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The transient shear and elongational flow behavior of HPC EF, G, and HBA/HNA (Vectra A900) have been measured in order to determine the behavior of liquid crystalline polymer systems and to establish whether this behavior is different from that for isotropic flexible-chain polymer melts and isotropic systems of rodlike polymers. In order to accomplish this a rotary clamp extensional rheometer was constructed which is capable of measuring the elongational flow behavior of polymer melts up to 320 °C and which can measure elongational viscosities as low as 1000 Pa's. Tests were conducted on HPC EF at 190 and 210 °C, on HPC G at 200 and 240 °C, and on HBA/HNA at 301 and 320 °C. It was determined that the transient shear stress behavior of the LCP systems scales with strain or alternately, reduced time and that the reduced stress is independent of shear rate over the range of rates investigated. This behavior is different from that for isotropic melts of flexible-chain and rodlike polymers in that the reduced stress for these systems is dependent on deformation rate. The transient elongational viscosity behavior of the LCPs was determined and found to follow linear viscoelastic response at very low strains and then shows mild strain hardening with increasing strain, which is qualitatively similar to the behavior of certain linear polyolefins such as PS and HDPE. From the elongational viscosity behavior determined for both isotropic and anisotropic HPC melts it was found that differences in the melt state can result in qualitative differences in the measured behavior. However, the presence of residual crystallinity in the systems studied makes it uncertain whether the results determined here are general for all LCP systems. The prediction of the Doi theory for both steady and transient shear and elongational flow were calculated in order to establish whether the theory can predict or model the flow behavior of LCPs and to establish whether the elongational flow behavior of LCPs can be predicted from their shear flow behavior. The Doi theory was evaluated with the viscous drag or rod-solvent friction term retained in the equation for the stress tensor. It was found that the Doi theory cannot predict the shear or elongational flow behavior of LCPs with parameters determined only from molecular properties. At the same time, the Doi theory was found to be able to semi-quantitatively model the steady shear viscosity behavior of isotropic and anisotropic systems of rodlike polymers with retention of the viscous drag contribution to the stress tensor. Also, the Doi theory was able to qualitatively model the transient flow behavior of the same systems, though agreement for the anisotropic systems depended on the use of a multidomain average to represent the globally unoriented state of the material at equilibrium. However, the Doi theory was not able to predict the transient elongational flow behavior of either isotropic or anisotropic systems with parameters fit to shear flow data. Furthermore, the predictions of the Doi theory for elongational flow showed only marginal qualitative agreement with the experimentally determined behavior of both isotropic and anisotropic systems. / Ph. D.

Solutions of cellulose esters with different concentrations in dimethylacetamide (DMAc) and with different types of substituents were studied in relation to their liquid crystalline (LC) solution behavior. Classical LC behavior was revealed for all solutions. Critical polymer concentration (V_p^c) is highest for cellulose acetate (CA) and lowest for cellulose acetate butyrate (CAB) with highest degree of butyration. This is opposite to the classical model by Flory which predicts an increase in V_p^c with decreasing aspect ratio (L/d). Fibers were spun from isotropic and anisotropic DMAc solutions of cellulose esters by dry jet/wet spinning process. The mechanical properties, orientation, and crystallinity of the fibers increased as spinning progressed from the isotropic to the anisotropic solution state. High butyryl content enhances both overall solubility and the formation of LC solutions at lower concentration, but it results in lower fiber properties. Unmodified cellulose (C) and cellulose hexanoate (CH) also exhibited LC behavior. The V_p^c value for CH was lower than that obtained for CAB with maximum degree of butyration. This indicates that bulky substituents may lower V_p^c values. The formation of high modulus (152 g/d) cellulose fibers from LC solutions is attributed to the air-gap that exists in the dry jet/wet spinning process. Presence of lithium chloride (LiCl) in the LC solutions of CAB exhibited ionic interactions. Mechano-sorptive creep behavior of the fibers spun from these solutions decreases in the presence of residual LiCl salt. Fibers from blends of CAB and of C with lignin (L) were spun from Lc solution. Morphological investigations demonstrate that CAB and L formed intimately mixed blends whereas C and L were partially mixed. The mechanical properties of the fibers with L increased due to good phase mixing of CAB and L molecules in the fiber matrix. / Ph. D.

