This thesis aims to improve the performance of latex-based pressure-sensitive adhesives (PSAs). PSA performance is usually evaluated by tack, peel strength and shear strength. Tack and peel strength characterize a PSA’s bonding strength to a substrate while shear strength reflects a PSA’s capability to resist shear deformation. In general, increasing shear strength leads to a decrease in tack and peel strength. While there are several commercial PSA synthesis methods, the two most important methods consist of either solvent-based or latex-based techniques. While latex-based PSAs are more environmentally compliant than solvent-based PSAs, they tend to have much lower shear strength, at similar tack and peel strength levels. Therefore, the goal in this thesis was to greatly improve the shear strength of latex-based PSAs at little to no sacrifice to tack and peel strength. In this study, controlling the polymer microstructure of latexes or their corresponding PSA films was used as the main method for improving the PSA performance. The research was sub-divided into four parts. First, the influence of chain transfer agent (CTA) and cross-linker on latex polymer microstructure was studied via seeded semi-batch emulsion polymerization of butyl acrylate (BA) and methyl methacrylate (MMA). Three techniques were used to produce the latexes: (1) adding CTA only, (2) adding cross-linker only, and (3) adding both CTA and cross-linker. It was found that using CTA and cross-linker simultaneously allows one to expand the range of latex microstructural possibilities. For example, latexes with similar gel contents but different Mc (molecular weight between cross-links) and Mw (molecular weight of sol polymers) could be produced if CTA and cross-linker concentration are both increased. However, for the corresponding PSAs with similar gel contents, the relationship between their polymer microstructure and performance was difficult to establish as almost all of the medium and high gel content PSAs showed very low tack and peel strength as well as extremely large shear strength readings. In the second part of this thesis, in order to improve the tack and peel strength of medium and high gel content PSAs, the monomer composition and emulsifier concentration were varied. It was found that changing the monomer mixture from BA/MMA to BA/acrylic acid (AA)/2-hydroxyethyl methacrylate (HEMA) while simultaneously decreasing emulsifier concentration dramatically improved the corresponding PSAs’ shear strength as well as tack and peel strength. The addition of polar groups to the PSA increased its cohesive strength due to the presence of strong hydrogen bonding; meanwhile, PSA films’ surface tension increased. In the third part, two series of BA/AA/HEMA latexes were generated by varying the amounts of CTA either in the absence or presence of cross-linker. The latexes produced in the absence of cross-linker exhibited significantly larger Mc and Mw compared to their counterparts with similar gel contents prepared with cross-linker. The PSAs with the larger Mc and Mw showed much larger shear strengths due to improved entanglements between the polymer chains. In the final part of the thesis, the performance of the BA/AA/HEMA PSAs was further improved by post-heating. Compared with original latex-based PSAs with similar gel contents, heat-treated PSAs showed not only significantly improved shear strengths, but also much larger tack and peel strengths. The different shear strengths were related to the PSAs’ gel structures, which were discrete in the original PSAs but continuous in the heat-treated PSAs. The improved tack and peel strengths were related to the PSA films’ surface smoothness. During the post-heating process, the PSA polymer flowed, resulting in much smoother surfaces than the original PSA films. In addition, the effect of post-heating was related to the polymer microstructure of the untreated PSAs. Decreasing the amount of very small or very big polymers or simultaneously increasing Mc and Mw could lead to post-treated PSAs with significantly better performance. Moreover, it was found that by optimizing the polymer microstructure of the original latex-based PSAs, it was possible to obtain a treated PSA with similar or even better performance than a solvent-based PSA with similar polymer microstructure. Our original objective was surpassed: in two cases, not only was shear strength greatly improved, but so were tack and peel strength due to the simultaneous modification of PSA bulk and surface properties.

