chemisorption measurement indicate dual electrical properties and chemical activity at their outer and inner layers.

Carbon nanotubes with a double coaxial structure of nitrogen-doped and undoped multiwalls were successfully prepared by the template technique using porous anodic aluminum oxide film as a template. The inner carbon layer (or the outer carbon layer) of the double coaxial carbon nanotubes is free from N, while the outer carbon layer (or the inner carbon layer) is uniformly doped with N. Transmission electron microscopy cannot differentiate between the outer and inner layers, but all the results by Raman, X-ray diffraction, and X-ray photoelectron spectroscopy provide evidence that the N-doped layer is less crystallized than the undoped one. Furthermore, the N-doped layer has apparently higher chemical reactivity toward oxygen than the undoped one due to more edge-active sites resulting from the introduction of nitrogen species. Electrical conductance measurement indicates that despite poorer crystallinity the N-doped layer has higher conductivity than undoped one. The resulting multiwalled carbon nanotubes thus have not only double-stack coaxial structure but also dual physicochemical properties.

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