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An investigation into the responses of microbeams to electric actuations is presented. Attention is focused mainly on the use of microbeams in two important MEMS-based devices: capacitive microswitches and resonant microsensors. Nonlinear models are developed to simulate the behavior of the microbeams in each device. The models account for mid-plane stretching, an applied axial load, a DC electrostatic force, and, for the case of resonant sensors, an AC harmonic force. Further, a novel method that uses a reduced-order model is introduced for simulating the behavior of microbeams under a DC electrostatic force. The presented method shows attractive features, like for example, a high stability near the pull-in and a low computational cost. Thus, it can be of significant benefit to the development of MEMS design software. The static behavior of microbeams under electrostatic forces is studied using two methods. One method employs a shooting technique for solving the boundary-value problem that governs the static behavior. The second method is based on solving an algebraic system of equations obtained from the reduced-order model. Further, the eigenvalue problem describing the vibrations of a microbeam around its statically deflected position is solved using a shooting method to obtain the microbeam mode shapes and natural frequencies. The dynamic behavior of resonant microbeams is also investigated. A perturbation method, the method of multiple scales, is used to obtain two first-order nonlinear ordinary-differential equations that describe the amplitude and phase of the response and its stability. The results show that an inaccurate representation of the system nonlinearities may lead to an erroneous prediction of the nonlinear resonance frequency of a microbeam. The case of three-to-one internal resonance between the lowest two modes is treated. Finally, the reduced-order model is used to study the dynamic behavior of the electrostatically actuated microbeams. The proposed models are validated by comparing their results with experimental results available in the literature. / Master of Science

Current research efforts have focused on the synthesis of novel, segmented, cross-linked networks and thermoplastics for emerging technologies. Tailoring macromolecular structures for improved mechanical performance can be accomplished through a variety of synthetic strategies using step-growth polymerization. The synthesis and characterization of novel Michael addition networks, ionene families, and ion-containing polyurethanes are described, with the underlying theme of fundamentally investigating the structure-property relationships of novel, segmented macromolecular architectures. In addition, it was discovered that both covalent and electrostatic crosslinking play an important role in the mechanical properties of all types of polymers described herein. Novel cross-linked networks were synthesized using quantitative base-catalyzed Michael chemistry with acetoacetate and acrylate functionalities. These novel synthetic strategies offer unique thermo-mechanical performance due to the formation of a multiphase morphology. In order to fundamentally elucidate the factors that influence the kinetics of the Michael addition reaction a detailed analyses of model compounds were conducted in the presence of an in-situ IR spectrometer to optimize reaction conditions using statistical design of experiments. Networks were then prepared based on these optimized conditions. The mechanical performance was evaluated as a function of molecular weight between crosslink points. Furthermore, the incorporation of hydrogen bonding within the monomer structure enhanced mechanical performance. The changes in morphological, thermal, and mechanical properties evaluated using dynamic mechanical analysis (DMA) and tensile behavior are described. In addition, the use of preformed urethane segments provides a safer method for incorporating hydrogen bonding functional groups into macromolecules. In order to compare the thermomechanical and morphological properties of ion-containing polyurethanes to non-charged polyurethanes, poly(tetramethylene oxide)-based polyurethanes containing either a novel phosphonium diol or 1,4-butanediol chain extenders were prepared using a prepolymer method. The novel phosphonium polyurethane was more crystalline, and it was presumed that hydrogen bonding in the non-charged polyurethane restricted polymer mobility, and reduced PTMO crystallinity, and hydrogen bonding interactions were significantly reduced due to the presence of phosphonium cations. These results correlated well with mechanical property analysis. The phase separation and ionic aggregation were demonstrated via wide-angle X-ray scattering, small-angle X-ray scattering, scanning transmission electron microscopy, and energy-dispersive X-ray spectroscopy during STEM imaging, as described herein. In addition, a novel polyurethane containing imidazolium cations in the hard segment was synthesized and behaved very similarly to the phosphonium cation-containing polyurethane. Ammonium ionenes, which contain quaternary nitrogen in the macromolecular repeating unit, have many potential uses in biomedical applications. They offer interesting coulombic properties, and the charge density is easily controlled through synthetic design. This property makes ionenes ideal polyelectrolyte models to investigate the influence of ionic aggregation on many physical properties. Ammonium ionenes were prepared via the Menshutkin reaction from 1,12-dibromododecane and 1,12-bis(N,N-dimethylamino)dodecane. The absolute molecular weights were determined for the first time using an on-line multi-angle laser light scattering (MALLS) in aqueous size exclusion chromatography (SEC). Tensile testing and DMA were used to establish structure-property relationships between molecular weight and mechanical properties for a series of 12,12-ammonium ionenes. Furthermore, degradation studies in the presence of base support the possibility for water-soluble coatings with excellent mechanical durability that are amenable to triggered depolymerization. A novel synthetic strategy was utilized to prepare chain extended 12,12-ammonium ionenes containing cinnamate functional groups. In the presence of UV light, the polymers chain extended, and the resulting ionenes possessed enhanced thermomechanical properties and increased molecular weight. In addition, the novel synthesis of imidazolium ionenes was demonstrated, and the charge density was tuned for appropriate applications using either low molecular weight segments or oligomeric precursors. The change in charge density had a profound role in imidazolium ionene thermal and mechanical behavior. / Ph. D.

