No description available.

Until present, many researchers relied on the conventional plug flow dispersion models to analyse the concentration profiles obtained from the tracer injection experiments to evaluate the dispersion coefficients in packed beds. The Fickian concept in the limit of long time duration is assumed to be applicable and it implies that the mean-square displacement of the tracer profile is constant with time and the concentration profile is Gaussian. There were very few studies on identifying the conditions under which this assumption is valid and delineate the range of applicability of the existing plug flow dispersion models. If the time scales of a tracer injection experiment are not sufficient for a tracer to traverse the bed radius and sample the velocity variations, this could give rise to persisting non-Fickian transients where the mean-square displacement of the tracer profile is not constant with time and the concentration profile deviates from the normal Gaussian distribution. These transients cannot be predicted by the conventional plug dispersion models. An extended axial non-Fickian macroscopic dispersion model is derived to describe the transient development of a solute tracer when injected into a fluid flowing through a cylindrical packed bed or empty tube and some non-Fickian effects in the dispersion process. The flow profile in beds packed with uniform particles exhibits radial non-uniformity due to the oscillatory variation in porosity because of the wall confinement (wall effect). Compared with the axial plug flow dispersion model, the extended model contains time-dependent coefficients such as the transient axial dispersion coefficient and higher order derivatives (higher than second order) of the cross-sectionally averaged concentration. Including them provides some insight on non-Fickian transport in the dispersion process. The model provides time criteria on the basis that the effelongitudinal dispersion coefficient in the packed bed reaches its asymptotic value and the non-Fickian transients will die out. Some experimental conditions in the literature were checked by these criteria and found to be either marginally satisfied, or not satisfied at all, which indicates that the Fickian concept is not valid. The model results for tracer dispersion in cylindrical packed beds show that the longitudinal dispersion coefficient converges to its asymptotic value on a time scale proportional to R2/(DT) where R is the column radius and (DT) is the area averaged lateral dispersion coefficient. The extended model encouraged study of the consequences of the additional dispersion terms in other applications such as the pulse spread in the field of capillary column inverse gas chromatography (CCIGC). CCIGC is used to evaluate the solute-polymer diffusion coefficient Dp and the partition coefficient K at infinite dilute conditions. The tube geometry in CCIGC is more complex than the conventional Taylor dispersion problem due to the polymer coating on the inside of the capillary wall. The extended CCIGC model presented in this study has advantages over the previous models by including the effects of Taylor dispersion and higher order derivatives of the pulse area-averaged concentration. Taylor dispersion effect causes more pulse spread in the longitudinal direction and by not including it in the CCIGC regression models may cause a significant error in the measured Dp values. The extended CCIGC model provides for the first time criteria on capillary dimensions for the transient coefficients (multiplying the second and higher order derivatives) to become constant and for the non-Fickian effects associated with the higher order derivatives to be neglected. Model results show that Taylor dispersion effect has a significant effect on the elution profiles at high values of Dp and/or low values of gas diffusion coefficients Dg and it can be used to increase the sensitivity range of the previous CCIGC models at extremely low and high Dp values.

Mass transport of chemicals into wood is important in kraft pulping. This thesis models small wood particles as cylinders and monitors how tritiated water and sulfide diffuse into the water-filled pores. Tritiated water diffusion is Fickian and diffuses completely into the water contained in the wood. Tortuosity values of the aspen and pine are tabulated. As particle size decreases, the tortuosity of the particles increases. As sulfide diffuses into wood, it is occluded from some water filled areas. Charge exclusion is a possible explanation for this. Sulfide and hydroxide transport into wood chips was displayed using indicators for each component. Pictures show sulfide ingress into the chip core faster, thus confirming the diffusion results. Fractionated sawdust was pulped to determine particle size effect on cooking and pulp properties.

