Description:Field of Invention
The present invention relates to the field of surface engineering and materials science, and more particularly to methods for modifying the surface topography of metallic materials. Specifically, the invention concerns the use of micropatterned surface structures to enhance the wettability characteristics and corrosion resistance of SS304 austenitic stainless steel. The invention is applicable in various industrial sectors where the control of surface-liquid interaction and long-term durability of stainless steel components in corrosive environments is critical, such as marine, biomedical, chemical processing, and energy sectors.
Objectives of the Invention
The primary objective of the present invention is to develop a method for modifying the surface of SS304 stainless steel through the incorporation of micropatterned structures to effectively control wettability and enhance corrosion resistance. The invention aims to utilize micro-engineered surface geometries, such as micropillar arrays, to manipulate the wetting behavior of water and other liquids on the steel surface, thereby maintaining either hydrophilic or hydrophobic characteristics depending on the application. A further objective is to reduce corrosion by limiting the liquid-solid interface and impeding the ingress of corrosive species such as chloride ions, particularly under partial wetting conditions. The invention also seeks to establish a correlation between surface topography parameters and electrochemical behavior, enabling optimization of geometric configurations for maximum protective effect.
Background of the invention
Stainless steel, particularly austenitic grade SS304, is widely used across various industries due to its excellent mechanical properties, good corrosion resistance, and aesthetic surface finish. It finds application in marine components, food processing equipment, biomedical implants, heat exchangers, and structural components exposed to harsh or corrosive environments. However, the performance of SS304 steel in these applications is often governed by its surface properties—especially wettability and corrosion resistance, which are influenced by both chemical composition and surface topography.
Surface roughness modification has emerged as a promising approach to improve functional properties such as hydrophilicity/hydrophobicity and resistance to corrosive media. By altering surface features at the micro- or nanoscale, one can significantly affect how liquids interact with the material (i.e., contact angle) and how corrosion-initiating agents penetrate or adhere to the surface. Despite its potential, conventional surface treatment methods such as mechanical polishing, grit blasting, and chemical etching either lack control, introduce contaminants, or alter the bulk properties of the steel. Therefore, there is a pressing need for a systematic and controllable method that tailors surface roughness to achieve the desired balance of wettability and corrosion protection, without degrading the inherent properties of SS304.
Several prior inventions have addressed improvements in stainless steel corrosion resistance or surface treatment, but often without focusing on the combined and controlled influence of surface roughness on both wettability and corrosion characteristics. For example, U.S. Patent No. 7,998,276 B2 discloses a method for increasing corrosion resistance of stainless steel via passivation and electropolishing, but does not emphasize surface roughness control or its effect on wettability. Another prior art, U.S. Patent No. 10,300,421 B2, discusses laser-induced surface texturing to produce hydrophobic surfaces, primarily for anti-fouling or self-cleaning applications, with limited reference to corrosion behavior.
Furthermore, WO2019012347A1 describes a surface modification technique using nanoparticle coatings to enhance corrosion resistance, but such approaches often involve complex chemical synthesis, high costs, and potential environmental concerns. In contrast, the present invention offers a mechanical or physical surface treatment route that is simple, scalable, and tunable, and addresses the dual requirement of enhancing wettability (either hydrophilic or hydrophobic based on need) and corrosion resistance.
Therefore, there is a clear technological gap and a need for a method that enables precise surface microstructuring of SS304 steel to achieve simultaneous control over wettability and corrosion behavior, without the use of chemical treatments or external coatings. By using micropillar arrays or similar geometric patterns, it is possible to create surfaces that exhibit reduced liquid contact, promote air entrapment, and thus delay or prevent the onset of corrosion. Such micro-engineered surfaces can effectively isolate corrosive agents from the underlying steel, especially under partial wetting conditions, and offer a passive yet durable strategy for corrosion protection.
The present invention addresses these needs by proposing a novel and scalable method for fabricating micropatterns on SS304 surfaces that not only tailor wettability but also significantly improve corrosion resistance. This dual-function approach is particularly beneficial for extending the service life of stainless steel components in aggressive and moisture-rich environments.
