| Title: | Comment on 'Bioinspired Reversible Switch between Underwater Superoleophobicity/Superaerophobicity and Oleophilicity/Aerophilicity and Improved Antireflective Property on the Nanosecond Laser-Ablated Superhydrophobic Titanium Surfaces' |
| Address: | "Faculty of Mechanical Engineering, University of Ljubljana, Askerceva 6, Ljubljana 1000, Slovenia" |
| Journal Title: | ACS Appl Mater Interfaces |
| ISSN/ISBN: | 1944-8252 (Electronic) 1944-8244 (Print) 1944-8244 (Linking) |
| Abstract: | "Laser-textured surfaces enabling reversible wettability switching and improved optical properties are gaining importance in cutting-edge applications, including self-cleaning interfaces, tunable optical lenses, microfluidics, and lab-on-chip systems. Fabrication of such surfaces by combining nanosecond-laser texturing and low-temperature annealing of titanium Ti-6Al-4V alloy was demonstrated by Lian et al. in ACS Appl. Mater. Inter. 2020, 12 (5), 6573-6580. However, it is difficult to agree with (i) their contradictory explanation of the wettability transition due to low-temperature annealing and (ii) their theoretical description of the optical behavior of the laser-textured titanium surface. This comment provides an alternative view-supported by both experimental results and theoretical investigation-on how the results by Lian et al. could be interpreted more correctly. The annealing experiments clarify that controlled contamination is crucial in obtaining consistent surface wettability alterations after low-temperature annealing. Annealing of laser-textured titanium at 100 degrees C in contaminated and contaminant-free furnaces leads to completely different wettability transitions. Analysis of the surface chemistry by XPS and ToF-SIMS reveals that (usually overlooked) contamination with hydrophobic polydimethylsiloxane (PDMS) may arise from the silicone components of the furnace. In this case, a homogeneous thin PDMS film over the entire surface results in water repellency (contact angle of 161 degrees and roll-off angle of 15 degrees ). In contrast, annealing under the same conditions but in a contaminant-free furnace preserves the initial superhydrophilicity, whereas the annealing at 350 degrees C turns the hydrophobicity 'off'. The theoretical calculations of optical properties demonstrate that the laser-induced oxide layer formed during the laser texturing significantly influences the surface optical behavior. Consequently, the interference of light reflected by the air-oxide and the oxide-metal interfaces should not be neglected and enables several advanced approaches to exploit such optical properties" |
| Keywords: | laser oxidation laser surface engineering polydimethylsiloxane surface contamination thin-film interference volatile organic compounds wettability; |
| Notes: | "PubMed-not-MEDLINEGregorcic, Peter eng 2020/03/27 ACS Appl Mater Interfaces. 2021 Jan 20; 13(2):2117-2127. doi: 10.1021/acsami.9b23462. Epub 2020 Apr 2" |
