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Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
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In 1968 Shirley Chisholm became the first Black woman elected to the United States Congress. In 1972 she launched a campaign for the Democratic presidential nomination, breaking another political barrier.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
A solvent dye is a dye soluble in organic solvents. It is usually used as a solution in an organic solvent. [1]
Solvent dyes are used to color organic solvents, hydrocarbon fuels, waxes, lubricants, plastics, and other hydrocarbon-based nonpolar materials. Fuel dyes are one use of solvent dyes. Their molecules are typically nonpolar or little polar, and they do not undergo ionization. They are insoluble in water. They form a colloidal solution in solvents. They have poor (basic dyes) to good (metal complex based) light fastness.
Solvent dyes are used for gold imitation (and other transparent metallic effects) of metallized polyester films. Also used in marking inks, inkjet inks, glass coloration, and so on.
Names of solvent dyes are often generic, of the scheme "solvent <color> <number>", e.g. Solvent Red 24, Solvent Red 26, Solvent Red 164, Solvent Yellow 124, Solvent Blue 35, etc.
Red and yellow solvent dyes are often azo dyes, green and blue ones tend to be anthraquinone dyes.
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
A solvent dye is a dye soluble in organic solvents. It is usually used as a solution in an organic solvent. Solvent dyes are used to color organic solvents, hydrocarbon fuels, waxes, lubricants, plastics, and other hydrocarbon-based nonpolar materials. Fuel dyes are one use of solvent dyes. Their molecules are typically nonpolar or little polar, and they do not undergo ionization. They are insoluble in water. They form a colloidal solution in solvents. They have poor (basic dyes) to good (metal complex based) light fastness. Solvent dyes are used for gold imitation (and other transparent metallic effects) of metallized polyester films. Also used in marking inks, inkjet inks, glass coloration, and so on. Names of solvent dyes are often generic, of the scheme "solvent ", e.g. Solvent Red 24, Solvent Red 26, Solvent Red 164, Solvent Yellow 124, Solvent Blue 35, etc. Red and yellow solvent dyes are often azo dyes, green and blue ones tend to be anthraquinone dyes.
A dye is a colored substance that is soluble in some solvent; by contrast pigments are insoluble or nearly so in all solvents. Because of their solubility, dyes can chemically bind to the material they color. Dye is generally applied in an aqueous solution and may require a mordant to improve the fastness of the dye on the fiber. The majority of natural dyes are derived from non-animal sources such as roots, berries, bark, leaves, wood, fungi and lichens. However, due to large-scale demand and technological improvements, most dyes used in the modern world are synthetically produced from substances such as petrochemicals. Some are extracted from insects and/or minerals. Synthetic dyes are produced from various chemicals. The great majority of dyes are obtained in this way because of their superior cost, optical properties (color), and resilience (fastness, mordancy). Both dyes and pigments are colored, because they absorb only some wavelengths of visible light. Dyes are usually soluble in some solvent, whereas pigments are insoluble. Some dyes can be rendered insoluble with the addition of salt to produce a lake pigment.
A leuco dye (from the Greek λευκό leuko: white) is a dye which can switch between two chemical forms, one of which is colorless. Reversible transformations can be caused by heat, light or pH, resulting in examples of thermochromism, photochromism and halochromism, respectively. Irreversible transformations typically involve reduction or oxidation. The colorless form is sometimes referred to as the leuco form. Leuco dyes form the basis of thermal printer papers and certain pH indicators. From the applications perspective, leuco dyes are "the most important class of thermochromic compounds". The dyes are typically applied in the form of microcapsules with the mixture sealed inside. An illustrative example is the Hypercolor fashion, where microcapsules with crystal violet lactone, weak acid, and a dissociable salt dissolved in dodecanol are applied to the fabric. When the solvent is solid, the dye exists in its lactone leuco form, while when the solvent melts, the salt dissociates, the pH inside the microcapsule lowers, the dye becomes protonated, its lactone ring opens, and its absorption spectrum shifts drastically, therefore it becomes deeply violet. In this case the apparent thermochromism is in fact halochromism. The dyes most commonly used are spirolactones, fluorans, spiropyrans, and fulgides. The acids include bisphenol A, parabens, 1,2,3-triazole derivates, and 4-hydroxycoumarin and act as proton donors, changing the dye molecule between its leuco form and its protonated colored form; stronger acids would make the change irreversible. Leuco dyes are suitable for general indicators of approximate temperature ("too cool", "too hot", "about OK"), or for various novelty items. They are usually used in combination with some other pigment, producing a color change between the color of the base pigment and the color of the pigment combined with the color of the non-leuco form of the leuco dye. Organic leuco dyes are available for temperature ranges between about −5 °C (23 °F) and 60 °C (140 °F), in wide range of colors. The color change usually happens in a 3 °C (37 °F) interval. An application of leuco dyes is in the Duracell battery state indicators. A layer of a leuco dye is applied on a resistive strip to indicate its heating, thus gauging the amount of current the battery is able to supply. The strip is triangular-shaped, changing its resistance along its length, therefore heating up a proportionally long segment with the amount of current flowing through it. The length of the segment above the threshold temperature for the leuco dye then becomes colored. Exposure to ultraviolet radiation, solvents and high temperatures reduce the lifespan of leuco dyes. Temperatures above about 200–230 °C (392–446 °F) typically cause irreversible damage to leuco dyes; a time-limited exposure of some types to about 250 °C (482 °F) is allowed during manufacturing. Thermochromic paints use liquid crystals or leuco dye technology. After absorbing a certain amount of light or heat, the crystallic or molecular structure of the pigment reversibly changes in such a way that it absorbs and emits light at a different wavelength than at lower temperatures. Thermochromic paints are seen quite often as a coating on coffee mugs, whereby once hot coffee is poured into the mugs, the thermochromic paint absorbs the heat and becomes colored or transparent, therefore changing the appearance of the mug. These are known as magic mugs or heat changing mugs. Another common example is the use of leuco dye in spoons used in ice cream parlors and frozen yogurt shops. Once dipped into the cold desserts, part of the spoon appears to change color.
Solvent Yellow 124 is a yellow azo dye used in European Union as a fuel dye. It is a marker used since August 2002 to distinguish diesel fuel intended for heating from a higher-taxed motor diesel fuel. It is added to fuels not intended for motor vehicles in amounts of 6 mg/L or 7 mg/kg under the name Euromarker.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Madam C.J. Walker