No description available.

No description available.

Nematic liquid crystals possess large optical nonlinearities owing to their large refractive index anisotropy coupled with the collective molecular reorientation. Doping absorbing dyes into liquid crystals increases their optical responses significantly due to increased absorption in the visible region, absorption-induced intermolecular torque, cis-trans photoisomerization, and other guest-host effects. The guest-host mixtures can be employed in display applications, optical storage devices, and others. In this dissertation, nonlinear optical studies were carried out on dye-doped nematic liquid crystal cells. The main objectives of the studies were to distinguish and characterize the several processes that can lead to the formation of dynamic gratings of different types in the samples, and to study the photorefractive and the orientational responses of these samples. Furthermore, we tried to explain and model the dynamical behaviors of the observed grating formations. The experimental techniques employed in this study include asymmetric two-beam coupling, forced light scattering, and polarization holographic method. The asymmetric two-beam coupling experiments revealed that the induced grating was a photorefractive phase grating created by the nematic director reorientation within the plane of incidence. The dynamics of the beam coupling showed that two different mechanisms with different temporal responses were involved. The grating translation technique identified both gratings as pure photorefractive index gratings with phase shifts of ~ p/2 between the grating and the interference pattern. In addition, the dynamical behavior of the grating formation, obtained from forced light scattering experiments, also exhibited a two-time constant response. The dynamical behaviors of the build-up and decay of the photocurrent were investigated. The two dynamics exhibited both a two-time constant behavior, suggesting that the origin of the two-time constant dynamics observed in the two-beam coupling and the forced light scattering experiments resides in the process of photo-charge generation. The photorefractive gain coefficients were found to be in the range of 100 – 400 cm-1. The values of the nonlinear optical Kerr index (~ 0.08 cm2/W) measured in samples with certain dye/liquid crystal combinations are higher than what has been observed in other dye-doped nematics and other liquid crystal/polymer systems. All the samples showed a threshold behavior with respect to the magnitude of the applied electric field. This threshold behavior was observed both in forced light scattering experiments and polarization holographic experiments. We believe that the origin of this threshold lies in the process of photogeneration, which was found to exhibit the same threshold behavior at the same value of the applied voltage. An asymmetry of the photorefractive gain with respect to the direction of the applied electric field was observed in samples with high dye concentration. This was attributed to the beam fanning effect, which has also been observed in other high-gain photorefractive materials. Polarization holographic measurements showed that the dye enhancement effect is primarily due to the intermolecular interaction between the dye molecules and the liquid crystal host, and that the trans-cis photoisomerization plays a lesser role. The photoinduced orientational response was also studied using polarization holographic experiments. A number of observations confirmed that the birefringent grating is due to the nematic director reorientation within the plane of incidence, under the combined effect of the applied electric field and the optical field. The diffraction efficiency was found to depend linearly on the writing beam power, while the dependence of the self-diffraction efficiency on the writing beam power roughly assumes a cubic relationship. The dynamical behavior of the birefringent grating formation was investigated. The build-up dynamics was found to be best modeled as a double-time constant response, while the decay is best fitted by a single exponential. The response of the samples to an oscillating electric field was studied as a function of the modulation frequency. Very interesting and reproducible dynamics was observed, revealing the complex dynamical response of the liquid crystal director to the magnitude and rate of change of an applied electric field. The small signal response was also measured, but did not reveal any sign of a resonance behavior. The conductivity and the photoconductivity of the samples were measured. The relationship between the measured current and the applied voltage was found to be cubic at low applied voltage, and to become linear at higher applied voltage. We could explain this behavior using a double-charge-injection-in-a-weak-electrolyte model, but this is only one of the possible mechanisms that could explain this behavior. The photocurrent was found to increase linearly with the illumination power, which indicates that the charge carrier recombination rate is proportional to the carrier density. The measured electrical conductivity was found to be proportional to the square root of the dye concentration, confirming the validity of the proposed charge-injection model. / Ph. D.

