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In this thesis, glucose responsive hydrogels based on cross-linked dextran molecules were studied to determine the diffusion rate of an insulin analogue. Investigations of the interaction between concanavalin A and dextran, both in free solution and in the form of glucose responsive hydrogels were conducted. The free solution results have shown that there is an increase of association constant between concanavalin A and dextran when the molecular mass of the dextran is increased. Free solution viscometric tests have shown that increasing the molecular mass or the concentration of the dextran increases the viscosity. The hydrogels have been shown to form for dextrans of molecular mass 43kD or greater. Experiments conducted with hydrogel membranes in a diffusion cell have shown that the batch to batch reproducibility of hydrogel transport properties is low. However, clear evidence of glucose enhanced transport was obtained and these results were compared with predictions obtained from a theoretical model of gel permeability that accounts for competitive displacement of affinity cross links. Oscillatory rheological tests of gelation mixtures which showed an increase in complex viscosity at the gel point with increasing molecular mass of dextran were in agreement with empirical observations that gels formed from the highest molecular mass dextrans were more physically robust and easier to handle. Swelling rate experiments have shown that the rate of hydration of a hydrogel in the presence of glucose is decreased due to the osmotic pressure of the glucose. This work has shown that the multivalent nature of concanavalin A may not be a necessary pre-requisite for this type of hydrogel due to spatial constraints decreasing the number of potential affinity bonds per tetramer. In-house production of more tightly defined dextrans might be expected to reduce heterogeneity and improve the reproducibility of this type of hydrogel membrane.

Graduation date: 1998

The hydraulic-mechanical behaviour of swelling clay is examined in this thesis. The study includes laboratory testing and numerical modeling which considers the influence of boundary conditions on the hydraulic-mechanical behaviour of a compacted unsaturated swelling clay soil. The laboratory testing component of this research consists of three (3) series of tests using a newly modified triaxial apparatus on which mechanical and hydraulic boundary conditions are altered during liquid infiltration. Mechanical boundary conditions range from constant volume to constant mean stress and also include constant stiffness which is a spring type boundary consisting of both volume expansion and mean stress increase. Hydraulic boundary conditions include drained and undrained flow into triaxial specimens. The numerical modeling component of this research includes the creation of a new capillary tube model for swelling clay materials and incorporates dynamic changes to the cross-sectional area for flow. Laboratory results are modeled using the capillary tube model, an empirical hydraulic model, D’Arcy’s Law, and in an elastic-plastic context for unsaturated soil. Results of the laboratory and numerical modeling components show that boundary conditions dominate the hydraulic-mechanical behaviour of unsaturated swelling clay soil during liquid infiltration. In particular, a mechanism is shown to explain how hydraulic conductivity of a swelling soil can decrease with increasing water content at constant void ratio. Finally hydraulic and mechanical behaviour cannot be considered separately in swelling materials due to the intimate relationship in their response. / October 2006

