Technological challenges and progress in nanomaterials plasma surface modification – A review

Nanoscale particulate materials draw great interest in an increasing number of applications, such as electronics, energy storage, automotive, health or environment. In particular, the addition of nanofillers in a polymer matrix can significantly improve the thermal, mechanical, electrical, optical, and biological or corrosion protection properties of a nanocomposite, provided that the fillers exist as discrete entities and strongly adhere to the matrix. Nanocomposite synthesis generates major technological challenges, due to the natural tendency of nanomaterials to agglomerate and to their poor compatibility with polymeric materials. The main approach to tackle these issues consists in modifying the fillers surface to enhance their affinity with the matrix and produce repulsive interactions between the particles. In this paper, after a brief review of the conventional "wet" methods used to modify the surface of nanomaterials, we highlight the numerous technical, environmental and economic advantages provided by dry and versatile plasma treatments. Then, we present the different plasma reactor configurations designed so far, for powders surface functionalization. In particular, we spotlight the advantages and drawbacks of each system regarding particle mixing, powder yields and up-scaling possibilities. Finally, we introduce the main characterization tools generally used to analyze modified nanopowders. In this last part, we underline the main results and achievements obtained up to now in terms of treatment uniformity, functionalization degree, dispersibility/stability enhancement and improvement of nanocomposite performances.