superhydrophobic surfaces and the "lotus effect." Water spilled on a superhydrophobic surface does not wet the surface, but simply rolls off. Additionally, as water moves across the superhydrophobic surface, it picks up and carries away any foreign material, such as dust or dirt. Students learn how plants create and use superhydrophobic surfaces in nature and how engineers have created human-made products that mimic the properties of these natural surfaces. They also learn about the tendency of all superhydrophobic surfaces to develop water droplets that do not roll off the surface but become "pinned" under certain conditions, such as water droplets formed from condensation. They see how the introduction of mechanical energy can "unpin" these water droplets and restore the desirable properties of the superhydrophobic surface.
Engineering Connection
Inspired by nature, the self-cleaning superhydrophobic products being engineered today are destined to become important and novel products in our everyday lives. Some products include: coatings that reduce the water drag on boats and protect surfaces and equipment exposed to fresh or salt water, building materials that remain clean with little maintenance and are better protected from wear from the elements, and textiles that are resistant to staining and/or remain dry when submerged in waterSuperhydrophobic Surfaces
When the lotus plant emerges on the surface of a pond or lake, it remains pristine despite its muddy environment. Flower Breaking the Surface, Palace Museum, Beijing, China. Painting by Yun Shouping, 17th century, Qing Dynasty.
In some Asian religions, the lotus plant is revered as a symbol of purity. The roots of the lotus plant take hold in the muddy bottoms of ponds and riverbeds. From there, thick stems rise above the water's surface and issue giant, pristine leaves and flowers. The leaves remain clean despite the water and mud on which they rest. Even water refuses to stick to the leaves of the lotus plant. Instead, it beads on the surface and rolls off at the slightest disturbance (see Figure 2).Figure 2. Leaves of Indian Lotus, Nelumbo nucifera, at Lotus Pond, Hyderabad, India. Water does not wet the lotus leaves, but instead forms beads of water that easily roll off its edges. In this computer-generated microscopic image of a lotus leaf with water droplets, notice the double structure of the leaf and the protrusions from the leaf covered in a rough, waxy material, which creates its superhydrophobic surface.
Scientists have found that the basis for both of these properties (self-cleaning and water-repellent) lies in the rough structure of the surface of the lotus leaves. The lotus leaf has a series of protrusions on the order of 10 μm (1.0 x 10-5 m) high covering its surface. Each protrusion is itself covered in bumps of a hydrophobic, waxy material that are roughly 100 nm (1 x 10-7 m) in height. When water droplets are applied to the lotus leaf, they sit lightly on the tips of the hydrophobic protrusions as if on a bed of nails (see Figure 2). This combined structure traps a layer of air in between the surface of the leaf and the water droplet. Hence, the water is not allowed to wet the surface and is easily displaced (see Figure 3).Figure 3. (left) The unique roughness of superhydrophobic surface forces water droplets into spherical drops that minimize contact with the surface, rolling off easily and carrying away dirt and other debris, leaving the surface clean. (right) Water drops roll off a screen door treated with a superhydrophobic powder coating developed at Oak Ridge National Laboratory. Even though the mesh is porous, water drops do not pass through due to the extreme water repellency of the powder coating.
The surface of a lotus leaf is an example of superhydrophobicity. On a superhydrophobic surface, the contact angle is greater than 150o, meaning almost no wetting of the surface by the liquid takes place. This leads to the second property associated with lotus plants — the ability to stay spotlessly clean. As rain falls on a superhydrophobic surface like the lotus leaf, the water droplets roll easily off the leaf surfaces (see Figure 3). As the droplets travel along the leaves, they pick up any dirt or other matter they encounter along the way. This process keeps the lotus leaves dry, clean and free of pathogens such as bacteria and fungi.
The self-cleaning and water-repellent qualities of superhydrophobic surfaces have the potential for many practical applications. House paints, roof tiles and various surface coatings are already on the market (see Figure 3). These products are examples of "biomimicry." By understanding how the lotus leaf and other plants create superhydrophobic surfaces by using a two-tiered surface layer, engineers have created human-made surfaces that "mimic" the properties of the natural ones. One of the most interesting uses of human-made superhydrophobic surfaces are fabrics made by Nano-Tex™ and other manufacturers that repel tomato sauce, coffee and even red wine. Researchers are also developing fabrics that can stay dry for days underwater, swimsuits that cannot become wet, and ship hulls with dramatically reduced drag.