Rheology modifiers such as hydrophobically-modified ethoxylated urethane (HEUR)thickeners are included in waterborne latex coatings to optimize shear-rate dependent viscosity and other rheological properties. While these HEUR polymers are commonly used in industry, the complex chemical interactions that contribute to rheological properties are still not completely understood. Prior work in this area has focused on understanding latex-HEUR and latex-surfactant-HEUR interactions that affect rheological properties. Additionally, studies have been previously conducted to understand the relaxation mechanisms of complex interactions present in HEUR-thickened waterborne latex coatings under various dynamic conditions. The objective of this work is to extend the experimental work to fully-formulated coatings and determine the effects of additional ingredients in a fully-formulated system. Coating formulations were prepared with a target 90 KU (Kreb Units) viscosity, having 0.23wt% HEUR. The pigment volume concentration (PVC) and non-volatiles by volume (NVV) were kept constant at 19.87% and 30.47%, respectively. An analysis of phase stability (presence or absence of syneresis), flow sweep (10-2 to 103 s-1), oscillatory strain (10-2 to 102 %), and oscillatory frequency (10-2 to 102 Hz) data was carried out in an attempt to determine connections among these properties. Furthermore, brief comparisons were made with previous results on latex-HEUR and latex-HEUR-surfactant systems that utilized the same HEUR thickener and latex used in this study. In the fully-formulated system, 0.23wt% HEUR was found to be in excess of what is needed to saturate latex surfaces. This HEUR level is less than half of the level needed to saturate latex surfaces in simpler latex-HEUR systems in previous studies. Fully-formulated coatings, in addition to having TiO2 and other ingredients are more crowded than the previous systems. It appeared that a depletion flocculation mechanism dominated at low surfactant concentrations for fully-formulated systems in this study as evident from syneresis; large HEUR aggregates appear to build enough osmotic pressure to drive aggregation of latex and pigment particles resulting in depletion flocculation. At increasing surfactant levels, the depletion flocculation mechanism was negated allowing the associative HEUR bridge networks to dominate and stabilize the system. Phase stability for fully-formulated systems in this study were associated with Newtonian viscosity plateaus on flow sweeps, strain hardening on oscillatory strain sweeps, and formation of high frequency moduli plateaus in frequency sweeps. Further increase of surfactant concentration appeared to disrupt the stable latex-HEUR network due to competitive adsorption of surfactant on latex particles, resulting in syneresis from bridging flocculation. Possible correlations between phase stability and high relaxation times were seen, although further analysis of relaxation time data and simulations will need to be carried out to better understand the behavior of HEUR in fully-formulated systems.

ABSTRACT THE EFFECTS OF COLOR CONCENTRATES ON THE RHEOLOGY OF TINT BASES Douglas James Herrick Waterborne coatings are formulated with a number of different ingredients; water, latex polymers, pigments, surfactants, dispersants, defoamers, biocides, coalescing aids, and rheology modifiers or thickeners. Rheology modifiers are necessary in order to improve the physical properties of the coating before, during, and after application to a substrate. There are two kinds of rheology modifiers used in waterborne coatings; associative thickeners and non-associative thickeners. Coatings formulated with associative thickeners are quite sensitive to coating variations; the slightest change in the formulation has profound effects on the rheology of the coating. The opposite is true for coatings formulated with non-associative thickeners, where the rheology of the coating is not affected by minor changes in the formulation. The rheological properties of coatings are most influenced by the latex, thickener, and surfactant components of the coating. Previous studies have shown that the most ideal balance of rheological properties come from using associative thickeners. However, when waterborne coatings with associative thickeners are tinted with colorants containing high levels of surfactants they exhibit a significant decrease in viscosity. This change in viscosity results in poor sag resistance, poor brush loading, and may also cause a reduction in tint strength of the coating. In this work, the effect of tinting paints with six different colorants on the viscosity of the paint was studied for four different paint formulations: a pastel base and a deeptone base formulated with hydroxyethylcellulose (HEC-type) non-associative thickeners, and a pastel base and a deeptone base formulated with hydrophobically-modified, ethoxylated polyurethane (HEUR-type) associative thickeners. Gloss values and tinting strengths were obtained in accordance with ASTM methods D523-08 and D4838-88. In addition, dynamic stress and frequency sweeps were taken in order to study the effect of colorant addition on the viscoelastic properties of each sample. Colorant addition had little to no effects on the viscosity of the bases formulated with HEC thickeners, while there was a dramatic decrease in viscosity upon colorant addition to the bases with HEUR thickeners. Similar results were observed in the viscoelastic property analysis: little to no effects on the elastic and viscous moduli was seen with the tinted coatings formulated with the non-associative thickeners, while both the elastic and viscous moduli decreased for the coatings formulated with associative thickeners. A few of the deeptone bases showed increased moduli upon tinting compared to the parent deeptone base. The addition of colorant resulted in a decrease in tinting strength and an increase in gloss for those samples with associative thickeners, while the opposite was found for those samples with non-associative thickeners.

