Alignment and Sample Preparation of Conductive Polymer/Carbon Nanocone Adhesives for TEM

Abstract

The four primary forms of carbon known as graphite, diamond, fullerenes and carbon nanotubes have been previously been vigorously studied for a wide range of applications and functional materials. During the last decade a new form of carbon has been in the spotlight, which is the carbon nanocones. These carbon nanocones are virtually pure elemental carbon in the form of disks or cones in the range of 200 nm – 4000 nm in diameter.

Carbon nanocones are highly interesting as filler materials for conducting adhesives since they offer a cheap and inexhaustible supply of raw materials where the production is capable of easy upscaling to industrial production quantities, like carbon black. The advantage of using carbon nanocones as filler material in conducting adhesives instead of carbon black is the possibly increased conducting properties of the particles, and the bigger particles offers decreased overall resistance in the conductive adhesives due to fewer particle boundaries.

To explore conductive polymer/carbon nanocone adhesives further than previously by the use of transmission electron microscopy (TEM), composite samples were prepared in-plane and out-of-plane by dielectrophoretic alignment of particles induced by an external AC field. Selected sample preparation routes for TEM were tested to establish a working method of investigation to discover the inner structure of the composites, and were investigated in such a microscope. Cryo-Ultramicrotomy proved to be a successful method, although at a mediocre success rate and with limited area for investigation.

The results revealed that the particles have a point contact rather than a larger flat surface contact. In the prepared sample, the contacts seem to occur at the singular points of the particles, that is facets of disk edges and cones, and at the apex for the carbon cones. The point contact of the particles may explain why the electrical conductivity of aligned composites is easily disrupted by mechanical stress. Wetting and filling of polymer/carbon were investigated by TEM and SEM, which revealed that electrowetting did not dominate the wetting properties.

Carbon nanocones were also investigated by HRTEM, and several interesting results were discovered. The tip of the cones was discovered to have facets, with subsequent layers having the same layer faceting and adding up to a group of layers. Such groups of layers were shown to be divided by cavities in the tip which separates the groups with different faceting. Facets at the circumference of the carbon nanocones were discovered, and these β-facets were also discovered to be highly non-uniform along the circumference of the cones. The layered structure of Carbon nanocones was discovered to have no domain-changes within a relatively large area, indicating single-domain layers throughout the particle.