Visual UV-sensitive colorimetric film deposited by PECVD

Abstract

The combination of ultraviolet (UV) light and oxygen has a detrimental effect on various materials. In polymers, this interaction can result in irreversible changes in the material's color and gloss, as well as a decline in its strength and flexibility. Changes in mechanical properties are the primary cause of crack formation due to chain splitting, impacting both the material's properties and the device's performance. In such cases, total or partial replacement of the product is necessary to prevent operational interruptions and accidents. The use of a visual colorimetric coating, applicable to different materials with complex geometries, that enables measurement of the exposure of the coated material to UV light may serve to predict in situ degradation of devices. This study explores the feasibility of creating a colorimetric film sensitive to ultraviolet light C (UV–C) deposited on a polypropylene substrate. The film was deposited using radiofrequency 13.56 MHz, 40 W, 30 min, low-pressure plasmas with oxygen (20 %), acetylene (40 %), and hexamethyldisiloxane (HMDSO) (40 %) in an atmosphere of 23 Pa. The impact of UV-C irradiation on the sample chemical structure, thickness, morphology, and roughness was investigated. Samples were examined every 3 h of UV-C exposure through Ultraviolet–Visible Spectroscopy (UV–Vis), Surface Plasmon Resonance (SPR), and photographs analyzed by Hue-Saturation-Lightness (HSL). The films are composed of C, O, H, and Si in a typical amorphous carbon-hydrogenated-oxygenated (CC, CO, O–H, and C–H) network doped with Si (Si–CH3, Si–O, Si–OH) groups, exhibiting an amber color. Upon UV-C irradiation, the concentration of unsaturated C bonds (CC and CO) decreases, Si is depleted, and a gradual color change occurs until the film becomes colorless after 30 h of exposure. The proposed mechanism for the modification in the composition and structural arrangement of the film leading to discoloration is based on the results of the analyses conducted.