Um novo método de medida (SAM -Spectral Analysis Method) mostra que, devído a um erro sistemático tradicionalmente desprezado, os valores medidos de polarização espontânea do cristal líquido ZLI-3654 (Merck) não seguem o que é previsto pela teoria de Landau das transições contínuas. Porém, a variação da susceptibilidade elétrica relativa com a temperatura proporcional à (T Tc) IND.-1, onde Te é a temperatura onde ocorre o máximo da susceptibilidade ...... está de acordo com o modelo de Landau. A resposta em freqüência da constante dielétrica mostra que, a fim de minimizar a corrente iônica, as medidas de polarização elétrica devem ser realizadas em frequências acima de 20 Hz. Por sua vez, os valores dos ângulos de fase dos harmônicos da polarização, obtidos pelo novo método, indicam que a intensidade do campo elétrico aplicado deve ser inferior a 1, 1 x 10 IND.6 Vrms/m (em 23Hz) para que não ocorram instabilidades elctrohidrodinâmicas, Finalmente, o ajuste das amplitudes dos harmônicos da polarização elétrica obtidos pelo SAM aos parâmetros da equação de Landau-Kalatnikov mostra um bom acordo dos valores medidos com o modelo, em contraste com os valores de polarização espontânea, A solução da equação de equilíbrio, levando em consideração os parâmetros ajustados, mostra como seriam os valores da polarização espontânea sem os erros sistemáticos. / A new proposed measurement method (SAM - Spectral Analysis Method) shows that, due a traditionally neglected systematic error, the values of the measured spontaneous polarization cf the ferroeleotric liquid crystal ZLI-3654 (Merck) doesn\'t follow what is predicted by the Landau theory of continuous transition. In contrast, the decay of the relative electric susceptibility with the temperature (T) - proportional to (T Tc)-l, where Tc is at the maximum of the susceptibility - is in good agreement with the Landau model. The frequency response of the dielectric constant shows that the measurements of the electric polarization of the sample must be done at frequencies hígher than 20Hz to avoid the actíons of the ionic currents. The phase values of the electric polarization harmonics obtained by the SAM indicates that the electric field must be lower thau 1,1 x l06Vrms/m (at 23Hz) to avoid electrohydrodynamic instabilities, Finally, the fitting of the amplitudes of the electric polarization harmonics obtained by the SAM to the parameters of the Landau-Kalatnikov equation shows a good agreement with the model, in contrast with the spontaneous polarization measurements. The solution of the Landau model, considering the fitted parameters, predicts how should be the spontaneous polarization values without the systematic errors.

Calamitic (rod-shaped) and discotic (disc-shaped) thermotropic liquid crystalline (LC) compounds were spread at the air-water interface, and their ability to form monolayers was studied. The calamitic LCs investigated were found to form monolayers which behave analogously to conventional amphiphiles such as fatty acids. The spreading of the discotic LCs produced monolayers as well, but with a behaviour different from classical amphiphiles. The areas occupied per molecule are too small to allow the contact of all hydrophilic groups with the water surface and the packing of all hydrophobic chains. Various molecular arrangements of the discotics at the water surface to fit the spreading data are discussed.

