Doctor of Philosophy / Department of Chemistry / Emily McLaurin / Semiconductors are materials whose conductivity is between metals and insulators. Semiconductor nanocrystals (NCs) have sizes in the range 2 to 10 nm. Because of their unique optical properties like tunable emission wavelength, narrow emission peak, and stability over dyes, they have potential applications in displays. Indium phosphide (InP) is considered a less toxic alternative to commercially used cadmium-based semiconductor NCs. Microwave-assisted (MA) methods using ionic liquids (ILs) afford fast reaction heating rates because of the good MW absorbing capacity of ILs. For tuning size and surface, which are some of the important problems associated with the InP NCs, new synthetic methods are reported herein. In MAIL etching HF generated in the microwave reaction etches the InP NCs surface. Pyridinium and imidazolium based ILs containing tetrafluoroborate (BF₄⁻) and hexafluorophosphate (PF₆⁻) ions yield luminescent NCs. In a silicon carbide (SiC) reaction vessel, which blocks most of the microwaves penetrating into the reaction, bigger NCs form than those from a Pyrex reaction vessel because of the higher reaction temperatures in the SiC vessel. By changing microwave set-power (SP), different reaction times can be achieved. Though a small degree of change in average NC diameter of the NCs is observed at different SPs and reaction temperatures, addition of dodecylamine (DDA) yields NCs with average sizes between 3.2 to 4.2 nm with a broad size distribution. At lower SPs smaller NCs form and at higher SPs bigger NCs form. NC luminescence can be tuned from green (545 nm) to red (630 nm) in the visible region with quantum yields as high as 30%. Rapid heating and InP precursor activation might be responsible for the larger change in NC size. The effect of DDA on NC size is also verified by microwave reactions in SiC vessels. ILs containing PF₆⁻ ions at 280 °C will modify the surface of the NCs so the NC dispersibility changes from non-polar (toluene) to polar (DMSO) as the amount of IL increases. This is due to ligand stripping, which is the removal of large palmitic ligands from the NC surface. These NCs have broad absorption features and emission peaks with QYs of up to 30%. Fourier transform infrared spectroscopy indicates the absence of palmitic acid ligands on the NC surface and zeta potential measurements indicate the presence of anions on the NC surface. From X-ray photoelectron spectroscopy and nuclear magnetic resonance spectroscopy, the inorganic ion PO₂F₂⁻ is identified on the NCs surface.

Metal-Organic Frameworks (MOFs) are highly porous materials built from inorganic nodes joined by organic linkers forming extended crystalline networks. One of the distinguishing features of metal-organic frameworks is the ability to adaptively change their crystal structure in response to external stimuli with significant porosity switching. Such structural switchability of MOFs offers new opportunities in gas separation, selective recognition, sensing, and energy storage. However, there are still open questions in understanding factors affecting switchability. The electronic structure of the metal in the building blocks, host-guest interactions, but also particle size, morphology, surface, desolvation conditions are involved into the responsiveness of the system. One of the representative of switchable metal-organic frameworks is pillared-layer DUT-8 (M2(2,6-ndc)2(dabco), M = Ni, Co, Cu, Zn, 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo[2.2.2]octane). Depending on the metal node and particle size, it is possible to synthesize either switchable or rigid materials differing in physisorption isotherm profiles. In order to understand switching behaviour of DUT-8, the important parameters influencing structural switchability are addressed in my work. For this purpose, the impact of crystal size and morphology, as well as crystal surface on adsorption-induced structural transformations of DUT-8(Ni) were investigated. DUT-8(Ni) shows reversible structural transition between open (op) and closed pore phase (cp) upon adsorption/removal of guest molecules. To understand which particular crystal surfaces dominate the phenomena observed, crystals similar in size and differing in morphology were involved in a systematic study. The analysis of the data shows that the width of the rods (corresponding to the crystallographic directions along the layer) represents a critical parameter governing the dynamic properties upon adsorption of nitrogen at 77 K. This observation is related to the anisotropy of the channel-like pore system and the nucleation mechanism of the solid-solid phase transition triggered by gas adsorption. To investigate the influence of external surface on adsorption-induced switchability, DUT-8(Ni) samples were exposed to different treatment techniques. By means of analytical methods, it was revealed that the surface of samples was modified leading to a significant increase of the gate-opening pressure, reflecting the increase of activation barrier for phase switching form cp to op upon adsorption of nitrogen at 77 K. Furthermore, the properties of DUT-8(Zn) were studied precisely, focusing on the variation of particle size and morphology, host-guest interactions, desolvation conditions, selectivity and thermoresponsivity. Depending on the synthesis conditions, DUT-8(Zn) can be synthesised in macro-sized regime (150 µm) and micron-sized regime (0.5 µm). The solvent removal process (pore desolvation stress contracting the framework) significantly controls the cp/op ratio after desolvation and, subsequently, the adsorption induced switchability characteristics of the system. Among the applied desolvation techniques, the solvent exchange with subsequent heating causes phase transition from open (op) to closed pore phase (cp). After desolvation, the dense cp phase of DUT-8(Zn) shows no adsorption-induced reopening and therefore is non-porous for N2 at 77 K and CO2 at 195 K. However, polar molecules with a higher adsorption enthalpy, such as chloromethane at 249 K and dichloromethane (DCM) at 298 K can reopen the macro-sized crystals upon adsorption, while micron-sized crystals retain the cp phase. For macro-sized particles (160 µm), the outer surface energy is negligible and only the type of metal (Zn, Co, Ni) controls the DCM-induced gate opening pressure. The node hinge stiffness increases from Zn to Ni as confirmed by DFT calculations, X-ray crystal structural analysis, and low frequency Raman spectroscopy. This softer Zn-based node hinges and overall increased stabilization of cp vs. op phase shift the critical particle size at which switchability starts to become suppressed to even lower values. Hence, the three factors affecting switchability (energetics of the empty host, (Eop–Ecp) (i), particle size (ii), and desolvation stress (iii)) appear to be of the same order of magnitude and should be considered collectively, not individually. Crystal downsizing (0.5 µm) facilitates the responsivity of DUT-8(Zn) towards different guest molecules, not opening for macro-sized crystals. Among investigated adsorptives, the alcohols are in the center of attention due to ability to induce so called shape-memory effect in micron-sized crystals. The adsorption of alcohols stimulates the change of initial shape of pores (cp) into a temporary shape (op) which is maintained even after desorption. To brighten the crystal size range and to study the dependence of gate opening pressure from crystal size and morphology, differently shaped crystals in micron-sized regime were produced by face-selective coordination modulation. Morphology modification allowed to determine the critical parameter controlling switchable transformations in DUT-8(Zn). Thus, the crystal size engineering and morphology modification provide an opportunity not only to control the structural dynamics of MOFs, but also to tailor responsivity towards guest molecules, influencing the selective adsorption behaviour.

