Harnessing biological inspiration to create metals that repel liquids, clean themselves, and resist ice and corrosion with remarkable efficiency.
Explore the ScienceHave you ever watched a raindrop skitter across a lotus leaf without leaving a trace, or wondered why water spreads into a thin film on a clean piece of metal? These everyday phenomena are governed by a property known as wettability, a field where nature has been the master engineer for millions of years 8 .
Today, scientists are borrowing these biological blueprints to endow ordinary metals with extraordinary abilities, transforming them into materials that can repel complex liquids, clean themselves, or resist ice and corrosion with remarkable efficiency. This isn't just laboratory curiosity; it's a surface revolution that is enhancing technology in fields from aerospace to biomedical engineering.
At its heart, wettability describes how a liquid interacts with a solid surface. The key measurement is the contact angle—the angle formed where a liquid droplet meets the solid. A low contact angle (less than 90°) means the liquid spreads out, indicating a hydrophilic (water-loving) surface. A high contact angle (greater than 90°) means the liquid beads up, revealing a hydrophobic (water-fearing) surface 8 .
Hydrophilic
Neutral
Superhydrophobic
The journey to understanding these states began in 1805 with Thomas Young, who related the contact angle to the balance of forces between solid, liquid, and gas interfaces 3 . But real surfaces aren't perfectly smooth.
Proposed that roughness amplifies the intrinsic wettability of a material. On a rough hydrophilic surface, liquid completely penetrates the grooves, making it even more hydrophilic 1 .
Later scientists built on this foundation to account for roughness, leading to more accurate models of extreme wettability.
Describes a state where air gets trapped in the textured grooves beneath the liquid droplet. This creates a composite interface that dramatically boosts repellency, leading to superhydrophobicity 1 .
While many methods exist to create these functional surfaces, a particularly innovative approach is the LasPlas process, which synergistically combines laser texturing (Las) with plasma coating (Plas) 1 . This hybrid technique overcomes the limitations of either method used alone, creating surfaces that are not only powerful but also permanent and instantly available.
Ultrashort laser pulses (femtosecond or picosecond) are scanned across a metal surface—such as stainless steel, copper, or titanium alloy. By precisely controlling parameters like fluence and scanning speed, the laser ablates the surface to create a variety of textures. These can range from fine nanoscale ripples (known as LIPSS) to rougher microtextures like spikes, holes, and groves 1 .
Without any cleaning in between, the laser-textured surfaces are placed in a plasma-enhanced chemical vapor deposition (PECVD) chamber. Here, a precursor gas is ionized into a plasma, which deposits an ultra-thin, conformal coating (as thin as 1 µm) over the complex topography created by the laser. The choice of coating dictates the final wettability:
The results of the LasPlas process are striking. The research demonstrated that this method can reliably produce both super-wettability states on multiple industrially relevant metals 1 . The superhydrophilic surfaces showed long-term stability and could be easily renewed with ultrasonic cleaning, while the superhydrophobic surfaces were instantly effective and even repelled complex liquids like milk and beer 1 .
The significance lies in the synergy. The laser creates a durable, multi-scale physical structure, while the plasma coating precisely tunes the surface chemistry without clogging the delicate textures. This combination produces stable, high-performance surfaces that are a significant step toward real-world, industrial applications.
| Item Name | Function in the Experiment |
|---|---|
| Ultrafast Laser | Creates micro/nano surface textures with minimal heat damage to the underlying metal 1 . |
| Galvanometer Scanner | Precisely directs and scans the laser beam across the metal surface at high speeds 1 . |
| PECVD System | Deposits ultra-thin, uniform coatings of glass or polymer to modify surface chemistry 1 . |
| HMDSO Precursor | A precursor gas used in the plasma to create a silicone-like polymer coating for hydrophobicity 1 . |
| C4F8 Precursor | A fluorinated precursor gas used to create a PTFE-like superhydrophobic coating 1 . |
| Material | Laser Process | Time to Reach Hydrophobicity | Maximum Contact Angle |
|---|---|---|---|
| 304 Stainless Steel | Nanosecond (Ns) | Several days | >120° |
| 304 Stainless Steel | Sequential Ns + Picosecond (Ps) | 1-2 days | 120° - 140° |
| Titanium Alloy (Ti64) | Nanosecond (Ns) | Several days | >120° |
| Titanium Alloy (Ti64) | Sequential Ns + Picosecond (Ps) | 1-2 days | 120° - 140° |
Longevity of hydrophobicity can reach up to 180 days for sequential laser processing 7 .
Researchers have developed a versatile arsenal of techniques to manipulate metal surfaces, broadly falling into two categories: subtractive methods, which remove material to create texture, and additive methods, which build up structures. Often, these are combined with chemical modifications to achieve the desired effect.
| Technique | Category | Brief Description | Key Advantage |
|---|---|---|---|
| Ultrafast Laser Texturing | Subtractive | Using femtosecond/picosecond pulses to ablate precise micro/nano structures 1 . | Unmatched precision, minimal heat damage, high flexibility . |
| Additive Manufacturing (3D Printing) | Additive | Building complex, monolithic metallic structures (e.g., re-entrant pillars) layer-by-layer 4 . | Creates mechanically robust, complex geometries ideal for omniphobicity 4 . |
| Chemical Etching | Subtractive | Using chemical solutions to selectively dissolve metal and create roughness 3 . | Relatively simple process, cost-effective 3 . |
| Electrodeposition | Additive | Using electric currents to deposit a layer of material onto the surface, building up roughness 3 . | Can create hierarchical structures and composite coatings. |
| Plasma Treatment | Chemical | Using ionized gas to clean, etch, or deposit a thin functional coating (as in PECVD) 1 5 . | Excellent for modifying surface chemistry homogeneously. |
The choice of fabrication technique depends on the specific application requirements, material constraints, and desired scale of production. Hybrid approaches like the LasPlas process often yield the most robust and tunable surfaces 1 .
The ability to precisely control wettability is already finding transformative applications across industries.
Superhydrophilic surfaces improve cell adhesion for implants, while superhydrophobic ones resist biofilm formation and blood coagulation 8 .
Surfaces that dynamically change wettability in response to external stimuli like temperature or light .
The future of metallic surfaces is not just strong and durable, but also intelligent and responsive. As research continues, we will see more surfaces that can dynamically change their wettability in response to external stimuli like temperature or light , paving the way for even smarter technologies that interact with liquids in once unimaginable ways. This fusion of biology-inspired design and advanced engineering is truly forging a new, more functional relationship between solids and liquids.