This thesis presents results of novel methodologies applied to oriented systems. Both pure liquid crystalline materials as well as molecules oriented in liquid crystalline matrices have been studied. In particular this thesis presents investigations related to various aspects of NMR in liquid crystalline media, such as, assignment of resonances and the study of director dynamics of spinning liquid crystals in different phases and with different symmetry. Simplified methods for structure determination of solutes dissolved in liquid crystal solvents have been proposed. Diffusion ordered spectroscopy has been used to study a mixture of liquid crystals of opposite diamagnetic susceptibility at its coexistent phase. The methods presented represent novel techniques to characterize the liquid crystalline phase. NMR spectroscopy which has become a method of choice for understanding ordering mechanisms of mesogens requires a robust method for obtaining assignments of the NMR spectra of various nuclei that are found in the mesogens [1, 2]. It turns out that the spectra in the isotropic phase and in the nematic phase of a liquid crystal molecule are very different due to the presence of chemical shift anisotropy in the mesophase spectrum. There are a host of methodologies available for assigning spectra in the isotropic phase [3]. These methods however fail, when applied to the spectrum of the molecules in the mesophase due to the dominating role of strong anisotropic interactions, such as homonuclear couplings among protons. Problems arising while assigning spectral lines of liquid crystals in their nematic phase have been dealt with in chapter 2. To circumvent these problems, a property of the liquid crystal molecules under off-magic angle sample spinning can be utilized. It has been shown by Courtieu et al. [4] that the director/symmetry axis of a Δχ + ve liquid crystal aligns along the spinning axis for θ between 0 ° and θm, where θ is the angle between the spinning axis and the magnetic field and θm = 54.7° is the magic angle. It may be noted that the spectrum of θ = 0° spinning angle corresponds to the normal static spectrum, while the spectrum of θ = θm corresponds to the isotropic spectrum. In an earlier study, Teearr et al. [5] had recorded the 13C liquid crystal spectra as a function of very closely spaced θ values from 90° all the way up to 0°. From these plots of chemical shift versus the angle of spinning, it is possible to follow the trajectory of each 13C line from its position from θ = θm to θ = 0° and then match the spectrum in the isotropic phase (equivalently the magic angle sample spinning spectrum of the nematic phase) to the spectrum of the static sample in the nematic phase. However this method requires recording spectra at closely spaced angle intervals, so that one can unambiguously follow the trajectory of each of the lines without missing out any crossover of trajectories. However, this operation is time consuming. In this thesis we propose an alternate method, where we utilize the fact that the above trajectory has a very distinct relationship to the isotropic and anisotropic chemical shift and the problem of assignment does not require a continuous variation of angles, but just a few selected experiments should enable the assignment of the spectrum in the anisotropic phase. Thus the method of assignment has been made simpler and faster. It is shown that in addition to the assigned isotropic spectrum, only one other Off-magic angle spinning spectrum whose spinning angle θ is accurately known is necessary to obtain the complete assignment of the static spectrum. This procedure is non-trivial due to possibilities of errors in assignments arising out of inaccuracies in the knowledge of chemical shifts and the spinning angle. A computational procedure is proposed to take into account deviations arising out of non-ideal experimental conditions. A discussion regarding the details of the procedure and also situations where there can be ambiguities and how they can be resolved has been elaborated. The developed method has been demonstrated on a well known thermotropic liquid crystalline system, N-(4-ethoxybenzylidene)-4-n-butlyaniline [EBBA]. Since assignment of resonances in the nematic phase is a primary requirement for any further analysis regarding the ordering and deeper understanding of the role of various substituents in the mesogens we believe our novel prescription will be of immense use and utility. The third chapter presents the study of director dynamics in a lyotropic liquid crystal composed of Potassium laurate, 1-Decanol and D2O [6] under variable angle sample spinning using 2H NMR spectrum of D2O. A very interesting interplay of the magnetic orienting torque due to interaction of the liquid crystal director with the magnetic field and viscous torque arising from the viscosity of the sample on the director comes to fore. The relative magnitude of these torques has a direct bearing on the spectral pattern and line shapes observed, providing valuable insights into magnetohydrodynamics of the spinning liquid crystals. This study leads to even more interesting behavior for liquid crystals which deviate from uniaxial symmetry. This competition between magnetic and viscous torques has been quantitatively visualized by simulation of the 2H spectrum. It has been possible to visualize the observed spread in the director distribution arising out of viscous torque in terms of the energetics of the system under fast spinning. If the magnetic torque dominates over the viscous torque, then the equilibrium corresponds to the director orientation of δ = 0° where the energy is at its minimum. However the viscous and magnetic torques can become comparable as it may happen if the spinning angle is close to the magic angle or when the Δχ of the system is small. In those circumstances additional energy from the viscous torque causes the distribution of the director orientation to spread further away from δ = 0° for a positive Δχ liquid crystal. The trigonometric factor [P2(cosθ)∗P2(cosδ)] being proportional to the total energy of the system has been plotted against the spinning angle. The spectrum of the biaxial phase [7] as a function of the spinning angle shows more interesting director distribution. Here the patterns of the director distribution are observed on either side of the magic angle due to the presence of more than one director. The patterns observed also have information about the symmetry of the phase. This work provides insights into magnetohydrodynamics of spinning liquid crystals and can also be of relevance to samples of biological interest such as bicelles with protein oriented in them [8]. The fourth chapter deals with a novel characterization method relevant for the biaxial phase [9]. As an off shoot of the previous chapter, it effectively overcomes the disadvantages of the previous experimental methods which require simulation and line shape fitting to extract useful parameters. The chapter also presents the measurement of geometrical parameters of oriented solutes in phases exhibiting biaxial symmetry. The measured parameters show the effect of the onset of biaxiality as significant deviation in the value of the measured parameter. The utility of liquid crystalline media as solvents in high resolution NMR spectroscopy has been very rewarding since the pioneering work of Saupe and Englert [6]. The intramolecular interactions within solutes are only partially averaged. As a result one obtains a liquid like spectrum while at the same time very useful anisotropic interactions such as dipolar couplings, chemical shift anisotropies, quadrupolar couplings and anisotropic part spin-spin J couplings are extracted [10]. NMR spectra of molecules dissolved in thermotropic liquid crystals have long been used to obtain structural and orientational information. As the same time the complexity of the spectrum increases with the increase in the number of spins and the reduction in symmetry of the molecule, which can make the spectral analysis forbidding. Generally proton spectra have been used to obtain the geometry of the proton skeleton of the molecule and the information that includes dilute X nuclei such as 13C and 15N are available only from satellites which are buried in the intense proton spectrum. Different inequivalent dilute spins coupled to protons form different coupled spin systems in their natural abundance and appear as satellites in the proton spectra. Identification of transitions belonging to each of the spin system is essential to determine heteronuclear dipolar couplings, which is a formidable task. The fifth chapter deals with development of the techniques to obtain the complete structure of the dissolved molecules including nuclei other than protons in their natural abundance. The use of inverse experiments has been elaborated to overcome the problems of sensitivity and complexity for solute molecules having larger number of spins. In the present study using HSQC and HMQC experiments, we have selectively detected spectra of each inequivalent rare spin coupled to protons in pyrazine, pyrimidine and pyridazine dissolved in thermotropic Phase 4 and Phase 5 liquid crystal solvents. This way we could obtain enhancement in the intensity of satellites signals without the interference from the signals connected to the major isotopomers. Besides, we could resolve a complex spectrum into its sub-spectra corresponding to individual 13C and 15N isotopomers. This separation of the spectra corresponding to individual sub-spin systems makes analysis easy and helps analyze larger systems with higher number of spins and lower symmetry. Besides 1H-1H dipolar couplings, 13C-1H and 15N-1H dipolar couplings have been determined in natural abundance, thereby giving the complete dipolar coupling network between all the spins in the molecule. In this treatment pyrazine, pyrimidine and pyridazine have been used as examples of methodology developed. It is expected that the method will be of wider use for several other similar systems. Chapter six describes the diffusion ordered spectroscopic investigation [11] of a phase arising out of mixing together two liquid crystals having opposite signs of diamagnetic susceptibility anisotropy [12]. Towards this end we have used CH3CN as a probe molecule. The spectrum of CH3CN has with it the information about the parallel or perpendicular orientation of the phase. Such a mixture of liquid crystals have shown interesting behavior at the critical temperature where the two phases seem to coexist. It has been an interesting question to understand what exactly happens for the molecular orientation when the macroscopic anisotropy Δχ vanishes. Earlier Jokisaari et al. [13] have varied the temperature very finely taking due precautions to maintain homogeneity and stability of temperature to the tune of ±0.05K across the sample volume. Their observation of a powder pattern exactly in the critical temperature was interpreted as arising out of a distribution of directors equally oriented in all directions. In our experiments we have measured the diffusion coefficient of the probe molecule i.e. acetonitrile as we change the temperature of the system through the critical temperature. At the critical temperature we have a situation of being able to measure the parallel and perpendicular orientational diffusion coefficients simultaneously. The measurements show that the parallel component of the diffusion coefficient has reduced and the perpendicular component has increased in comparison to the trend in the immediate neighboring temperatures, thereby indicating that at the exact critical condition the liquid crystal mixture consists of an isotropic distribution of molecules. As a check to rule out any exchange of molecules in different domains of parallel and perpendicular orientations an EXSY experiment was conducted with a mixing time which was same as that of the diffusion delay in the DOSY experiment. The EXSY spectrum showed no exchange cross peaks between the two orientations, this confirms that the anisotropy of the diffusion vanishes at the critical temperature. Nematic liquid crystals exhibit a rich variety of phases and properties. NMR is a very powerful tool to study the various phases at the microscopic and molecular level. It has also turned out that some of these properties can be usefully utilized for investigation of both small and large molecules by NMR. Thus this thesis has attempted to expand several of the techniques already available for various applications and extend the utility of NMR for the study of partially ordered systems.

