An improved knowledge of wood material behavior in hot-pressing environments can provide the benefit of an increased understanding of material properties during the manufacture of wood-based composites as well as insight into the development of new processes and products which manipulate the viscoelastic nature of wood. Two specific areas where additional knowledge is needed are: the high temperature equilibrium moisture content (EMC) behavior and the moisture dependent softening behavior. EMC data was collected and desorption isotherms were generated for mature and juvenile wood of aspen, loblolly pine and yellow-poplar at 50 and 160°C. High temperature EMC behavior was found to be distinct from that at lower temperatures, and considerable differences between the isotherms for juvenile and mature wood were detected. Substantial thermal degradation was observed during desorption at 160 °C and found to be strongly influenced by relative humidity. The thermal softening behavior of wood was evaluated using dielectric thermal analysis (DETA) at moisture levels from 0 to 20 percent. Coincident in situ relaxations of hemicellulose and amorphous cellulose in the range of 20 to 200 °C were observed and found to exhibit the characteristics of a secondary (glass) transition. The moisture dependence of this transition was characterized, and differences in the observed Tg were detected between juvenile and mature wood. Time-temperature superposition was also shown to be applicable to the wood-water system. / Ph. D.

Cellulose nanomaterials (CNMs) have been widely studied for their potential as sustainable fillers in polymer nanocomposites, optical responsiveness in suspensions and thin films, and their orientation-dependent liquid crystalline behavior in suspensions. Cellulose nanocrystals (CNCs) have seen a particular prominence due to their versatility across a breadth of applications. The unique structure of CNCs, represented as nanoscale rods with a slight twist, provides for their self-assembly into liquid crystalline phases when their concentration is increased and can be used to generate iridescent materials with tunable wavelengths. Further, CNCs are often used as fillers in nanocomposites, due to their high single crystal Young's modulus, achieving vast enhancements in stiffness when incorporated above a critical concentration where a percolating network is formed. The breadth of applications for CNCs strongly depend not only on their crystalline structure, but crucially on the interactions between particles. These interactions are well-known, yet a complete understanding to enable the full exploitation of the properties attainable in CNC-based materials is lacking. The principal emphasis of this dissertation lies in further improving our comprehension of the interactions between CNCs across a variety of applications such that their full potential can be achieved. A review of the current research of CNC-based materials is provided to guide the discussion herein. Interparticle interactions are studied in aqueous suspensions of CNCs in evaporating sessile droplets. This system provides a complex interrelationship between mass, heat, and momentum transport which collectively provide a change in the local CNC concentration as a function of time. CNC interactions can be controlled throughout the evaporation process as a result of these local concentration variations. We implement a novel approach using time-resolved polarized light microscopy to characterize the evolution of these particle interactions via the orientation of CNCs as a function of CNC concentration and droplet volume. Ultimately, boundary interactions at the leading edge of the contact line during evaporation was found to drive a cascade of local CNC interactions resulting in alignment post-deposition. Computational analysis evaluated the influence of evaporation-induced shear flow during evaporation. Orientation was found to be independent of the bulk fluid flow, corroborating the importance of interparticle interactions on the ensuing alignment of CNCs. Characterization of an evaporating droplet of initially liquid crystalline suspension of CNCs verified the simulations which predicted that orientation was not coupled with entrainment. Finally, the multiple modes of orientation showed that local control over CNC properties can be realized through governance of the interactions between CNCs. The interactions of CNCs in polymer nanocomposites were also studied for the development of smart materials which can adapt their properties in response to external stimuli. A well-known example of this phenomena is found when CNCs are introduced as fillers in thermoplastic polyurethanes (TPUs) above a critical concentration required to achieve percolation. The interactions between CNCs in the percolating network provide a strong enhancement to the modulus of these materials. However, these materials soften upon exposure to water following the disruption of inter-CNC hydrogen bonding by the diffusing water molecules, as prevailing theories suggest. CNCs simultaneously enhance water transport into hydrophobic matrices. Thus, a complete understanding of the interrelationship between the mass transport and mechanical performance can facilitate the development of humidity sensing or shape memory materials which operate as a result of the interactions between CNCs inside of a polymer matrix. Despite an increase in the equilibrium water uptake with increasing CNC concentration, a decrease in the apparent diffusivity of water within the nanocomposites was observed as a result of swelling of the bulk polymer. Additionally, we developed a modification to the commonly used percolation model to predict the time-dependent evolution of storage modulus during water-induced softening. We found that the solvent mass transport can be directly coupled to the mechanical integrity of the percolating network of CNCs by evaluating the hydrogen bonding state of the network as a function of time. Finally, a novel nanocomposite filler comprised of CNCs and 2,2,6,6- tetramethylpiperidine 1-oxyl (TEMPO) oxidized cellulose nanofibrils (TOCNFs) was prepared through solution casting to improve the mechanical performance of the individual reinforcements alone. The physical interaction length is increased by incorporating CNMs of different length scales resulting in increased tensile strength and elongation. Further, the morphology, evaluated with polarized light microscopy, atomic force microscopy, and simulated with dissipative particle dynamics, revealed the combined fillers exhibit a cooperative enhancement between CNMs. Characterization of the crystallinity through x-ray diffraction confirmed the interactions occur primarily between the crystalline domains of each material. Accordingly, the combination of CNMs resulted in nanocomposite fillers which can be implemented such that the weak interfaces with polymer matrices can be bridged with fillers providing reinforcement over a broader length scale. / Doctor of Philosophy / Cellulose nanocrystals (CNCs) are sustainable and biorenewable nanoparticles derived from cellulose. These materials have been widely studied and are commonly used among a plethora of applications such as in reinforcing fillers in polymer nanocomposites, optically responsive materials that can be used in packaging or anti-counterfeiting technologies, as well as in suspension modifiers for skin care products. These techniques tune the interactions between individual CNCs to modify the behavior of the bulk material. The specific interactions are well-known, yet a complete understanding of the influence of these interactions resulting in the utility of CNC-based materials in various applications is lacking. The principal emphasis of this dissertation lies in further improving our comprehension of the interactions between CNCs across a variety of applications such that their full potential can be achieved. Interactions between CNCs were investigated in three systems comprising of a range of typical use cases for CNC-based materials. The behavior of CNCs was examined in evaporating droplets of aqueous suspensions. These materials exhibited a change in orientation in the final deposit which is dependent on variations in local CNC concentration during drying. These concentration changes describe the relative strength of interactions between CNCs which ultimately influences the final alignment of these materials. Further, these interactions provide a pathway to deposit a controlled orientation of CNCs on a substrate which can be utilized for optically responsive materials or serve as templates for other orientation-dependent materials. CNCs were also incorporated into a thermoplastic polyurethane (TPU) matrix to provide increased stiffness. In these composites, water preferentially interacts with CNCs preventing the nanoparticles from interacting with one another. As water is absorbed, these materials soften as a result of the reduced interactions between CNCs. We investigated the influence of dynamically changing CNC interactions on the mechanical performance of these materials during water absorption and developed an analytical model to describe the observed softening behavior. Finally, CNCs were combined with 2,2,6,6- tetramethylpiperidine 1-oxyl oxidized cellulose nanofibers (TOCNFs) and cast into thin films. The mechanical properties of these differently sized, yet chemically similar, nanoparticles were compared as a function of CNC composition. A cooperative enhancement of the ultimate tensile strength and elongation was observed at low CNC loadings where CNCs and TOCNFs were found to self-organize during casting in a mutually beneficial manner.

