Effect of Heat Treatment Temperature on the Wettability Transition from Hydrophilic to Superhydrophobic on Laser‐Ablated Metallic Surfaces

Abstract

Superhydrophobic metallic surfaces made via pulsed laser ablation have been utilized recently. Immediately after laser ablation, metallic surfaces become hydrophilic. By aging the laser‐ablated surface in ambient air for a relatively long period of time (several weeks to several months) or using a chemical coating post process, this type of surface becomes superhydrophobic. Herein, a facile post‐process heat treatment that does not use any harsh chemicals is introduced to reduce the wettability transition time from hydrophilicity to superhdyrophobicity compared to surfaces treated for extended periods of time in ambient air. Grid patterns are ablated on aluminum, copper, and titanium by a nanosecond pulsed laser. Then, facile post‐process heat treatment is applied at different temperatures. The effect of temperature on the wettability transition time is studied. The transition time is reduced from several weeks/months to a few hours. The wettability transition mechanism for each metal is also explained. Additionally, several potential applications, such as self‐cleaning, water positioning, and water transport, are proposed.

Expedited Transition in the Wettability Response of Metal Meshes Structured by Femtosecond Laser Pulses for Oil-Water Separation

“…Moreover, to test the sustainability of the superhydrophobic state on the meshes that were aged in vacuum for a few hours, we repeated the contact angle measurements after keeping those samples exposed to air for many weeks; yet they showed the same superhydrophobic behavior. Our observations on the transition in the wettability response, from superhydrophilic to superhydrophobic, under a high vacuum environment, of the structured metal surfaces are also consistent with previously reported data (Ngo and Chun, 2018 ). As has been reported earlier (Jagdheesh et al, 2017 ; Ngo and Chun, 2018 ), the wettability measurements of laser structured metal mesh immediately after laser ablation demonstrates superhydrophilic behavior due to the large presence of metal-oxides formed as a result of laser ablation.…”

“…Our observations on the transition in the wettability response, from superhydrophilic to superhydrophobic, under a high vacuum environment, of the structured metal surfaces are also consistent with previously reported data (Ngo and Chun, 2018 ). As has been reported earlier (Jagdheesh et al, 2017 ; Ngo and Chun, 2018 ), the wettability measurements of laser structured metal mesh immediately after laser ablation demonstrates superhydrophilic behavior due to the large presence of metal-oxides formed as a result of laser ablation. The unsaturated cations-anions formed after laser ablation stabilize themselves by heterolytic dissociative adsorption of H 2 O molecules from the atmosphere, giving birth to a hydroxylated layer over a metal-oxides layer (Jagdheesh et al, 2017 ).…”

“…The structured meshes demonstrated superhydrophilic response behavior immediately after ablation, as shown in Figure 3 . This behavior is attributed to the formation of a metal oxides layer during laser structuring (Ngo and Chun, 2018 ). The water contact angle for the freshly ablated metal meshes was ~0° and the water droplet permeated through the mesh in ~0.1 ms, exhibiting superhydrophilic characteristics.…”

Robust Self‐Cleaning and Marine Anticorrosion Super‐Hydrophobic Co–Ni/CeO2 Composite Coatings

“…[ 9 ] The superhydrophobic surfaces achieve distinct nonwetting properties through the combination of chemical compositions and hierarchical structures. Many techniques, such as chemical or electrochemical etching, [ 10 ] chemical vapor deposition, [ 11 ] laser processing, [ 12,13 ] colloidal synthesis, [ 14,15 ] and anodic oxidation [ 16 ] have been exploited for the fabrication of effective artificial superhydrophobic surfaces. However, all these methods involve complex treatments and/or expensive materials, limiting their mass production.…”

Controlling the Wetting Properties of Superhydrophobic Titanium Surface Fabricated by UV Nanosecond-Pulsed Laser and Heat Treatment

“…Recently, a solution combining nanosecond pulsed laser and heat treatment to prevent the usage of toxic chemicals and long fabrication time has been reported to form superhydrophobic copper [ 17 ], titanium [ 18 ], and aluminum grid-patterned surfaces [ 19 ]. However, research has focused mainly on the change in wetting behavior on only grid-patterned surfaces.…”