Hydrophobicity, Freezing Delay, and Morphology of Laser-Treated Aluminum Surfaces

Abstract

Until recently, superhydrophobicity was considered as a hint to predict surface icephobicity, an association of concepts that is by no means universal and that has been proven to depend on different experimental factors and material properties, including the actual morphology and chemical state of surfaces. This work presents a systematic study of the wetting and freezing properties of aluminum Al6061, a common material widely used in aviation, after being subjected to nanosecond pulsed IR laser treatments to modify its surface roughness and morphology. All treated samples, independent of their surface finishing state, presented initially an unstable hydrophilic wetting behavior that naturally evolved with time to reach hydrophobicity or even superhydrophobicity. To stabilize the surface state and to bestow the samples with a permanent and stable hydrophobic character, laser-treated surfaces were covered with a thin layer of CF x prepared by plasmaenhanced chemical vapor deposition. A systematic comparison between freezing delay (FD) and wetting properties of water droplets onto these plasma-/polymer-modified laser-treated surfaces that, under conditions where a heterogeneous nucleation mechanism prevails, surface morphology rather than the actual value of the surface roughness parameter the key feature for long FD times. In particular, it is found that surface morphologies rendering a Cassie−Baxter wetting regime longer FDs than those characterized by a Wenzel-like wetting state. It is that laser treatment, with or without additional coverage with thin CF x coatings, affects wetting and ice formation behaviors and might be an efficient procedure to mitigate icing problems on metal surfaces.

Omniphobic Etched Aluminum Surfaces with Anti-Icing Ability

“…In contrast, if the droplet is placed on a surface with a structured morphology in the Cassie–Baxter wetting regime, air will be trapped below the water droplet, thereby minimizing the contact area between the surfaces of the substrate and water droplet. The air trapped in the surface cavities is a poor thermal conductor and, together with the reduction of the contact area, will considerably hinder the heat transfer between the substrate and the liquid, significantly delaying the freezing time of the droplet. − The low hysteresis CA (7°) along the high CA (160°) displayed by the PFPE-modified rough aluminum reveals that the droplet on this surface is in the Cassie–Baxter wetting regime, preventing the water penetration between the surface topography features and trapped air pockets and delaying the frost formation process. Despite the heterogeneous ice nucleation theory, which establishes that a critical radius of ice nuclei smaller than the size of the surface features allows spontaneous ice growth, and an ice nucleus radius of 4.5 nm calculated at −10 °C, significantly smaller than the size of the surface features on the rough aluminum (see Figures , S2 and Table S1), the substantial increase in the freezing delay time observed on the PFPE-modified rough aluminum, is attributed to the surface topography and to the small solid–liquid contact area and air pockets entrapped on the hierarchical micro/nanostructure (hindering the heat transfer), providing a low rate for ice nucleation and growth as was previously described in refs and .…”

3D Organic Nanofabrics: Plasma-Assisted Synthesis and Antifreezing Behavior of Superhydrophobic and Lubricant-Infused Slippery Surfaces

“…9,11,12 In addition, in a recent article, we reported on the application of nanosecond laser treatment on aeronautical aluminum alloy supports for the development anti-icing surfaces covered with a CF x polymer. 61 The linear patterning structure of the laser-ablated substrate is reported in the Supporting Information Figure S4. Figure S4 (see also Figure 4a) gathers SEM micrographs at different magnifications presenting the 3D-ONF(400 nm) growth on the ns-laser treated substrate.…”

Simulation of salt spray corrosion behaviour of micro-arc oxidation coating by laser induced Ag infiltration

“…Laser treatments to infiltrate the Ag into the MAO coating were performed using two different lasers in Laser Beam Scan (LBS) mode: an ns n-IR Yb fiber laser and a 300 ps UV laser. The laser beam scan process has been described elsewhere [22,23]. The first laser treatment was performed using the following parameters: a maximum power of 20 W, wavelength of 1 μm, spot size of 36 μm and pulse duration from 4 ns to 200 ns.…”