Injection Molding The effects of partial miscibility on the mechanical properties and morphology of thermotropic liquid crystalline polymer blends were investigated in this part of the work. Blends of an immiscible (Vectra A900) and partially miscible (HX1000) thermotropic liquid crystalline polymer (TLCP) with a polyetherimide (PEI) were used in the investigations. The blends were injection molded into mini-tensile bars and rectangular plaques, and their mechanical properties were evaluated. Interfacial, rheological, and morphological properties along with molecular orientation analysis were carried out in order to explain the mechanical properties of the blends. Mechanical tests showed that both the tensile and flexural modulus deviate positively from the law of mixtures. However, for the PEI/HX1000 system the deviation from the law of mixtures appeared at lower TLCP concentrations compared to the PEI/Vectra A900 system. It was found that the tensile modulus correlated well with the structure developed during injection molding. Morphological tests show that finer higher aspect ratio TLCP fibers developed in the PEI/HX1000 system relative to the PEI/Vectra A system. In addition, both blends showed a maximum in the tensile modulus at 90 wt% TLCP. Rheological tests indicated that for TLCP-rich compositions, a higher viscosity was observed for the blends in comparison to the neat TLCPs. Therefore, due to a greater viscosity, higher magnitudes of stresses, consequently inducing a higher degree of molecular orientation, were experienced by the blends relative to the neat TLCPs. Although partial miscibility seemed to affect more strongly the stiffness of the in situ composite, the ultimate properties of the TLCP strongly dominated the ultimate properties of the PEI/TLCP composite. Mechanical tests showed that the ultimate properties of Vectra A were at least twice those of HX1000. Consequently, for TLCP-rich compositions, higher values of toughness, elongation at break and tensile strength were observed for PEI/Vectra A blends compared to PEI/HX1000 blends. The study presented here seems to suggest that the selection of a TLCP to reinforce a polymeric matrix is not only dependent upon whether partial miscibility or compatibility between the TLCP and matrix polymer exist, but also on the mechanical properties of the TLCP. Shearfree Elongational Deformation The effects of uniaxial, planar and biaxial deformations on the morphology and mechanical properties of bends of a polyetherimide with thermotropic liquid crystalline polymers were investigated in this part of the work. Extruded sheets and molded plaques of PEI/Vectra A and PEI/HX1000 blends were used in the studies. In the case of injection molded plaques, in which the initial morphology was that of fibers and droplets, the direction of the applied deformation relative to the initial direction of the TLCP fibrils was an important factor in affecting the resultant morphology and corresponding mechanical properties of the blends. If the direction of the applied uniaxial deformation was parallel to the initial fiber direction, the deformation tended to increase the average aspect ratio of the TLCP fibers and mechanical properties were enhanced along the direction of deformation. However, if the deformation was applied transverse to the initial fiber direction, the fibers tended to follow the deformation and a 90° rotation was observed. In terms of mechanical properties, an increase in the transverse direction properties accompanied by a reduction in the flow direction properties followed the realignment of the fibers. In addition, equal flow and transverse mechanical properties appeared at 0.5 units of transverse uniaxial strain. Planar deformation led to the spreading of the fibers in the plane of deformation and a ribbon-like morphological structure developed. However, at comparative magnitudes of planar strains, transverse planar compression tends to promote a greater spreading of the fibers relative to planar compression applied parallel to the initial direction of the fibers. In addition, planar stretching applied in a direction perpendicular to the initial direction of the TLCP fibers was effective in reducing the mechanical anisotropy of the molded plaques. Samples showing equal flow and transverse properties were obtained when planar strains greater than 0.5 units were applied in a direction perpendicular to the initial direction of the fibers. In the case of extruded sheets, in which the initial morphology was that of drops, it appeared that partial miscibility was an important factor in affecting the final morphology of the sheet. For the immiscible PEI/Vectra A system, longer and more stable TLCP fibrils were found compared to PEI/HX1000 system. It is believed that, due to lower interfacial tension, stress induced fiber breakup occurred during stretching of the PEI/HX1000 blend. Thermoforming of In Situ Composites The use of in situ thermoplastic composites based on blends of a polyetherimide with an amorphous and a semicrystalline liquid crystalline polymer in the thermoforming process was explored in this part of the work. Injection molded and extruded samples, in which the initial morphology of the dispersed TLCP phase was either in the form of fibers or droplets, were subjected to thermoforming. It was found that in the case where the initial morphology of the dispersed TLCP phase was that of droplets, the elongational stresses generated during forming were capable of deforming the TLCP phase into fibers, and the aspect ratio of the fibers was increased with depth of draw. However, when the initial morphology of the the TLCP phase was in the form of fibers, then the relative alignment of the fibers with respect to the forming direction was an important factor in affecting the final structure of the TLCP phase in the formed tray. When the fibers were aligned parallel to the forming direction, the elongational strains generated during forming tended to further increase the aspect ratio of the fibers. In the case where the initial TLCP fibers were aligned transversely to the forming direction, the fibers tended to spread into a ribbon-like structure after forming. Pre-stretching of the samples prior to thermoforming tended to contribute to an increase in the aspect ratio of the TLCP fibers. As a result, an enhancement in the deflection resistance of the prestretched/formed samples was observed. In situ thermoplastic composites seemed to be advantageous compared to glass reinforced thermoplastics in thermoforming applications. The elongational stresses generated during forming tended to deform the TLCP phase into a specific morphology. Depending on the relative direction of the deformation, either fibers or a ribbon-like structure may be developed. This is in contrast to glass reinforced PEI, in where breakage of the glass fibers occurred upon forming, which may contribute to a reduction in the mechanical performance of glass reinforced materials. / Ph. D.

