Thermochromic sensors

PETC/C18-RG blends after annealing as indicated, (b) Pictures of an initially quenched 3.1% w/w PETG/C18-RC blend immersed in hot ( 100 °C) silicon oil for 1 min. Reproduced with permission from Ref [38]. 

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A spectral shift due to interconversion between monomer and excimer/exciplex emission can be exploited to develop temperature sensors for the macroscopic environment. For example, a thermochromic sensor film was developed by immobilising perylene in a polystyrene film with iV-aUyl-iV-methylaniline (NA) [41]. In solution and in the absence of NA, perylene emits blue fluorescence — 475 nm). In thin films and in the presence of NA, an additional broad red emission band is observed (Aem = 551 nm), which is attributed to the perylene-NA exciplex. The fluorescence spectrum is temperature dependent on heating between 25 and 85 °C the relative intensity of the blue monomer emission increases at the expense of the exciplex emission band, indicating that at higher temperatures the monomer-exciplex equilibrium is shifted in favour of the monomer. A wavelength ratiometric approach based on the relative intensities of the two emission peaks as a function of temperature was used to calibrate the sensor film [41]. 

Among all Fe(II) spin crossover compounds known to date, the extensively studied polymeric [Fe(4-R-l,2,4-triazole)3](anion)2 systems (R=amino, alkyl, hydroxyalkyl) appear to have the greatest potential for technological applications, for example in molecular electronics [1, 24, 25] or as temperature sensors [24, 26]. This arises because of their near-ideal spin crossover characteristics pronounced thermochromism, transition temperatures near room temperature, and large thermal hysteresis [1, 24, 27]. 

M Brenci, Thermochromic transducer optical fibre temperature sensor, SPIEProc. 515, 155 (1984). 

Although the bulk of PDA sensors involve vesicles and Langmuir monolayers, a few examples of responsive PDA assemblies based on bolaamphiphiles and diyne silica nanocomposites have been reported (Lu et al. 2001 Song et al. 2001, 2004 Yang et al. 2003 Peng et al. 2006). Although these materials have not been broadly utilized for analyte sensing, they do exhibit the thermochromic, solvatochro-mic, and pH responsive behavior seen with monolayers and liposomes and hold promise for future development. 

Thermochromic dyes change color with temperature (heat). The effect may be due to a single dye or a composite system, and the color change may be reversible or irreversible. Thermochromic dyes find use in direct thermal printing and as temperature sensors, as well as in clothing and novelties. 

Because in zeolites the silver clusters change their color when in contact with water, it has been suggested that these compounds may be used as water-vapor-sensing materials. Ozin et al. observed the vapor-pressure chromic, cathode-ray chromic, water chromic, photochromic, and thermochromic properties for silver-sodalite, and they proposed that these compounds hold promise for use as sensors.[30] In addition, the silver clusters in zeolites are also sensitive to other molecules, and therefore, they have great potential as chemical-sensing materials. 

It is important to differentiate between sensors that simply indicate a change by responding in real time and sensors that enable a system to gather and store information. A textile product smartened with a thermochromic print is able to provide a visual indication in real time of temperature fluctuations as the colours change with heat. However, its usefulness is limited in the context of the functionalities highlighted in Table 8.1. Such products do not enable the wearer or coach to review the information retrospectively. 

Applications, especially those in analytical chemistry (e.g. bio-, photo- or electrochemical sensors) [17, 18] have currently been developed, as has the preparation of photochromic, thermochromic, luminescent or electrooptical materials [19-24],... 

Major Appiications Fuel cell power generation system, liquid crystal displays, solor cells, sensors, thermochromic materials,coloring wood,n detergents, assessment of tobacco smoke, cosmetics,14 detect bacterial infections,i multidrug resistance inhibitors, treatment of bums, endodontic, diabetes, obesity, 5 cancer,2o age-related macular degeneration, viral diseases Safety/Toxicity Acute toxicity, combustion toxicity, 4 cytotoxicity, genotoxicity, mutagenicity, nephrotoxicity, phototoxicity, soil toxicity ... 

It is difficult to measure the actual polymer melt temperatures inside an extruder. The reason is that an immersion probe cannot be used because the rotating screw will shear it off. Flush-mounted temperature sensors do not give a good indication of the actual stock temperature. Thermochromic materials can be added to the feedstock to determine whether the stock temperatures in the extruder exceed the color transition temperature of the material. 

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