A low-pressure plasma technology was applied for the first time to modify the surface of filter media used for separation of liquid particles from air streams without affecting their bulk properties. The effect of surface wettability on the filtration performance and internal liquid distribution of glass microfiber filters was investigated experimentally. It was found that typical jump and channel characteristics existed in the evolution of both pressure drop and penetration of the filters, which means that in the jump stage of pressure drop, the penetration of oleophobic filters decreased steeply with loading time and the rate of decrease was greater in low-efficiency grade media. However, the variation trends of penetration were opposite in high- and low-efficiency grade oleophilic filters; that is, increased and decreased, respectively. In the channel stage of pressure drop, the penetration increased gradually with loading time in the oleophilic filters but changed little in the oleophobic ones. The oleophobic filters demonstrated lower jump pressure drop, film thickness, equilibrium saturation and loss of efficient fibers compared with their oleophilic counterparts. Furthermore, the oleophobic filters exhibited a remarkable advantage in overall filtration performance due to their comparable pressure drop and significantly higher filtration efficiency at steady state compared with their oleophilic counterparts. It was demonstrated that the most penetrating particle size remained almost constant for filters with the same structure but different wettabilities, although the filtration efficiency for particles across the whole size range was improved in oleophobic filters. Additionally, the dependence of filter performance on the surface modification method was also explored using an oleophilic medium as the control. The results showed that different approaches were capable of changing the media wettability to various degrees. Compared with the unmodified filter or those modified only by nanoparticles or fluoride copolymer, the filters modified by the combination of nanoparticles and fluoride copolymer had the overall best filtration performance. (C) 2019 Published by Elsevier B.V.