Cemented paste backfill (CPB) technology is widely used in the mining industry as an effective means of tailings disposal. CPB is a mixture of tailings, binder, water, and additional admixtures when required. It is prepared in a mixing plant on the ground surface and then transported into the mine cavities through pipelines either by gravity and/or using pumps. To ensure efficiency during transportation and avoid pipe clogging (which can cause unnecessary delays and loss of productivity), fresh CPB must have sufficient flowability. To achieve that, high-range water reducing admixtures, also known as superplasticizers, are usually added to the CPB during mixing. These admixtures are widely used in the construction industry due to their ability to improve flowability without undermining other important engineering properties. However, their influence on the rheology, mechanical strength and environmental performance (reactivity and permeability) of CPB is not fully understood. Thus, experimental studies were conducted to investigate the effects of superplasticizers on the performance properties of cemented paste backfill at different curing temperatures. Yield stress and viscosity of fresh CPB cured for 0, 1, 2, and 4 hours were measured using a vane shear device and a Brookfield Viscometer respectively. Unconfined compressive strength (UCS) of samples cured for 1, 3, 7, and 28 days was determined in accordance with ASTM - C39. Superplasticizer contents were varied as 0%, 0.125%, and 0.25% of the total weight of the CPB. Preparations and curing of the specimens were performed at controlled conditions of 2, 20, and 35 °C to investigate the effect of ambient or curing temperatures. To have a better understanding of the environmental performance of CPB containing superplasticizer, reactivity, and hydraulic conductivity up to 90 days of curing were also investigated. The reactivity was measured using oxygen consumption test while hydraulic conductivity was measured using flexible wall permeability test. Microstructural analyses (thermogravimetric analyses, X-Ray diffraction, and mercury intrusion porosimetry) and monitoring tests (pH, zeta potential, electrical conductivity, and matric suction) were carried out to understand the principles behind the changes of the observed properties. The obtained results show that superplasticizer dosage and temperature variation have significant effects on the rheology, strength development, hydraulic conductivity and reactivity of the CPB. The polycarboxylic ether-based superplasticizer significantly reduces the yield stress and viscosity by creating strong electrostatic repulsion between the solid particles in the CPB and by steric hinderance. The CPB containing the superplasticizer remains fluid for longer period (as compared with the CPB without superplasticizer) due to the retardation of binder hydration. However, high curing temperature induces faster cement hydration, which thickens the fresh CPB. The unconfined compressive strength (UCS) of the CPB containing superplasticizer was observed to be lower in the early age (up to 7 days), which is also attributed to retardation of the binder hydration. At later ages, the superplasticizer improves the mechanical strength as the binder hydration accelerates and the solid particles self-consolidate. Coupled THMC processes in the CPB showed the role played by the changes in electrical conductivity, volumetric water content, matric suction, and temperature on the development of mechanical strength of the CPB containing superplasticizer. Similarly, addition of the superplasticizer in the CPB decreases both the hydraulic conductivity and reactivity of CPB, thus improving its environmental performance. The improvement is largely attributed to enhanced binder hydration and self-consolidation which decrease the porosity of the CPB. Increasing the curing temperature was found to magnify the improvement of the CPB properties by inducing faster binder hydration. The findings from this study will undoubtedly inform the design of CPB structure with better mechanical stability and environmental performance.