Abstract Jet impingement heat transfer is an enhanced heat transfer technique.This article reports results on the local heat transfer coefficients for confined impinging air jet.A transient thermochromatic liquid crystals technique is used to visualize and record isotherms on an impingement surface. Quantitative temperature measurement using thermochromatic liquid crystals is a field temperature measurement technique. It utilizes the feature that TLCs change their reflex light colors with variation of temperature and apply an image capturing and processing system to calibrate the characteristic curve of TLCs colour-temperature,and then use it to measure the distribution of surface temperature. Therefore , it can solve some problem that cannot be solved by traditional point Temperature measuring methods in heat transfer field. The main object of this articale is to set up a temperature measurement system of transient thermochromatic liquid crystals. Furthermore, an experimental is carried out in the present study to investigate the characteristics of heat transfer resulting from a low speed air jet impinging onto a horizontal circular disk confined in a vertical adiabatic cylindrical chamber. Experiments are conducted at low nozzle-to-disc spacing (0.5<H/D <3.5) and Reynolds number in the range of500 to 1500 for two different injection pips. The results show that the effects of Reynolds number and nozzle-to-disc spacing on the local heat-transfer coefficient are reported and compared with different diameter of injection pipes.Finally , empirical equations are proposed to correlate the effect of Reynolds number and nozzle-to-disc spacing .

