Fig 1.
Schematic diagram of surface fabrication and experimental processes.
(a) Plasma treatment of PTFE by controlling variables. (b) Measure the contact angle and sliding angle of the surface using a surface tension measuring equipment. (c) Check the self-cleaning effect of the specimen using graphite and water droplets.
Table 1.
Design of surface treatment parameters for plasma treatment.
Fig 2.
Graph of contact angle and change of contact angle according to slide angle and surface treatment parameters of treated specimen.
(a) contact angle and sliding angle graph of before and after treatment (b) i) Before treatment, ii) After PE treatment, iii) After RIE treatment, the image where the droplet is located and the contact angle. (c, d) The contact angle graph according to the surface treatment parameter (RF power, exposure time). The PE-treated specimen is expressed in red and the RIE-treated specimen is expressed in black.
Fig 3.
Analysis of surface characteristics.
(a) FE-SEM image i) Before treatment, ii) After RIE treatment, iii) After PE treatment. More detailed structures of columnar shapes can be observed on the RIE surface, and leaf vein-like structures can be observed on the PE surface. (b) SPM images of surfaces i) pristine, ii) after PE treatment and iii) after RIE treatment. (c) FT-IR spectrum analysis confirmed no significant difference in the chemical composition of the surface before and after treatment. (d) XPS results of pristine, PE, and RIE Specimens.
Fig 4.
Observation and analysis of droplet collisions.
(a) Composition of experimental equipment for droplet collision observation. The needle dropped droplets at a height of 20 mm from the surface and the droplet size is 2.8±0.2 mm. The velocity of the droplet was 1.02 m/s. (b) Results of high speed cameras from contact with droplets to removal from surfaces. Compared with the specimen treated with the PE method, water droplets splashed faster on the specimen treated with RIE. (c) When water droplets bounced from the specimen treated with the PE method, small water droplets are scattered. The small droplets were between 0.4 and 0.5 mm in size.
Table 2.
Interface tension and We of the surface before and after treatment.
Fig 5.
Verifying the self-cleaning effect of the produced specimen.
(a) The process of removing fine contaminants from the manufactured specimen. (b) The process of removing contaminants from the treated specimen. The water droplets repeatedly bounced off the surface. In this process, particles in the path were removed, and finally, they were off the surface of the specimen. As a result of repeating the same process for 20 seconds, almost all particles on the surface were removed, and only a few particles remained in the place where water droplets did not contact.