This work is concerned with the processing of pellets of polypropylene (PP) containing pregenerated microfibrils of thermotropic liquid crystal polymers (TLCPs), referred to as microcomposites. The processing methods used are injection molding, sheet extrusion, and extrusion blow molding. The TLCPs used are HX6000 and Vectra A950. The microcomposites are produced by drawing strands of PP and TLCPs generated by means of a novel mixing technique and pelletizing the strands. The work was undertaken in an effort to improve on the properties observed for in situ composites in which the TLCP fibrils are generated in elongational flow fields that occur during processing. In situ composites usually exhibit highly anisotropic mechanical properties and the properties do not reflect the full reinforcing potential of the TLCP fibers. Factors considered include the effect of in situ composite strand properties on the properties of the injection molded composite, the melt temperature used in injection molding, TLCP concentration, and the melt temperature of the TLCP. It was found in this work that microcomposites can be processed by means of injection molding, sheet extrusion, and extrusion blow molding. It was necessary to process the materials at low temperatures to maintain the TLCP fibrils. However, HX6000, the higher melting TLCP allowed higher processing temperatures than Vectra A. When the TLCP fibrils were maintained, the properties of the TLCP reinforced composites did show reduced anisotropy as compared to an in situ composite. The tensile strength of the composites produced by all three methods was about equal. The modulus of the injection molded composites was slightly higher than that of the composite sheets, but the composite sheets showed a lower degree of anisotropy. In all three processing methods the modulus of the TLCP reinforced composite was a function of the modulus of the in situ composite strand used to produce the microcomposite. Therefore, it is recommended that to improve the properties of the microcomposites the properties of the in situ composite strands should be improved. Furthermore, the mechanical properties of the composites increased with increasing TLCP composition. To provide a basis of comparison the properties of the extruded sheets and the injection molded composites were compared to both the predictions of composite theory and the properties of glass reinforced composites. It was found that the modulus of the 10 wt% composites approached the predictions of composite theory, but at higher TLCP loadings the modulus showed negative deviations from the predictions of composite theory. This is believed to be the result of a reduction of fiber aspect ratio due to poor fiber distribution and fiber breakup. The modulus of the TLCP reinforced composites was about the same as the modulus of the glass reinforced composites produced by both sheet extrusion and injection molding. The tensile strengths were slightly lower than that of the glass reinforced composites. It is expected that as the modulus and strength of the reinforcing TLCP fibrils are improved the properties of the TLCP reinforced composites should exceed those of glass reinforced composites. It was concluded that the processing of microcomposites is a viable means of producing composites based on TLCPs and thermoplastics with good mechanical properties and low degrees of mechanical anisotropy. / Ph. D.

Methods of processing polypropylene (PP)/ liquid crystalline polymer blends to obtain high mechanical properties from injection molded samples were investigated in this dissertation. Three liquid crystalline polymers (LCPs), two liquid crystalline (LC) copolyesters and one LC poly(ester-amide), were used. The PP/LCP blends were compatibilized with a maleic anhydride grafted polypropylene (MAP) to enhance the mechanical properties. The effect of increasing MAP content on the mechanical properties, morphology, and interfacial tension of injection molded tensile bars and plaques made from blends with 30 wt% LCP was investigated. It was determined that MAP enhances both the tensile strength and modulus, but the tensile strength is increased to a greater degree than the tensile modulus. For the LC copolyesters, the tensile strength appeared to reach a maximum while for the LC poly(ester-amide) the tensile strength increased without limit in the range of MAP contents studied. Simultaneously, a finer dispersion was created as the MAP content was increased. Calculation of the interfacial tension from contact angle measurements indicated that the interfacial tension decreased as MAP was added to the PP matrix. Analysis of the MAP concentration after blending indicated that MAP did not react with the LCP, but enhanced tensile properties resulted from physical interaction such as hydrogen bonding. This mechanism is consistent with the greater property improvements found in the LC poly(ester-amide) blends where the amide group is expected to undergo stronger hydrogen bonding than the ester group. Analysis of the injection molding of these blends found that heat transfer and solidification significantly affected the flexural modulus of these blends. Injection molding conditions such as fill time, mold thickness, mold temperature and melt temperature were investigated in three molds of different thicknesses. Different processing relationships were found between the LC copolyesters and the LC poly(ester-amide). For the former LCP blends, the highest moduli were obtained from the thinnest mold in a manner parallel to that of the moduli of neat LCPs. For the latter LCP blends, the highest moduli were obtained in the intermediate thickness mold. The differences between the copolyester and LC poly(ester-amide)s processing / property relationships were related to the melt rheology of the LCPs. For the LC copolyesters, maximum mechanical properties were obtained when the melt temperature was selected so that the storage and loss moduli of the LCP were nearly equal. This equality of storage and loss moduli could not be achieved with the LC poly(ester-amide). In addition, upon cooling, the storage and loss moduli of the LC poly(ester-amide) indicated that rapid solidification occurred while a much lower rate of solidification was indicated for the LC copolyesters. In addition the mechanical properties were sensitive to the rate of cooling as indicated by the Graetz number. It was speculated that attainment of the highest mechanical properties was related to the LCP being deformed during the filling stage followed by rapid solidification of the LCP morphology upon cessation of flow. / Ph. D.