Collective oscillation of conduction electrons in metallic nanoparticles known as localized surface plasmon resonance has been studied for nano-optics applications. The excitation of localized surface plasmons on nano-structured metal material leads to strong light scattering and absorption. Since the localized surface plasmon resonance is strongly dependent on the shape, size, size distribution, and dielectric property of surrounding environment of nano-structured metal, the dependence can be applied in wide applications. However, the direct and non-destructed observation of nano-structured metal is required to the development of nano-technology, we proposed a real time optical observation due to the optical respons of metal nano-particles system. Furthermore, we proposed a fast and simple method to fabricate a high order metal nano-particles array and used liquid crystal material to directly modulate the surface plasmon effect on the metal nanoparticles. The purpose of this work is to study the surface plasmon effect excited on metal nanoparticles. These works are described as follows: A. The topic of the first work is ¡§Real time absorbance spectra due to optical dynamics of silver nano-particles film¡¨, we report the real time absorbance spectra due to optical dynamics of silver nano-particles film under a heating treatment from 28 to 300 ¢J. A 7nm-thicked sliver film was thermally deposited on an indium tin oxide glass substrate. In the process of heating, the real time absorbance spectra of silver nano-particles film were measured by an optical spectrometer. It was noted that the absorbance spectra of the film varied with the heat-treating temperature and time. The peak position in the spectra curve shifted to shorter wavelength below the temperature of 250 ¢J, then shifted to red band due to higher temperature treatment. With the comparison of scanning electron micrograph analysis, the real time absorbance spectra exhibited a particular optical property confirmed by the dynamic dark-field optical microscopy system. The real-time absorbance spectra and dark-field micrographs analyses lead to a direct and non-destructed observation of growing evolution of metal nano-particles. B. The topic of the second work is ¡§Laser pulse induced gold nanoparticles grating¡¨. We report the results of our experimental investigation of laser induced gold nano-particle gratings and their optical diffraction properties. A single shot of a pair of Nd-YAG laser pulses of the same polarization is directed toward a thin gold film of thickness 6 nm on a substrate of polymethyl methacrylate (PMMA). As a result of the laser illumination, the thin gold film is fragmented into an array of nano-particles. Using scanning electron and dark-field optical micrographs, we discovered that the morphology of the gold nanoparticles grating is dependent on the fluence of laser pulse. The spectrum of first order diffraction shows a spectral dependence, possibly due to the presence of the nano-particles of various sizes. The ablation of thin films of nano-thickness via the use of laser pulses may provide a simple and efficient method for the fabrication of nano-scale structures, including 2D arrays of nano-particles. C. The topic of the second work is ¡§Surface plamons induced extra diffraction band of cholesteric liquid crystal grating¡¨. We investigated the diffraction behavior of cholesteric liquid crystal (CLC) grating with the surface plasmon effect was investigated. One indium-tin-oxide plate of the CLC grating cell was covered with silver nanoparticles. With the application of a proper voltage, a well formed phase grating was constructed in the CLC cell. The CLC grating was probed by a beam of the polarized-monochromatic light, and the wavelength range was from 450 to 700 nm. It was shown that an extra first-order diffraction band was observed around 505 nm. The physical reason of the extra diffraction band could be the surface plasma effect emerged from silver nanoparticles. The extra diffraction band due to the surface plasmon effect can offer potential applications in nano-optics, such as the optical switch function.

