Bio-Inspired Surfaces and Applications

The following sections are included:

• Preface
• Contents
• List of Contributors

Recently superhydrophobic surfaces have attracted considerable interest due to their potential applications in the design and preparation of self-cleaning surfaces. Generally speaking, a superhydrophobic surface is defined as possessing water contact angle greater than 150 degrees. Such surfaces already commonly exist in the biological world, as especially exhibited by the lotus leaf, that is, the so-called lotus effect. To the best of our knowledge, many plant leaves and specific surfaces of animals in nature all exhibit this so-called lotus effect, where the interplay of surface microstructure and chemical composition causes water droplets to remain spherical on the surface. In this chapter, different aspects of the self-cleaning function and superhydrophobic surfaces are systematically illustrated, including advanced wetting theory, methods of fabricating different superhydrophobic surfaces and the potential applications of superhydrophobic surfaces, which can help readers better understand recent progress in investigating the self-cleaning effect and superhydrophobic surfaces.

Sharks have been living on the Earth for more than 400 million years, and they appeared 100 million years earlier than the dinosaurs. Although dinosaurs have become extinct for more than 60 million years, different kinds of sharks still live on Earth now, which demonstrates their perfect properties to survive in the environment. In this chapter, the characteristics and properties of shark skin are investigated and explored, and the model of shark skin is built, which can give us intuitive impressions. Additionally, treatments for biological shark skin in order to keep its good mechanical properties are illustrated; the research can help readers better understand the fundamental knowledge of shark skin, which has great significance.

Through millions of years of natural selection, the surfaces of some natural creatures have evolved into unique hierarchical micro-structures with superior function to perfectly adapt to their survival environment. Shark is the fast swimming animal in the ocean, and it is well-known for the “shark skin effect.” Shark skin is covered with tiny and rigid scales which can stick out of the viscous sublayer and have the function of effectively inhibiting the occurrence of turbulence and reducing wall friction. However, conventional methods cannot realize the fabrication due to its complicated and subtle morphology, and how to fabricate vivid shark skin has developed into a hot topic nowadays. Many researchers have investigated and explored different fabricating methods and put the biomimetic drag-reducing technology into applications in fluid engineering; the results are very satisfactory and striking. In this chapter, different methods to fabricate real shark skin surfaces are presented in detail, including direct bio-replicated forming, micro-rolling, large-scale solvent-swelling, additive low-releasing design, synthetic drag-reduction bio-replication, transscale enlarged 3-D imprinting, flexible 3-D imprinting and so on.

Natural selection, survival of the fittest — through millions of years of evolution, different animals have developed their own functional surfaces, for example, the shark has become one of the fastest swimming animals in the ocean, and it is very well-known for the shark skin effect, especially for the “shark skin swimsuit.” Due to its superior properties in drag reduction, anti-wear, self-cleaning and so on, investigations on its essential mechanisms and fabricating methods have attracted much attention from all over the world, and the achievements have been widely put into application in industry, agriculture, transportation, airspace and so on, and profits have been obtained so far. In this chapter, the method of fabricating artificial composite drag-reduction surface based on biological shark skin morphology and mucus nano-long chain is investigated and studied, and the chemical, mechanical and hydrodynamic properties are explored from different angles in depth. Experimental results in water tunnel revealed that the drag-reducing efficiency could surpass 20% with smooth skin as reference. The drag-reduction mechanism is systematically explained and discussed from different angles. This has significance for understanding the status of recent research and for expanding the use of shark skin in the fluid engineering.

For purpose of increasing the transportation capacity of natural gas pipelines and protecting them from corrosion, internal coating technology has been widely used, with remarkable benefit. However, with the reduction of inner wall roughness, small convex regions are all completely submerged within the viscous sublayer, and the pipeline can be termed a “hydraulic smooth pipe,” which implies that wall friction is difficult to lower further even with continuous smoothing of the coated surface. Therefore, how to reduce flow friction and increase transmission capacity on the basis of the internal smooth coating is gradually becoming an urgent problem to be resolved; perhaps bioinspired/ biomimetic drag-reducing technology is a good approach. In this chapter, according to the actual working circumstances of the West-to-East Project in China, the relevant parameters are calculated to justify the existence of the “hydraulic smooth pipe.” And then, the forming property of AW-01 Epoxy Resin which is widely adopted in China is analyzed comprehensively via the light-sectioning method, and the relationship of forming precision and curing degree of epoxy resin is made certain, laying the foundation for the manufacturing process of bio-inspired natural gas pipelines. For completing the bio-inspired surface in a large area, the Pre-Cured Micro-Rolling Technology (PCMRT) is advanced. To verify the drag-reduction and forming effect, experiments with air are carried out, followed by the experiment with actual natural gas in the field transmitting pipeline. The results of the experiments are consistent with that in numerical simulation, which proved the accuracy and reliability of applying the bio-inspired drag-reducing technology in natural gas pipelining.

