Smart materials change

Other examples of materials that respond smartly to changes in temperature are the poly(ethylene glycol)s-modifted cottons, polyesters, and... 

This class of smart materials is the mechanical equivalent of electrostrictive and magnetostrictive materials. Elastorestrictive materials exhibit high hysteresis between strain and stress (14,15). This hysteresis can be caused by motion of ferroelastic domain walls. This behavior is more compHcated and complex near a martensitic phase transformation. At this transformation, both crystal stmctural changes iaduced by mechanical stress and by domain wall motion occur. Martensitic shape memory alloys have broad, diffuse phase transformations and coexisting high and low temperature phases. The domain wall movements disappear with fully transformation to the high temperature austentic (paraelastic) phase. 

Shape-memory polymers (SMPs) are a class of smart materials with the ability to change shape on demand in response to an environmental stimuli [322-325]. So far, the most commonly investigated SMPs are temperature-induced SMPs, whose shape-recovery behavior is triggered by thermal stimuli. Such SMPs have one shape at certain temperature and are converted to another shape at a different temperature (Fig. 22). Temperature-responsive SMPs usually require the combination... 

We have had smart materials as materials for a long time though the term is relatively new. Some of the first smart materials were piezoelectric materials, such as poly(vinylene fluoride), which emit an electric current when pressure is applied and change volume when a current is passed through it. Most smart materials are polymeric or have a critical portion of the smart system that is polymeric. 

The use of smart materials as sensing devices and shape-changing materials has been enhanced because of the increased emphasis on composite materials that allow the introduction of smart materials as components. 

The actuator part may also be a smart material, such as a piezoelectric bar, placed in a wind foil that changes orientation according to a current imputed by the computer center allowing a machine such as an automobile to handle better and be more fuel efficient. 

Muscles contract and expand in response to electrical, thermal, and chemical stimuli. Certain polymers, such as synthetic polypeptides, are known to change shape on application of electric current, temperature, and chemical environment. For instance, selected bioelastic smart materials expand in salt solutions and may be used in desalination efforts and as salt concentration sensors. Polypeptides and other polymeric materials are being studied in tissue reconstruction, as adhesive barriers to prevent adhesion growth between surgically operated tissues, and in controlled drug release, where the material is designed to behave in a predetermined matter according to a specific chemical environment. 

Smart Materials— Materials That Adapt to Changing Conditions... 

Using smart materials in objects such as eyeglasses means that the function can change depending on environmental conditions or the needs of the user. Smart materials can also be critical components of systems— assemblies of interacting parts—that adapt to varying conditions. Such systems are known as adaptive or intelligent systems. 

Materials that respond to electricity or magnetism were some of the earliest smart materials to be discovered. The British researcher James Joule (1818-89) found in 1842 that iron changes length in response to a magnetic field, a process called magnetostriction. Since electric and magnetic fields are easy to produce and control with precision, these smart materials can be extremely useful. 

How far can smart materials go Futuristic depictions such as in the 1991 film Terminator 2 have androids made of shape-changing metal that can quickly flow and set into any desired form. A more realistic vision for the future of smart materials and systems can be viewed by observing nature. Organisms move, adapt, and evolve, and they are made of materials that are complex but have been studied by biologists for decades. 

Beylerian, George M., Michele Caniato, Andrew Dent, and Bradley Quinn. Ultra Materials How Materials Innovation Is Changing the World. New York Thames Hudson, 2007. This well-illustrated book focuses on smart materials developed for appUcations in textiles, fashion, and design. 

---