Rheological properties of idealised models which exhibit all the non-Newtonian flow phenomenology commonly seen in dense suspensions are investigated by particulate-dynamics computer-simulations. The objectives of these investigations are: (i) to establish the origins of various aspects of dense suspension rheology such as shear-thinning, shear thickening and dilatancy; (ii) to elucidate the different regions of a typical dense suspension rheogram by examining underlying structures and shear induced anisotropies in kinetic energy, diffusivity and pressure; (iii) to investigate the scaling of the simplest idealised model suspension; i.e. the hard-sphere model in Newtonian media and its relationship to the isokinetic flow curves obtained through non-equilibrium molecular dynamics (NEMD) simulations; (iv) to preliminarily determine the effect of perturbations present in all real colloidal suspensions, namely particle size polydispersity and a slight 'softness' of the interparticle potential. Non-equilibrium isokinetic simulations have been performed upon ;systems of particles interacting through the classical hard-sphere potential and a perturbation thereof, in which the hard-core is surrounded by a 'slightly soft' repulsive skin. The decision to base the present work upon isokinetic studies was made in order to obtain a better under- standing of suspension rheology by making a direct connection with previous NEMD studies of thermal systemst(93). These studies have shown that the non-linear behaviour exhibited by these systems under shear is atttributable to a shear-induced perturbation of the equilibrium phase behaviour. The present study shows this behaviour to correspond to the high shear region of the generalised suspension flow curve. / Science and Engineering Research Council and Unilever Research

Asphaltenic crude oil is a complex fluid containing various components with different chemical properties. When it comes in contact with water, its polar components adsorb at the oil/water interface, reducing the interfacial tension and eventually developing viscoelastic films. The interfacial films impact emulsion stability and adhere to the oil-bearing reservoirs rocks, altering their wettability and thus hindering oil mobilization. Here, we investigate the formation of crude oil/water interfacial films. We measure both the time-dependent shear and extensional interfacial rheology moduli, and we relate it to the chemical composition of the films, highlighting the role of polar aromatic molecules in film formation. Varying chemical composition of the aqueous phase, we show that the properties of the interfacial films depend not only on the concentration of ionic species in water but also on their chemical nature. In particular, we highlight the role of sulfate salt in promoting interfacial viscoelasticity and in altering the composition of fully developed films. To study the rock/fluid interaction, we fabricate mixed-wet capillaries with angular cross-sections inspired by the naturally occurring primary drainage of pore-filling brine by invading crude oil. After employing our novel coating procedure, we experimentally investigate water invasion in mixed-wet capillaries and compare it with predictions of dynamic and quasi-static (Mayer-Stowe-Princen (MSP)) meniscus-invasion models. None of the dynamic models built for uniformly-wet pores can fully describe our experimental data in mixed-wet capillaries. However, the experimental results agree with predictions of MSP theory. To our knowledge, this is the first direct experimental validation of MSP theory under mixed-wet conditions. We confirm the possibility of spontaneous piston-type imbibition with high ($> 90^{\circ}$) advancing contact angles into mixed-wet pores, given that the contact angle is lowered below a critical value that is a function of pore geometry and residual water saturation. In oil reservoirs, injection of specific brines would be required to change the contact angle to values below the imbibition threshold. Finally, we extend our study and introduce a powerful 3D high-speed laser imaging of dynamic fluid flow in angular capillaries and investigate its capability to capture non-equilibrium shapes of fluid interfaces.

The traditional method of modifying the properties of polymeric materials is their filling with mineral particles. The use of synthetic nano-sized fillers in comparison with coarse-dispersed natural ones is very promising due to the large specific surface of nanomaterials. The study of such compositions by rheometric methods makes it possible to assess the structural changes that occur when nanoparticles are introduced into the polymer solution. In this study, studies were carried out in the mode of harmonic oscillations with solutions of cellulose acetate DAC in DMSO in the concentration range of 5-20% by weight. polymer containing 3 and 5% of the mass. amorphous silica. The experiments were carried out on a Haake MARS rotary rheoscope with a working cone-plane unit in the voltage range of 0.1-100 Pa and frequencies of 0.1-100 Hz at temperatures of 298, 318 and 338 K. Measurements of the frequency dependences of the complex viscosity, elastic modulus and loss modulus were performed at a constant voltage of 10 Pa. It was found that the DAC solutions in DMSO are non-Newtonian fluids that exhibit elastic properties with a DAC content of more than 10% by weight. It is shown that the concentration of AC, at which the solution begins to show elastic properties, decreases with increasing concentration of aerosil. For the DAC-DMSO-Aerosil system, there is a temperature-concentration range in which the elastic modulus is greater than the loss modulus, that is, the introduction of aerosil leads to a significant change in the system behavior during deformation. According to the data obtained, the concentration dependences of the enthalpies of activation of the flow of DAC solutions in DMSO and DAC-DMSO-aerosil systems were calculated. / Традиционным методом модификации свойств полимерных материалов является их наполнение минеральными частицами. Применение синтетических наноразмерных наполнителей по сравнению с грубодисперсными природными является очень перспективным из-за большой удельной поверхности наноматериалов. Исследование таких композиций реометрическими методами дает возможность оценить структурные изменения, происходящие при введении наночастиц в раствор полимера. В данной работе исследования проводили в режиме гармонических колебаний с растворами ацетата целлюлозы ДАЦ в ДМСО в диапазоне концентраций 5-20% масс. полимера, содержащих 3 и 5 % масс. аморфного диоксида кремния. Опыты проводили на ротационном реоскопе Haake MARS с рабочим узлом типа конус-плоскость в диапазоне напряжений 0,1 -100 Па и частот 0.1-100 Гц при температурах 298, 318 и 338 К. Измерения частотных зависимостей комплексной вязкости, модуля упругости и модуля потерь проводили при постоянном напряжении 10 Па. Обнаружено, что растворы ДАЦ в ДМСО являются неньютоновскими жидкостями, проявляющими упругие свойства при содержании ДАЦ более 10%масс. Показано, что величина концентрации АЦ, при которой раствор начинает проявлять упругие свойства, уменьшается с увеличением концентрации аэросила. Для системы ДАЦ-ДМСО-аэросил существует температурно- концентрационный диапазон, в котором модуль упругости больше модуля потерь, то есть введение аэросила приводит к существенному изменению поведения системы при деформировании. По полученным данным рассчитаны концентрационные зависимости величин энтальпий активации течения растворов ДАЦ в ДМСО и систем ДАЦ-ДМСО-аэросил.

