Selective and quantitative irradiation of surfaces with O and OH radicals in room air for investigating their effects on plasma treatments of solid, liquid, and biological surfaces

In atmospheric-pressure plasma surface treatment, surface reactions of reactive species play a critical role. However, quantitative evaluation of individual species has been limited due to the difficulty in selectively supplying them. To address this issue, we have developed a novel method to selectively supply reactive species such as O and OH to a surface in ambient air. The method utilizes vacuum ultraviolet (VUV) photolysis of precursor gases (e.g., O₂, H₂O, CO₂) to generate reactive species including O, OH, O₃, H₂O₂, H, and O₂(a). The densities of these species can be estimated through simulations. This enables quantitative evaluation of surface treatment effects by each species. For instance, our results showed that an OH dose (Nt) of 1.2 × 10¹³ s/cm³ is required to reduce the water contact angle by 1° on a polypropylene surface, while O atoms exhibit approximately four times higher effectiveness. The principle and some results of this method are presented. As the reactive species flux is quantifiable, the method is also applicable for validating surface reaction simulations, and we are currently working on the development of surface reaction models for reactive species based on this approach.