Condensation and Sperhydrophobic Surfaces
In nature, when dew condenses on lotus leaves, the dew soon rolls off the leaf, just as water droplets falling onto the leaf do. However, when scientists began to study the superhydrophobic properties of the lotus leaf, they discovered water behaved differently in laboratories. Water poured or dropped on leaves in a controlled setting still demonstrated superhydrophobic properties. However, when water vapor was allowed to condense onto a lotus leaf in the lab, the water droplets were "sticky" and clung to the leaves.Figure 4. The Wenzel wetting state. When water condenses on a rough surface, it condenses from within the texture and forms a droplet in the "sticky" Wenzel wetting state.
When water vapor condenses on a rough surface, it forms from inside the texture of the surface. As this water droplet grows it enters the "sticky" Wenzel wetting state in which the droplet is "pinned" to the surface (see Figure 4). These droplets do not display the easy motion of droplets on a superhydrophobic surface. In the lab, droplets remain in this "sticky" state, but in nature water vapor condensation, such as dew, soon transitions into a second wetting state known as the Cassie-Baxter wetting state.Figure 5. Comparison of the Wenzel and Cassie-Baxter droplet wetting states. In the Wenzel state, the water droplet fills the spaces in the rough surface. In the Cassie-Baxter state, the water droplet sits on top of the rough surface with a layer of air underneath.
When water is dropped or poured onto superhydrophobic surfaces, the water droplets sit lightly on the very tips of the surface protrusions, leaving a layer of air between the droplets and the leaf surface. Water droplets in this Cassie-Baxter state demonstrate the extreme water repellency that characterize superhydrophobicity (see Figure 5).
The transition between the Wenzel and Cassie-Baxter states requires an input of energy. In nature, this energy might be provided by the mechanical energy supplied by wind or water movement. When dew forms on a lotus leaf in the "sticky" Wenzel state, the movement of the leaf provides enough energy to "unpin" the water droplet and allow it free movement to roll off the leaf. In a laboratory setting, this mechanical energy must be provided by the experimenter, such as placing the lotus leaf on a stereo speaker or shaking the lotus leaf by hand..Superhydrophobicity — The Lotus Effect - Lesson - www.TeachEngineering.org
Engineering (from Latiningenium, meaning "cleverness" and ingeniare, meaning "to contrive, devise") is the application of scientific, economic, social, and practical knowledge in order toinvent, design, build, maintain, research, and improve structures, machines, devices, systems, materials andprocesses.
The discipline of engineering is extremely broad, and encompasses a range of more specialized fields of engineering, each with a more specific emphasis on particular areas of applied science, technology and types of application.
The creative application of scientific principles to design or develop structures, machines, apparatus, or manufacturing processes, or works utilizing them singly or in combination; or to construct or operate the same with full cognizance of their design; or to forecast their behavior under specific operating conditions; all as respects an intended function, economics of operation or safety to life and property.[2][3]
Relief map of the Citadel of Lille, designed in 1668 by Vauban, the foremost military engineer of his age.
Engineering has existed since ancient times as humans devised fundamental inventions such as the wedge, lever, wheel, and pulley. Each of these inventions is consistent with the modern definition of engineering, exploiting basic mechanical principles to develop useful tools and objects.
The term engineering itself has a much more recent etymology, deriving from the word engineer, which itself dates back to 1300, when an engine'er (literally, one who operates an engine) originally referred to "a constructor of military engines."[4] In this context, now obsolete, an "engine" referred to a military machine, i.e., a mechanical contraption used in war (for example, a catapult). Notable examples of the obsolete usage which have survived to the present day are military engineering corps, e.g., the U.S. Army Corps of Engineers.
