Characterization of distribution and arrangement of filler particles in polymer composites is of primary importance to understand and maximize their mechanical, electrical and thermal properties. An innovative procedure that allows reliable and straightforward preparation of cross-sections of polymer composites with the use of mechanical polishing, ion beam etching and soft gaseous etching is presented in this paper. Because of the inherent difference between the organic amorphous matrix and the inorganic crystalline nature of composite fillers, the removal of matrix layers at the surface of the cross-section at the expense of the inorganic materials allowed characterizing the composite filler particles structure and distribution over the surface. Since beam broadening did not occur before the beam hit the nanoparticles, high-resolution imaging in the scanning electron microscope was possible and true dimensions and orientation of the particles were observed. This provided more flexibility in selecting the primary beam voltage; especially, the use of low beam energy greatly improved the image contrast and reduced charging effects resulting from the primary electron beam bombardment. It was shown that only polymers with a carbonated main chain could be etched selectively by the gaseous etching process. Lay Description Since the invention of polymers, several tens of years ago, they have been involved in lots of applications in the everyday life, the main one being the plastic industry which permitted replacing wood and metal based objects by more light weighted plastic objects, more easily shaped than metals and wood. Depending on their use, they provide better mechanical behaviors combined to a better corrosion resistance which greatly improved the lifetime of such objects. Later, their mechanical properties and more importantly, their electrical conductivity were enhanced by adding small particles of harder materials leading to the development of polymer composites, or nanocomposites when the filler particles were nanometer sized. These provide a mesh of hard and/or conductive material which is filled with the polymer. To understand the impact of these particles, it is necessary to know exactly how they are distributed inside the polymer and how they interact with each other, especially for electrical conductivity purposes. Optical microscopes are generally used to image the distribution of these particles but scanning electron microscopes (SEM) are more suited when nanoparticles are used. In this technique, the polymer surface is bombarded with electrons extracted from a sharp metal tip. These electrons interacts with the atoms of the matter below the specimen surface and give rise to the emission of several electronic signals which are collected by the detectors of the SEM. These signals are used to reconstruct an image of the specimen surface with permits to see smaller details than with the optical microscope. Generally, the specimen is fractured at very low temperature to provide a way to see the structure of the composite inside the sample. However, certain types of polymer composites are difficult to fracture due to the different materials that are part of its composition. The work reported here describes a new technique to produce high quality cross sections of polymer nanocomposites based on hand polishing followed by ion polishing (using ions instead of bulk materials) and surface etching with a corrosive gas. The use of a powerful SEM applied to such cross-sections permitted to obtain images that gave an overview of the whole material as close as possible of the true microstructure. However, it was shown that only polymers composed mainly of carbon bonds could be etched selectively by the etching process with the corrosive gas and provide such high quality cross-sections.