I have used computer simulations to investigate the behavior of polymeric materials at the molecular level. The simulations were performed using the molecular dynamics method with Lennard-Jones potentials defining the interactions between particles in the system. Significant effort was put into the creation of realistic materials on the computer. For this purpose, an algorithm was developed based on the step-wise polymerization process. The resulting computer-generated materials (CGMs) exhibit several features of real materials, such as molecular weight distribution and presence of chain entanglements. The effect of the addition of a liquid crystalline (LC) phase to the flexible matrix was also studied. The concentration and distribution of the second phase (2P) were found to influence the mechanical and tribological properties of the CGMs. The size of the 2P agglomerates was found to have negligible influence on the properties within the studied range. Moreover, although the 2P reinforcement increases the modulus, it favors crack formation and propagation. Regions of high LC concentration exhibit high probability of becoming part of the crack propagation path. Simulations of the tensile deformation under a uniaxial force have shown that the molecular deformation mechanisms developing in the material depend on several variables, such as the magnitude of the force, the force increase rate, and the level of orientation of the chains. Three-dimensional (3D) graphical visualization tools were developed for representation and analysis of the simulation results. These also present interesting educational possibilities. Computer simulations provide us information which is inaccessible experimentally. From the concomitant use of simulations and experiments, a better understanding of the molecular phenomena that take place during deformation of polymers has been established.

Aniline Black, a polymer containing p-benzoquinodiimine groups, was synthesized chemically or electrochemically by the oxidation of aniline. The polymer salts showed the conductivity of 10⁻¹-10⁻³ ohm⁻¹cm⁻¹. Polymers containing anthroquinodiimine units were also prepared by polycondensations. The syntheses of model compounds containing p-benzoquinodiimine were attempted. Multiazobisphenol monomers were synthesized. 4,4'-(3,3'-Dimethyl-4,4'-biphenylenebisazo) bisphenol 7, 4,4'-[azobis(p-phenyleneazo)] bisphenol 8, and 4,4'-(2-methoxy-1,4-phenylenebisazo) bisphenol 10 displayed liquid crystal (l.c.) properties, while model derivatives of 7, 8, and 4,4'-(4,4'-stilbenebisazo) bisphenol 9 did likewise. Monomers and derivatives of 4-[(4-hydroxyphenyl)azo]-1-naphthol 5, and 4,4'- [oxybis(p-phenyleneazo)] bisphenol 6 showed no l.c. behavior. New thermotropic polyesters based on these multiazobisphenols were synthesized. Sebacates of 5, 6, 7, 8, and 10 showed l.c. behavior, while polymers based on isophthalic or 5-t-butylisophthalic acid did not do so. Polyformals were also synthesized from these momoners, only that of 4 showed weak l.c. behavior. The correlation between the structure of these polymers and their tractabilities, electrical properties, liquid crystal behaviors was studied. Polymers and copolymers containing p-azoarylene and p-azoxyarylene groups were synthesized by oxidative coupling of various aromatic diamines. Films were cast directly from the reaction mixtures or from the polymer solution. The films were n-doped by sodium naphthalide or p-doped by iodine. They showed electrical conductivities of 10⁻⁴ to 10⁻⁵ ohm⁻¹cm⁻¹. AB monomers containing dipolar p-phenyleneazo groups were synthesized: 4-(4-hydroxy-2-methoxyphenylazo) benzoic acid 21, 4-[4-(4-hydroxy-2-methoxyphenylazo)-2-methoxyphenylazo] benzoic acid 22, and 4-(4-hydroxy-2-methoxyphenylazo)-3-nitrobenzoic acid 23. The monomers were polymerized by direct polycondensations. The polyester synthesized from 21 formed a red, transparent film. A polymethacrylate containing dipolar p-phenyleneazo groups in the side chains was also prepared by the free radical polymerization of 1- [3-methoxy-4-(p-nitrophenylazo)-phenoxy] hexyl methacrylate 28.

