Thermochromic material

Thermochromic substances can be very useful in temperatin-e-related problems. These materials change color irreversibly at a particular temperature, and they are used in a number of applications. For instance, thermochromic paints are used on heat shrinkable sleeves so that the installer who is heating the sleeve with a torch can see whether the product has reached proper installation temperature. 

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. 

Mennig [160] published a paper quite some time ago on a preliminary investigation into the use of temperature-indicating materials in extrusion. The thermochromic materials that were used in the study were not clearly identified and sufi ered from the fact that the color transition temperature was time dependent. Obviously, this limits the usefulness of these materials for accurate temperature indication. 

Rauwendaal [152] conducted a study using thermochromic powders used commercially in thermochromic paints to study melt temperature in extruders. The study involved a small laboratory twin screw extruder processing a highly filled HDPE. It was found that the material degraded inside the extruder even though the barrel temperatures and exit melt temperature were quite reasonable. The barrel temperatures were set a 200°C and the exit melt temperature was measured at about 215 to 220°C. 

These are normal temperatures for HDPE and should not cause degradation under normal circumstances. However, it was suspected that the melt temperatures inside the extruder were much higher than the barrel temperature. Therefore, a thermochromic powder with a color transition temperature of 250°C was added to the feed. With this material, a very clear discoloration was noticed in the material exiting the die. Next, a thermochromic powder was added with a color transition temperature of 300°C. This material unexpectedly resulted in very clear discoloration just as in the first material, indicating that stock temperatures in the extruder exceeded 300°C. 

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Thermochromic material CAS Registry Number Thermochromic transition p,°c References... 

Microencapsulation is a revolutionary technology enabling liquids to be treated as solids. The technology was first used to produce carbonless copying paper, but today it is widely used in a number of industrial fields such as medicine, agricultural chemicals, thermochromic materials, cosmetics, and toiletries. 

Chloropentakis(ethanol) cobaltCII), thermochromic material, 6 615 Chloroperoxidases, as bleaching agents, 4 66-67... 

SIP requirements, 1 812, 814 sodium nitrite and, 22 855 thermochromic material, 6 614 Nitrogen donor ligands, thorium and, 24 766-768... 

Poly(arylether ketone), conducting, 7 524 Poly(aryl ether ketone)s, sulfonation reaction of, 23 717-718 Poly(di-n-alkylsilanes), thermochromic materials, 6 619... 

Scheelite, 25 349-350 Scheelite sorting, 16 626 Scheibel column, 10 777-778 Scheibler filter, 11 364 Schiff base(s), 21 203, 204, 25 100-101 chelating agents, 5 712t reaction with amino acids, 2 567 reaction with aniline, 2 786 thermochromic materials, 6 622-623 Schiff base chemistry, 24 42 Schiff base (reductive amination) method, for covalent ligand immobilization, 6 396t... 

Liquid crystal, thermochromic material Fiber itself Lithium niobate Gallium arsenide, various phosphors... 

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). 

Figure 2.9 (a) The crystal structure of the new type of Sulfite-Dawson above, compared to the known sulfate-Dawson below, showing the S-S interaction, (b) are photographs of the thermochromic material at 77, 298 and 500 K. (c) Shows two polyhedral views of the low temperature sulfite-Dawson (on the left) at 77 K and the resulting high temperature... 

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. 

There are many types of photochromic and thermochromic materials. Due to the introductive nature and consequent brevity of this work, only selected subject areas will be examined. This work is intended to introduce product designers, chemists, color matchers, and laboratory technicians to the special colorant area of photo-and thermochromics. 

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