The relative rates of the diffusional and relaxational processes during the absorption of penetrant molecules in glassy polymers determine the nature of the transport process and lead to Fickian, Case II, and anomalous absorption behavior. While previous models account for anomalous behavior, there is still a disconnect between theory and experiment, as data must be fit to the model with previously determined independent parameters. With trends leading to smaller device scales and increasingly complex polymer structures, there is a need for a quantitative understanding of the manner in which a polymer’s network structure alters both the rate and the mode of penetrant transport. To this end, samples of glassy poly(methyl methacrylate), poly(2-hydroxyethyl methacrylate), and poly(vinyl alcohol) were synthesized primarily by an iniferter-mediated, thermally-initiated free radical polymerization procedure. The thermal and mechanical properties of these polymers, as well as the polymer network structure, were varied through crosslinking and confirmed by detailed characterization. The dynamics of small molecule penetrant transport were examined in each polymer, with an emphasis on the occurrence of non-Fickian and Case II transport. The degree of crosslinking and choice of crosslinking molecule were shown to be powerful tools in tuning the observed penetrant transport process. For instance, the transport dynamics were altered from Fickian to Case II by increasing the degree of crosslinking and from Case II to Fickian by increasing the crosslinking interchain bridge length. Within the purely Case II regime, the rate of penetrant transport, or the Case II front velocity, was shown to scale with the square root of the degree of crosslinking in all systems investigated. A novel procedure for the in situ examination of penetrant transport in glassy polymers was developed utilizing high-resolution X-ray computed tomography. This completely nondestructive technique was used to visualize features in the interior of opaque solid objects and obtain digital information on their 3-D structure and properties. In this manner, the time-dependent penetrant concentration profiles throughout a swelling polymer were determined and analyzed. / text

The effect of peptide charge on the self-assembly and gelation behaviour of three octa-peptides: VEVKVEVK (VEK2), VKVKVEVK (VEK3) and VEVEVKVE (VEK1) has been investigated and characterised. The critical gelation concentration of each peptide was found to correlate with the charge modulus carried by the peptide and to be independent of the sign of the charge. Hydrogels formed were found to be transparent and stable when the peptide charge modulus is > 1. No differences in hydrogel structure or mechanical properties, as probed by TEM and SAXS and shear rheology, were found when the peptides were at the same concentration and carried the same charge modulus. These peptides were shown to form dense fibrillar network formed by β-sheet rich single fibre which lateral aggregation is controlled by the peptide charge modulus. The increase in fibre lateral aggregation with decreasing charge modulus was found to correlate with the increase in hydrogel mechanical properties, showing that fibre lateral aggregation pays a key role in controlling the mechanical properties of these hydrogels. The release profiles from VEK1 and VEK3 at pH 7 of two hydrophilic model drug molecules, namely napthol yellow (NY) and martius yellow (MY) was analysed using UV-Vis spectrophotometry. The incorporation of the guest molecules did not affect the self-assembly of the peptide at a molecular level but did affect the level of lateral fibre aggregation observed and therefore the mechanical properties of the hydrogels. The release of each of the model compounds was monitored over time and shown to be controlled by Fickian diffusion. The guest molecule diffusion rate D was dependent on the ratio between the overall effective charges carried by the peptide, i.e.: the fibrillar network, and the overall charges carried by the guest molecules but independent from the hydrogel concentration and mechanical properties, in the concentration and guest loading range investigated. This work shows that the rate of release of small drug molecules can be manipulated, not only by changing the charges on the guest molecules, but also by manipulating the charged state of the self-assembling peptide molecule and through it the charge state of the fribrillar network. Furthermore the VEK3 system was conjugated to a series of thermo-responsive synthetic polymers which imparted a significant change in mechanical properties, assembled structures and release profiles upon heating. Observed changes when above the polymers LCST include increased mechanical strength, fibre thickening and increased diffusion coeffcients. The synthesis, and subsequent characterisation, of these materials is the first time responsive hydrogels of OEGMA copolymers has been reported.

No description available.

No description available.