Water vapor condensation plays a key role in a wide range of industrial applications involving phase change heat transfer process, such as power generation, thermal management, water harvesting and desalination. When water vapor is cooled below its equilibrium saturation temperature at the specified pressure, it can transition to the liquid phase with a latent energy release during this phase change process. Compared to the homogeneous nucleation taking place completely within a supersaturated vapor, the heterogeneous nucleation is more ubiquitous, and is characterized by a low reduced energy barrier owing to the presence of solid interfaces. Thus, the heterogeneous nucleation is intricately reliant on the physicochemical properties of solid surfaces. For a hydrophilic surface with high excess energy, the condensed water tends to form a liquid film covering the entire surface, which is termed as filmwise condensation. In contrast, on a hydrophobic surface, liquid condensates ball up, and it has been shown that the condensation heat transfer coefficient associated with this so-called dropwise condensation was tenfold higher than that of filmwise condensation. Yet, despite exciting progress, the state of the art condensation materials still could not satisfy the demanding requirements on the thermal management in high heat-flux electronic devices, thermal management in aerospace and chemical processing, etc…

Shark skin possess unique hierarchical structure and superior drag reduction performance. Recently, bio-replication approach has been proposed and developed to directly take use of its surface function. However, optimum drag reduction performance of real shark skin just appear at his living conditions. If the application conditions is great different fromits living conditions, the drag reduction performance will be declined. In order to widen its application, large-scale adjustment should be developed for its hierarchical structure. Then in this chapter, we will introduce swelling and shrunken process to adjust the vivid microstructure.

Drag reduction of flow over a circular cylinder is done by having a dimpled surface. Computational fluid dynamics (CFD) simulations are done to investigate the degree of drag reduction by dimpled cylinder as compared to smooth cylinder, and the results are to be validated by wind tunnel experimentations…

Research in the 1970s has shown that small grooves on surfaces, which are known as riblets, are inspired by biometric structures that occur naturally and are capable of reducing drag that resulted from the fluid flow. These structures form a constraint against Reynolds stresses when aligned with the flow, which is related to the growth of eddies in low speed region. Such a region usually occurs along the internal surface of a duct. Through many years of research, various forms of riblets have been created to optimize drag reduction in fluid flows. We hypothesized that a set of riblets that are spaced reasonably far enough and of sufficiently small size, as well as having the least cross sectional area can be optimal in drag reduction. Therefore, in our experiments, we aim to research the most effective type of riblet geometry (i.e. L, U, and V). To achieve this, we carried out series of experiments to test the effectiveness of riblets in reducing air flow in pipes using the wind tunnel. Besides working on the type of riblets, we also attempt to discover the optimal spacing between riblets for highest drag reduction. Our results show that 3mm V-shaped riblets spaced 13 mm apart gives the optimal design. A nozzle pertaining to a unique curvature was constructed, and air flow through it resulted in different speeds at different region of the nozzle. In conclusion, the findings in this experimental study were based on the nozzle design such that the best riblets with the optimal spacing between them were used. Our research proved to be a success when we demonstrate how riblets when applied on the nozzle can reduce drag significantly.

With the advanced development of computer-based enabling technologies, many engineering, medical, biology, chemistry, physics and food science etc have developed to the unprecedented levels, which lead to many research and development interests in various multi-discipline areas. Among them, biomimetics is one of the most promising and attractive branches of study. Biomimetics is a branch of study that uses biological systems as a model to develop synthetic systems. To learn from nature, one of the fundamental issues is to understand the natural systems such animals, insects, plants and human beings etc. The geometrical characterisation and representation of natural systems is an important fundamental work for biomimetics research. 3D modeling plays a key role in the geometrical characterisation and representation, especially in computer graphical visualization. This chapter firstly presents the typical procedure of 3D modelling methods and then reviews the previous work of 3D geometrical modelling techniques and systems developed for industrial, medical and animation applications. Especially the chapter discusses the problems associated with the existing techniques and systems when they are applied to 3D modelling of biological systems. In addition, the chapter also presents two case studies of authors' own work. Based upon the discussions, the chapter proposes some areas of research interests in 3D modelling of biological systems and for Biomimetics.

