Dielectric Behavior of Nematic Mixtures

As mentioned in Section 2 .2.2 of this chapter, connecting molecular data with the dielectric constant is a general problem. Therefore, it is difficult to calculate the behavior of an ideal mixture as can be done in thermodynamics. Nevertheless one can 

In this case it was assumed that the factors of the internal field F and h are the same for both compounds. The former discussed problem of different degrees of order for the two components was considered. N means the number of particles per unit volume. Equation (4) can be simplified if component B is not oriented in the nematic matrix or exhibit a very small degree of order 5b(x, T). By this approximation one should expect a change of Ae(x, T) with the molar fraction x and with the temperature. 

For technical application Afg is an important quality. Therefore, for the calculation according to the mixing rule, often between 5 and 10 mol% of compound B are added to the basic mixture A. In this way the beginning of the slope shown as a dotted line in Fig. 28 is estimated. In our case these data are better for calculating Agg at Xg 0.4. This method is also used for the estimation of an approximated value of Agg(B) which is in about +0.90. The experimental value of Agg (B)=0.68 makes it clear that the approx- 

All the problems discussed can be neglected if the interactions in the mixtures are strong. A classical example for this is substituted acids which form dimeric associates by hydrogen bonding. With increasing temperatures the monomer concentration increases and therefore, the slope of Eq versus temperature becomes different from the classical one, for example an increase of js 0 with increasing temperature [157] can be observed. By addition of derivatives of benzoic acid with a longitudinal dipole moment like 

If this idea is correct one should expect an increasing dielectric anisotropy and a dielectric relaxation effect of efj at low frequencies. The last one can be observed only if there is a longitudinal dipole moment. 

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Nwabunma D, Kyu T (2(X)1) Phase behavior, photopolymerization and morphology development in mixtures of eutectic nematic liquid crystal and photocurable monomer. Polymer 42 801-806 Ohta S, hiasawa S, Yamaguchi Y (2012) Size control of phase-separated liquid crystal droplets in a polymer matrix based on the phase diagram. J Polym Sci Part B Polym Phys 50 863-869 Parab SS, Malik MK, Deshmukh RR (2012) Dielectric relaxation and electro-optical switching behavior of nematic liquid crystal dispersed in poly (methyl methacrylate). J NonCryst Solids 358 2713-2722... 

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