Insights into the wettability transition of nanosecond laser ablated surface under ambient air exposure

Abstract

Super-hydrophobic surfaces are attractive due to self-cleaning and anti-corrosive behaviors in harsh environments. Laser texturing offers a facile method to produce super-hydrophobic surfaces. However, the results indicated that the fresh laser ablated surface was generally super-hydrophilic and then gradually reached super-hydrophobic state when exposed to ambient air for certain time. Investigating wettability changing mechanism could contribute to reducing wettability transition period and improving industrial productivity. To solve this problem, we have studied the bare aluminum surface, fresh laser ablated super-hydrophilic surface, 15-day air exposed surface, and the aged super-hydrophobic surface by time-dependent water contact angle (WCA) and rolling angle (RA), scanning electron microscopy (SEM), 3D profile and X-ray photoelectron spectroscopy (XPS). The origins of super-hydrophilicity of the fresh laser ablated surface are identified as (1) the formation of hierarchical rough structures and (2) the surface chemical modifications (the decrease of nonpolar carbon, the formation of hydrophilic alumina and residual unsaturated atoms). The chemisorbed nonpolar airborne hydrocarbons from air moisture contributed to the gradual super-hydrophobic transition, which can be proved by the thermal annealing experiment. Particularly, to clearly explore the wettability transition mechanism, we extensively discussed why the laser-induced freshly outer layer was super-hydrophilic and how the airborne hydrocarbons were chemisorbed. This work not only provides useful insights into the formation mechanism of laser ablated super-hydrophobic surfaces, but also further guides industry to effectively modify surface chemistry to reduce wettability transition period and rapidly produce stable and durable super-hydrophobic surfaces.

Short- and Long-Term Wettability Evolution and Corrosion Resistance of Uncoated and Polymer-Coated Laser-Textured Steel Surface

“…Therefore, the intrinsic hydrophilicity of the polar metal oxides is amplified by the laser-induced surface roughness according to Wenzel's theory. The conversion of surface wettability, on the other hand, is known to be caused by the adsorption of organic matters from the surrounding atmosphere over time [5,28]. This was confirmed by evaluating the atomic ratio between carbon and metal species (C/M), which is governed by the amount of adsorbed organic matters (Figure 5b).…”

Fabrication of super-hydrophobic nickel film on copper substrate with improved corrosion inhibition by electrodeposition process

“…1(h). are other sources to increase the amount of the four abovementioned functional groups [21][22][33][34]. However, the result implied that the as-prepared surface was dominated by the nonpolar C-C(H) groups with the concentration of 90.62% as shown in the Fig.…”

“…Regarding laser ablation method, although stable threedimensional (3D) hierarchical structures can be acquired by its precise control, the previous studies proved that the fresh laser textured surfaces showed the hydrophilic or super-hydrophilic nature. It will take a relatively long time from serval days to several months under ambient air exposure to reach the super-hydrophobic state [21][22][23], which will limit the economic efficiency for any practical applications due to very long processing time. For thermal embossing approach, the micro/submicron periodic structures were imprinted on the thermoplastic polymers, but such surfaces cannot show super-hydrophobic property.…”

Atmosphere-Mediated Superhydrophobicity of Rationally Designed Micro/Nanostructured Surfaces

“…The increasing hydrocarbon content detected via ToF-SIMS was in accordance with the increasing C-C (or C-H) components measured via XPS, confirming the more relevant role of non-polar hydrocarbon groups responsible for the surface hydrophobicity. [49][50][51] In it took approximately three weeks to reach saturation in the USA (Figure 3a). The improved superhydrophobicity and accelerated adsorption stemmed from the higher levels of VOCs in Beijing 38,53 when compared to Urbana (Section S4, Supporting Information).…”