Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.
Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.
(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)
The orientation of low-molecular weight nematic liquid crystals in transverse electrical fields
Abstract
The orientation of nematic liquid crystals in electrical fields is commonplace in flat-panel watch and calculator displays. In 99% of these devices, the optical path and the electrical field are parallel to each other. When an alternating electrical field is applied perpendicular to the optical path unusual optical patterns result. The physics and properties of the wave-like optical pattern were previously unreported. The geometry and wave-like optical pattern are described in chapter two for a room-temperature nematic liquid crystal: 4-4$\sp\prime$-n-pentylcyanobiphenyl. Physical conditions of wave stability, i.e. temperature, field and frequency were investigated and discussed in terms of nematic liquid crystalline theory. It was determined that the wave pattern was stabilized at low temperatures and high frequencies. It was also concluded that the mechanism of deformation was dielectric rather than ionic. The macroscopic observations were quantified into two molecular orientation profiles in the succeeding chapter. The orientation profiles given are based on two possible cases of surface orientation for the nematic layer. The analysis of molecular orientation relies heavily on the theory of electrical deformation developed by Deuling. To understand the importance of the material parameters of the nematic in relationship to the optical effect, binary blends of 4-4$\sp\prime$-n-pentylcyanobiphenyl and 4-(4-alkylcyclo-hexyl) -cyanophenyl homologs were prepared. The complete phase behavior of these mixtures is the subject of chapter 4. A thorough physical characterization, regarding the dielectric and elastic properties, response times and threshold voltages, of four selected nematic fluids is given in chapter five. Finally, in chapter six, the effect of the blending on the electrical deformation of the nematic mesophase in a transverse-electrode cell is studied.
Subject Area
Polymer chemistry|Organic chemistry|Optics
Recommended Citation
Schell, Kevin Thomas, "The orientation of low-molecular weight nematic liquid crystals in transverse electrical fields" (1991). Doctoral Dissertations Available from Proquest. AAI9207456.
https://scholarworks.umass.edu/dissertations/AAI9207456