The word "engine" itself is of even older origin, ultimately deriving from the Latiningenium (c. 1250), meaning "innate quality, especially mental power, hence a clever invention."[5]
Later, as the design of civilian structures such as bridges and buildings matured as a technical discipline, the term civil engineering[3] entered the lexicon as a way to distinguish between those specializing in the construction of such non-military projects and those involved in the older discipline ofmilitary engineering.
Chinese, Greek and Roman armies employed complex military machines and inventions such asartillery which was developed by the Greeks around the 4th century B.C.,[10] the trireme, the ballistaand the catapult. In the Middle Ages, the trebuchet was developed.
With the rise of engineering as a profession in the 18th century, the term became more narrowly applied to fields in which mathematics and science were applied to these ends. Similarly, in addition to military and civil engineering the fields then known as the mechanic arts became incorporated into engineering.
The early stages of electrical engineering included the experiments of Alessandro Volta in the 1800s, the experiments of Michael Faraday, Georg Ohm and others and the invention of the electric motor in 1872. The work of James Maxwell and Heinrich Hertz in the late 19th century gave rise to the field ofelectronics. The later inventions of the vacuum tube and the transistor further accelerated the development of electronics to such an extent that electrical and electronics engineers currently outnumber their colleagues of any other engineering specialty.[3]
The inventions of Thomas Savery and the Scottish engineer James Watt gave rise to modernmechanical engineering. The development of specialized machines and their maintenance tools during the industrial revolution led to the rapid growth of mechanical engineering both in its birthplace Britainand abroad.[3]
John Smeaton was the first self-proclaimed civil engineer, and is often regarded as the "father" of civil engineering. He was an English civil engineer responsible for the design of bridges, canals, harbours and lighthouses. He was also a capable mechanical engineer and an eminentphysicist. Smeaton designed the third Eddystone Lighthouse (1755–59) where he pioneered the use of 'hydraulic lime' (a form of mortar which will set under water) and developed a technique involving dovetailed blocks of granite in the building of the lighthouse. His lighthouse remained in use until 1877 and was dismantled and partially rebuilt at Plymouth Hoe where it is known asSmeaton's Tower. He is important in the history, rediscovery of, and development of modern cement, because he identified the compositional requirements needed to obtain "hydraulicity" in lime; work which led ultimately to the invention of Portland cement.
Chemical engineering, like its counterpart mechanical engineering, developed in the nineteenth century during the Industrial Revolution.[3] Industrial scale manufacturing demanded new materials and new processes and by 1880 the need for large scale production of chemicals was such that a new industry was created, dedicated to the development and large scale manufacturing of chemicals in new industrial plants.[3] The role of the chemical engineer was the design of these chemical plants and processes.[3]
Aeronautical engineering deals with aircraft design whileaerospace engineering is a more modern term that expands the reach of the discipline by includingspacecraft design. Its origins can be traced back to the aviation pioneers around the start of the 20th century although the work of Sir George Cayley has recently been dated as being from the last decade of the 18th century. Early knowledge of aeronautical engineering was largely empirical with some concepts and skills imported from other branches of engineering.[13]
The first PhD in engineering (technically, applied science and engineering) awarded in the United States went to Josiah Willard Gibbs at Yale University in 1863; it was also the second PhD awarded in science in the U.S.[14]
Only a decade after the successful flights by the Wright brothers, there was extensive development of aeronautical engineering through development of military aircraft that were used in World War I . Meanwhile, research to provide fundamental background science continued by combining theoretical physics with experiments.
Engineering is a broad discipline which is often broken down into several sub-disciplines. These disciplines concern themselves with differing areas of engineering work. Although initially an engineer will usually be trained in a specific discipline, throughout an engineer's career the engineer may become multi-disciplined, having worked in several of the outlined areas. Engineering is often characterized as having four main branches:[15][16][17]
New specialties sometimes combine with the traditional fields and form new branches - for exampleEarth Systems Engineering and Management involves a wide range of subject areas includinganthropology, engineering, environmental science, ethics and philosophy. A new or emerging area of application will commonly be defined temporarily as a permutation or subset of existing disciplines; there is often gray area as to when a given sub-field becomes large and/or prominent enough to warrant classification as a new "branch." One key indicator of such emergence is when major universities start establishing departments and programs in the new field.