In this work, using the idea of an electrically conducting "functional unit," monomers and polymers with possible electronic and electro-optic applications were synthesized. The synthesis and polymerizations were, in many cases, novel and non-trivial. Dithiafulvene (1,3-dithiole) and variations of this functional unit were synthesized and incorporated into new condensation polymers. Polyesters, polyamides and polyhydrazones were all successfully synthesized and could be cast into films. These new polymers might be applicable as processable conducting materials if compatible dopants are employed or by themselves in the area of third order non-linear optics. Using a (meth)acrylate backbone, a spacer group of six methylene units, and a phenyl-CO₂-phenyl mesogen, linked by an ester group to a strongly polar optically active center containing a methoxy group, three new novel monomers and polymers were designed to exhibit smectic C* liquid-crystal phases. The polymers exhibited liquid crystalline behavior as was shown in differential scanning calorimetry and optical microscopy. Further studies and investigations in the synthesis of pure (meth)acrylate esters and their homopolymers yielded surprising results with regard to the Schotten-Baumann reaction. Interestingly, the use of meth(acryloyl) chloride in this scheme leads to (meth)acrylic anhydride, which is not easily isolable from distillable products. This anhydride is responsible for gelation in the polymerization of glycolate esters, and cannot be removed by work-up with various nucleophiles without disrupting desired ester functions. An S(N)2 method is recommended in this work.

A liquid crystal (LC) at its boundary surface adopts a preferential alignment, which is referred to as anchoring. The direction of this alignment (i.e., anchoring direction) may be perpendicular, parallel or tilted with respect to the surface. Transitions from one anchoring condition to another may occur when the parameters (e.g., temperature) charactering the surface change, as referred to as anchoring transitions. In the LC-polymer composite systems under our study, the anchoring and temperature- driven anchoring transitions of nematic fluids is very sensitive to the structure of the side chain of poly (alkyl acrylate) matrixes that encapsulate the LC. We have shown that the anchoring transition temperature of these systems can be tuned far below the nematic-to-isotropic transition temperature, by varying either the length, branching structure of the side chains of homopolymers, or the composition of copolymer of two dissimilar monomers. Both sharp and broad anchoring transitions with respect to the temperature range over which a transition occurs were observed. It is postulated that microscopic interactions between the polymer side chains and LC molecules play an important role in determining the anchoring. In particular, the conformation of the polymer side chain is proposed to have important control over the anchoring. Anchoring strength and tilt angle as a function of temperature during the anchoring transitions were also experimentally investigated, which contribute to understanding of the microscopic mechanism for such transitions. Based on the LC-polymer composites with controlled anchoring, a LC display with reverse switching mode and a novel electrically switchable diffraction grating have been demonstrated. The advantages of these devices are ease of manufacturing, low operation voltage, and mechanical stability offered by polymer matrix. Moreover, a detailed study of the director configuration of wall defects found in these composite films was carried out using fluorescence confocal polarized microscopy.

Perylene-based materials, including charge-transport discotic liquid crystals and charge-transfer long-wavelength absorbing chromophores, for potential organic electronic and optoelectronic applications, were designed, synthesized and characterized. Two types of discotic liquid crystals, perylene diimides and coronene diimides, can form columnar liquid crystalline phases over a wide temperature range; many of them can have room-temperature liquid crystalline phases after cooling from isotropic liquid. Their charge transport properties were studied by space-charge limited current method; high charge carrier mobilities, with the highest being up to 6.6 cm2/Vs, were found in liquid crystalline phases of these materials under ambient conditions. Structural variables, including aromatic cores and side groups, were examined to get a certain degree of understanding of charge transport properties in these discotic liquid crystals. It was found that mesophase order can have an important effect on charge carrier mobilities. The discotic liquid crystals with high charge carrier mobilities are serious candidates for use in large-area low-cost applications such as solar cells. Long-wavelength, highly absorbing chromophores, featuring donor-substituted perylene diimides, were generated by a combination of charge-transfer process and conjugation extension. The charge-transfer chromophores are expected to lead to further investigation on their potentials as sensitizers in Grtzel solar cells.