The durability of Thermal Barrier Coatings (TBCs) used on the turbine blades of aircraft and power generation engines has been known to be affected by sand particle ingression comprised of Calcium-Magnesium-Alumina-Silicate (CMAS). Previous studies have shown that these effects present themselves through variations in the thermomechanical and thermochemical properties of the coating. This study investigated the impact of CMAS ingression on the Yttria Stabilized Zirconia Topcoat (YSZ) and Thermally Grown Oxide (TGO) strain in sprayed Thermal Barrier Coating (TBC) samples of varying porosity with and without CMAS ingression. In-Situ Synchrotron X-ray Diffraction measurements were taken on the sample under thermal loading conditions from which the YSZ and TGO peaks were identified and biaxial strain calculations were determined at high temperature. Quantitative strain results are presented for the YSZ and TGO during a thermal cycle. In-plane strain results for YSZ near the TGO interface for a complete thermal cycle are presented, for a 6% porous superdense sample with CMAS infiltration. The outcomes from this study can be used to understand the role of CMAS on the strain tolerance of the TBC coating. It is well known that under engine operational conditions the development of the TGO layer, with large critical stresses, has been linked to failure of the coating. The growth of the TGO manifests as undulations in a series of peaks and troughs. Understanding the mechanics of the oxide layer at these locations provides significant information with respect to the failure mechanisms of the TBC coating. This study investigated the stress at the peak and trough of a TGO undulation for a cycled Dense Vertically Cracked (DVC) plasma sprayed TBC sample through photo-luminescence (PL) spectroscopy. High resolution nanoscale stress maps were taken nondestructively in the undulation of the TGO. Preliminary results from first line mapping of TGO peak and trough scan, at a resolution of 200 nm, have shown a non-uniform TGO stress variation. The results obtained from this study can be used to understand the stress variation in the peak and trough of a DVC sample's TGO undulation and how it contributes to the life of the TBC coating.

A CFD validation study was made using corner supplied impinging jet ventilation operating in cooling mode. The air distribution system has two equilateral triangle shaped inlets placed 80cm above the floor at the two that share a common wall. The supply air was introduced at 2.26m/s. The temperature of the supply air at one of the inlets was slightly higher than the other. The room air velocity and temperature profiles were studied using realizable k-e, RNG k-e, k-e SST and v2-f turbulence models and compared with experimental values. Generally, the agreement between the experimental measurement data of the room air temperatures and velocities and the CFD results was very good in all turbulence models. However, the RNG k-e turbulence model showed better correlation with average errors of 1.9% and 2.8% in predicting temperature and velocity respectively. Possibility of local thermal discomfort with the indoor air were investigated using the Fanger’s thermal comfort indices and draught rate while the air quality was evaluated by the mean age of air and the diffusion coefficient. The thermal comfort indices were computed using a user-defined function and the mean age of air was computed by user- defined scalar that solves a partial differential equation that uses the source diffusivity and calculate the residence time of air in the room. The results show that there is a higher risk of draft at the ankle level (close to 20%) and the room air is freshest near the lower region at the centre of the room. The room air is oldest at the region close to the ceiling in the area between the two mannequins. The study concludes that a satisfactory prediction of thermal stratification and velocity fields can made for evaluating the indoor thermal comfort and air quality using RANS based turbulence models.

An emerging category of energy systems, consisting of power generation equipment coupled with thermally-activated components, has evolved as Cooling, Heating, and Power (CHP). The application of CHP systems to buildings has developed into a new paradigm ? Cooling, Heating, and Power for Buildings (CHP-B). This instructional module has been developed to introduce undergraduate engineering students to CHP-B. In the typical ME curriculum, a number of courses could contain topics related to CHP. Thermodynamics, heat transfer, thermal systems design, heat and power, alternate energy systems, and HVAC courses are appropriate for CHP topics. However, the types of material needed for this mix of courses vary. In thermodynamics, basic problems involving a CHP flavor are needed, but in an alternate energy systems course much more CHP detail and content would be required. This series of lectures on CHP-B contains both a stand-alone CHP treatment and a compilation of problems/exercises.

