Keywords: Anisotropic superhydrophobic, Liquid Method Contact Angle (LMCA), Micro-nano composite structure, Directed droplet transport, Bionic coating, Agricultural efficiency, Ship drag reduction, 4D printing, Environmental adaptive interface, Cross-medium functionality

Abstract
The anisotropic superhydrophobic surface formed on rice (Oryza sativa L.) leaves through long-term evolution exhibits intelligent water management capabilities across media. Its contact angle in the air reaches 153° (roll-off angle 3°), and the underwater LMCA is 77°, significantly outperforming traditional superhydrophobic models like the lotus leaf. This study systematically reveals the synergistic mechanism of micro-groove and nano-wax through multi-scale characterization (SEM/AFM/XPS/CLSM), molecular dynamics simulations, and field trials. Additionally, innovative applications such as drag-reducing coatings for ships (35% reduction in resistance) and pesticide efficiency systems (223% increase in deposition) are developed. The study further proposes a bionic design framework driven by 4D printing and AI, providing theoretical support and technological pathways for developing environmentally adaptive interfaces. These innovations offer new technological solutions for improving agricultural production efficiency, fuel savings in shipping, and other industrial applications.

1. Introduction
1.1 Paradigm Evolution in Plant Interface Science
Since the discovery of the "lotus effect" in the 1990s, plant surface science has undergone significant development, divided into three main stages:

• Morphological Biomimicry Stage (1997-2010): Focused on studying existing surface structures in nature, such as the micro-nano structure of lotus leaves, and developing self-cleaning coatings.
• Chemical-Structural Coupling Stage (2011-2020): This stage integrated chemical modification and structural design, focusing on optimizing surface performance through the synergistic effects of chemistry and structure, such as in the rose petal effect.
• Intelligent Response Stage (2021-present): Current research not only focuses on surface structure and chemical properties but also aims to develop surfaces that are environmentally adaptive, with rice leaf's anisotropic superhydrophobic surface being a prime example.
  As these studies have deepened, the design of plant interfaces has moved beyond simply mimicking natural surfaces to exploring intelligent surfaces that can self-adjust and respond to environmental conditions. Thus, bionic superhydrophobic technology no longer focuses solely on water droplet rolling but on enhancing functionality across media and environments.

1.2 Unique Evolutionary Strategy of Rice Leaves
The anisotropic superhydrophobic surface of rice leaves is an adaptation to tropical monsoon climates. In the special environment of paddy fields, rice leaves exhibit the following unique survival adaptations:

• Rapid Rainwater Drainage: In heavy rain, the surface structure of rice leaves can rapidly drain water, preventing water retention on the leaf surface. This feature is achieved through the longitudinal droplet transport of micro-groove structures, with the droplet's longitudinal transport speed reaching over 28mm/s, significantly improving drainage efficiency.
• Adaptation to Paddy Field Environment: The high LMCA of rice leaves not only enhances water repellency but also inhibits the attachment of algae and pathogens. Field trials show that this superhydrophobic surface significantly reduces disease incidence on rice leaves, with a reduction rate of up to 41%.

2. Materials and Methods
2.1 Sample Preparation
To better characterize the structure and properties of rice leaf surfaces, rice at the booting stage (variety: Nihon-hare) was chosen as the experimental sample. The leaves of this variety exhibit excellent anisotropic superhydrophobic performance. To prevent structural collapse during processing, critical point drying was used for pretreatment, effectively preserving the microstructure of the leaves and ensuring the accuracy of subsequent characterization experiments. As a control, lotus (Nelumbo nucifera) and Commercial Superhydrophobic, which also exhibit good superhydrophobicity, were used for comparative analysis.

2.2 Multi-scale Characterization Platform
To systematically study the microstructure of rice leaf surfaces, various high-precision characterization techniques were employed.

These platforms effectively measure the microstructure, mechanical properties, and wetting properties of rice leaf surfaces, providing theoretical support for subsequent bionic design.

3. Surface Structure and Wetting Mechanism
3.1 Multi-level Structural Quantitative Analysis (Figure 2)
3.1.1 Macroscopic Groove Fluid Guiding Effect
CFD (Computational Fluid Dynamics) simulations revealed that the macroscopic grooves on the rice leaf surface significantly guide droplet movement. When the groove's aspect ratio exceeds 5, the longitudinal droplet movement resistance coefficient ($C_d$) significantly decreases to 0.17, 68% lower than that of lateral movement. This finding indicates that the rice leaf structure has evolved to efficiently guide rainwater along the longitudinal direction, preventing water retention on the leaf surface.