Many superhydrophobic surfaces (both manmade and natural) normally exhibit micro- or nanosized roughness as well as hierarchical structure, which somehow can influence the surface's water repellence. In this chapter, the recent progress in preparing manmade superhydrophobic surfaces through a variety of methodologies, particularly within the past several years, and the fundamental theories of wetting phenomena related to superhydrophobic surfaces are reviewed, and the perspective of natural superhydrophobic surfaces utilized as mimicking models are discussed. The physics related to superhydrophobic surfaces is also discussed with attention of its potential applications. A facile method for preparing superhydrophobic surfaces based on micro and nano scaled structures is reported. Composite thin films are formed by using SiO2 nanoparticles and poly(dimethylsiloxane) (PDMS). It is demonstrated that the hierarchical structure in micro and nano scale on the surface, plays an important role in prompting the superhydrophobic (water-repelling) properties. Wetting phenomena and related theories are also discussed within the paper.

The force of attraction between particles is a natural phenomenon, and can be termed as cohesion—if it occurs among similar molecules, and as adhesion—if found among unlike molecules. With a focused interest on agricultural soils, soil cohesion is of greater importance with regard to soil erosion and its binding strength, while its adhesive nature results in undesired increase in draft forces on soil-interacting tools. May it be farm implements, construction machinery or any soil-engaging tool, their larger force requirement increases the input energy and hence less work is done per unit effort supplied. Working performance is badly impaired with a large mass of adhered soil carried along with the tool under operation. This is especially significant in sticky soils…

Soil adheres to the surfaces of soil-engaging components of various machinery and equipment. The adhesion of soil to the surfaces of soil-engaging components increases draft and energy consumption and affects the quality of work adversely. The adhesion of soil is primarily from the capillary pressure and the viscous resistance of the water film at the interface due to molecular attraction and negative air pressure. The factors affecting soil adhesion include the nature and properties of the soil, surface characteristics of soil-engaging components, the working conditions and the environment. Conventional methods for reducing soil adhesion include working soil when it is comparatively dry, improving surface shapes of soil-engaging components, producing soil-engaging components from materials with better scouring properties, and application of electro-osmosis, magnetic fields, vibration and lubrication, etc. An ideal technique should be safe and simple, economical to manufacture, easy to use, synchronize with other components of the machine and tools, have no requirement for extra controls and power, consume lesser energy and be efficient with scouring abilities 90% or higher. For practical field conditions, many attempts have been made to reduce friction and soil adhesion on the surfaces of soil-engaging components of various machines. So far, many of such attempts have not been very successful. Some techniques, such as air injection at the soil–tool interface are useful but add weight to the existing set up and in many cases make the system more complicated to operate. Enamel coating is cheap and simple to apply but has poor wear resistance and cannot be used in abrasive soil conditions…

The reduction of water resources and soil fertility in Northeast China requires increasing the working efficiency of agricultural soil-engaging components. Adhesion and resistance are the main problems for soil-engaging tillage components. However, soil-burrowing or soildigging animals give inspiration for resolving those problems. Their fair, claws, toes, textured surfaces and scales have anti-adhesion or resistance reduction functions. Those results provide a way to realize the sustainable development of modern agriculture by developing novel bionic agricultural machinery systems with independent intellectual property rights to meet conservation tillage requirements in the Northern China region. This chapter reviews biological structures of some soil-burrowing or soil-digging animals, such as the beetle, mole cricket, earthworm, mole, vole, pangolin and snake, then presents their mechanism of anti-adhesion or resistance reduction. Bioinspired applications which have been used in Northeast China are also presented in the chapter, including moldboard, subsoiler components, furrow opener, roller, and bionic rototilling-stubble-breaking blade. Subsequently, the existed problems in agricultural engineering and the future development trend are discussed.

The following sections is included:

• Index