Doctor of Philosophy / Department of Chemistry / Daniel A. Higgins / This dissertation describes single-molecule tracking (SMT) studies for the quantitative characterization of one-dimensional (1D) solvent-filled surfactant-templated mesoporous silica (STMS) materials and other nanostructured materials, such as double-stranded DNA. SMT permits the simultaneous and quantitative assessment of the nanoscale and microscale morphologies and mass-transport properties of the materials with nanometer-scale spatial resolution. The efficiency and selectivity of catalytic reactions and chemical separations occurring in liquid-filled mesoporous materials are governed by the translational and orientational mobilities and surface interactions of the incorporated reagents and analytes. Polarization dependent SMT results demonstrate that the dye molecules used as probes of materials nanostructure are tightly confined within the one-dimensional (1D) pores of surfactant-templated mesoporous silica films. Spectroscopic single molecule tracking (sSMT) data reveal that the hydrophobic probe dyes are confined within nonpolar regions of the nanomaterials For this dissertation, surfactant templated mesoporous silica films were prepared by the spin coating of acid catalyzed tetramethoxysilane (TMOS)-based silica sols on glass substrates in the presence of Cetyltrimethylammonium bromide (CTAB). Cylindrical CTAB micelles formed during evaporation of the solvent acted as a structure directing template, forming nanometer-sized one-dimensional pores within the silica films. SMT experiments were performed using a wide-field fluorescence microscope that was sufficiently sensitive to allow detection of the fluorescence from individual dye molecules. A series of perylene diimide (PDI) dyes was employed for basic structural characterization of the silica materials. Single molecule fluorescence was recorded in the form of fluorescence videos. These videos revealed the presence of immobile dye molecules, along with those diffusing in one and two dimensions (1D and 2D). The 1D diffusing molecules provided basic evidence for the confinement mass transport of the dye molecules within the silica mesopores. Spectroscopic single molecule tracking (sSMT) studies served as an extension of basic SMT experiments and were employed to determine the location of the molecules. The polarity sensitive dye Nile Red (NR) was employed in these studies. It exhibits 1D diffusion, consistent with its confinement to the cylindrical pores, as was also the case for the PDI dyes. The sSMT data revealed that the majority of NR molecules were found in nonpolar environments having polarities similar to that of n-hexane. Single molecule emission polarization (SMEP) measurements were employed to explore the orientational confinement of the dyes. The results of these experiments demonstrated that the PDI and NR molecules diffuse with their long axes aligned parallel to the long axis of the pores. All of the dyes employed were found to be orientationally confined to ∼1 nm diameter pathways within the pores. The diffusion coefficient for the dyes was also shown to be ∼10^3 -fold smaller than in bulk solution. The results of the NR studies demonstrate that the dye molecules were confined to the hydrophobic cores of the micelles, and provide support for the conclusion that the PDI dyes are similarly confined. These studies afford an enhanced understanding of how nanostructuring of the pore-filling medium in solvent- and surfactant-filled mesoporous materials governs the mass transport and surface interactions of incorporated reagents and analytes. The dependence of molecular confinement on dye charge and structure was also explored in this dissertation. The confined translational and orientational motions of a series of four different PDI dyes diffusing along one dimension (1D) within individual cylindrical silica mesopores were investigated in these studies. Specifically, the motions of cationic and anionic PDI dyes were compared to those of two uncharged PDIs having different alkane tail lengths. All four dyes exhibited populations that were immobile, along with separate populations that diffused in either 1D or 2D. The anionic and cationic PDI dyes exhibited the largest and smallest populations, respectively, of immobile molecules, suggesting that electrostatic interactions between the charged dyes and the cationic surfactant head groups play a significant role in limiting molecular motion. The cationic and anionic PDI dyes also exhibit the largest populations of 2D diffusing molecules, suggesting they may more readily pass between the cylindrical micelles and through the silica pore walls. All four dyes also emit strongly polarized fluorescence as they move in 1D, indicating they are orientationally confined within the nanochannels. Nile Red dye was used to determine the dielectric constant, ε, of nonpolar microenvironments in double-stranded DNA (ds-DNA) single molecules both in aqueous buffer solution and when adsorbed on amine-modified chemical gradient surfaces. The value of ε within the DNA decreased with increasing buffer concentration. Values of ε ∼ 6.75 and ∼3.00 were obtained in 0.1 mM phosphate buffered saline (PBS) and in 10 mM PBS, respectively. Similar effects were observed upon adsorption to chemically graded amine-modified silica surfaces. Under 1 mM buffer, ε was measured to be ∼2.84 and ∼1.90 at the low amine (high silica), and high amine (low silica) ends of the gradient, respectively. An increase in the buffer concentration again led to a decrease in ε, but only at the low amine end. It is concluded that high buffer concentrations and binding to an amine surface cause condensation of the ds-DNA, forming less polar microenvironments within its structure. These results provide important knowledge of the factors governing the polarity of DNA microenvironments to which intercalators bind.