Получены композиции на основе альгината натрия и фторкаучука СКФ-26, наполненные частицами магнитных материалов: Ni, Fe, Fe3O4, SrFe12O19, MQP-Системы изучены методами изотермической микрокалориметрии, механического динамического анализа и магнитометрии. Методом микрокалориметрии измерены энтальпии смешения компонентов композитных пленок и рассчитаны значения предельной энтальпии адгезии полимерных матриц к поверхности магнитных порошков. Показано, что для систем на основе СКФ-26 энтальпия адгезии является отрицательной величиной, абсолютные значения которой увеличиваются в ряду Ni-Fe-Fe3O4. В системах альгинат натрия/Ni и альгинат натрия/Fe реализуется атермическое смешение, а в системах альгинат натрия/ФС и альгинат натрия/ Fe3O4 – экзотермическое. С помощью метода ДМА получены концентрационные зависимости динамических модулей потерь и упругости, а также угла сдвига для систем на основе раствора альгината натрия и магнитных порошков Fe, Fe3O4 и SrFe12O19 при частоте 1 Гц и напряжении 1 Па. Обнаружено, что с увеличением концентрации частиц неорганического вещества в суспензиях наблюдается увеличение динамических модулей и уменьшение угла сдвига, причем для суспензии, содержащей магнетит, характер течения не меняется. При течении суспензий, содержащих порошки Fe или SrFe12O19 начинают преобладать упругие свойства. Методом магнитометрии для систем СКФ-26/Ni и CКФ-26/Fe были получены петли магнитного гистерезиса в диапазоне напряженности магнитного поля от -15 кЭ до 15 кЭ. Показано, что с ростом содержания порошка в композите остаточная намагниченность и намагниченность насыщения не меняются, а коэрцитивная сила уменьшается, т. е. на размагничивание магнитного материала требуется меньше энергии. Методом магнитометрии получены данные для систем на основе альгината натрия, содержащих 30% Fe или Fe3O4. Обнаружено, что для системы альгинат натрия/Fe значения намагниченности насыщения для композита больше, чем для индивидуального порошка Fe, что может быть обусловлено упорядочением спинов на поверхности магнитных частиц при формировании композита. / Compositions based on sodium alginate and SKF-26 fluoro-rubber filled with particles of magnetic materials: Ni, Fe, Fe3O4, SrFe12O19, MQP-systems were studied by isothermal microcalorimetry, mechanical dynamic analysis and magnetometry. The enthalpy of mixing of composite film components was measured by microcalorimetry and the values of the limiting enthalpy of adhesion of polymer matrices to the surface of magnetic powders were calculated. It is shown that for systems based on SKF-26, the enthalpy of adhesion is a negative value, the absolute values of which increase in the series Ni-Fe-Fe3O4. In the sodium alginate/Ni and sodium alginate/Fe systems, athermic mixing is realized, and in the sodium alginate/FS and sodium alginate/ Fe3O4 systems, exothermic mixing is realized. The DMA method is used to obtain the concentration dependences of the dynamic loss and elasticity modulus, as well as the shear angle, for systems based on a solution of sodium alginate and magnetic powders Fe, Fe3O4, and SrFe12O19 at a frequency of 1 Hz and a voltage of 1 Pa. It is found that with an increase in the concentration of inorganic matter particles in the suspensions, an increase in the dynamic modules and a decrease in the shear angle are observed, and for a suspension containing magnetite, the flow pattern does not change. During the course of suspensions containing Fe or SrFe12O19 powders, elastic properties begin to prevail. Magnetic hysteresis loops in the magnetic field strength range from -15 kE to 15 kE were obtained by magnetometry for the SKF-26/Ni and SKF-26/Fe systems. It is shown that with an increase in the powder content in the composite, the residual magnetization and saturation magnetization do not change, and the coercive force decreases, i.e., less energy is required to demagnetize the magnetic material. Data for systems based on sodium alginate containing 30% Fe or Fe3O4 were obtained by magnetometry. It is found that for the sodium alginate/Fe system, the saturation magnetization values for the composite are greater than for the individual Fe powder, which may be due to the ordering of spins on the surface of magnetic particles during the formation of the composite.

