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Mechanochromism
The change of colour which occurs when chemicals are put under stress in the solid state by mechanical grinding, crushing and milling; by friction and rubbing; or in the solid or solution state by high pressure or sonication is covered by the generic term mechanochromism. Specifically colour change under pressure is known as piezochromism and under grinding or attrition tribochromism. See also * Chromism * Photoelasticity (for the physical process) References 1. Bamfield, Peter and Hutchings, Michael G, Chromic Phenomena: the technological applications of colour chemistry, Royal Society of Chemistry, Cambridge UK, pages 104-5, 2010. . Chromism {{spectroscopy-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chromism
In 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 the electron density of substances. It is known that there are many natural compounds that have chromism, and many artificial compounds with specific chromism have been synthesized to date. It is usually synonymous with chromotropism, the (reversible) change in color of a substance due to the physical and chemical properties of its ambient surrounding medium, such as temperature and pressure, light, solvent, and presence of ions and electrons. Chromism is classified by what kind of stimuli are used. Examples of the major kinds of chromism are as follows. * thermochromism is chromism that is induced by heat, that is, a change of temperature. This is the most common chromism of all. * pho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photoelasticity
Photoelasticity describes changes in the optical properties of a material under mechanical deformation. It is a property of all dielectric media and is often used to experimentally determine the stress distribution in a material, where it gives a picture of stress distributions around discontinuities in materials. Photoelastic experiments (also informally referred to as ''photoelasticity'') are an important tool for determining critical stress points in a material, and are used for determining stress concentration in irregular geometries. History The photoelastic phenomenon was first discovered by the Scottish physicist David Brewster, who immediately recognized it as stress-induced birefringence. That diagnosis was confirmed in a direct refraction experiment by Augustin-Jean Fresnel.A. Fresnel, "Note sur la double réfraction du verre comprimé" (read 16 September 1822), ''Annales de Chimie et de Physique'', Ser. 2, vol. 20, pp. 376–83 (nominally f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sonication
A sonicator at the Weizmann Institute of Science during sonicationSonication is the act of applying sound energy to agitate particles in a sample, for various purposes such as the extraction of multiple compounds from plants, microalgae and seaweeds. Ultrasonic frequencies (> 20 kHz) are usually used, leading to the process also being known as ultrasonication or ultra-sonication. In the laboratory, it is usually applied using an ''ultrasonic bath'' or an ''ultrasonic probe'', colloquially known as a ''sonicator''. In a paper machine, an ultrasonic foil can distribute cellulose fibres more uniformly and strengthen the paper. Effects Sonication has numerous effects, both chemical and physical. The chemical effects of ultrasound are concerned with understanding the effect of sonic waves on chemical systems, this is called sonochemistry. The chemical effects of ultrasound do not come from a direct interaction with molecular species. Studies have shown that no direct coupl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Piezochromism
Piezochromism, from the Greek ''piezô'' "to squeeze, to press" and ''chromos'' "color", describes the tendency of certain materials to change color with the application of pressure. This effect is closely related to the electronic band gap change, which can be found in plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...s, semiconductors (e.g. hybrid perovskites) and hydrocarbons. One simple molecule displaying this property is 5-methyl-2- 2-nitrophenyl)amino3-thiophenecarbonitrile, also known as ROY owing to its red, orange and yellow crystalline forms. Individual yellow and pale orange versions transform reversibly to red at high pressure. References External linksPiezochromism Chromism {{materials-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tribochromism
Tribochromism refers to a change in colour of a material caused by mechanical friction. Tribochromatic materials are used when friction has to be detected. These materials generally change colour under mechanical stress conditions and then the colour gradually fades once the stress is removed. See also * Triboluminescence Triboluminescence is a phenomenon in which light is generated when a material is mechanically pulled apart, ripped, scratched, crushed, or rubbed (see tribology). The phenomenon is not fully understood, but appears to be caused by the separation a ... – An optical phenomenon in which light is generated when material is subject to mechanical breaking, especially noticeable when crushing Wint-O-Green Life Savers in the dark. Chromism {{Tech-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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