Diffusion of linear and cyclic poly(oxyethylene) (POE) oligomers in poly(methyl methacrylate) (PMMA) matrix was investigated in situ using attenuated total reflectance (ATR) infrared (IR) spectroscopy technique. The temperatures of studies were 60 oC, 85 oC and 110 oC. A film of PMMA was solution-cast onto an ATR zinc selenide crystal and POE was added to the surface. The IR peak at 1109 cm-1 characteristic to ether bond present in POE was used for quantitative analysis. Deconvolution of this peak from IR spectra allowed us to determine the absorbance of diffusing component as a function of interdiffusion time. The data were fit using appropriate mathematical models from where the interdiffusion constants were extracted and used in diffusion interpretation. By looking at different molecular weight of cyclic and linear POE oligomers diffusing into high molecular weight PMMA matrix, it was possible to analyze how penetrant topology and its molecular weight are influencing the diffusion process. The results indicated that cyclic POE moves faster than linear analogous one and an increase in penetrant molecular weight slows down the interdiffusion. The knowledge gained from this study gives us a deeper understanding of transport behavior of low-molecular-weight additives, such as oligomers into polymer matrices and, in particular the influence of topology on diffusion.

Des questions fondamentales concernant les propriétés de diffusion des systèmes biologiques dans des conditions isothermes et non-isothermes restent en suspens en raison de l’absence de techniques expérimentales capables de visualiser et de mesurer les phénomènes de diffusion avec une très bonne précision. Il existe en conséquence un besoin de développer de nouvelles techniques expérimentales permettant d’approfondir notre compréhension des phénomènes de diffusion. La convection naturelle en cavité tridimensionnelle inclinée est elle-aussi très peu étudiée. Cette inclinaison de la cavité peut correspondre à un léger défaut expérimental ou être imposée volontairement. Dans cette thèse, nous étudions les phénomènes de transport de chaleur et de masse en cavité parallélépipédique, nous intéressant particulièrement à la thermodiffusion en situation sans convection et à la convection naturelle en fluide pur (sans thermodiffusion). La diffusion de masse est étudiée à l’aide d’une nouvelle technique optique, tandis que la convection naturelle est tout d’abord étudiée en détails avec une méthode numérique sophistiquée, puis visualisée expérimentalement à l’aide du même système optique que pour les mesures de diffusion. Nous présentons l’interféromètre optique de haute précision développé pour les mesures de diffusion. Cet interféromètre comprend un interféromètre polarisé de Mach–Zehnder, un polariseur tournant, une caméra CCD et un algorithme de traitement d’images original. Nous proposons aussi une méthode pour déterminer le coefficient de diffusion isotherme en fonction de la concentration. Cette méthode, basée sur une analyse inverse couplée à un calcul numérique, permet de déterminer les coefficients de diffusion à partir des profils de concentration transitoires obtenus par le système optique. Mentionnons de plus que c’est la première fois que la thermodiffusion est visualisée dans des solutions aqueuses de protéines. La méthode optique proposée présente trois avantages principaux par rapport aux autres méthodes similaires : (i) un volume d’échantillon réduit, (ii) un temps de mesure court, (iii) une stabilité hydrodynamique améliorée. Toutes ces méthodes ont été validées par des mesures sur des systèmes de référence. La technique optique est d’abord utilisée pour étudier la diffusion isotherme dans des solutions de protéines : (a) dans des solutions binaires diluées, (b) dans des solutions binaires sur un large domaine de concentration, (c) dans des solutions ternaires diluées. Les résultats montrent que (a) le coefficient de diffusion isotherme dans les systèmes dilués décroit avec la masse moléculaire, comme prédit grossièrement par l’équation de Stokes-Einstein ; (b) la protéine BSA a un comportement diffusif de type sphère dure et la protéine lysozyme de type sphère molle ; (c) l’effet de diffusion croisée est négligeable dans les systèmes ternaires dilués. La technique optique est aussi utilisée (d) dans des solutions binaires diluées non-isothermes, révélant que les molécules d’aprotinin (6.5 kDa) et de lysozyme (14.3 kDa) sont, respectivement, thermophiliques et thermo-phobiques, quand elles sont en solutions