Summary of the invention
The present invention provides a novel and effective method for enhancing both wettability control and corrosion resistance of SS304 stainless steel through the fabrication of micropatterned surface structures, specifically micropillar arrays. By precisely engineering the surface morphology at the microscale, the invention enables manipulation of the wetting behavior—promoting either hydrophobic or hydrophilic characteristics depending on the design—while simultaneously reducing the steel’s susceptibility to corrosion in aggressive environments. The method involves creating micropatterns with defined geometric parameters, such as pillar height, width, spacing, and pitch coefficient (PC), directly onto the SS304 surface using physical or chemical microfabrication techniques. These patterns modify the interaction between water droplets and the surface by controlling the transition between Cassie-Baxter and Wenzel wetting states. Surfaces designed to remain in the Cassie-Baxter state maintain higher contact angles, reduced contact area, and air pockets that act as barriers against corrosive electrolyte penetration.
Experimental results demonstrate that specific micropattern configurations significantly decrease wettability (increase in contact angle) and reduce corrosion current density and rate, as validated through potentiodynamic polarization tests and SEM imaging. The micropatterned surfaces restrict ion transport, prevent chloride ingress, and maintain the protective passive layer, resulting in improved electrochemical stability compared to unpatterned or flat surfaces.

Detailed description of the invention
Wettability is a fundamental surface property that describes the ability of a liquid to spread over or adhere to a solid surface when exposed to the environment. It is governed by the balance between cohesive forces (the attraction between molecules within the liquid) and adhesive forces (the attraction between molecules of the liquid and the substrate). Depending on the dominance of these forces, the surface may exhibit hydrophilic behavior (strong adhesion, resulting in spreading or "sticky" surfaces) or hydrophobic behavior (weak adhesion, resulting in non-sticky, water-repelling surfaces).
In the present invention, micropillar patterns were fabricated on the surface of SS304 stainless steel as shown in figure 1 to induce hydrophobicity and reduce wettability. Reduced wettability subsequently helps in mitigating corrosion, especially in aqueous or aggressive environments. The fabricated micropillar surfaces exhibit isotropic wetting behavior, meaning the contact of the liquid with the surface remains uniform in all directions. This behavior has been studied in earlier works.
The morphology of a water droplet resting on a surface depends on the surface's microstructural features. Two common wetting models—Cassie-Baxter and Wenzel states—describe how the droplet interacts with the surface asperities. Surfaces exhibiting higher static contact angles typically fall under the Cassie-Baxter regime (indicative of hydrophobicity), while lower contact angles suggest the Wenzel regime, where the liquid completely wets the surface roughness.
The water droplet on a micropillar-patterned surface makes significantly less contact with the substrate compared to a flat surface, due to air pockets trapped between the pillars. The degree of wetting is influenced by the geometrical dimensions of the micropillars—particularly the pillar width to channel width ratio, also termed Pitch Coefficient (PC). A shift from the Cassie-Baxter to Wenzel regime is observed when PC exceeds a critical value.
Among the fabricated samples, one specimen with a PC value of 0.58 demonstrated superior hydrophobic performance with a contact angle of approximately 164.89° and a reduced contact diameter. This surface effectively resisted wetting due to the formation of capillary pressure and an air cushion within the micropatterned channels, which prevented water infiltration and countered gravitational effects. For maintaining hydrophobicity, it is essential that the capillary pressure exceeds the gravitational pressure acting on the droplet.
However, when the PC value was further increased, the wetting behavior shifted from the Cassie-Baxter to Wenzel regime, allowing water to infiltrate the channels, similar to the behavior observed on flat surfaces. This shift indicates a loss of equilibrium between cohesive and adhesive forces due to changes in surface geometry. This trend was consistent with variations observed in both contact angle and contact diameter measurements across different micropillar configurations.
