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Thermography Using Liquid Crystals

Gleeson H F 1998 Thermography using liquid crystals Handbook of Liquid Crystals Vol 1. Fundamentals ed D Demus, J Goodby, G W Gray, H-W Speiss and V Vill (New York Wiley-VCH)... [Pg.2571]

The above analyses assume that the bubble remains in position above the nucleation site from which it arose. However, bubbles may slide along the surface without being released from it and continue to grow during this process. This phenomenon is discussed by Cornwell [54], and observations on sliding bubbles on inclined planes and curved surfaces (carried out using liquid crystal thermography and... [Pg.1014]

In composite materials, flaws, bonding faults and internal defects have all been examined using liquid crystal thermography, [177-184]. Surface and subsurface flaws have been detected, including regions of unstable plastic flow in aluminum alloys (Lueder lines) [185], faults in welded metals [186], and cracks, voids and leaks in pressure vessels [187-188]. Potential fracture sites have been determined in metals... [Pg.864]

By far the most important commercial applications of nematic liquid crystals are in the a multi-billion dollar display industry. Cholesteric, or chiral nematic liquid crystals have been used in coloured guest-host displays and in thermography/ther-mochromic applications. [Pg.306]

Cholesteric liquid crystal films are applied by painting or spraying a solution of the liquid crystal onto a surface. Cholesteric liquid crystals have been used to measure microwave energy, infrared light (such as in surface thermography), visible... [Pg.198]

The reflective wavelength of cholesteric liquid crystals varies according to temperature. Such an effect has been made useful in thermography. It has been applied in the diagnosis of cancers by displaying the skin temperature distribution. It has also been applied to test faults in integrated circuits. The applications also include thermometers and temperature warning indicators and non-destructive detection. [Pg.317]

Segura R, Cierpka C, Rossi M, Joseph S, Bunjes H, Kahler CJ (2012) Digital particle tracking thermography of individual non-encapsulated micro thermo-liquid crystals using a multi-variable calibration approach. Microfluid Nanofluid 14 445-456. doi 10.1007/s 10404-012-1063 -y... [Pg.3279]

Liquid crystals (LCs) are widely used In Informationprocessing devices, for optical visualization of physical Influences (heat, IR, high-frequency radiation, pressure, etc.), for nondestructive testing, and for thermography. [Pg.941]

From a historical point of view as well as due to their applications, thermotropic and lyotropic liquid crystals have always been treated separately. While thermotropics and the concept of liquid crystallinity in general were discovered as late as in 1888 [3], lyotropic phases were known to mankind since the Bronze Age [4], as they occur during the soap-making process. Due to this, lyotropic liquid crystals find their main applications in the detergent industry and in cosmetics. As various biological systems, e.g. cell membranes, take a lyotropic liquid crystalline form, they also possess some medical and pharmaceutical importance [5]. In contrast, thermotropic liquid crystals are used for completely different applications, e.g. for displays, thermography, tunable filters or lasers [6]. Thus, it is not astonishing, that two distinct fields of research evolved for the two types of liquid crystals. However, thermotropic and lyotropic liquid crystals share a common state of matter with many similarities. For example, many mesophases which occur in thermotropics can also be found in lyotropics. Still, there are some thermotropic phases which do not seem to have a lyotropic counterpart. [Pg.4]

The dramatic variation of liquid crystalline properties with respect to temperature has resulted in the widespread use of cholesteric (chiral nematic) liquid crystals for thermography. The property that has been exploited most in liquid crystal thermography is the critical temperature dependence of the selective reflection from cholesteric liquid crystals, though other temperature dependent properties of mesophases have been utilized (e.g. the birefringence of nematic systems and selective reflection from other chiral phases). The helicoidal structure of cholesteric materials results in the selective reflection of visible light within a band of wavelengths of width AX, centered at a wavelength Xq, such that ... [Pg.855]

The use of cholesteric liquid crystals for thermography was reviewed some years ago by Elser and Ennulat [4], and more recently in the commercial literature of Hallcrest [5]. Amongst the substances with the largest temperature coefficient are cholesteryl oleyl carbonate [6] and 5-cholesteryl esters... [Pg.856]

Other techniques of encapsulating liquid crystalline materials exist, and find application in areas apart from thermography. In particular, the methods used in the fabrication of polymer dispersed liquid crystal N and Sm display devices can be readily applied to cholesteric materials. Polymer dispersed displays are fabricated by dissolving the liquid crystal in the monomeric form of the continuous medium of the final device. [Pg.858]

Microencapsulation avoids many of the problems associated with the use of neat liquid crystal. McElderry [40] used microencapsulated material to study flat plates placed in a supersonic air stream, to produce a color display that had relatively low angular dependence. The encapsulation of material is particularly important if liquid crystal thermography is to be used in water tunnels. Here, it is useful to apply microencapsulated liquid crystal using an air brush, protect the capsules from contamination by solvents with an initial coating of acrylic polymer, and finally apply a waterproof polyurethane top coat. Fig. 4. Ogden and Hendricks [41] report the use of this technique for the study of turbulent water flow... [Pg.859]

It seems clear that while medical applications of liquid crystal thermography are extensive and imaginative, the technique is most useful for screening procedures, and there are only a few cases where it has proven diagnostic capability. [Pg.863]


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William A. Crossland and Timothy D. Wilkinson 3 Thermography Using Liquid Crystals

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