Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3816. Adviser: Paul W. Bohn. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph. D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3843. Adviser: Kenneth S. Suslick. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

This dissertation describes the synthesis, structure and phase behavior of polyurethanes based on the mesogenic biphenol 4,4$\sp\prime$-bis(6-hydroxyhexoxy)biphenyl (BHHBP) and meta substituted tolylene/phenylene diisocyanates. The structure-property relationships were determined as a function of hydrogen-bonding, the position of the methyl group in the tolylene diisocyanate moiety (TDI) and the biphenol moiety. The liquid crystalline phase (mesophase) and crystalline phase were investigated primarily with differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS) and infrared spectroscopy. From this combination of characterization techniques, a more detailed description emerges about the thermodynamic stability and kinetic accessibility of each phase. Previous investigation of the (2,4-TDI/BHHBP) mesogenic polyurethane, 2,4-LCPU-6, has shown that this polymer is a monotropic liquid crystal. The influence of H-bonding on the structure and phase behavior of 2,4-LCPU-6 was determined by the synthesis of high molecular weight N-Methyl 2,4-LCPU-6, using a novel high temperature polymerization of a biscarbamoyl chloride with the BHHBP mesogenic diol. The comparison of the structure and physical properties of these two polymers revealed that H-bonding does not affect the mesophase morphology although its absence disrupts crystallinity and results in an enantiotropic liquid crystal. In addition, it was found that the effect of H-bonding on the mesophase-isotropic transition is enthalpic in nature. In contrast to the "regular" ($\alpha,\omega$-hexane diol) based polyurethanes (PUs), BHHBP derived polyurethanes (LCPUs) crystallize rapidly from their melts. This is due to the strong nucleating power of their thermodynamically unstable mesophases (monotropic L.C.) Hexafluoroisopropanol fast solvent-evaporation casting or rapid cooling from the melt resulted in thin films or bulk samples with a glassy mesophase morphology. During the subsequent heating scan, the mesophase to crystal transition takes place. Considerable amount of effort was expended to understand the nature of this transition. With the combination of vibrational spectroscopy which provides a measure of the localized structure, along with DSC and WAXS (which examine the long range order) we established the microstructural changes occurring in the different phases. Applying the results of previously mentioned analysis (kinetic control and phase perfection), highly oriented fibers were obtained for the mesogenic polyurethanes. Atomistic molecular simulations coupled with X-ray intensity refinement allowed us to determine the crystalline chain conformation and packing characteristics for the 2,6-LCPU-6 and 1,3-LCPU-6 (2,6-TDI and 1,3-Phenylene Diisocyanate (1,3-PDI) derived LCPUs). On the basis of structural similarity and well resolved WAXS powder patterns we extended the similar analysis to the "regular" polyurethanes as well (2,6-PU-6 and 1,3-PU-6). The good correlation between H-bonding distance and melting temperature for these four polymers suggests that melting is primarily controlled by the dissociation of H-bonds in the ordered domains.

A study of the adsorption of block copolymers with respect to such variables as adsorption rate, concentration, molecular weight, relative block sizes, architecture, adsorption solvent, and temperature was conducted for the adsorption block copolymers to silanol surfaces. Poly(styrene-b-isoprene) and poly(styrene-b-1,2-butadiene) with precise molecular weight and narrow polydispersity were synthesized by anionic polymerization techniques. These block copolymers were then specifically modified to incorporate an organic moiety (sticky foot) which would promote adsorption. Hydrosilylation to incorporate trimethoxysilanes into the diene block was unsuccessful due to low reaction yields and crosslinking. Hydroboration/oxidation to incorporate alcohols into the diene block was used to prepare polymers for adsorption studies due to the high reaction yields with no crosslinking. Adsorption studies examining the effects of molecular weight, number of adsorbing segments, time, concentration, polymer architecture, and adsorption solvent were conducted for the adsorption to aerosil 130. Adsorptions were analyzed by UV spectroscopy and thermal gravimetric analysis. Adsorption studies examining the effects of molecular weight, relative block sizes, and temperature were conducted for the adsorption to glass slides. Adsorptions were analyzed by water contact angle and X-ray photoelectron spectroscopy. The competitive polymer adsorptions between two different polymers adsorbing to aerosil 130 were studied. Simultaneous adsorptions for two polymers with respect to concentration were examined for three separate sets of polymers. The polymers were adsorbed to aerosil 130 and analyzed by gel permeation chromatography. Sequential competitive adsorptions for these same polymer sets were also conducted using the same substrate and analysis technique. The effect of surface affinity on polymer adsorption was examined by adsorbing one polymer sample to a series of different surfaces. Poly(chlorotrifluoroethylene) polymers with carboxylic acid, alcohol, amine, and ethyl ester surfaces as well as glass slide and aminated glass slide surfaces were prepared and used for adsorptions. These adsorptions were analyzed by X-ray photoelectron spectroscopy.