Photonic crystals (PCs) are structures with spatially periodic variations in dielectric constants. The prime property of PCs is the existence of the photonic band gaps (PBGs) which could prohibit the propagation of light within a certain frequency range. Once the PC structures are fabricated, it is hard to tune their optical properties for the fixed geometries. Thus, it is important to develop tunable PC waveguide devices for the applications in the photonic integrated circuits. We utilize the mode-gap effect to design two-dimensional (2-D) tunable Y-shaped PC waveguides with the polyaniline type electrorheological (ER) fluids. The propagation of light on the Y-shaped waveguide can be controlled by applying the electric field in specific regions. Besides, we also propose a tunable multi-channel PC waveguide with the polyaniline type ER fluids. We then investigate the tunable propagation characteristics of a 2-D single line-defect PC waveguide with liquid crystals (LCs) by varying the direction of LCs and the hole sizes. We also simulate the tunable optical properties of a 2-D Y-shaped PC waveguide utilizing LCs. Finally, we consider a 3-D Y-shaped PC slab waveguide with LCs. The effects of the direction of LCs and the slab thickness are discussed.

Thesis (Ph. D.)--Open University. BLDSC no. DXN043595.

Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains 130 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 128-130).

Thesis (M.S.)--Textile and Fiber Engineering, Georgia Institute of Technology, 2004. / Griffin, Anselm, Committee Member; Srinivasarao, Mohan, Committee Chair; Park, Jung O., Committee Member. Includes bibliographical references (leaves 101-105).

Thesis (Ph.D.)--Kent State University, 2009. / Title from PDF t.p. (viewed Feb 25, 2010). Advisor: Oleg Lavrentovich. Keywords: electro-optical applications of liquid crystals, beam steering devices, polarization rotator, negative refraction, electrically tunable lens, colloidal dynamics, bidirectional motion of colloidal particles in liquid crystals controlled by backflow. Includes bibliographical references.