To evaluate the corrosion resistance, potentiodynamic polarization tests were performed on both flat and micropillar-patterned surfaces under conditions of partial and complete wetting, following a 7-day immersion in an electrolyte solution. The results revealed that the current density increased gradually until iron ions began dissolving from the SS304 surface. As corrosion progressed, chloride ions (Cl⁻) from the saline electrolyte deposited on the electrode, leading to a drop in current density. This drop was more pronounced on flat surfaces than on micropillar-patterned surfaces, for both partial and complete wetting scenarios.
Furthermore, the corrosion potential (Ecorr) for the micropatterned surfaces was found to be closer to zero compared to that of flat surfaces, indicating enhanced corrosion resistance. The current density did not increase proportionally with Ecorr in micropillar surfaces, suggesting that the microstructure effectively impedes ion transport. The corrosion rate in partial wetting was observed to be significantly lower—by nearly an order of magnitude—compared to that in complete wetting conditions.
Scanning Electron Microscopy (SEM) observations before and after corrosion testing further confirmed the superior corrosion resistance of micropillar surfaces. The flat surfaces exhibited visible corrosion products and surface degradation, while micropillar-patterned surfaces—especially under partial wetting—showed minimal morphological changes. These findings are consistent with the electrochemical test results, supporting the effectiveness of the micropillar structure in resisting corrosion.
Among all tested configurations, the specimen with a PC value of 0.58 and a solid fraction (φ) of 0.367 exhibited the best performance in both wettability and corrosion resistance. A clear correlation was established between contact angle and corrosion rate: as the contact angle increased, the corrosion rate decreased. This confirms that wettability and corrosion resistance are directly related, and both are strongly influenced by the presence of air cushions between the micropillars. These air pockets reduce the solid–liquid interface area, maintaining a stable Cassie-Baxter state in wetting and providing physical isolation that helps protect the passive oxide layer on the stainless steel surface from ionic attack.
In conclusion, the invention demonstrates that carefully engineered micropillar surface textures can effectively manipulate surface wettability and improve corrosion resistance of SS304 stainless steel. This is achieved by optimizing geometrical parameters that promote the Cassie-Baxter wetting regime, inhibit ionic transport, and maintain the integrity of the passive layer under corrosive conditions.

Brief description of Drawing
In the figures which are illustrate exemplary embodiments of the invention.
Figure 1 SEM Image of Micro Patterned Surface , Claims:1. A method for enhancing wettability control and corrosion resistance of SS304 stainless steel, the method comprising:
a. Fabricating micropatterns on the surface of SS304 stainless steel, wherein the micropatterns comprise a periodic array of micropillars with defined geometrical parameters including height, width, spacing, and pitch coefficient (PC);
b. Modifying the surface topography to induce a wetting regime corresponding to the Cassie-Baxter state, wherein the contact angle between the surface and a water droplet exceeds 150°;
c. Reducing the liquid–solid contact area and facilitating the formation of an air cushion between the micropillars, thereby limiting the penetration of corrosive agents; and
d. Improving the corrosion resistance of the SS304 steel by restricting ion transport and preserving the passive oxide layer under partial or complete wetting conditions.
2. The method as claimed in claim 1, wherein the pitch coefficient (PC), defined as the ratio of pillar width to channel width, lies in the range of 0.4 to 0.7 to maintain the Cassie-Baxter wetting state.
3. The method as claimed in claim 1, wherein the contact angle of the water droplet on the micropatterned surface is at least 160°, and the corresponding contact diameter is reduced in comparison to a flat, unpatterned surface.
4. The method as claimed in claim 1, wherein the corrosion resistance is evaluated by potentiodynamic polarization testing, and the micropatterned surface demonstrates a corrosion rate at least one order of magnitude lower than that of a flat surface under similar environmental conditions.
5. The method as claimed in claim 1, wherein the fabricated micropatterns suppress the shift from the Cassie-Baxter regime to the Wenzel regime by maintaining higher capillary pressure than the gravitational pressure of the water droplet.
6. The method as claimed in claim 1, wherein the micropatterned SS304 surface demonstrates improved surface morphology retention after long-term exposure to corrosive environments, as confirmed by post-exposure scanning electron microscopy (SEM).