Colour change Subject

Mitsui etal. (2003) studied the colour change of wood that had been previously irradiated with light and then subjected to a relatively mild heat treatment (no higher than 90 °C). The extent of colour change was dependent upon the wavelength of irradiation and was found to be considerably greater when the irradiated wood was heated under conditions of high humidity. 

Secondly there are direct techniques, notably electron spin resonance spectroscopy (ESR), in which the free radicals produced by the fracture of covalent bonds are directly observed, both in respect of their chemical nature and their number. Much of this review is orncemed with the results of ESR studies and this technique is therefore treated at some length below. One little used technique for the direct assessment of free radicals produced by n chanical means is that of Pazonyi et al and Salloum and Eckert They dropped various polymers in an ethanolic solution of diphenyl picryl hydrazyl, a chemical indicator, and determined the free radical concentration in the cut surfaces by colorimetrie measurements of the colour change. This method is subject to soixm uncertainty on account of possible side reactions. 

Silica aerogels are highly porous solids with specific surfaces up to 1000 m g [1]. The doping of aerogels with transition metal oxides like vanadia to form efficient catalysts has been a subject of great interest [2-5]. Vanadia doped silica gels show in addition colour changes upon adsorption of small molecules such as water, ammonia or formaldehyde [6] and may therefore used as optical sensors. 

Random errors are introduced whenever there is a subjective part to the experiment (such as estimating when a solution has reached the mark in a pipette, or recognizing the onset of a colour change during a titration), or where the experimental measurements are influenced by rapidly fluctuating conditions (e.g. air draughts). 

The FRP cladding panels of buildings do not have to support large stresses, because a steel framework can do this, but in the same way as with boat hulls, their aesthetic appearance and moisture barrier qualities must not be allowed to deteriorate. Often they have been subject to colour changes caused by the action of ultraviolet light on fiame retardant additives in the resin. 

Polymers are subject to unsaturation, which leads to a colour change during processing, as a result of temperature and pressnre [1, 2]. The use of stabilisers should ensure adequate stability of polymers during processing. Repeated processing with additional heat steps... 

In some applications, particularly in the nuclear industry, medical instrumentation and food sterilisation, plastics are subjected to damage, which is associated with a loss in molecular weight and deterioration of some physical properties, such as impact strength and colour change upon exposed the plastics to gamma rays [65, 66]. 

An electrically controlled flexible colour-changing device can be obtained when an electrochromic material is apphed to textile. The first patent for such a structure was published in 1976 [70]. Since then, more than 30 patents have been pubhshed, with a notable increase since 2010, showing the considerable gain of interest in this subject. Over the same time, the role played by the textile material in these structures has increased. The 1976 patent describes a structure composed of two glass or plastic electrodes, coated with tin dioxide (as the electrode) and tungsten trioxide (as the... 

The yellow substance was studied under deep space conditions. After being subjected to UV-irradiation for about four months, it changed colour to brown, possibly due to enrichment in carbon or carbon-containing compounds. IR analysis showed that the new brown substance showed the same absorption lines as those observed in interstellar dust. A special IR study carried out at Stanford University indicated that the brown substance contained many PAHs. 

The problem of using words to describe the colour of a dye or pigment is that it is very subjective, people may be able to agree that a product is red, but what shade It can be described as rose red or pillar-box red, the arguments can be endless. Additionally the appearance of a colour can change in different circumstances, such as the surrounding colours and lighting conditions. 

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