3.1.2 Nano-Wax Chemical Barrier Effect
XPS (X-ray photoelectron spectroscopy) analysis revealed that the wax composition on the rice leaf surface is primarily made up of alkyl esters and fatty acids.

• Surface layer (0-50nm): C31H64O2 alkyl esters account for 82%, contributing 76% to the contact angle.
• Deep layer (50-200nm): C29H60 fatty acids increase to 43%, enhancing surface structural stability.
  This chemical barrier effectively prevents water droplets from adhering to the surface, maintaining superhydrophobic properties.

3.2 Anisotropic Wetting Model
To explain the anisotropic wetting behavior of rice leaves, a three-dimensional Wenzel-Cassie mixed wetting model was developed. The theoretical calculated value of the model is 151.8°, with an error of less than 0.5° compared to the measured value. This model provides an important theoretical basis for understanding and optimizing the wetting behavior of anisotropic superhydrophobic surfaces.

4. Cross-Media Function Verification
4.1 Air Environment Performance
4.1.1 Anti-pollution Test (ASTM D3719)
The superhydrophobicity of the rice leaf surface is not only manifested in water repellency but also in excellent anti-pollution performance. Using standardized anti-pollution testing methods (ASTM D3719), the anti-adhesion ability of the rice leaf bionic surface to various pollutants (such as red clay dust, diesel soot, and fungal spores) was tested. The results showed that the pollution residue rate on the rice leaf bionic surface was significantly lower than that of commercial PTFE coatings, especially in tests involving red clay dust and diesel soot, where the rice leaf bionic surface performed significantly better.

4.1.2 Impact Durability
Through repeated impact testing (5000 times) using a rain droplet simulation device, we found that after strong impacts, the contact angle of the rice leaf bionic surface remained above 145°, and the groove structure remained intact. This indicates that the rice leaf surface not only exhibits excellent water-repelling properties but also excellent durability.

4.2 Underwater Environment Performance
4.2.1 Air Film Stability Test
To evaluate the performance of the rice leaf bionic surface in underwater environments, it was immersed in a 3.5% NaCl solution for long-term testing. The results showed that the air film stability of the rice leaf bionic surface was good, maintaining an air film coverage rate of over 85%, and electrochemical impedance spectroscopy (EIS) analysis showed that the bionic surface exhibited a corrosion current density several orders of magnitude lower than bare metal.

4.2.2 Biofouling Inhibition

To evaluate the anti-biofouling ability of the rice leaf bionic surface, marine immersion tests were conducted. The results showed that the rice leaf bionic surface significantly reduced barnacle attachment and demonstrated good suppression of algae coverage, particularly when compared to traditional commercial antifouling coatings, where the rice leaf bionic surface showed superior performance.

5. Biomimetic Applications and Engineering

5.1 Agricultural Efficiency System Development

5.1.1 Pesticide Deposition Mechanism Optimization

The superhydrophobic surface of rice leaves not only excels in rainwater management but also demonstrates great potential in agricultural applications, especially in pesticide use and deposition. Through high-speed imaging analysis, we found that the application of biomimetic additives significantly improved the spreading speed of pesticide liquids, from 0.12 m/s to 0.38 m/s. This speed enhancement ensures that the pesticide quickly covers the entire leaf surface, significantly reducing pesticide loss and improving deposition efficiency. Compared to traditional methods, the pesticide deposition on the leaf backsides increased from 9% to 34%. This improvement not only enhances pesticide use efficiency but also helps farmers reduce pesticide usage, thereby lowering production costs.

We also conducted field trials to evaluate the effectiveness of this biomimetic treatment in actual agricultural production. The trials showed that rice treated with the biomimetic surface had a significantly reduced incidence of pests and diseases, with pesticide use reduced by about 58% compared to traditional application methods. This technology not only has great economic benefits but also offers significant advantages in reducing pesticide residues and improving crop quality.

5.1.2 Field Economic Analysis

To comprehensively assess the practical application value of bionic technology in agriculture, we conducted simulation analyses in preparation for a two-year field trial. The trial results showed that rice treated with biomimetic surfaces performed exceptionally well in growth. The detailed economic analysis is as follows:

The biomimetic treatment not only saved on pesticide costs but also increased rice yield, ultimately bringing higher economic returns. This shows that biomimetic technology is not only an environmentally friendly solution but also an important means of improving agricultural productivity.

5.2 Ship Drag Reduction Coating Industrialization

The application of biomimetic rice leaf surfaces in ship drag reduction coatings has achieved remarkable results. Modern heavy industry application cases show that biomimetic coatings have tremendous potential in reducing ship resistance and improving fuel efficiency. The biomimetic coating  utilizes laser-engraved grooves and plasma-enhanced chemical vapor deposition (PECVD) technology, successfully transferring the superhydrophobic properties of rice leaves to practical ship surface coatings.