The structure-property relationships in a new class of segmented copolymers, the smectic forming main chain liquid crystal polymers (LCPs), were systematically investigated. Soft segment length effects on polymer thermal phase behavior were studied. A series of segmented copolymers with different soft segment average lengths were prepared and characterized. Increasing soft segment length was found to favor the formation of smectic mesophases, irrespective of soft segment polydispersity. For interpreting the observations, a semi-quantitative thermodynamic theory was formulated, and a universal thermal phase diagram was proposed for segmented copolymers. Crystalline state structure and mesophase aggregation of these polymers were investigated. A crystalline state structure, in which the hard and soft segments are microphase separated, some of the soft segments have nearly fully extended conformation, and the hard segment crystal structure is independent of soft segment length, was proposed for smectic forming LCPs. The soft segment length was found to have significant effects on hard segment aggregation in the smectic phase. The observed thermal properties were interpreted. Morphology in the smectic state and melting behavior of a smectic forming LCP were studied. In the stable smectic state, the polymer showed a macrophase separated morphology, comprising smectic domains and an isotropic 'sea'. These smectic domains are cylindrical in shape and tens of microns in size. On cooling from smectic state, both smectic and isotropic phases crystallized and formed two different crystal structures. Consequently, the polymer showed dual melting endotherms, with their appearance strongly depending on sample thermal history. Crystallization kinetics of three different phases were investigated in a smectic forming LCP. The purely isotropic phase showed similar crystallization behavior as ordinary polymers. The crystallization of the purely smectic mesophase was found to be a local reorganization process and occurs within hard segment layers. The crystallization of the smectic-isotropic biphase showed complicated behavior, due to the simultaneous crystallization of both phases. The smectic phase was believed to nucleate the crystallization of the isotropic phase. Rheological behavior in the smectic state was investigated. A strong shear thinning at low shear rates was observed. On frequency sweeps, the polymer showed a two zone behavior, a 'solid-like' zone and 'liquid-like' zone. Further morphological investigations indicated that by low-rate shearing, the smectic domains were aligned along the shear direction. The domain alignment by flow was believed to be responsible for the observed rheological properties. By elongational flow, the polymer chains can also be oriented.

Diverse experimental techniques were used for the determination of acetaminophen (N-(p-Hydroxyphenyl)acetamide, N-acetyl-p-aminophenol) in aqueous and non-aqueous media. A study was performed on the electrochemical characterization of acetaminophen at a noble-metal electrode. A pretreatment procedure on the gold electrode was developed under basic conditions. The anodic peak current was the analytical parameter used. Spectrometric techniques were used as detection means, and their analytical potential was evaluated. Infrared techniques such as transmission and attenuated total internal reflection (ATR) were used for the quantitative determination of acetaminophen. The molar absorptivity of acetaminophen was calculated at the carbonyl infrared band from the calibration data obtained from the experiments performed in non-aqueous solvents using the transmission technique. The attenuated total internal reflection technique was used to overcome limitations on the use of the infrared transmission technique for aqueous based systems. A quantitative study was undertaken of the possibilities for the determination of acetaminophen in aqueous solutions by coupling flow injection analysis (FIA) with Fourier transform-infrared (FT-IR) spectrometry. Optimization of the basic flow injection FT-IR system was performed. The cylindrical internal reflection cell for liquid evaluation (CIRCLE$\sp\circler$) was used as the detector cell compatible with aqueous solutions. Applications to systems involving on-line chemical reactions by coupling the flow injection analysis technique with infrared spectrometric detection were described. Flow injection spectrophotometric and infrared detection methods were developed for the determination of acetaminophen based on its hydrolysis reaction with sodium hydroxide to form p-aminophenol and its oxidation with potassium ferricyanide to produce an orange-red species, p-benzoquinonemonoimine. The developed methods were evaluated by analysis of tablets of a commercial formulation. The ability of flow injection techniques for generating transient product profiles combined with the infrared mode for monitoring reaction species was investigated to help in the study of reaction mechanisms. Ab initio calculations were performed on acetaminophen at the 3-21G level of the theory. Structural parameters were optimized for the two conformations of acetaminophen. The calculated and experimental spectra were compared in terms of the infrared vibrational frequencies.