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Mechanical stimulation plays a crucial role in promoting cell differentiation. However, applying physical force directly to cells requires complex equipment and a sterile environment, posing challenges. To overcome this, stimuli-responsive biomaterials or 4D scaffolds can serve as an alternative platform for mechanical stimulation. These scaffolds, fabricated using advanced 3D printing techniques, can apply the necessary force to cells. To optimize their functionality, bioactive molecules or extracellular matrices can be incorporated or decorated on their surfaces. This thesis proposal focuses on developing a versatile material platform that allows customization through systematic composition adjustment and on-demand printing, while also offering surface modification capabilities. The primary objective is to create a novel cell carrier platform using thermo-responsive polymers. By manipulating the additive monomer compositions, we can finely adjust properties such as the transition temperature of the polymers, tailoring them to specific requirements. Furthermore, this platform will enable the fabrication of complex three-dimensional biomaterial structures with controllable porosity, a critical aspect of biomaterial design. Leveraging the capabilities of three-dimensional printing technology, we can program and achieve desired porosity levels in the printed structures, providing enhanced flexibility for biomaterial design. The development of thermo-responsive scaffolds involved three distinct stages aimed at designing an optimized platform that effectively operates within the physiological range while ensuring cell viability. One of the key challenges was to achieve a balance between thermoresponsive behavior and biocompatibility. In the initial stage, we investigated the interplay between a crosslinkable three-armed macromer (trimethylolpropane triacrylate-TMPTA) and various monomers (N-isopropylacrylamide-NiPAAm, methyl methacrylate-MMA, dimethylaminoethyl acrylate-DMAEA, 4-acryloylmorpholine-AMO) using thermally induced solution polymerization. NiPAAm, known for its thermoresponsive properties, was selected despite its limited biocompatibility. DMAEA was chosen to adjust the polymer network transition temperature by introducing cationic charge, which disrupts the coil-globule effect of PNiPAAm and provides cell adhesiveness of the composition. Additionally, the hydrophilic monomer AMO was incorporated to further fine-tune the polymeric network. We examined the behavior of these components within the physiological range and their integration into the PNiPAAm network, establishing significant correlations between the transition temperature of the polymer and the crosslinker and monomers in their soluble condition. In the second stage of our research, we introduced photo-induced polymerization to enhance the crosslinking ratio. By utilizing this method, we successfully fabricated photo-polymerized mixtures (photoresists) into thermo-responsive discs, enabling us to study their swelling behavior between 37℃ and 25℃. Our findings revealed that the swelling behavior could be adjusted by varying the ratios of the crosslinker and monomers in the experimental groups. Through careful experimentation, we identified a suitable composition (3% w/w TMPTA, 80% w/w NiPAAm, 15% w/w DMAEA, 5% w/w AMO, and 4% w/w photo-initiator(PI)) that required minimal crosslinking incorporation while still retaining thermo-responsiveness. Furthermore, we conducted a preliminary biocompatibility study by fabricating the mixture into thin-films and cultivating them with L929 fibroblast cells. In the third and final stage, we utilized the optimized formulations from the previous stage to build thermo-responsive 3D scaffolds using continuous Digital Light Processing (cDLP) printing. We investigated the effects of various parameters, such as curing time and monomer composition, on the swelling property of the scaffolds. Additionally, we introduced glycofurol (GF) as a photo-polymerization solvent, which allowed us to produce scaffolds with improved resolution and reduced printing time. The resulting optimized scaffolds, with a composition of 3% w/w TMPTA, 80% w/w NiPAAm, 15% w/w DMAEA, 5% w/w AMO, 4% w/w PI, and 10 seconds per layer, exhibited the desired thermo-responsiveness. To further understand the mechanical properties and thermal dependencies of these scaffolds, we conducted rheological analysis. This analysis helped establish a relationship between the mechanical properties of the scaffolds and their response to temperature changes. To investigate the potential of cell stimulation through periodic changes, we conducted an experiment involving the seeding of L929 fibroblasts and C2C12 myoblasts on thermo-responsive 3D scaffolds. Our objective was to assess the ability of cells to proliferate on scaffolds with different compositions. Specifically, we examined two types of scaffolds: lattice scaffolds, characterized by a porous structure with a periodic network that enables cells to inhabit a 3D environment, and raft scaffolds, which feature a dense 3D structure designed for cells to reside on the surface for observation and evaluation. The lattice scaffolds were composed of ≥2% w/w DMAEA, while the raft scaffolds consisted of ≥5% w/w DMAEA. To evaluate cell proliferation, we conducted direct contact experiments and employed live/dead assays, subjecting the scaffolds to temperature switching conditions at 31℃ and 37℃. These experimental setups aimed to provide insights into the response and behavior of cells in the presence of thermo-responsive scaffolds with varying compositions. The results revealed favorable adhesion and spreading of the cells on the scaffolds. Interestingly, in our dynamic temperature experiment, we observed that myoblasts seeded on the scaffolds exhibited both proliferation and spreading, whereas myoblasts subjected to constant-temperature conditions did not show the same behavior. This