For each of these fields there exists considerable overlap, especially in the areas of the application of sciences to their disciplines such as physics, chemistry and mathematics.
Design of a turbine requires collaboration of engineers from many fields, as the system involves mechanical, electro-magnetic and chemical processes. The blades, rotor and stator as well as the steam cycle all need to be carefully designed and optimized.
Engineers apply mathematics and sciences such as physics to find suitable solutions to problems or to make improvements to the status quo. More than ever, engineers are now required to have knowledge of relevant sciences for their design projects. As a result, they may keep on learning new material throughout their career.
If multiple options exist, engineers weigh different design choices on their merits and choose the solution that best matches the requirements. The crucial and unique task of the engineer is to identify, understand, and interpret the constraints on a design in order to produce a successful result. It is usually not enough to build a technically successful product; it must also meet further requirements.
Constraints may include available resources, physical, imaginative or technical limitations, flexibility for future modifications and additions, and other factors, such as requirements for cost, safety, marketability, productibility, andserviceability. By understanding the constraints, engineers derive specifications for the limits within which a viable object or system may be produced and operated.
A drawing for a booster engine for steam locomotives. Engineering is applied to design, with emphasis on function and the utilization of mathematics and science.
Usually multiple reasonable solutions exist, so engineers must evaluate the different design choices on their merits and choose the solution that best meets their requirements. Genrich Altshuller, after gathering statistics on a large number of patents, suggested that compromises are at the heart of "low-level" engineering designs, while at a higher level the best design is one which eliminates the core contradiction causing the problem.
Engineers take on the responsibility of producing designs that will perform as well as expected and will not cause unintended harm to the public at large. Engineers typically include a factor of safety in their designs to reduce the risk of unexpected failure. However, the greater the safety factor, the less efficient the design may be.
The study of failed products is known as forensic engineering, and can help the product designer in evaluating his or her design in the light of real conditions. The discipline is of greatest value after disasters, such as bridge collapses, when careful analysis is needed to establish the cause or causes of the failure.
A computer simulation of high velocity air flow around a Space Shuttleduring re-entry. Solutions to the flow require modelling of the combined effects of fluid flow and the heat equations.
As with all modern scientific and technological endeavors, computers and software play an increasingly important role. As well as the typical business application software there are a number of computer aided applications (computer-aided technologies) specifically for engineering. Computers can be used to generate models of fundamental physical processes, which can be solved using numerical methods.
These allow products and components to be checked for flaws; assess fit and assembly; study ergonomics; and to analyze static and dynamic characteristics of systems such as stresses, temperatures, electromagnetic emissions, electrical currents and voltages, digital logic levels, fluid flows, and kinematics. Access and distribution of all this information is generally organized with the use of product data management software.[21]
In recent years the use of computer software to aid the development of goods has collectively come to be known as product lifecycle management (PLM).[22]
RoboticKismet can produce a range of facial expressions.
Engineering as a subject ranges from large collaborations to small individual projects. Almost all engineering projects are beholden to some sort of financing agency: a company, a set of investors, or a government. The few types of engineering that are minimally constrained by such issues are pro bono engineering and open-design engineering.
By its very nature engineering has interconnections with society and human behavior. Every product or construction used by modern society will have been influenced by engineering. Engineering is a very powerful tool to make changes to environment, society and economies, and its application brings with it a great responsibility. Many engineering societies have established codes of practice and codes of ethics to guide members and inform the public at large.
Engineering is a key driver of human development.[23] Sub-Saharan Africa in particular has a very small engineering capacity which results in many African nations being unable to develop crucial infrastructure without outside aid.[citation needed] The attainment of many of the Millennium Development Goals requires the achievement of sufficient engineering capacity to develop infrastructure and sustainable technological development.[24]
All overseas development and relief NGOs make considerable use of engineers to apply solutions in disaster and development scenarios. A number of charitable organizations aim to use engineering directly for the good of mankind:
Engineering companies in many established economies are facing significant challenges ahead with regard to the number of skilled engineers being trained, compared with the number retiring. This problem is very prominent in the UK.[26] There are many economic and political issues that this can cause, as well as ethical issues[27] It is widely agreed that engineering faces an "image crisis",[28] rather than it being fundamentally an unattractive career. Much work is needed to avoid huge problems in the UK and well as the USA and other western economies.
