Nonthermal plasma technologies for advanced functional material processing and current applications: Opportunities and challenges

In recent years, there has been a large demand for processing technologies that are environmentally safe, energy efficient, and that generate low levels of waste byproduct. For these reasons, and due to their versatility, plasma-based technologies have come to the forefront of material processing and fabrication in both research and industry. At its core, plasma is a gas that has been excited to the next state of matter, which contains an abundance of free radicals, free electrons, ions, neutral atoms, and UV radiation. This cocktail of chemistries can be generated at, or close to, room temperature and is therefore known as “cold plasma”. As such, it has become a preferred method of surface modification as these generated species can be used for both chemical and physical alterations, without interfering with the bulk properties of the material. Cold plasma systems have been used for over a decade from assisting in material process modifications to surface patterning at the nanoscale. This review summarizes the recent advances made in the development and utilization of key nonthermal plasma technologies. State-of-the-art plasma systems, such as microbubble and pin-to-plate reactors, are discussed in detail. Furthermore, the use of plasma in surface modification, water treatment, micro-organism decontamination, and food treatment applications are explored in depth. Despite recent developments and methodologies, current plasma systems still have many challenges, such as processing time, scalability, material suitability, and limited theoretical understanding of the dynamics present at each interface present in the treatment process. These factors need to be addressed before plasma-based technologies can be fully integrated at an industrial scale and in more fields of application.