aqueuses à température ambiante. Enfin, la technique optique est utilisée pour l’étude de la convection de Rayleigh-Bénard en cavité cubique horizontale. Puisque la convection peut aussi être étudiée de façon réaliste en utilisant les équations de Navier-Stokes, une analyse numérique de bifurcation est proposée, permettant une étude approfondie de la convection naturelle dans des cavités tridimensionnelles parallélépipédiques. Pour cela, une méthode de continuation a été développée à partir d’un code aux éléments finis spectraux. La méthode numérique proposée est particulièrement bien adaptée aux études de convection correspondant à des diagrammes de bifurcation complexes. [...] / Fundamental questions concerning the mass diffusion properties of biological systems under isothermal and non-isothermal conditions still remain due to the lack of experimental techniques capable of visualizing and measuring mass diffusion phenomena with a high accuracy. As a consequence, there is a need to develop new experimental techniques that can deepen our understanding of mass diffusion. Moreover, steady natural convection in a tilted three-dimensional rectangular enclosure has not yet been studied. This tilt can be a slight defect of the experimental device or can be imposed on purpose. In this dissertation, heat and mass transfer phenomena in parallelepiped enclosures are studied focusing on convectionless thermodiffusion and on natural convection of pure fluids (without thermodiffusion). Mass diffusion is studied with a novel optical technique, while steady natural convection is first studied in detail with an improved numerical analysis and then with the same optical technique initially developed for diffusion measurements. A construction of a precise optical interferometer to visualize and measure mass diffusion is described. The interferometer comprises a polarizing Mach–Zehnder interferometer, a rotating polariser, a CCD camera, and an original image-processing algorithm. A method to determine the isothermal diffusion coefficient as a function of concentration is proposed. This method uses an inverse analysis coupled with a numerical calculation in order to determine the diffusion coefficients from the transient concentration profiles measured with the optical system. Furthermore, thermodiffusion of protein molecules is visualized for the first time. The proposed method has three main advantages in comparison to similar methods: (i) reduced volume sample, (ii) short measurement time, and (iii) increased hydrodynamic stability of the system. These methods are validated by determining the thermophysical properties of benchmark solutions. The optical technique is first applied to study isothermal diffusion of protein solutions in: (a) dilute binary solutions, (b) binary solutions with a wide concentration range, and (c) dilute ternary solutions. The results show that (a) the isothermal diffusion coefficient in dilute systems decreases with molecular mass, as roughly predicted by the Stokes-Einstein equation; (b) BSA protein has a hard-sphere-like diffusion behaviour and lysozyme protein a soft sphere characteristic; and (c) the cross-term effect between the diffusion species in a dilute ternary system is negligible. The optical technique is then applied to (d) non-isothermal dilute binary solutions, revealing that that the aprotinin (6.5 kDa) and lysozyme (14.3 kDa) molecules are thermophilic and thermophobic, respectively, when using water as solvent at room temperature. Finally, the optical technique is applied to study Rayleigh-Bénard convection in a horizontal cubical cavity. Since natural convection can be studied in more depth by solving the Navier-Stokes equations, a bifurcation analysis is proposed to conduct a thorough study of natural convection in three-dimensional parallelepiped cavities. Here, a continuation method is developed from a three-dimensional spectral finite element code. The proposed numerical method is particularly well suited for the studies involving complex bifurcation diagrams of three-dimensional convection in rectangular parallelepiped cavities. This continuation method allows the calculation of solution branches, the stability analysis of the solutions along these branches, the detection and precise direct calculation of the bifurcation points, and the jump to newly detected stable or unstable branches, all this being managed by a simple continuation algorithm. This can be used to calculate the bifurcation diagrams describing the convection in tilted cavities. [...]