Applications of Thermochromic Materials

Inorganic systems have found only relatively limited applications being mainly used in paints and crayons for indicating hot spots on equipment Of the intrinsi- 

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Commercial and consumer applications of thermochromic materials [all sites accessed July 2011] ... 

The potential applications of thermochromic material include temperature tim-able light and heat radiation filters, large area displays, and temperature indicators visualizing the temperature of the surrounding medium or the temperature profile of a surface which is coated with the thermochromic material. 

Typically the chromophores used are pH sensitive, i.e. acidochromic or ionochromic (see section 1.4), and the medium is one whose pH varies with temperature. A variety of pH sensitive chromophores are known that are readily synthesised and can be modified to provide a wide range of shades. Application of these pH sensitive dyes in pressure and thermally sensitive papers for digital printing, e.g. fax papers, where the whole object is for the process to be irreversible, will be covered under ionochromism. The main area of application for reversible indirect thermochromic materials is as thermochromic organic pigments, as will be described below (section 1.3.4.1). 

In addition, the optical properties of these materials, which include luminescence and thermochromism, are promising for optoelectronic applications, specifically the TCNQ species as a candidate for new semiconducting materials in view of the clear scanning electron microscope (SEM) image observed for crystals of this product.173... 

Bernard Mark Heron was born in Workington, England in 1965. After graduation (GRSC) from Lancashire Polytechnic (Preston) in 1987 and a brief period in industry he obtained his PhD (CNAA) in Benzothiopyran Chemistry in 1992 under the supervision of Professor John Hepworth at the University of Central Lancashire. A postdoctoral fellowship in heterocyclic chemistry (1992-95) and an industrially funded lectureship at Central Lancashire (1995-98) were followed by appointment to a James Robinson Lectureship at the University of Hull (1998-2000). Dr. Heron was appointed as a senior lecturer (2000-present) in the Department of Colour and Polymer Chemistry at the University of Leeds. His research interests include the chemistry and applications of heterocyclic compounds, color chemistry, and organic photo- and thermochromic materials. 

The second volume of this new treatise is focused on the physicochemical properties and photochromic behavior of the best known systems. We have included chapters on the most appropriate physicochemical methods by which photochromic substances can be studied (spectrokinetic studies on photostationary states, Raman spectroscopy, electron paramagnetic resonance, chemical computations and molecular modeling, and X-ray diffraction analysis). In addition, special topics such as interactions between photochromic compounds and polymer matrices, photodegradation mechanisms, and potential biological applications have been treated. A final chapter on thermochromic materials is included to emphasize the chemical similarities between photochromic and thermochromic materials. In general, the literature cited within the chapters covers publications through 1995. However, in several cases, publications from as late as 1997 are included. 

Materials of this type may find application in thermochromic or liquid crystal devices. 

Major Applications Antireflective coatings, " thermochromic materials," photoresists, electrorhe-ological materials, " film patterning, " recording materials, " lithium battery, semiconductors, printing materials, " inks, " corrosion inhibitors, " adhesives,"" drugs," detecting viable cells,"" treatment of Alzheimer s disease ... 

Major Applications Thermochromic materials, cosmetics, measurement of hydrophobicity of therapeutic drugs ... 

A huge number of other applications exist, where the chemical and physical requirements are totally different. These applications include reflectors, temperature measurement with thermochromic materials, nonlinear optics, polymer materials, SAMs (self-assembled mono-layers) and LB (Langmuir-Blodgett) Aims, the use of liquid crystals in template synthesis of porous materials, drug delivery, and many more. 

In addition to depressing the liquid ciystal phase stability and often reducing melting points, a branched chain that introduces chirality increases viscosity. A high viscosity is not a problem in the non-display, thermochromic applications of chiral nematic materials. The steric effect of a chiral centre is well illustrated by difluoroterphenyl 5. 

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