The technique of Fluorescence Lifetime Imaging Microscopy (FLIM) has been employed to quantitatively and spatially map the fluid composition and temperature within microfluidic systems. A molecular probe with a solvent-sensitive fluorescence lifetime has been exploited to investigate and map the diffusional mixing of fluid streams under laminar flow conditions within a microfluidic device. Using FLIM, the fluid composition is mapped with high quantification and spatial resolution to assess the extent of mixing. This technique was extended to quantitatively evaluate the mixing efficiency of a range of commercial microfluidic mixers employing various mixing strategies, including the use of obstacles fabricated within the channels. A fluorescently labelled polymer has been investigated as a new probe for mapping temperature within microfluidic devices using FLIM. Time Correlated Single Photon Counting (TCSPC) measurements showed that the average fluorescence lifetime displayed by an aqueous solution of the polymer depended strongly on temperature, increasing from 3 ns to 13.5 ns between 23 and 38 oC. This effect was exploited using FLIM to provide high spatial resolution temperature mapping with sub-degree temperature resolution within microfluidic devices. A temperature-sensitive, water-soluble derivative of the rhodamine B fluorophore, effective over a wide dynamic temperature range (25 to 91 oC) has been used to map the temperature distribution during the mixing of fluid streams of different temperatures within a microchannel. In addition, this probe was employed to quantify the fluid temperature in a prototype microfluidic system for DNA amplification. FLIM has been demonstrated to provide a superior approach to the imaging within microfluidic systems over other commonly used techniques, such as fluorescence intensity and colourimetric imaging.

Single molecule studies on CdSe quantum dots functionalized with oligo-phenylene vinylene ligands (CdSe-OPV) provide evidence of strong electronic communication that facilitate charge and energy transport between the OPV ligands and the CdSe quantum dot core. This electronic interaction greatly modify, the photoluminescence properties of both bulk and single CdSe-OPV nanostructure thin film samples. Size-correlated wide-field fluorescence imaging show that blinking suppression in single CdSe-OPV is linked to the degree of OPV coverage (inferred from AFM height scans) on the quantum dot surface. The effect of the complex electronic environment presented by photoexcited OPV ligands on the excited state property of CdSe-OPV is measured with single photon counting and photon-pair correlation spectroscopy techniques. Time-tagged-time-resolved (TTTR) single photon counting measurements from individual CdSe-OPV nanostructures, show excited state lifetimes an order of magnitude shorter relative to conventional ZnS/CdSe quantum dots. Second-order intensity correlation measurements g(2)(τ) from individual CdSe-OPV nanostructures point to a weak multi-excitonic character with a strong wavelength dependent modulation depth. By tuning in and out of the absorption of the OPV ligands we observe changes in modulation depth from g(2) (0) ≈ 0.2 to 0.05 under 405 and 514 nm excitation respectively. Defocused images and polarization anisotropy measurements also reveal a well-defined linear dipole emission pattern in single CdSe-OPV nanostructures. These results provide new insights into to the mechanism behind the electronic interactions in composite quantum dot/conjugated organic composite systems at the single molecule level. The observed intensity flickering , blinking suppression and associated lifetime/count rate and antibunching behaviour is well explained by a Stark interaction model. Charge transfer from photo-excitation of the OPV ligands to the surface of the CdSe quantum dot core, mixes electron/holes states and lifts the degeneracy in the band edge bright exciton state, which induces a well define linear dipole behaviour in single CdSe-OPV nanostructures. The shift in the electron energies also affects Auger assisted hole trapping rates, suppress access to dark states and reduce the excited state lifetime.