Aluminum salts are used as the primary coagulants in the majority of United States drinking water treatment plants. Despite decades of practical experience, there are important knowledge gaps regarding the effects of residual Al on distribution system materials as well as specific types of solids formed. The first phase of this work examined the formation of aluminosilicate deposits in copper and lead pipes using water from Denver, Colorado. It was anticipated was that these deposits could form barrier films on the pipe, protecting it from corrosion. However, the deposits had slightly detrimental effects on leaching of metal to water, and higher levels of aluminosilicates could further worsen corrosion by-product release. The second phase of work attempted to extend understanding of aluminum solubility controls by accounting for effects of sulfate and formation of solids other than Al(OH)₃ during water treatment. Sulfate was found to destabilize small Al(OH)₃ colloids resulting in agglomeration into larger flocs from pH 5.0-6.2 . At pH 9.0 and above, Al-Mg, Al-Mg-Si and Al-Si solids were discovered to control Al solubility, while also having significant impacts on the precipitation of calcite in the presence of silica and overall softening effectiveness. This could be of considerable importance to water treatment practice. These solids also had some potential for removal of arsenic, TOC and boron. / Master of Science

Rubber-like materials are submitted to cyclic loading conditions in various applications. Fillers are always incorporated within rubber compounds. They improve the mechanical properties but induce a significant stress-softening under cyclic loadings. The physical source of the softening is not yet established and its modeling remains a challenge. For a better understanding of the softening, filled rubbers are submitted to cyclic loadings. In order to quantify the effects of the loading intensity and the number of cycles, original methods are proposed to characterize the softening. To study the influence of the material microstructure on the softening, compounds with various compositions are considered.Non proportional tensile tests including uniaxial and biaxial loading paths are applied in order to highlight the softening induced anisotropy. Such unconventional experimental data are used to provide a general criterion for the softening activation. A constitutive modeling grounded on a thorough analysis of experimental data is proposed. The model is based on a directional approach. The Mullins softening is accounted for by the strain amplification concept and is activated by a directional criterion. The model ability to predict non proportional softened material responses is demonstrated

