Smart material
Material that can be externally controlled
From Wikipedia, the free encyclopedia
Smart materials, also called intelligent or responsive materials,[1][page needed] are designed materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress, moisture, electric or magnetic fields, light, temperature, pH, or chemical compounds.[2][3] Smart materials are the basis of many applications, including sensors and actuators, or artificial muscles, particularly as electroactive polymers (EAPs).[4][page needed][5][page needed][6][page needed][7][page needed][8][page needed][9][page needed]
Types
There are a wide array of smart materials, each classified by its functional mechanism. Examples include:
Electromechanical: Responsive to electrical and/or mechanical stimuli.
- Piezoelectric materials can produce a voltage when mechanical stress is applied. This effect also applies in a reverse manner, a voltage applied across the material will produce mechanical stress within sample. Therefore structures made from these materials can be designed to bend, expand, or contract when a voltage is applied[10].
- Electroactive polymers (EAPs) change their volume with applied electrical stimulation[11].
- Dielectric elastomers (DEs) are smart material systems which produce large strains (up to 500%) when an external voltage is applied[12].
Magnetic Responsive: Responsive to an exposure to or change of a magnetic field.
- Magnetostrictive materials exhibit a change in volume when exposed to a magnetic field and when mechanically stressed can produce a magnetic field of its own[13].
- Magnetic shape memory alloys are materials that change their shape in response to a significant change in the magnetic field[14].
- Ferrofluids are magnetic fluids composed of suspended nanoscale ferromagnetic particles that are affected by magnetic fields[15].
- Magnetocaloric materials are compounds that undergo a change in temperature upon exposure to a changing magnetic field[16].
Shape Memory: The ability to return to an original shape after deformation. This transformation can be controlled through a change in temperature, magnetic field, electric field, or light[17][18].
- Shape-memory alloys and shape-memory polymers are materials in which large deformation can be induced and the original shape recovered through temperature or stress changes (pseudoelasticity)[19][20]. The shape memory effect results due to respectively martensitic phase change and induced elasticity at higher temperatures. A common example is nitinol.
- Polycaprolactone (polymorph) can be molded by immersion in hot water.
Chromogenic: A color change in response to electrical, optical, or thermal stimuli.
- Electrochromic materials, which change their color or opacity with applied voltage (e.g., liquid crystal displays)[21].
- Thermochromic materials change in color depending on their temperature[22].
- Photochromic materials change color in response to light (e.g., transition sunglasses that darken when exposed to bright sunlight)[23].
- 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 in the metal underneath them[24].
Stimuli Responsive: Responsive to environmental stimuli.
- Temperature-responsive polymers are materials that changes in response to temperature[25].
- pH-sensitive polymers are materials that change in volume when the pH of the surrounding medium changes.[26]
- Chemoresponsive materials change their physical properties such as optical properties, size, volume, shape, electrical conductivity, and hydrophobicity/hydrophilicity with the exposure of external chemical or biological compounds.[27][28]
- Smart inorganic polymers showing tunable and responsive properties[29].
Energy Conversion: Can transform stimuli into electrical current.
- Photovoltaic materials or optoelectronics convert light to electrical current[30].
- Thermoelectric materials are used to build devices that convert temperature differences into electricity and vice versa[31].
Optically Driven Mechanical Responsive: A change in mechanical properties in response to optical stimuli.
- Photomechanical materials change shape under exposure to light[32].
Self Repairing: The ability to repair mild damage with little to no external intervention.
- Self-healing materials have the intrinsic ability to repair damage due to normal usage, thus expanding the material's lifetime[33][34][35][36].