Expansive soils are characterized as having high amount of clay minerals such as smectite, which lead to swelling during wet seasons by absorbing water and shrinking during dry seasons owing to moisture loss by evapotranspiration. The soil volumetric changes due to moisture fluctuations cause extensive damage to civil engineering structures, namely pavements, retaining walls, low rise buildings and canals founded on such soils. The primary swelling portion of the swell curve has been studied in significant details in previous studies. However, there is a dearth of literature concerning the secondary swelling phenomenon in expansive clays, which has also been observed in experimental studies. While it may be argued that the magnitude of secondary swelling is significantly less as compared to primary swelling, the characterization of the rate of secondary swelling is relevant for fully characterizing the swell potential of the soil. The rate of secondary swelling has been used to predict the long-term swelling of expansive soils. Conventional laboratory swell tests may take over a month for specimens to demonstrate secondary swelling behavior. A centrifuge based method has been recently developed at The University of Texas at Austin to achieve this objective in multiple specimens, and within less than a day. The effects of soil fabric, soil type, relative compaction, molding water content, gravitational gradient, and infiltrating fluid, on the rate of secondary swelling, are thoroughly investigated in this thesis. Four different expansive clays found widely in and around Texas, namely – Eagle Ford Clay, Tan Taylor Clay, Black Taylor Clay and Houston Black Clay, have been used in the study. Based on this extensive experimental evaluation, it may be concluded that secondary swelling behavior could be explained by flow processes associated with the bimodal pore size distribution in expansive clays. The rate of secondary swelling was found to increase with increasing molding water content and increasing compaction dry unit weight. The experimental results revealed that clays with a flocculated structure (compacted dry of optimum) demonstrate rapid primary swelling but exhibit less swelling in the secondary region, as compared to clays with a dispersed structure (compacted wet of optimum). The slope of secondary swelling showed a decline with increasing gravitational gradient. The rate of secondary swelling showed evidence of upward trend with an increase in the plasticity index and clay fraction of the soil. It was observed that soils which exhibit higher primary swelling also demonstrate higher secondary swelling. / text

A hydrogel consists of a cross-linked polymer network and solvent molecules, capable of large, reversible deformation in response to a variety of external stimuli. In particular, diverse instability patterns have been observed experimentally in swelling hydrogels under mechanical constraints. The present study develops a general theoretical framework based on a variational approach, which leads to a set of governing equations coupling mechanical and chemical equilibrium conditions for swelling deformation of hydrogels, along with proper boundary conditions. A specific material model is employed for analytical and numerical studies, for which the nonlinear constitutive behavior of the hydrogel is derived from a free energy function combining rubber elasticity with a polymer solution theory. A finite element method is then developed and implemented as a user-defined material (UMAT) in the commercial package, ABAQUS. By numerical simulations, the effect of constraint on inhomogeneous swelling of substrate-attached hydrogel lines is elucidated. It is found that crease-like surface instability occurs when the width-to-height aspect ratio of the hydrogel line exceeds a critical value. Next, by considering a hydrogel layer on a rigid substrate, swell-induced surface instability is studied in details. A linear perturbation analysis is performed to predict the critical condition for onset of the surface instability. In contrast to previously suggested critical conditions, the present study predicts a range of critical swelling ratios, from about 2.5 to 3.4, depending on the material properties of the hydrogel system. A stability diagram is constructed with two distinct regions for stable and unstable hydrogels with respect to two dimensionless material parameters. Numerical simulations are presented to show the swelling process, with evolution of initial surface perturbations followed by formation of crease-like surface patterns. Furthermore, with combined swelling and mechanical compression, the stability analysis is extended to predict a general critical condition that unifies the swell-induced surface instability of hydrogels with mechanically induced surface instability of rubbers. The effect of surface tension is found to be critical in suppressing short-wavelength modes of surface instability, while the substrate confinement suppresses long-wavelength modes. With both surface tension and substrate confinement, an intermediate wavelength is selected at a critical swelling ratio for onset of surface instability. Both the critical swelling ratio and the characteristic wavelength depend on the initial thickness of the hydrogel layer as well as other material properties of the hydrogel. It is found that the hydrogel layer becomes increasingly stable as the initial layer thickness decreases. A critical thickness is predicted, below which the hydrogel layer swells homogeneously and remains stable at the equilibrium state. Finally, three-dimensional finite element models are developed to simulate swelling deformation of hydrogel lines. Depending on the aspect ratio of the cross section as well as the material properties of the hydrogel, two types of swell-induced instability patterns are envisaged, i.e., localized surface instability versus global buckling. / text

The characterization of the swell potential of expansive clay is complicated by the fact that traditional swell testing methods require an excessive amount of time for specimens to swell to their maximum heights. As a result, the practicing engineer has typically referred to correlations between swell potential and index properties rather than directly measuring swelling in a laboratory experiment. The purpose of this study is to evaluate an alternate testing method using a geotechnical centrifuge in an attempt to decrease the time required to evaluate the swell potential of expansive clays so that expermientally obtained swelling properties may be obtained within a reasonable time period. This study includes an experimental program involving a series of tests in which compacted clay specimens are flown in a cetrifuge and their heights are monitored as water infiltrates into them. / text