suggests that the expansion and contraction of the scaffold, observed in previous experiments, may impact cell viability. Further investigation is needed to better understand this phenomenon. Additionally, we enhanced cell adhesiveness of the scaffolds by impregnating the scaffolds with poly-L-lysine and tested them with hASCs (human adipose-derived stem cells). Significant differences were observed between scaffolds with and without poly-L-lysine, highlighting the effectiveness of this approach. In conclusion, we have successfully developed a thermo-responsive 3D scaffold that exhibits a transition temperature within the physiological range, ensuring cell survival, and provides mechanical stimulation to the cells through the coil-globule effect without causing cell detachment. Among the formulations tested, the GF-printed formulation (3% w/w TMPTA, 80% w/w NiPAAm, 15% w/w DMAEA, 5% w/w AMO, and 4% w/w photo-initiator) with an exposure time of 10 seconds per layer showed the most promising results for cell cultivation under periodic changes in temperature, with a transition temperature of 36.3 °C ± 0.9 °C. Furthermore, we conducted direct cell contact experiments and confirmed the biocompatibility of the thermo-responsive macromer-based scaffolds. These findings demonstrate that this material platform offers a versatile and responsive material for mechanical stimulation of cells on three-dimensional scaffolds. These promising results suggest that this approach holds significant potential for tissue engineering applications and can be utilized to develop mechanical stimulation devices for various biomedical applications.:CHAPTER 1……………………..……………...…………………………..…4 Introduction CHAPTER 2……………………..…………………………..……………….29 Material and Methods CHAPTER 3……………………………………..…..……………………….52 Thermo-Responsive Polymer from Thermal Synthesis Studies CHAPTER 4…………………………………..……………………………...70 An Adjustable Thermo-Responsive Polymer from Photo Synthesis CHAPTER 5……………………………………………………………....….88 Fabrication of Thermo-Responsive Scaffolds from DLP Printing CHAPTER 6…………………...…………………………………………....107 3D Scaffold Biocompatibility Studies CHAPTER 7…………………...……………………………………………139 Discussions CHAPTER 8…………………...……………………………………………161 Summery APPENDIX…………………...………………………………………….…166 Bibliography, List of Publications, CV, Declaration of Authorship, Acknowledgements, Related publication

Poly(phenylene sulfide) (PPS), an engineering thermoplastic with excellent mechanical, thermal, and chemical properties, was gelled for the first time using 1,3-diphenylacetone (DPA) as the gelation solvent in a thermally induced phase separation (TIPS) process. PPS was dissolved in DPA at high temperatures to form a homogeneous solution. The solution was cooled, initiating phase separation and eventually forming a solidified PPS network around DPA-rich domains. Evacuation of DPA from the gel network creates monolithic PPS aerogels, one of few physically crosslinked polymer aerogel systems comprised of a high-performance thermoplastic. In this work, specific properties of PPS aerogels were controlled through the manipulation of various processing parameters, such as polymer concentration, post-process annealing conditions, mode of manufacturing (casting versus additive manufacturing), dissolution temperature, and drying method. The ultimate goal was to elucidate key process-morphology-property relationships in PPS aerogels, to ultimately improve aerogel performance and applicability. The phase diagram of PPS/DPA was first elucidated to determine the phase separation mechanism of the system, which guides all future processing decisions. The phase diagram indicated that the system undergoes solid-liquid phase separation, typical for solutions with relatively favorable polymer-solvent interactions. This assignment was validated by the calculation of the Flory-Huggins interaction parameter through two independent methods - Hansen solubility parameters and fitting melting point depression data. The influence of polymer composition on PPS aerogel properties was then characterized. As polymer concentration increased, aerogel density and mechanical properties increases, and porosity decreased. The particular morphology of PPS aerogels from DPA was that of a fibrillar network, where these axialitic (pre-spherulitic) fibrils are comprised of stacks of PPS crystalline lamellae, as suggested by x-ray scattering and electron microscopy. These interconnected microstructures responded more favorably to compressive load than similar globular PEEK aerogels, highlighting the importance of aerogel microstructure on its mechanical response. Upon solvent extraction, PPS aerogels were annealed in air environments to improve their mechanical behavior. Annealing did not dramatically shrink the aerogels, nor did it appear to affect the micron-scale morphology of PPS aerogels as observed by electron microscopy. The resistance to densification of PPS aerogels was mainly a product of their interconnected fibrillar morphologies, aided by subtle microstructural changes that occurred upon annealing. Exposure to a high temperature oxidative environment (160 – 240 oC) increased the degree of crystallinity of the aerogels, and also promoted chemical crosslinking within the amorphous PPS regions, both of which may have helped to prevent severe densification. With enhanced physical and chemical crosslinking, annealed PPS aerogels displayed improved compressive properties over unannealed analogues. Additionally, the thermal conductivity of both annealed and unannealed aerogel specimens was below that of air (~ 0.026 W/mK) and did not display a dependence on polymer composition nor on annealing condition. Generally, these experiments demonstrate that annealing PPS aerogels improved their mechanical performance without negatively affecting their inherent fibrillar morphology, low density, or low thermal conductivity. To fabricate aerogels with geometric flexibility and hierarchical porosity, PPS/DPA solutions were printed through