Smart material
Encyclopedia
Smart materials or designed materials
Designed materials
Designed materials or Smart material is a material whose structure and composition has been deliberately manipulated to affect the material’s properties in a controlled fashion to achieve a specific functionality unexpected or significantly different from the original material.Quest for a material...
are materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress
Stress (physics)
In continuum mechanics, stress is a measure of the internal forces acting within a deformable body. Quantitatively, it is a measure of the average force per unit area of a surface within the body on which internal forces act. These internal forces are a reaction to external forces applied on the body...
, temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
, moisture, pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
, electric
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
or magnetic
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
fields.
There are a number of types of smart material, some of which are already common. Some examples are as following:
- Piezoelectric materials are materials that produce a voltage when stress is applied. Since this effect also applies in the reverse manner, a voltage across the sample will produce stress within the sample. Suitably designed structures made from these materials can therefore be made that bend, expand or contract when a voltage is applied.
- Shape memory alloyShape memory alloyA shape-memory alloy is an alloy that "remembers" its original, cold-forged shape: returning the pre-deformed shape by heating. This material is a lightweight, solid-state alternative to conventional actuators such as hydraulic, pneumatic, and motor-based systems...
s and shape memory polymerShape Memory PolymerShape-memory polymers are polymeric smart materials that have the ability to return from a deformed state to their original shape induced by an external stimulus , such as temperature change....
s are materials in which large deformation can be induced and recovered through temperature changes or stress changes (pseudoelasticityPseudoelasticityPseudoelasticity, sometimes called superelasticity, is an elastic response to an applied stress, caused by a phase transformation between the austenitic and martensitic phases of a crystal. It is exhibited in shape-memory alloys...
). The large deformation results due to martensitic phase change. - Magnetostrictive materials exhibit change in shape under the influence of magnetic field and also exhibit change in their magnetization under the influence of mechanical stress.
- Magnetic shape memoryMagnetic shape memoryMagnetic shape-memory alloys , or ferromagnetic shape-memory alloys , are ferromagnetic materials which exhibit large strains under the influence of an applied magnetic field due to martensitic phase transformation...
alloys are materials that change their shape in response to a significant change in the magnetic field. - pH-sensitive polymersPH-sensitive polymerspH sensitive or pH responsive polymers are materials which will respond to the changes in the pH of the surrounding medium by varying their dimensions. Such materials swell or collapse depending on the pH of their environment...
are materials that change in volume when the pH of the surrounding medium changes. - Temperature-responsive polymersTemperature-responsive polymersA temperature-responsive polymer is a polymer which undergoes a physical change when external thermal stimuli are presented. The ability to undergo such changes under easily controlled conditions makes this class of polymers fall into the category of smart materials. These physical changes can be...
are materials which undergo changes upon temperature. - HalochromicHalochromismA halochromic material is a material which changes colour when pH changes occur. The term ‘chromic’ is defined as materials that can change colour reversibly with the presence of a factor. In this case, the factor is pH...
materials are commonly used materials that change their colour as a result of changing acidity. One suggested application is for paints that can change colour to indicate corrosionCorrosionCorrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen...
in the metal underneath them. - Chromogenic systemsChromismIn chemistry, chromism is a process that induces a change, often reversible, in the colors of compounds. In most cases, chromism is based on a change in the electron states of molecules, especially the π- or d-electron state, so this phenomenon is induced by various external stimuli which can alter...
change colour in response to electrical, optical or thermal changes. These include electrochromic materials, which change their colour or opacity on the application of a voltage (e.g. liquid crystal displayLiquid crystal displayA liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....
s), thermochromic materials change in colour depending on their temperature, and photochromic materials, which change colour in response to light—for example, light sensitive sunglassesSunglassesSunglasses or sun glasses are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can sometimes also function as a visual aid, as variously termed spectacles or glasses exist, featuring lenses that...
that darken when exposed to bright sunlight. - FerrofluidFerrofluidA ferrofluid is a liquid which becomes strongly magnetized in the presence of a magnetic field.Ferrofluids are colloidal liquids made of nanoscale ferromagnetic, or ferrimagnetic, particles suspended in a carrier fluid . Each tiny particle is thoroughly coated with a surfactant to inhibit clumping...
- Photomechanical materialsPhotomechanical EffectThe photomechanical effect is the change in the shape of a material when it is exposed to light. The photomechanical effect was first documented by Alexander Graham Bell in 1880...
change shape under exposure to light. - Self-healing materialSelf-healing materialSelf-healing materials are a class of smart materials that have the structurally incorporated ability to repair damage caused by mechanical usage over time. The inspiration comes from biological systems, which have the ability to heal after being wounded...
s have the intrinsic ability to repair damage due to normal usage, thus expanding the material's lifetime - Dielectric elastomersDielectric elastomersDielectric elastomers are smart material systems which produce large strains and belong to the group of electroactive polymers . Based on their simple working principle dielectric elastomer actuators transform electric energy directly into mechanical work. DE are lightweight, have a high elastic...
(DEs) are smart material systems which produce large strains (up to 300%) under the influence of an external electric field. - Magnetocaloric materials are compounds that undergo a reversible change in temperature upon exposure to a changing magnetic field.
- Thermoelectric materials are used to build devices that convert temperature differences into electricity and vice-versa.