Manufacturing Process:

• Laser-engraved grooves (width 80 μm, depth 25 μm), processing speed of 12 m/min.
• PECVD fluorocarbon coating, enhancing the durability of the coating.
• Nano-imprinting technology to enhance the long-term stability of the structure.

Ship Test Data (320,000-ton VLCC tanker):

From the test data, it is evident that the biomimetic coating demonstrates significant advantages in fuel consumption and CO₂ emissions, especially for ships like large oil tankers that operate for extended periods. By reducing ship drag, the biomimetic coating effectively lowers energy consumption and extends the coating’s lifespan.

Moreover, the application of the biomimetic drag-reduction coating has extended the ship's dry-docking maintenance cycle from the traditional 5 years to 8 years, reducing the frequency of maintenance and lowering maintenance costs. These improvements not only save significant energy costs but also reduce the environmental impact of ships during voyages.

5.3 Cross-Medium Performance Comparison (Table 3)

By comparing the cross-medium performance of different superhydrophobic surfaces, we further validated the superior performance of the biomimetic rice leaf surface in various environments.

The inconsistency between the left and right contact angles in the above data indicates the anisotropy of the sample surface, with the anisotropy of the rice surface being particularly evident. The method used to calculate the contact angles is the ADSA-RealDrop method.

From the comparison, it can be seen that the biomimetic rice leaf surface performs optimally in several indicators such as static contact angle, rolling angle, LMCA, and adhesion force. Its low adhesion force characteristics provide significant advantages in applications such as ships and medical equipment, effectively reducing droplet attachment and maintaining excellent self-cleaning ability in underwater environments.

3D Morphology of Rice Leaf

3D Morphology of Rice Leaf

3D Morphology of Commercial Superhydrophobic

Sessile Drop of Rice Leaf

Captive Bubble of Rice Leaf

LMCA of Rice leaf

Sessile Drop of Lotus Leaf

Captive Bubble of Lotus Leaf

LMCA of lotus leaf

6. Technological Challenges and Breakthrough Pathways

6.1 Large-Scale Manufacturing Bottlenecks

Despite the tremendous potential of biomimetic superhydrophobic technology in various fields, large-scale production still faces several technological bottlenecks, particularly in the following areas:

• Microstructure Processing Precision: Currently, the precision and stability of microstructure processing in large-scale production remain significant challenges. Existing technologies like laser engraving and nano-imprinting have precision down to ±1 μm and ±5 nm, respectively, but in certain applications, they still cannot meet the required standards.
• Cost Issues: High-precision processing techniques (such as femtosecond laser two-photon polymerization) have high costs, limiting their application in large-scale industrialization.

6.1.1 Microstructure Processing Technology Comparison

Although existing technologies can meet the requirements of certain specific applications, for large-scale production, the universality and cost control of these technologies remain key issues to address.

6.1.2 Exploration of New Technologies

To address these problems, researchers are exploring new processing techniques such as roll-to-roll (R2R) nano-imprinting and femtosecond laser two-photon polymerization. These new technologies can achieve high-precision microstructure production at lower costs and higher efficiency, and they are expected to be widely used in the coming years.

6.2 Durability Enhancement Strategies

As biomimetic superhydrophobic technology continues to develop, improving its durability has become an important issue in industrial applications. Researchers are attempting to combine self-healing materials and enhanced interface adhesion technologies to improve the long-term stability of coatings.

6.2.1 Self-Healing Materials Integration

For instance, microcapsule technology has been applied to epoxy resin-based coatings. When the coating is damaged, the microcapsules release repair agents (such as fluorosilane) to automatically heal the damaged area, maintaining the coating’s performance. In addition, light-responsive materials have also been used in the self-healing of biomimetic superhydrophobic surfaces. By activating the material’s morphology reconstruction ability through ultraviolet light, the surface durability is further enhanced.

7. Interdisciplinary Research Frontiers

7.1 AI-Assisted Design

With the rapid development of artificial intelligence (AI) technology, AI’s application in biomimetic material design has gradually become a research hotspot. AI-driven design platforms, especially in the optimization of complex biomimetic structures, show great potential. The DeepBionic optimization platform we developed, by training on a large amount of environmental parameters (such as temperature, humidity, flow speed) and performance requirements (such as contact angle, LMCA), can output optimal surface structure parameters based on given needs. This process greatly shortens the design cycle, reducing it from the traditional 6 months to only 72 hours, with an experimental verification success rate of over 85%, significantly improving R&D efficiency.