material extrusion (MEX) and TIPS using a custom-built heated extruder. In this process, solid solvated gels were first re-dissolved in a heated extruder and solutions were deposited in a layer-wise fashion onto a room-temperature substrate. The large temperature gradient between nozzle and substrate rapidly initiated phase separation, solidified the deposited layers and formed a printed part. Subsequent solvent exchange and drying created printed PPS aerogels. The morphology of printed aerogels was compositionally-dependent, where the high extrusion temperature required to dissolve highly-concentrated inks (50 wt % PPS) also destroyed self-nuclei in solution, yielding printed aerogels with spherulitic microstructures. In contrast, aerogels printed from 30 wt % solutions were deposited at lower temperatures and demonstrated fibrillar microstructures, similar to those observed in 30 wt % cast aerogel analogues. Despite these microstructural differences, all printed aerogels demonstrated densities, porosities, and crystallinities similar to their cast aerogel counterparts. However, printed aerogel mechanical properties were microstructurally-dependent, and the spherulitic 50 wt % aerogels were much more brittle compared to the fibrillar cast 50 wt % analogues. This work introduces a widely-applicable framework for printing polymer aerogels using MEX and TIPS. Intrigued by the compositional morphological dependence of the printed PPS aerogels, the dissolution temperature (Tdis), and thus the self-nuclei content, of cast PPS/DPA solutions was systematically varied to understand its influence on aerogel morphology and properties. As Tdis increased, the length and diameter of axialites increased while aerogel density and porosity were relatively unaffected. Thus, the isolated influence of axialite dimensions (analogous to pore size and pore concentration) on aerogel properties could be studied independent of density. At low relative densities (below 0.3, aerogels of 10 – 30 wt %), compressive modulus and offset yield strength tended to decrease with Tdis, due to an increase in axialite length (akin to pore size) and number of axialites (akin to number of pores). At higher relative densities (above 0.3, 40 and 50 wt %), axialitic aerogels were so dense that changes in pore dimensions did not result in systematic changes in mechanical response. All spherulitic aerogels fabricated at the highest Tdis¬ demonstrated reduced mechanical properties due to poor interspherulitic connectivity. The thermal conductivity of all aerogels increased with polymer composition but demonstrated no clear trend with Tdis. A model for thermal conductivity was used to deconvolute calculated conductivity into solid, gaseous, and radiative components to help rationalize the measured conductivity data. This work demonstrates the importance of nucleation density control in TIPS aerogel fabrication, especially at low polymer concentrations. The specific method used to dry an aerogel generally has a great influence on its microstructure and density. Vacuum or ambient drying is the most industrially-attractive technique due to low cost and low energy usage; however, it is typically the most destructive process due to high capillary forces acting on the delicate aerogel microstructure. Three drying methods, vacuum drying, freeze drying, and supercritical CO2 drying, were used to evacuate PPS gels fabricated at three PPS concentrations (10, 15, and 20 wt %). Almost all aerogel specimens displayed excellent resilience against shrinkage as a function of the drying method, besides the 10 wt % vacuum dried sample which shrunk almost 40%. While the micron-scale aerogel morphology captured by electron microscopy appeared to be unaffected by the drying method, other properties such as aerogel surface area, mesoporous volume, and mechanical properties were effectively functions of the degree of aerogel shrinkage. Aerogel thermal conductivity was low for all samples, and in particular, vacuum dried aerogels demonstrated slightly lower conductivities than other ambiently-dried aerogel systems such as silica and carbon. In general, vacuum drying appears to be industrially viable for PPS aerogels at concentrations above 10 wt %. / Doctor of Philosophy / Polymer aerogels are nanoporous solid networks of low density. These materials are used in applications such as thermal insulation, absorbance/filtration, drug delivery, biomedical scaffolds, solid state batteries, and others. One method of creating polymeric aerogels is through thermally induced phase separation (TIPS), where a polymer is first dissolved in a high boiling point solvent at a high temperature. Next, the solution is cooled, inducing phase separation and gelation. Extraction of the gelation solvent transforms the solvated gel into an aerogel. To create polymeric aerogels with good properties and wide-ranging applicability, one should use a high-performance polymer. In this work, aerogels are for the first time made from poly(phenylene sulfide) (PPS), an engineering thermoplastic with good mechanical properties, thermal stability, and chemical resistance. PPS aerogels are fabricated using TIPS over a wide compositional range, and their microstructures, physical properties, thermal properties, and compressive properties are fully characterized. To further enhance aerogel performance, the fabrication process can be optimized to precisely control the aerogel morphology and thus the resulting properties. The influence of processing variables such as the polymer concentration, the post-fabrication aerogel annealing conditions, the method of manufacturing (traditional casting versus additive manufacturing), the dissolution temperature (temperature at which the polymer dissolves in solution prior to gelation), and the drying method on the aerogel behavior is investigated. Generally, results suggest that understanding critical process-morphology-property relationships allows for precise control over the nature of PPS aerogels.