No description available.

An ionic liquid (IL) is a salt, which usually is in the liquid state at normal temperature and pressure. The properties of ILs can be adjusted for various processes and applications by choosing different combinations of ions. Similar to other salts, ILs contain only ions with positive (cations) and negative (anions) charges in equal proportions. However, to prevent solidification, ions in ionic liquids usually contain bulky organic chemical groups, which, apart from electrostatic interactions, promote other types of interactions between ions, such as: (i) van-der-Waals interactions; (ii) hydrogen bonding; (iii) - stacking, etc., depending on the particular chemical structure of the ions. All these interactions, in combination, may lead to formation of specific microstructures in ILs, which may vary with temperature caused by changing thermal rotational and translational energies of the ions. Ions in these microstructures may have preferential orientations relative to each other, maintain anisotropic properties similar to those in liquid crystals or, in some specific cases, may even separate into microscopically organised liquid phases. Therefore, the dynamics of ILs may also be dependent on their microstructure. In many practical applications ionic liquids are placed on surfaces or in confinements. Solid surfaces introduce extra forces, which may be specific to the charge of the ions or/and to functional groups in the ILs. The geometry and interactions of ions in confinements or/and pores of materials may also disrupt specific bulk microstructures of ILs. Both confinement effects and interactions of ions with surfaces are manifested in the translational dynamics of the ions. One of the most direct and informative methods to study translational dynamics of ILs is pulse-field-gradient nuclear magnetic resonance (PFG-NMR).In this thesis the results of PFG-NMR studies on a few classes of ILs are reported: (i) the historically “standard” (since Walden’s discovery in 1914) ionic liquid, the ethylammonium nitrate (EAN) and (ii) halogen-free orthoborate-based phosphonium, imidazolium and pyrrolidinium ILs with varied structure and lengths of alkyl chains in cations, and varied structures of orthoborate anions. These ILs were studied in bulk at different temperatures, and also in confinements, such as between parallel glass and Teflon plates and in mesoporous Vycor glass. It was found that diffusion coefficients of cations and anions in EAN, phosphonium and pyrrolidinium orthoborate ILs in bulk are different, but according to the standard Stocks-Einstein model, they correspond to diffusion of ions in homogeneous liquids. A change in the chemical structure of one of the ions results in a change in both the diffusion coefficient of the oppositely charged ion and the activation energy of diffusion for both ions in an IL. Similar effects were observed from the chemical shifts and diffusion coefficients measured by NMR for imidazolium orthoborate ILs dissolved in polyethylene glycol solutions, in which imidazolium cations strongly interact with PEG molecules, further affecting the diffusion of orthoborate anions via electrostatic interactions. A liquid-liquid phase separation was suggested for a few phosphonium and pyrrolidinium bis(mandelato)borate ILs, in which a divergence of diffusion coefficients and activation energies of diffusion for cations and anions was detected at temperatures below ca 50 °C. In addition, a free-volume theory was invoked to explain the dependences of density of ILs on the alkyl chain length in cations.It was also found that for a phosphonium bis(salicylato)borate IL confined in 4 nm mesoporous Vycor glass the diffusion coefficients of ions increase by a factor of 35! This phenomenon was explained by the dynamic heterogeneity of this IL in micropores and empty voids of the Vycor glass. For EAN IL in confinements between glass and Teflon plates, the diffusion of ethylammonium cations and nitrate anions is significantly anisotropic, i.e. slower in the direction of the normal to the plates and faster along the plates compared to diffusion of the ions in bulk. A plausible explanation of this PFG NMR data is that EAN forms layers near polar and non-polar solid surfaces. A similar phenomenon, to a lesser extent, was also observed for phosphonium cations of bis(mandelato)borate, bis(salicylato)borate and bis(oxalato)borate confined between glass plates. The results of these studies may have implications in modeling tribological performance, i.e., friction and wear reduction for contact pairs of different materials lubricated by various classes of ionic liquids. / För godkännande; 2016; 20160420 (andfil)