Additive manufacturing (AM) is a form of production that directly processes raw materials into their final form by building the product in a layer-by-layer fashion. Numerous types of AM exist, including selective laser sintering (SLS) of polymeric powders, vat polymerization (VP) of low viscosity photocurable resins, and material extrusion (MatEx) of thermoplastic or high viscosity composite materials. Because of its ability to reduce material waste while printing complex geometries, AM has the potential to revolutionize the manufacturing industry for a diverse set of materials and products. MatEx of thermoplastic feedstocks is most commonly performed using fused filament fabrication (FFF) – a form of melt extrusion. A solid filament is fed directly into a heated nozzle, where it melts onto a build bed before resolidifying in a matter of seconds. While this is the most common form of AM, especially among hobbyists, the material catalog is limited to thermoplastic polymers, and difficulties arise when fillers are introduced (e.g. reactions at elevated temperatures, clogging, disruption of polymer chain diffusion, and large increases in viscoelastic properties). To combat these challenges, direct ink write (DIW) AM extrudes highly viscous composites by applying pneumatic backpressure to a syringe, such that the material can be extruded in ambient conditions. This method enables processing of unreacted, thermosetting resins which have been filled with a large proportion of solid particulate fillers, called "highly filled" inks. The interparticle network formed from particle-particle interactions in the form of weak surface forces (e.g. Van der Waals forces) provides structural stability of the printed lines, such that they can sustain the weight of subsequent layers. In the realm of DIW 3D printing material discovery and processing, there are currently three major challenges. First, the high shear region of the nozzle frequently disrupts the interparticle network through a de-agglomeration process, such that there is a finite timescale for the interparticle network to reestablish itself. During this timeframe, the deformation/reformation process causes printed lines to sag, which negatively impacts both print quality and mechanical properties. Second, printed parts require a post-processing step to develop adequate mechanical properties suitable for the final product. The kinetics of this cure process are extremely slow, often taking multiple days or weeks to reach completion. Third, high shear rheological characterization of highly filled inks is challenging because of the numerous artifacts of error associated with high shear testing environments (e.g. sample loss/edge fracture, slip, and large sample size requirements). A literature review in Chapter 2 outlines the most recent advances in highly filled polyurethane processing for DIW, with a particular focus on how interparticle network recovery – in the form of thixotropy – can be tailored using a variety of reactive inks. The subsequent chapters of this dissertation address these challenges by systematically downselecting reactive inks appropriate for highly filled DIW extrusion while introducing numerous process relevant rheological protocols. An initial discussion in Chapter 3 covers the potential drawbacks of thermoplastic polyurethane (TPU) processing as it relates to industrial scale melt extrusion. Specifically, multiple side reactions and degradation processes are identified for a variety of TPU manufacturers. Such reactions elicit undesirable solid-like particulate buildup within the extrusion line, and the impacts/causes of these reactions are quantified using rheological criteria. These protocols offer evidence that differences in processability can arise not just between manufacturers, but also between lots of TPU from the same manufacturer. To address these concerns, Chapter 4 offers an alternative form of polyurethane processing in the form of a thermosetting reaction between hydroxyl-terminated polybutadiene (HTPB) and isophorone diisocyanate (IPDI). When uncatalyzed at room temperature, full conversion takes place over the course of multiple weeks which necessitates an accelerated kinetic analysis. Hence, a combination of chemorheological and spectroscopic methods are used to rapidly probe for changes in isocyanate reactivity using limited sample quantities, which substantiate the advantages and disadvantages of chemorheology and spectroscopy in the context of curing studies. While this synthetic pathway provides mechanical properties appropriate for the final printed product, a major concern is retention of green body strength post deposition. In order to maintain the shape of printed beads, ultraviolet (UV) light can be shined in-situ onto the nozzle of a DIW printhead, which actively cures the urethane acrylate ink through free radical polymerization. This technique, termed UV-assisted direct ink write (UV-DIW), assists recovery of the interparticle network. A novel rheological method proposed in Chapter 5, termed the "UV-assisted three interval thixotropy test" (UV-3ITT), quantifies the contribution of UV light towards structural stability and printability. This is accomplished by applying stepwise changes in strain on a torsional photorheometer, optionally applying UV light in the third interval, and then quantifying the contribution of UV light towards process-relevant recovery parameters. Resultingly, the threshold of solid particulate fillers required for UV light to improve print fidelity is determined. While most discussions revolve around torsional rheology, this method has one major drawback: it cannot probe the high shear properties of high solids content materials due to sample loss/edge fracture during steady shear