The AI optimization platform not only provides efficient design solutions for structural optimization but also makes intelligent recommendations regarding material selection and manufacturing process decisions. For example, through deep learning algorithms, the platform can identify and predict which microstructure designs are most likely to achieve the best superhydrophobic performance in real-world environments. In addition, the platform also integrates physical simulations and machine learning models, using interdisciplinary optimization to achieve environmentally adaptive surface performance.

These breakthroughs provide strong technological support for the rapid development of biomimetic superhydrophobic technology and offer new possibilities for the development of environmentally responsive coatings and multifunctional materials.

7.2 Biomimetic-Optoelectronic Coupled Systems

In the application of biomimetic superhydrophobic surfaces, biomimetic-optical coupling systems also show great promise. These systems combine biomimetic surfaces with optoelectronic technology, making them more applicable in energy harvesting and intelligent control fields.

7.2.1 Self-Cleaning Photovoltaic Glass

The self-cleaning property of biomimetic superhydrophobic surfaces has been explored for application on photovoltaic glass. By mimicking the surface structure of rice leaves, the adhesion of dust to photovoltaic glass can be significantly reduced. Experiments show that biomimetic groove structures can reduce dust accumulation by over 60%, keeping the photovoltaic glass clean and significantly slowing down the degradation rate of optoelectronic conversion efficiency. Over a month-long experimental cycle, the conversion efficiency degradation rate dropped from 2.1% per month to 0.4%, offering a new approach to improving photovoltaic power generation efficiency.

7.2.2 Intelligent Moisture Collection

MIT's team developed an efficient dew collection system by mimicking the compound structure of rice leaves and cactus spines. This system can collect large amounts of water through natural dew condensation at night, with a collection rate of up to 5.2 L per square meter per night. This technology not only solves the water scarcity problem in arid regions but also provides innovative solutions for the sustainable use of global water resources. By applying this technology to water collection devices, smart homes, and agricultural irrigation systems, it is expected to offer a new pathway for global water resource management.

7.3 Nanotechnology and Biomimetic Surfaces Integration Prospects

With the continuous advancement of nanotechnology, biomimetic superhydrophobic surfaces will play an even more significant role at the nanoscale. Nanomaterials can not only enhance surface functions but also improve material strength, durability, and self-healing capabilities. Nano-imprinting technology and nano-coating technologies are widely applied in the processing of biomimetic surfaces, achieving large-scale production while maintaining high performance.

For example, combining nanostructures with biomimetic surface designs can further improve water droplet rolling speed and achieve self-healing at the microscopic scale. Nanostructures can automatically restore their original surface properties through specific photochemical reactions when scratched or damaged. These technological advancements will greatly promote the application of biomimetic superhydrophobic surfaces in various fields, including smart surfaces, environmental protection materials, and medical devices.

8. Conclusion and Outlook

The anisotropic superhydrophobic surface of rice leaves is a highly inspiring technology in nature. Its advantages in water management and cross-medium functions have already made significant progress in various application fields. From agriculture and shipping to environmental management and smart systems, biomimetic superhydrophobic technology has shown tremendous potential.

In future development, the following key issues need to be addressed:

• Manufacturing Revolution: The promotion of large-scale, low-cost 4D printing and roll-to-roll nano-imprinting technology will greatly accelerate the widespread application of biomimetic superhydrophobic materials.

• Smart Upgrades: By integrating sensing elements with responsive materials, the development of real-time adjustable "living" coatings will address environmental changes. This will allow biomimetic surfaces to not only respond to external environmental changes but also adjust their wetting properties based on actual needs.

• Ecological Integration: To ensure the sustainability of biomimetic materials in practical applications, evaluating the environmental impact of biomimetic materials throughout their lifecycle and establishing a green manufacturing system will be a key focus of future research. This will not only enhance the environmental friendliness of the technology but also provide technical support for achieving sustainable development goals.

8.1 Application Prospects

With continuous technological advancements, the application fields of biomimetic superhydrophobic materials will become even broader. Especially in areas such as carbon neutrality, precision agriculture, marine development, and environmental management, biomimetic superhydrophobic technology is expected to play a transformative role. Under the carbon neutrality goal, by improving energy efficiency and reducing environmental pollution, biomimetic technology will contribute significantly to global ecological protection and sustainable development.

Furthermore, in the biomedical field, biomimetic superhydrophobic surfaces will offer new technological solutions to reduce bacterial attachment and improve the durability and comfort of medical devices. By combining biomimetic surface technology with advanced medical materials, it will help develop more advanced medical instruments and sensor systems.

References

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Environmental Policy

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