The overall objectives of this work were to improve a dual extrusion process (DEP) which is used to blend thermotropic liquid crystalline polymers (TLCPs) with thermoplastics, determine the mechanism by which TLCP morphology is developed in the DEP and to determine the optimal properties possible in composite materials generated from the blends. The DEP consists of two single screw extruders within which the TLCP and matrix material are plasticated separately. The two continuous polymer streams are joined and then mixed in a series of static mixing elements. Composite materials were formed from pelletized pregenerated strands by processing at temperatures below the melting point of the TLCP. The DEP was improved by the addition of a gear pump to the TLCP stream, a multiple port phase distribution system, static mixing design, minimization of residence time, die design, and introduction of thermal control over the entire strand production process. The TLCP material was introduced into the matrix phase by means of a multiple port phase distribution system which injected 12 individual TLCP streams parallel to the flow direction of the matrix stream. This design resulted in improvements in the axial continuity of the TLCP phase during mixing and improved radial mixing as compared with a simple T-injection system. Both Kenics and Koch static mixer designs were evaluated in this investigation and it was found that the use of either could produce similar mechanical property enhancement in the resulting blends provided that an excessive number of elements were not used. Furthermore, it was found that the most stable strand materials were formed when the die was designed with respect to the flow exiting the static mixer elements. For example, a dual strand die with each capillary having an L/D ratio of 1 produced the most stable strands when used with the Kenics mixing elements. Finally, it was found that drawing the molten blend strand in a vertical drawing chimney provided a favorable thermal environment and resulted in much higher draw ratios and high mechanical properties of the strand. The other objectives of this work including the development of morphology and composite materials produced from pregenerated strands is presented in two manuscripts formatted for submission to appropriate journals. Detailed abstracts dealing with these two topics are included therein. / Master of Science

No / Widefield surface plasmon resonance (WSPR) microscopy provides high resolution imaging of interfacial interactions. We report the application of the WSPR imaging system in the study of the interaction between keratinocytes and liquid crystals (LC). Imaging of fixed keratinocytes cultured on gold coated surface plasmon substrates functionalized with a thin film of liquid crystals was performed in air using a 1.45 NA objective based system. Focal adhesion of the cells adhered to glass and LC were further studied using immunofluorescence staining of the vinculin. The imaging system was also simulated with 2 × 2 scattering matrix to investigate the optical reflection of the resonant plasmonic wave via the glass/gold/cell and glass/gold/LC/cell layers. WSPR imaging indicated that keratinocytes are less spread and formed distinct topography of cell–liquid crystal couplings when cultured on liquid crystal coated substrates. The simulation indicates that glass/LC shifted the surface plasmon excitation angle to 75.39° as compared to glass/air interface at 44°. The WSPR microcopy reveals that the cells remodelled their topography of adhesion at different interfaces.

Yes / Cell migration is a key contributor to wound repair. This study presents findings indicating that the liquid crystal based cell traction force transducer (LCTFT) system can be used in conjunction with a bespoke cell traction force mapping (CTFM) software to monitor cell/surface traction forces from quiescent state in real time. In this study, time-lapse photo microscopy allowed cell induced deformations in liquid crystal coated substrates to be monitored and analyzed. The results indicated that the system could be used to monitor the generation of cell/surface forces in an initially quiescent cell, as it migrated over the culture substrate, via multiple points of contact between the cell and the surface. Future application of this system is the real-time assaying of the pharmacological effects of cytokines on the mechanics of cell migration.

No description available.

Electric vehicles aim to carry the torch into a sustainable future. An optimized cooling system is crucial to an Electric Drive Unit (EDU). A smartly designed cooling system will deliver high-performance, efficient and long-lasting EDUs at lower costs. One way to achieve that is to have an integrated cooling system. When the electric motor and transmission share a common oil, the oil returning from the transmission side is aerated due to spraying and splashing. This aeration affects the pump performance and may reduce the cooling performance of the oil. Thus, this thesis is initiated to understand the impact of aeration on heat transfer.     Oil aeration is the presence of air in oil. This aeration depends on the air content and bubble sizes mixed in the oil. Typically, there is also some amount of dissolved air in any oil. Depending on the type of aeration, the oil will appear lighter than its usual colour and have a very foamy texture, showing a change in the properties of the fluid, for example density, viscosity and heat transfer.    An experimental setup is built in order to replicate and study the effect of aeration on local heat transfer. A flat channel with rectangular cross-section is designed with three parts – a bottom plate, a flow spacer channel and a top transparent plate. The oil and air are mixed before they enter the channel and then heated using thin film heaters. A groove within the bottom plate houses an insulating material, the thin film heater, a thermocouple touching the heater and a thermochromic liquid crystal sheet facing the fluid mixture. The thermocouple gives temperature readings from a single point between the heater and the insulating material. Meanwhile, the liquid crystal sheets come in different desired temperature ranges and change in colour from red to blue to show the surface temperatures over an area. So, the surface temperature of the mixed fluid flow can be recorded visually over an area with the thin film heater under it to calculate the heat transfer coefficients accordingly.    The drop in Nusselt number and heat transfer rates with increased aeration in the working fluid is the main highlight and result. The size of the air bubbles in the channel also determine how fast the heat transfer rate drops.