measurement. Capillary rheometers are able to probe the viscosity profiles of highly filled materials in high shear environments, but the cost of the device and the sample requirements are burdensome. To resolve this challenge, the "microcapillary rheometer" is developed in Chapter 6 using common laboratory equipment at a fraction of the cost of a full-scale capillary rheometer, which enables rapid characterization of high solids content materials at extrusion-relevant conditions while exploiting small sample quantities. This study illustrates the accuracy and precision of the microcapillary rheometer when comparing the high shear properties of several highly filled systems to the full-scale capillary rheometer. Results highlight that application of the Bagley and Weissenberg-Rabinowitsch corrections is possible using this novel device, which facilitates calculation of true shear viscosity of high solids content systems. The limited sample requirement facilitates characterization of novel or potentially hazardous materials in a much safer, efficient manner, which accelerates material discovery while improving safety standards. / Doctor of Philosophy / Subtractive manufacturing technologies, which reduce raw materials down from their bulk state into a final product, make up a significant portion of the manufacturing sector today due to the convenience and ease of material processing. Some of the most common forms of subtractive manufacturing include lathing, milling, cutting, drilling, and grinding; these methods are applicable for a diverse set of materials ranging from metals to plastics. By the nature of this process, subtractive manufacturing yields substantial material waste, while limiting the complexity of a final product's design. To combat these unintended consequences, a novel form of production termed additive manufacturing (AM) has grown dramatically in the past several decades. AM directly processes raw materials into their final form which reduces material waste while enabling complex geometries to be "printed." Although there are numerous types of additive manufacturing, the most common forms utilize material extrusion, whereby the raw material is deposited through a nozzle and stacked in a layer-by-layer fashion onto a build bed, thus constructing a final product. For materials that melt and flow at elevated temperatures (i.e. thermoplastic materials), fused filament fabrication (FFF) is ideal since a solid filament can be fed into a heated nozzle, melted onto a build bed, and then quickly re-solidified. However, many polymers do not melt at elevated temperatures, and instead degrade; these materials are termed "thermosetting." To print these materials, unreacted thermosetting precursors, which are filled with a large proportion of solid fillers ("highly filled inks"), can be extruded by applying pneumatic back pressure to a syringe at ambient conditions. The process of extruding these materials layer-by-layer describes the direct ink write (DIW) technique. The solid particulate fillers form structural "networks" due to weak electrostatic forces on the surface of the fillers. These forces provide structural stability and enable the printed lines to hold the weight of subsequent layers. Unfortunately, the high-pressure region of the nozzle disrupts this network, causing the printed lines to sag over time. This effect can be reduced by actively applying ultraviolet (UV) light onto the nozzle during extrusion, which helps to hold the particles in place by curing the resin, thus increasing the capacity for a line to sustain the weight of subsequent layers. This form of material extrusion is termed UV-assisted direct ink write (UV-DIW). Because UV light only partially cures the material during prints, a separate, slower thermosetting reaction can occur as the material rests in an oven or in ambient conditions, which completely cures the printed part and provides sufficient mechanical properties. The combination of UV-curable resins, thermosetting resins, and sufficiently large amounts of solid particulate fillers for material extrusion describes the dual-cure nature of this highly filled UV-DIW process. To understand the curing patterns, flow behavior, and the amount of structural deformation that occurs within the nozzle, rheology becomes a powerful characterization tool. This branch of physics deals with the deformation and flow of matter ranging from simple fluids to complex polymer melts. As such, it is possible to probe reaction progress (chemorheology), structural deformation/reformation (thixotropy), and high-shear regimes representative of the DIW process. The research contained within this dissertation provides a holistic understanding of the overlap between rheology and DIW material extrusion for dual-reactive materials. This process begins by evaluating challenges during melt extrusion of thermoplastic polyurethane while quantifying the rate of degradation side reactions. An alternative form of polyurethane synthesis in the form of a thermosetting reaction is then introduced, whereby the reaction progress is evaluated using both rheological and spectroscopic techniques. Next, a novel rheological protocol is introduced which can predict the structural deformation/reformation of an ink during UV-DIW. This research concludes by proposing a downscaled version of the high-shear capillary rheometer which requires only several grams of material in contrast to the dozens of grams required for full-scale capillary rheometry. In essence, the work presented here rapidly evaluates the complex flow behavior and cure progression of various materials relevant for extrusion processes by utilizing limited sample quantities, thus preserving valuable resources while improving the economics of material discovery.