Engineers, Scientist and Technician works on target positioner inside National Ignition Facility (NIF) target chamber.
There exists an overlap between the sciences and engineering practice; in engineering, one applies science. Both areas of endeavor rely on accurate observation of materials and phenomena. Both use mathematics and classification criteria to analyze and communicate observations.[citation needed]
Scientists may also have to complete engineering tasks, such as designing experimental apparatus or building prototypes. Conversely, in the process of developing technology engineers sometimes find themselves exploring new phenomena, thus becoming, for the moment, scientists.[citation needed]
In the book What Engineers Know and How They Know It,[32] Walter Vincenti asserts that engineering research has a character different from that of scientific research. First, it often deals with areas in which the basic physics and/or chemistry are well understood, but the problems themselves are too complex to solve in an exact manner.
Examples are the use of numerical approximations to theNavier–Stokes equations to describe aerodynamic flow over an aircraft, or the use of Miner's rule to calculate fatigue damage. Second, engineering research employs many semi-empirical methods that are foreign to pure scientific research, one example being the method of parameter variation.[citation needed]
As stated by Fung et al. in the revision to the classic engineering text Foundations of Solid Mechanics:
"Engineering is quite different from science. Scientists try to understand nature. Engineers try to make things that do not exist in nature. Engineers stress invention. To embody an invention the engineer must put his idea in concrete terms, and design something that people can use. That something can be a device, a gadget, a material, a method, a computing program, an innovative experiment, a new solution to a problem, or an improvement on what is existing. Since a design has to be concrete, it must have its geometry, dimensions, and characteristic numbers. Almost all engineers working on new designs find that they do not have all the needed information. Most often, they are limited by insufficient scientific knowledge. Thus they study mathematics, physics, chemistry, biology and mechanics. Often they have to add to the sciences relevant to their profession. Thus engineering sciences are born."[33]
Although engineering solutions make use of scientific principles, engineers must also take into account safety, efficiency, economy, reliability and constructability or ease of fabrication, as well as legal considerations such as patent infringement or liability in the case of failure of the solution.[citation needed]
Leonardo da Vinci, seen here in a self-portrait, has been described as the epitome of the artist/engineer.[34] He is also known for his studies on human anatomy and physiology.
The study of the human body, albeit from different directions and for different purposes, is an important common link between medicine and some engineering disciplines.Medicine aims to sustain, enhance and even replace functions of the human body, if necessary, through the use oftechnology.
Modern medicine can replace several of the body's functions through the use of artificial organs and can significantly alter the function of the human body through artificial devices such as, for example, brain implants andpacemakers.[35][36]The fields of bionicsand medical bionics are dedicated to the study of synthetic implants pertaining to natural systems.
Conversely, some engineering disciplines view the human body as a biological machine worth studying, and are dedicated to emulating many of its functions by replacing biology with technology. This has led to fields such as artificial intelligence, neural networks, fuzzy logic, and robotics. There are also substantial interdisciplinary interactions between engineering and medicine.[37][38]
Both fields provide solutions to real world problems. This often requires moving forward before phenomena are completely understood in a more rigorous scientific sense and therefore experimentation and empirical knowledge is an integral part of both.
Medicine, in part, studies the function of the human body. The human body, as a biological machine, has many functions that can be modeled using engineering methods.[39]
The heart for example functions much like a pump,[40] the skeleton is like a linked structure with levers,[41] the brain produces electrical signals etc.[42] These similarities as well as the increasing importance and application of engineering principles in medicine, led to the development of the field ofbiomedical engineering that uses concepts developed in both disciplines.
Newly emerging branches of science, such as systems biology, are adapting analytical tools traditionally used for engineering, such as systems modeling and computational analysis, to the description of biological systems.[39]
Among famous historical figures Leonardo da Vinci is a well-known Renaissance artist and engineer, and a prime example of the nexus between art and engineering.[34][50]