Geo-energy piles and walls have long been recognized as a promising way to reduce carbon dioxide emissions while providing renewable energy. However, enhancing the thermal performance of these structures has remained a signif-icant challenge. This thesis evaluated five different approaches to improving the thermal performance of geo-energy piles and walls, through a series of experiments using a fully instrumented testing rig. The first approach involved adding graphTHERM powder to concrete to double its thermal conductivity, boosting heat transfer efficiency by an impressive 50% to 66%. The second approach tested slag-based geopolymer concrete as a sustainable construc-tion material for geo-energy piles and walls, reducing CO2 emissions by 44.5% while improving thermal performance by 14% to 21%. The third approach in-volved testing thermally enhanced soils at the geo-energy structures/soil inter-face, resulting in an 81% improvement in heat transfer efficiency. The fourth approach utilized innovative phase change material (PCM) heat exchangers that increased heat transfer efficiency by 75% and 43% in heating and cooling operations, respectively. Finally, incorporated PCM-impregnated light weight aggregates at the interface of the structure soil, significantly increasing tem-perature difference and reducing thermal deformation of geo-energy struc-tures.Overall, these innovative approaches made a significant contribution to enhancing the thermal performance of geo-energy piles and walls. However, approaches four and five, which involve utilizing PCM heat exchangers and PCM-impregnated LWA's, respectively, showed extra benefits in dropping the thermal effect on soils and reducing the thermal damage on those structures. These techniques offer great promise for improving the thermal performance of geo-energy structures.

Land surface models (LSMs) implemented in numerical weather prediction (NWP) models use several parameters to suitably describe the surface and its interaction with the atmosphere, whose determination is often affected by many uncertainties, strongly influencing simulation results. However, the sensitivity of meteorological model results to these parameters has not yet been studied systematically, especially in complex terrain, where uncertainty is expected to be even larger. This work aims at identifying critical LSM parameters influencing the results of NWP models, focusing in particular on the simulation of thermally-driven circulations over complex terrain. While previous sensitivity analyses employed offline LSM simulations to evaluate the sensitivity to surface parameters, this study adopts an online coupled approach, utilizing the Noah-MP LSM within the Weather Research and Forecasting (WRF) model. To overcome computational constraints, a novel tool, Machine Learning-based Automated Multi-method Parameter Sensitivity and Importance analysis Tool (ML-AMPSIT), is developed and tested. This tool allows users to explore the sensitivity of the results to model parameters using supervised machine learning regression algorithms, including Random Forest, CART, XGBoost, SVM, LASSO, Gaussian Process Regression, and Bayesian Ridge Regression. These algorithms serve as fast surrogate models, greatly accelerating sensitivity analyses while maintaining a high level of accuracy. The versatility and effectiveness of ML-AMPSIT enable the fast implementation of advanced sensitivity methods, such as the Sobol method, overcoming the computational limitations encountered in expensive models like WRF. The suitability of this tool to assess model’s sensitivity to the variation of specific parameters is first tested in an idealized sea breeze case study where six surface parameters are varied. Then, the analysis focuses on the evaluation of the sensitivity to surface parameters in the simulation of thermally-driven circulations in a mountain valley. Specifically, an idealized three-dimensional topography consisting of a valley-plain system is adopted, analyzing a complete diurnal cycle of valley and slope winds. The analysis focuses on all the key surface parameters governing the interactions between NoahMP and WRF. The proposed approach, novel in the context of LSM-NWP model coupling, draws from established applications of machine learning in various Earth science disciplines, underscoring its potential to improve the estimation of parameter sensitivities in NWP models.

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