Owens-Wendt Method for Comparing the UV Stability of Spontaneous Liquid-Repellency with Wet Chemical Treatment of Laser-Textured Stainless Steel

Abstract

The liquid-repellent properties of AISI 304 stainless steel surfaces textured with a femtosecond laser were studied, both after spontaneous hydrophobization and when treated with stearic acid and octyltrimethoxysilane. Surface topography has been shown to play a critical role in determining these properties. Although textures containing only LIPSS exhibited poor liquid-repellency, the performance was significantly improved after engraving the microtexture. The most effective topography consisted of 45 µm-wide grooves with a pitch of 60 µm and protrusions covered with a rough microcrystalline structure. Liquid-repellency, chemical treatment efficiency, and UV resistance were compared using derived Owens-Wendt parameters. The surface of femtosecond-laser-textured steel after spontaneous hydrophobization was found to be significantly less stable under UV irradiation than surfaces treated with stearic acid or octyltrimethoxysilane modifiers.

Keywords: LIPSS; Owens–Wendt approach; UV stability; laser microprocessing; liquid-repellency; stainless steel; wet chemical treatment.

Figure 1

The structural formulas of modifiers used for surface treatment.

Figure 2

An example of an Owens–Wendt plot where the X axis is $\frac{\sqrt{{\sigma }_L^P}}{\sqrt{{\sigma }_L^D}}$ and the Y axis is $\frac{{\sigma }_L(1+cos\theta )}{2\sqrt{{\sigma }_L^D}}$.

Figure 3

Sample surface topography under SEM: (a) LIPSS pattern on the sample “L”; (b) LIPSS on the sample “6030L” and 30 µm-wide grooves with a pitch of 60 µm; (c) LIPSS on the sample “10030L” and 30 µm-wide microgrooves with a pitch of 100 µm; (d) LIPSS on the sample “6045L” and 45 µm-wide microgrooves with a pitch of 60 µm; (e) 45 µm-wide microgrooves on the sample “6045” with a pitch of 60 µm; (f) crystal-like texture on the sample “6045” at high magnification.

Figure 4

Texture scan areas for EDS analysis: (a) sample “6030L”; (b) sample “10030L”; (c) sample “6045L”, and (d) sample “6045”.

Figure 5

Wetting properties of textured surfaces before and after treatment compared to a reference plate (designated as “Flat St”).

Figure 6

Owens–Wendt plots for reference plate and textured surfaces: (a) reference plate; (b) sample “L”; (c) sample “6030L”; (d) sample “10030L”; (e) sample “6045L”; and (f) sample “6045”.

Figure 7

Owens–Wendt plots for the sample “6045L” under the influence of UV irradiation: (a) spontaneous hydrophobization; (b) treatment with stearic acid; (c) treatment with OCTEO.

Figure 8

Derivative parameters of the Owens–Wendt plot for textured surfaces of the sample “6045L” under UV irradiation: (a) for the parameter ${\sigma }_{TS}^D$/${\sigma }_S^D$; (b) for the parameter ${\sigma }_{LIN}^P$.