Les applications pour lesquelles des élastomères sont soumis à des sollicitations cycliques sont nombreuses. Des charges sont généralement utilisées afin d'améliorer leurs propriétés, cependant, elles induisent également un adoucissement important de la contrainte lors de sollicitations cycliques. A ce jour, les phénomènes physiques conduisant à l’apparition de cet adoucissement ne sont pas clairement établis et sa modélisation demeure une difficulté majeure.Afin d'étudier l'adoucissement, des élastomères chargés sont soumis à des chargements cycliques. Des méthodes de caractérisations originales sont proposées afin de quantifier les effets de l'intensité du chargement et du nombre de cycles. Pour faire le lien avec la microstructure du matériau, plusieurs mélanges de compositions différentes sont utilisés. Des chargements non proportionnels de traction uniaxiale et biaxiale sont appliqués afin de mettre en évidence l'anisotropie induite par l'adoucissement. Ces données expérimentales non conventionnelles sont utilisées afin de définir un critère général pour l'activation de l'adoucissement Mullins. Une loi de comportement fondée sur une analyse approfondie des données expérimentales est proposée. La modélisation est basée sur une approche directionnelle. L'adoucissement Mullins est modélisé en utilisant le concept d'amplification de la déformation et son activation est pilotée par un critère directionnel. La capacité du modèle à prédire les réponses d'un matériau ayant subit un historique de chargement non proportionnel est validée / Rubber-like materials are submitted to cyclic loading conditions in various applications. Fillers are always incorporated within rubber compounds. They improve the mechanical properties but induce a significant stress-softening under cyclic loadings. The physical source of the softening is not yet established and its modeling remains a challenge. For a better understanding of the softening, filled rubbers are submitted to cyclic loadings. In order to quantify the effects of the loading intensity and the number of cycles, original methods are proposed to characterize the softening. To study the influence of the material microstructure on the softening, compounds with various compositions are considered.Non proportional tensile tests including uniaxial and biaxial loading paths are applied in order to highlight the softening induced anisotropy. Such unconventional experimental data are used to provide a general criterion for the softening activation. A constitutive modeling grounded on a thorough analysis of experimental data is proposed. The model is based on a directional approach. The Mullins softening is accounted for by the strain amplification concept and is activated by a directional criterion. The model ability to predict non proportional softened material responses is demonstrated

In this research, we aimed to develop thin-film devices on a polymer substrate and an alternative 3D-printed device with macroelectrodes for treating gastrointestinal (GI) conditions. First, the fabrication of thin-film devices was demonstrated on a softening thiol-ene/acrylate polymer utilizing titanium nitride (TiN) as electrode material. This was achieved by utilizing cleanroom fabrication processes such as photolithography, wet and dry etching. The functionality of the device was shown by performing electrochemical characterization tests, mainly cyclic voltammetry, electrochemical impedance spectroscopy, and voltage transient. We synthesized a novel thiol-ene/acrylate polymer based on 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATATO), trimethylolpropanetris (3-mercaptopropionate) (TMTMP), and polyethylene glycol diacrylate (PEGDA). We show that this stretchable shape memory polymer substrate is well suited for cleanroom processes. Finally, for the high throughput of the wearable devices with electrodes size 10 mm in diameter, we implemented single electrode fabrication using printed circuit boards (PCBs) and depositing gold (Au) and TiN on the plated side of PCBs utilizing the sputtering tool. This step was followed by the assembly of those single electrodes on the flexible 3D printed device. We showed that the TiN electrode material performed better in terms of charge storage capacity and charge injection capacity than the widely used stainless steel electrode material for wearables.

