Magnetic resonance and light scattering studies of nematics

Kunimatsu, Noboru (2000) Magnetic resonance and light scattering studies of nematics. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

This Thesis reports the results of investigations into the effect of dopants on the physical properties of nematic liquid crystals, mainly the rotational viscosity coefficient, γ₁, and the twist elastic constant K₂, which play important roles in the response times and threshold voltages of liquid crystal displays. The measurement techniques chosen are the magnetic resonance method based on ESR spectroscopy to determine γ₁, and the dynamic light scattering method to determine K₂ and γ₁. Chapter 1 gives an introduction to the physical properties of liquid crystals, including visco-elastic properties, liquid crystal displays and physical properties of nematic mixtures. In Chapter 2, we discuss the measurement of the rotational viscosity coefficient for nematic liquid crystals by ESR spectroscopy; the advantage of this method is that we can monitor the distribution as well as the orientation of the director of a nematic. Here, theory and the methodology of this measurement are mainly discussed and γ₁ values obtained from the relaxation times are found to be in good agreement with the literature values for γ₁. In chapter 3, using this technique, the effect of dopants on γ₁ was examined. The temperature dependence of these properties are significantly different depending on the temperature scales used for their comparison, here we consider the absolute and the reduced temperature scales. However, the absolute value of γ₁ is not available by the ESR method without a knowledge of the value of the diamagnetic anisotropy, Δχ̃;. Therefore, Δχ̃;was determined by ESR spectroscopy and the results described in Chapter 4, they are found to be in good agreement with the literature values. In Chapter 5, the effect of dopants on K₂ is investigated using dynamic light scattering. By this method, γ₁ can also be obtained and is seen to be in good agreement with the values determined by the ESR method.