Smart materials, also called intelligent or responsive materials, are designed materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as

stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...

, moisture,

electric Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...

or magnetic fields, light,

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measurement, measured with a thermometer. Thermometers are calibrated in various Conversion of units of temperature, temp ...

, pH, or chemical compounds. Smart materials are the basis of many applications, including

sensors A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...

and

actuators An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover". An actuator requires a control device (controlled by control signal) an ...

, or

artificial muscles Artificial muscles, also known as muscle-like actuators, are materials or devices that mimic natural muscle and can change their stiffness, reversibly contract, expand, or rotate within one component due to an external stimulus (such as voltage, cur ...

, particularly as electroactive polymers (EAPs). Terms used to describe smart materials include shape memory material (SMM) and shape memory technology (SMT).

Types

There are a number of types of smart material, of which are already common. Some examples are as following: *

Piezoelectric Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word '' ...

materials are materials that produce a voltage when stress is applied. Since this effect also applies in a reverse manner, a voltage across the sample will produce stress within sample. Suitably designed structures made from these materials can, therefore, be made that bend, expand or contract when a voltage is applied. *

Shape-memory alloy In metallurgy, a shape-memory alloy (SMA) is an alloy that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. It may also be called memory metal, memory alloy, smart metal, smart alloy, or muscle wire. P ...

s and

shape-memory polymer Shape-memory polymers (SMPs) are polymeric smart materials that have the ability to return from a deformed state (temporary shape) to their original (permanent) shape when induced by an external stimulus (trigger), such as temperature change. P ...

s are materials in which large deformation can be induced and recovered through temperature changes or stress changes (

pseudoelasticity Pseudoelasticity, sometimes called superelasticity, is an elastic (reversible) 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. O ...

). The shape memory effect results due to respectively martensitic phase change and induced elasticity at higher temperatures. * Photovoltaic materials or

optoelectronics Optoelectronics (or optronics) is the study and application of electronic devices and systems that find, detect and control light, usually considered a sub-field of photonics. In this context, ''light'' often includes invisible forms of radiat ...

convert light to electrical current. * Electroactive polymers (EAPs) change their volume by voltage or electric fields. * Magnetostrictive materials exhibit a change in shape under the influence of magnetic field and also exhibit a change in their magnetization under the influence of mechanical stress. * Magnetic shape memory alloys are materials that change their shape in response to a significant change in the magnetic field. *

Smart inorganic polymers Smart inorganic polymers (SIPs) are hybrid or fully inorganic polymers with tunable (smart) properties such as stimuli responsive physical properties (shape, conductivity, rheology, bioactivity, self-repair, sensing etc.). While organic polymers ar ...

showing tunable and responsive properties. * pH-sensitive polymers are materials that change in volume when the pH of the surrounding medium changes. * Temperature-responsive polymers are materials which undergo changes upon temperature. * Halochromic materials are commonly used materials that change their color as a result of changing acidity. One suggested application is for paints that can change color to indicate

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...

in the metal underneath them. * Chromogenic systems change color in response to electrical, optical or thermal changes. These include

electrochromic Electrochromism is a phenomenon in which a material displays changes in color or opacity in response to an electrical stimulus. In this way, a smart window made of an electrochromic material can block specific wavelengths of ultraviolet, vis ...

materials, which change their colour or opacity on the application of a voltage (e.g., liquid crystal displays),

thermochromic Thermochromism is the property of substances to change color due to a change in temperature. A mood ring is an excellent example of this phenomenon, but thermochromism also has more practical uses, such as baby bottles which change to a differen ...

materials change in colour depending on their temperature, and

photochromic Photochromism is the reversible transformation of a chemical species ( photoswitch) between two forms by the absorption of electromagnetic radiation ( photoisomerization), where the two forms have different absorption spectra. In plain language, ...

materials, which change colour in response to light—for example, light-sensitive sunglasses that darken when exposed to bright sunlight. *

Ferrofluid Ferrofluid is a liquid that is attracted to the poles of a magnet. It is a colloidal liquid made of nanoscale ferromagnetic or ferrimagnetic particles suspended in a carrier fluid (usually an organic solvent or water). Each magnetic particle ...

s are magnetic fluids (affected by magnets and magnetic fields). * Photomechanical materials change shape under exposure to light. *

Polycaprolactone Polycaprolactone (PCL) is a biodegradable polyester with a low melting point of around 60 °C and a glass transition temperature of about −60 °C. The most common use of polycaprolactone is in the production of speciality polyureth ...

(polymorph) can be molded by immersion in hot water. *

Self-healing material Self-healing materials are artificial or synthetically created substances that have the built-in ability to automatically repair damages to themselves without any external diagnosis of the problem or human intervention. Generally, materials will ...

s have the intrinsic ability to repair damage due to normal usage, thus expanding the material's lifetime. * Dielectric elastomers (DEs) are smart material systems which produce large strains (up to 500%) 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. * Smart self-healing coatings heal without human intervention. *

Thermoelectric materials Thermoelectric materials show the thermoelectric effect in a strong or convenient form. The ''thermoelectric effect'' refers to phenomena by which either a temperature difference creates an electric potential or an electric current creates a t ...

are used to build devices that convert temperature differences into electricity and vice versa. * Chemoresponsive materials change size or volume under the influence of external chemical or biological compound.''Chemoresponsive Materials /Stimulation by Chemical and Biological Signals'', Schneider, H.-J.; Ed:, (2015)''The Royal Society of Chemistry,'' Cambridge https://dx.doi.org/10.1039/97817828822420 Smart materials have properties that react to changes in their environment. This means that one of their properties can be changed by an external condition, such as temperature, light, pressure, electricity, voltage, pH, or chemical compounds. This change is reversible and can be repeated many times. There is a wide range of different smart materials. Each offer different properties that can be changed. Some materials are very good and cover a huge range of the scales.

References

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External links

Smart Materials Book Series
Royal Society of Chemistry Artificial materials

Types

See also

References

External links