In recent years, the excessive specific conductance (SC) of Appalachian coal mining runoff waters has become a parameter of concern with the EPA due to its negative effect on aquatic life and water quality. In order to comply with the EPA guidance suggesting an effluent SC of 500 µS/cm, the Appalachian Research Initiative for Environmental Science (ARIES) Center at Virginia Tech requested that testing be done to determine the most effective technologies for reduction of SC. Runoff water was collected from two sites in southwestern Virginia and characterized to determine the source of SC in the water. The main contributing ions were determined to be Na⁺, Mg²⁻, Ca²⁺, and SO₄²⁻. Testing was performed to assess the possibility of using the speciation software, MINEQL+, with a set of empirical equations which predict SC using ionic composition for natural waters with a low to medium SC. The physicochemical treatment methods tested were ion exchange, excess lime-soda softening, and the Cost Effective Sulfate Removal (CESR) process. Both cation (H⁺ exchanger) and anion (Cl⁻ exchanger) exchange media were tested separately in batch reactors, which resulted in a higher effluent SC than initial SC. The softening method investigated, excess lime-soda softening, also resulted in increased SC levels because non-carbonate hardness levels were high and carbonate concentrations were low. The CESR process successfully lowered SC from 1,500-2,500 µS/cm to below the proposed EPA limit of 500 µS/cm. The success of this process was due to its ability to remove more than 85% of the calcium, magnesium, and sulfate from the water, which together accounted for more than 90% of ions in the source water. / Master of Science / In recent years, mining activities have generated large amounts of unweathered rock from blasting. This rock, which is often stored in valleys near the blasting sites, releases salts into water that passes over the rocks when it rains. The salty water flows into nearby streams populated with freshwater fish and other organisms that suffer when their environmental conditions are changed. The Appalachian Research Initiative for Environmental Science (ARIES) Center at Virginia Tech requested that testing be done to determine which engineering techniques would be most effective for reduction of these salts. The amount of salt in the water is measured by specific conductance (SC), which measures how well the water conducts electricity. Testing was also done to determine which types of salts were in the water; the results showed that the largest contributors were sodium, magnesium, calcium, and sulfate ions. Three engineering techniques were investigated for removal of the contributing ions: ion exchange, softening, and the Cost Effective Sulfate Removal (CESR) process. Two types of ions exchange, one that targeted the positive ions (cation exchange) and one that targeted the negative ions (anion exchange), were tested. Both forms of ions exchange raised the SC to a higher concentration than the original water. Softening had a similar effect because one of the chemicals added during the process released additional sodium ions into the water. Finally, the CESR process was able to successfully reduce the SC below the limit proposed by the EPA as safe for stream life. This was due to the large reduction of three of the four major ions that was achieved during the CESR process.

Passive detrusor smooth muscle exhibits both viscoelastic softening and strain softening. Strain softening is a loss of stiffness following a stretch to a longer length and is reversible upon muscle activation. Because of this behavior, steady state passive force in detrusor is not constant for a given muscle length and can be adjusted by an intracellular mechanism. Thus, passive detrusor exhibits adjustable passive stiffness. Existing three-component mechanical models for muscle, the Kelvin and Voigt, are insufficient to display this characteristic. The goal of this thesis is to develop a new biomechanical model for passive force in detrusor by adding additional elements to the Kelvin or Voigt models. Eight mechanical characteristics of detrusor are identified from the literature and with three new experiments, and a novel adjustable passive stiffness model for smooth muscle is proposed. Simulations are performed to demonstrate that the model qualitatively exhibits each of the eight tissue characteristics.

Two Systems were designed. The first permits tunable on-demand softening of a hydrogel network. The second permits reversible on demand ligand exchange within a hydrogel network. Both means were shown to be cytocompatible and their uses demonstrated in cell culture of mesenchymal stem cells and 3T3 fibroblast cells.

Emotionally Focused Couple Therapy (EFT; Johnson, 2004) addresses relationship distress by facilitating the development of new patterns of interaction between partners. These new patterns of interaction are based on partners' vulnerable acknowledgement and expression of attachment needs. Partners' engagement in these new patterns of interaction is thought to improve their relationship-specific attachment bond. Although previous studies have shown EFT to result in excellent relationship satisfaction outcomes (Johnson, Hunsley, Greenberg & Schindler, 1999), research had yet clearly to demonstrate if and how EFT facilitates increases in partners' relationship-specific models attachment security over the course of therapy. To address this research gap, the current study employed Hierarchical Linear Modelling (HLM; Singer & Willet, 2003) to investigate the pattern of change in couples' (n=32) self-reported relationship satisfaction and relationship-specific attachment over the course of EFT. Couples reported significant linear increases in their relationship satisfaction and significant linear decreases in their relationship-specific attachment avoidance over the course of therapy. Couples who completed the blamer-softening therapeutic change event (n=16) demonstrated significant linear decreases in their relationship-specific attachment anxiety after completing this event. Decreases in relationship-specific attachment anxiety predicted increases in couples' relationship satisfaction over the course of therapy. Couples also demonstrated significant increases in the security of their pre-post-therapy relationship-specific attachment behaviour, as coded Secure Base Scoring System (Crowell, Treboux, Gao, Fyffe, Pan & Waters, 2002). The current study also used HLM (Singer & Willet, 2003) to examine how the completion of blamer-softening impacted softened couples' relationship-specific attachment anxiety, and whether the completion of blamer-softening had a similar impact on softened couples' relationship-specific attachment avoidance and relationship satisfaction. Softened couples reported an immediate increase in relationship satisfaction and immediate decrease relationship-specific attachment avoidance at the softening session. Further, softened couples' post-softening decreases in relationship-specific attachment anxiety were initially preceded by an increase at the softening session. These results provided an understanding of how EFT leads to increases in couples' relationship-specific attachment security. These results provide support for the use of attachment theory in the treatment of relationship distress, and also provide an illustration of how attachment can shift over the course of a therapeutic intervention.