Colors changes with temperature

Ski Pole s Color Changes with Temperature. Design News, p. 41, Jan. 1990. 

One of the primary fields of application for P.R.151 is in polystyrene, although there is a slight color change at temperatures above 260°C, at which the pigment partially dissolves. It is also used to a considerable extent in ABS. Cast resins based on methylmethacrylate and unsaturated polyesters are also frequently colored with P.R.151, which is resistant to the peroxide catalysts that are used to harden the plastic. The lightfastness in these media is good it equals step 6-7 on the Blue Scale. 

The copper (I) and silver salts of tetrarodomercuric (II) add, H2[HgI, exhibit color changes with variations in temperature which are reversible in nature. 

To optimize the reduction process, variations in the parameters such as pH, concentration of AgNOj, and temperature were made. Under alkaline conditions and at room temperature, the color changes with time from colorless to light pink, reddish brown, and finally to dark brown (Figure 15.2) with increasing intensity and were indicative of the formation of Ag nanoparticles both intracellularly on fungal mycelium and extracellularly in media. 

Composition. Bitumen paints contain bituminous substances as binders. Bitumen is defined in DIN 55 946 as A low-volatile, darkly-colored mixture of organic substances obtained in the processing of mineral oils and petroleum, whose viscoelastic behavior changes with temperature. The typical properties of bitumen can be attributed to a colloidal system in which the disperse phase (asphaltenes) is stably distributed in a coherent phase of high-boiling oils (maltenes). ... 

Fig. 5.16 Color change with time of 6.8 wt% of 21 in E7 a upon UV irradiation with 365 nm light and b during thermal relaxation. Color photographs are taken perpendicular to the surface of the film at room temperature. Reproduced with permission from [94]. Copyright 2006 John Wiley...

Another type of thermotropic liquid crystals is called cholesteric liquid crystals. The color of cholesteric liquid crystals changes with temperature and therefore they are suitable for use as sensitive thermometers. In metallurgy, for example, they are used to detect metal stress, heat sources, and conduction paths. Medically, the temperature of the body at specific sites can be determined with the aid of liquid crystals. This technique has become an important diagnostic tool in treating infection and mmor growth (for example, breast tumors). Because locahzed infections and tumors increase metabolic rate and hence temperature in the affected tissues, a thin film of liquid crystal can help a physician see whether an infection or tumor is present by responding to a temperature difference with a change of color. 

Fig. 9.16 Correlated color temperature (CCT) with color coordinates. Table 9.1 shows the range of CCT changes with temperature changes from 0 to 100 °C [61]...

Gel Networks for Reversible Transparency and Color Control with Temperature. A novel class of polymer gel networks which change both their color and transparency with changing temperature has been developed (61). Starting from a... 

Liquid absorbance standards provide a theoretically perfect way of checking the linearity of the photometric scale of an instrument because absorbance is directly proportional to concentration or path length. However, technical imperfections in instruments, cuvets, and filter solutions limit the accuracy of absolute photometric determinations (60). Liquid standards should be prepared for each calibration session. Solid samples should be checked and recertified periodically by an accredited standards testing laboratory. Color standards that change with temperature or light exposure such as the National Bureau of Standards red glass filter No. 2101 that is doped with selenium (50) must be used cautiously as recommended by the standards issuing laboratory. 

Instrument operators must always scrutinize color samples for unusual spectral properties. Thermochromism, for example, is a specimen property that will cause its color to change with temperature. The temperature must be recorded along with the color measurements to be meaningful to future users of the color information. Figure 14 demonstrates graphically this condition in a colored glass long bandpass filter. 

Additional soluble polydiacetylenes have been discovered which show temperature- or solvent-induced color changes with absorption shifts similar to poly4BCMU(6-8). These solutions are believed to... 

Liquid crystals can also be used in thermometers (Figure 25.12). The spacing between ciys-tal layers depends on temperature, and the wavelength of light reflected by the crystal depends on this spacing. Thus, the color reflected by the liquid crystal will change with temperature, and this color can be used to indicate the temperature to which the liquid crystal is exposed. 

The indicator method is especially convenient when the pH of a weU-buffered colorless solution must be measured at room temperature with an accuracy no greater than 0.5 pH unit. Under optimum conditions an accuracy of 0.2 pH unit is obtainable. A Hst of representative acid—base indicators is given in Table 2 with the corresponding transformation ranges. A more complete listing, including the theory of the indicator color change and of the salt effect, is also available (1). 

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