Colour-changing devices

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... 

Gaseous sterilization Ethylene oxide (EO) Reactive chemical Indicator paper impregnated with a reactive chemical which undergoes a distinct colour change on reaction with EO in the presence of heat and moisture. With some devices rate of colour development varies with temperature and EO concentration Gas concentration, temperature, time (selected devices) NB a minimum relative humidity (rh) is required for device to function... 

Radiation sterilization Radiochromic chemical Plastic devices impregnated with radiosensitive chemicals which undergo colour changes at relatively low radiation doses Only indicate exposure to radiation... 

The use of metal-ion indicators to indicate the end-point of complexometric titrations is based on a specific colour change. Some individuals may find it difficult to detect a particular colour change (e.g. those with colour blindness). Alternative approaches for end-point detection are available based on a colorimeter/spectrophotometer (devices for measuring colour, see Chapter 26) or electrochemical detection (see Chapter 34). 

Sensor materials responding to chemical changes with colour changes obviously could prove useful in new devices. Also new food additives as colourants are of... 

There are many examples of the use of very small colorimetric devices for POC applications, such as urine dipsticks and test strips for blood sample screening. While not instruments as such, they are based on clever chemistries and reactions and are often single use, throwaway devices. The reagents required for the test are embedded and dried into a strip which is then dipped into the sample, e.g. urine or blood. The colour changes that result are compared to a colour chart, which is usually provided on the side of the container for the test strips. 

Even smaller than the handheld devices above is a newly developed pen-like device which can detect sub-milligramme amounts of peroxide-based explosives . The prototype costs less than 23 per unit. A suspect sample is placed on a silicone rubber test pad. Three test chemicals are sequentially injected into the transparent chamber in the pen and a blue-green colour change occurs on reaction with any peroxide present in the sample within three seconds. 

PANI is suited to the production of very fa.st devices, because the time necessary for the colour changes is about one order of magnitude shorter than in electro-chromic oxides [34]. In fact, it is the cell resistance which controls the switching speed of the device, and if it were possible to take into account just the transport inside the film, it would be possible to obtain response times as short as 100 ps [17]. 

The device by Corradini et al uses an ITO counter-electrode at which occurs, without significant colour change, an electrochemical process that is presumably due to lithium ion insertion and involves up to ca. 7.5mCcm [29]. Figure 7.7 shows the transmittance in the visible and IR regions of the electrochromic-electrode in the undoped and doped states as well as of the ITO counter-electrode before and after lithium insertion. 

The colour change is from purple to transparent pale blue for both devices. Light modulation in devices with a colourless optically passive counterelectrode is governed solely by changes in the electrochromic electrode. 

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