Various anchorage systems including both cast-in-place and post-installed anchors have been developed for fastening both non-structural and structural components to concrete structures. The need for increased flexibility in the design of new structures and strengthening of existing concrete structures has led to increased use of various metallic anchors in practice. Although millions of fasteners are used each year in the construction industry around the world, knowledge of the fastening technology remains poor. In a sustainable society, buildings and structures must, from time to time, be adjusted to meet new demands. Loads on structures must, in general, be increased to comply with new demands, and the structural components and the structural connections must also be upgraded. From the structural connection point of view, the adequacy of the current fastenings for the intended increased load must be determined, and inadequate fastenings must either be replaced or upgraded. The current design models are generally believed to be conservative, although the extent of this behavior is not very clear. To address these issues, the current models must be refined to allow the design of new fastenings and also the assessment of current anchorage systems in practice. The research presented in this thesis consists of numerical and experimental studies of the load-carrying capacity of anchors in concrete structures. Two different types of anchors were studied: (I) cast-in-place headed anchors, and (II) post-installed adhesive anchors. This research focused particularly on the tensile load-carrying capacity of cast-in-place headed anchors and also on the sustained tension loading performance of post-installed adhesive anchors. The overall objective of this research was to provide knowledge for the development of improved methods of designing new fastening systems and assessing the current anchorage systems in practice. For the cast-in-place headed anchors (I), the influence of various parameters including the size of anchor head, thickness of concrete member, amount of orthogonal surface reinforcement, presence of concrete cracks, concrete compressive strength, and addition of steel fibers to concrete were studied. Among these parameters, the influence of the anchor head size, member thickness, surface reinforcement, and cracked concrete was initially evaluated via numerical analysis of headed anchors at various embedment depths. Although these parameters have considerable influence on the anchorage capacity and performance, this influence is not explicitly considered by the current design models. The numerical results showed that the tensile breakout capacity of headed anchors increases with increasing member thickness and/or increasing size of the anchor head or the use of orthogonal surface reinforcement. However, their capacity decreased considerably in cracked concrete. Based on the numerical results, the current theoretical model for the tensile breakout capacity of headed anchors was extended by incorporating several modification factors that take the influence of the investigated parameters into account. In addition, a supplementary experimental study was performed to verify the numerically obtained findings and the proposed refined model. The experimental results corresponded closely to the numerical results, both in terms of failure load and failure pattern, thereby confirming the validity of the proposed model. The validity of the model was further confirmed through experimental results reported in the literature. Additional experiments were performed to determine the influence of the concrete compressive strength and the addition of steel fiber to concrete on the anchorage capacity and performance. These experiments showed that the anchorage capacity and stiffness increase considerably with increasing concrete compressive strength, but the ductility of the anchor decreases. However, the anchorage capacity and ductility increased significantly with the addition of steel fibers to the concrete mixture. The test results also revealed that the tensile breakout capacity of headed anchors in steel fiber-reinforced concrete is significantly underestimated by the current design model. The long-term performance and creep behavior of the post-installed headed anchors (II) was evaluated from the results of long-time tests on adhesive anchors under sustained loads. In this experimental study, adhesive anchors of various sizes were subjected to various sustained load levels for up to 28 years. The anchors were also exposed to several in-service conditions including indoor temperature, variations in the outdoor temperature and humidity, wetness (i.e., water on the surface of concrete), and the presence of salt (setting accelerant) additives in the concrete. Among the tested in-service conditions, variations in the outdoor temperature and humidity had the most adverse effect on the long-term sustained loading performance of the anchors. Based on the test results, recommendations were proposed for maximum sustained load levels under various conditions. The anchors tested under indoor conditions could carry sustained loads of up to 47% of their mean ultimate short-term capacities. However, compared with these anchors, the anchors tested under outdoor conditions exhibited larger creep deformation and failure occurred at sustained loads higher than 23% of their mean ultimate short-term capacities. Salt additives in concrete and wet conditions had negligible influence on the long-term performance of the anchors, although the wet condition resulted in progressive corrosion of the steel. Based on the experimental results, the suitability of the current testing and approval provisions for qualifying adhesive anchors subjected to long-term sustained tensile loads was evaluated. The evaluations revealed that the current approval provisions are not necessarily reliable for qualifying adhesive anchors for long-term sustained loading applications. Recommendations were given for modifying the current provisions to ensure safe long-term performance of adhesive anchors under sustained loads.