Dichroic Parameters and Their Measurement

A dichroic mixture is basically a homogeneous mixture of dye(s) in a liquid crystal host. The various physical properties of dichroic mixtures are dependent on the physical properties of the dyes, the host, and their combination. 

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A particularly useful aspect of dichroic measurements is the chance to probe orientational order using more than one electronic transition in a molecule. Thus optical order parameters can be determined for different absorption bands, and if the transition moment directions are known, it is possible to determine both order parameters 5 and D. If it is assumed that there is a relationship between the uniaxial and biaxial order parameters, as given in Fig. 5 of Sec. 1 in this chapter, then it is possible to obtain both order parameters from the polarized spectra from a single absorption band [25]. This method has been applied [26] to the determination of order parameters of rigid aromatic probes, such as azulene, phenan-threne, and anthracene and related compounds. Dichroism measurements on impurity molecules in liquid crystal solvents have also been used [27, 28] to study inter-molecular interactions, and their influence on electronic absorption bands. Polarization effects of the type described above for sim-... 

As dichroic displays provide a man-machine interface through human eyes, their features and parameters must be optimized for human vision requirements [75]. For a clear understanding and detailed description of human vision, color and its measurement, visual requirements, and reliability issues of LCDs, the reader is referred to the article by Bahadur [75]. Some of the issues... 

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