Stimuli-responsive hydrogels swell or contract in response to external pH, ionic strength or temperature, and are of considerable interest as pharmaceutical controlled release devices. Alginate, a linear polysaccharide consisting of mannuronic and guluronic acids, was used as starting material in semisynthesis of pH-responsive hydrogel. Linear alginate was chemically modified with di-aldehyde via acid-catalyzed acetalization, forming a tetrafunctional acetal-linked semisynthetic network alginate polymer (SNAP) with carboxylate moieties preserved as stimuli-responsive sensors. The kinetics of acetalization were found to undergo zero and second-order reaction with respect to di-aldehyde and alginate respectively. With the determined rate constant of 19.06 L•mole-1•s-1 at 40oC and activation energy of 78.58 kJ•mol-1, a proposed predictive reaction model may be used a priori to select reaction conditions providing specific polymer properties. Gel swelling and average pore size were then able to be kinetically or thermodynamically controlled between 80-1000 fold and 30 nm-1 m respectively. As a proof of concept, SNAP hydrogel was fine-tuned with specific swelling and pore sizes for absorptive encapsulation and controlled release of a wide spectrum of molecular sizes of proteins ranging between 1.3 to 546 kDa. SNAP hydrogels/granules demonstrated limited swelling in the simulated gastric environment, protecting proteins from enzymatic and acid degradation, while swelling in alkaline media, releasing active therapeutics in a simulated intestinal lumen (pH ~ 7.8), so is under the consideration as an oral delivery vehicle for protein therapeutics. A constitutive polyelectrolyte gel model based on non-Gaussian polymer elasticity, Flory-Huggins liquid lattice theory, and non-ideal Donnan-membrane equilibria was derived, to describe SNAP gel swelling in dilute and ionic solutions. The derived model accurately describes the SNAP hydrogel swelling in acid and alkaline solutions of wide range of ionic strength. The pore sizes of SNAP hydrogel were estimated by the derived model and were comparable to those determined experimentally by thermoporometry and protein diffusion. The derived model can characterize hydrogel structure such as molecular weight between crosslinks, or can be used as predictive model for swelling and pore size if gel structural information is known, and can potentially be applied to other point-link network polyelectrolytes such as hyaluronic acid gel. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2009-07-20 11:48:17.508

The hydraulic-mechanical behaviour of swelling clay is examined in this thesis. The study includes laboratory testing and numerical modeling which considers the influence of boundary conditions on the hydraulic-mechanical behaviour of a compacted unsaturated swelling clay soil. The laboratory testing component of this research consists of three (3) series of tests using a newly modified triaxial apparatus on which mechanical and hydraulic boundary conditions are altered during liquid infiltration. Mechanical boundary conditions range from constant volume to constant mean stress and also include constant stiffness which is a spring type boundary consisting of both volume expansion and mean stress increase. Hydraulic boundary conditions include drained and undrained flow into triaxial specimens. The numerical modeling component of this research includes the creation of a new capillary tube model for swelling clay materials and incorporates dynamic changes to the cross-sectional area for flow. Laboratory results are modeled using the capillary tube model, an empirical hydraulic model, D’Arcy’s Law, and in an elastic-plastic context for unsaturated soil. Results of the laboratory and numerical modeling components show that boundary conditions dominate the hydraulic-mechanical behaviour of unsaturated swelling clay soil during liquid infiltration. In particular, a mechanism is shown to explain how hydraulic conductivity of a swelling soil can decrease with increasing water content at constant void ratio. Finally hydraulic and mechanical behaviour cannot be considered separately in swelling materials due to the intimate relationship in their response.