<p dir="ltr">The goal of this thesis is to design nature-inspired biomimetic materials that recapitulate essential features of tissues for biomedical applications including tissue modeling of drug transport and surgical adhesion.</p><p dir="ltr">The first part of this thesis utilizes collagen and glycosaminoglycans to mimic tissues for preclinical modeling of large-molecule drug transport. We first utilize hydrazone crosslinking chemistry with hyaluronic acid to form interpenetrating networks with collagen at different concentrations. The interpenetrating networks enabled a wide range of mechanical properties, including stiffness and swellability, and microstructures, such as pore morphology and size, that can better recapitulate diverse tissues. The mechanical and microstructural differences translated into differences in transport of the macromolecules of different sizes and charges from these matrices. Large macromolecules were impacted by mesh size, whereas small macromolecules were influenced primarily by electrostatic forces. The tunable properties demonstrated by the collagen and crosslinked hyaluronic acid hydrogels can be used to mimic different tissues for early-stage assays to understand drug transport and its relationship to matrix properties.</p><p dir="ltr">We then explore how the glycosaminoglycans hyaluronic acid, chondroitin sulfate, and heparin in collagen hydrogels influence drug transport via glycosaminoglycan-drug interactions and network development. Incorporating different types and concentrations of glycosaminoglycans led to glycosaminoglycan-collagen hydrogels with a range of collagen networks and negative charge densities to recapitulate different tissue compositions. Hyaluronic acid increased the overall viscosity of the hydrogel matrix, and chondroitin sulfate and heparin altered collagen fibrillogenesis. All three GAGs formed concentration-dependent polyelectrolyte complexes with positively charged macromolecules. Transport of positively charged macromolecules through collagen gels with chondroitin sulfate and high concentrations of heparin was inhibited due to complexation and charge effects. Conversely, collagen with low concentrations of heparin hastened the transport of macromolecules due to the limited collagen network resulting from fibrillogenesis inhibition. Overall, the addition of different GAGs into tissue models can better recapitulate native tissue to accurately predict therapeutics transport through a variety of tissues.</p><p>17</p><p dir="ltr">The second part of this thesis investigates the impact of pH and oxidation on an elastin- and mussel-inspired surgical sealant. We combined sodium periodate, an oxidizer, with an L-3,4-dihydroxyphenylalanine-modified elastin-like polypeptide to elucidate how the crosslinking mechanism and intermediate formation impacted adhesion, cure time, and stiffness. Formulations resisted burst pressures greater than physiological internal pressures. They did not swell and had stiffnesses similar to those of soft tissues, and their gelation times varied from seconds to hours. Small increases in the formulation pH led to the formation of α,β-dehydrodopamine intermediates which facilitated the development of multiple crosslinking networks. The mussel-inspired elastin-like adhesive can serve as a model of mussel proteins to further improve our understanding of mussel chemistry. This study exemplifies the importance of pH and oxidation on the performance of mussel-inspired adhesives in surgical sealing within physiological environments.</p><p dir="ltr">The final part of this thesis explores using biomimetic designs in an outreach activity aimed at engaging high school women in chemical engineering. The design and application of the activity led to increased interest in chemical engineering among the participants. There was greater alignment between students' aspirations and the field of chemical engineering, highlighting the potential for such outreach initiatives to inspire future generations of chemical engineers.</p>