no abstract provided by author / Master of Science

In this thesis, MEMS switches actuated using electrostatic actuation is explored. MEMS switches that are lateral switches and clamped-clamped switches are designed, fabricated, and tested in this thesis. This thesis extensively explains the process by which the MEMS Switches were designed and fabricated. In addition, it explains the changes in the switches when issues called for a modification to devices. Contact resistances were extensively studied, in this thesis. There has been a trade-off between the reliability of switches and their contact resistances. Many actions were taken to mitigate this trade-off and to allow both reliable devices with low contact resistances. The efforts to do so ranged from thermal oxidation to reduce the scalloping on the sidewalls, to modifying the dry etching recipe, to modifying the sputtering recipe, to electroplating, and many more. However, reliability of the MEMS Lateral switches was accomplished independent to the contact resistances. In addition, low contact resistances were accomplished independent to reliability. A novel approach to designing clamped-clamped MEMS switches is also showcased in this thesis. These devices experienced unique challenges compared to those faced with lateral switches. Both lateral and clamped-clamped switches are discussed in-depth in this thesis. / Master of Science

Though modifications and improvements continue on the Virginia Polytechnic Institute electrostatic accelerator, the basic machine has been completed and put into operation. The emphasis thus far has been on experiments at energies below 750 kev and no attempt has been made to determine the maximum operating potential. This work describes the author's contributions to the overall project through the design and construction of many of the electronic control and instrumentation circuits. Through a study of the inelastic collisions of protons with fluorinet, a resolution of 9:1 key was determined. / Master of Science

Wide literature precedence exists for polymers containing electrostatic interactions and polymers containing hydrogen bonding motifs, however the combination of electrostatic and hydrogen bonding interactions is not widely investigated in current literature. Polyelectrolytes containing hydrogen bonding groups are expected to exhibit properties of both classes of supramolecular interactions. A series of adenine- and thyminecontaining PDMAEMA and tert-butyl acrylate copolymers were synthesized to investigate the effect of incorporating hydrogen bonding groups into a polyelectrolyte. Incorporation of the styrenic nucleobases significantly affected the solubility of these copolymers on aqueous solutions and showed salt-triggerability with higher contents of these groups. Polyelectrolytes are capable of binding and condensing DNA through electrostatic interactions with the negatively charged phosphate groups of the DNA backbone; however a high degree of cytotoxicity is also often observed for these gene delivery systems. The high level of cytotoxicity is attributed to high degree of cationic character for the polyplexes formed with these systems according to the proton-sponge hypothesis. One method of reducing the overall cationic character for these systems is incorporation of non-electrostatic binding mechanisms such as hydrogen bonding. A series of nucleobase-containing PDMAEMA copolymers were utilized in order to investigate the effect of incorporation of these groups on the cell viability, binding efficiency, and transfection efficiency of PDMAEMA. / Master of Science

The electrostatic properties of a molecule are often essential in determining its behavior; as such, the ability to approximate these electrostatic potentials computationally is often essential to obtaining a full understanding of how these molecules function. An approximate, analytical solution to the (linearized) Poisson-Boltzmann equation is proposed that is suitable for realistic biomolecules of virtually any size. A comparison with accepted numerical approaches on a large test set of biomolecular structures shows that the proposed method is considerably less expensive computationally, yet accurate enough to be considered as a possible alternative. The utility of the approach is demonstrated by computing and analyzing the electrostatic potential generated by full capsid of the tobacco ringspot virus (half a million atoms) at atomic resolution. The details of the potential distribution on the molecular surface sheds light on the mechanism behind the high selectivity of the capsid to the viral RNA. These results are generated with the modest computational power of a desktop PC. The applicability of the analytical approximation as an initial guess for traditional numerical methods as a means of improving the convergence of iterative solutions is investigated and found to be quite promising. / Master of Science

Stent is one of the coronary angioplasty techniques that expands the narrowed coronary arteries due to the accumulation of fat, cholesterol and other substances in the lumen of the arteries. The major complication of stent is restenosis. Current development of drug-eluting stents shows successfully reduce the occurrence of restenosis. Other than using drugs, electrostatic self assembled (ESAd) thin films may be the potential candidates to prevent restenosis. ESA is a process to fabricate thin films bases on the electrostatic attraction between two oppositely charges. We used this technique to fabricate four PVP films and four PEI films. All films were examined by XPS and AFM. XPS data showed our coatings were successfully fabricated on substrates. AFM images revealed PVP coating was uniform, but PEI coatings had different morphologies due to diffusion and pH during the process. Three preliminary hemocompatibility testes were performed to evaluate the hemocompatibility of the coatings. Platelet adhesion study showed the thin films inhibited platelet adhesion. All thin films were able to inhibit coagulation and were less cytotoxic. The studies suggested the ESA films were potentially hemocompatible. / Master of Science

Tout composant envoyé dans l'espace est soumis à de nombreuses contraintes (radiations, température) qui peuvent conduire à une défaillance de l'ensemble du système. Dans un avenir proche, ces contraintes deviendront de plus en plus critiques à mesure que les agences spatiales développeront des missions visant d'autres planètes, telles que Jupiter, pour lesquelles la contrainte radiative est extrême. Dans ce travail, deux types d'effets dus aux radiations sont étudiés : les effets cumulatifs et les effets transitoires. L'un correspond à la dégradation induite par les radiations au cours du temps, tandis que l'autre correspond à un événement ponctuel qui peut se produire à tout moment lorsque le système est dans l'espace. Pour garantir le bon fonctionnement en vol, des normes de qualification des composants électroniques ont été élaborées par différentes agences spatiales. Toutes ces normes précisent que les effets cumulatifs et transitoires doivent être vérifiés à l'aide de composants intacts pour chaque essai. Par conséquent, les effets cumulatifs sont traités séparément des effets transitoires, alors qu'il y a une forte probabilité qu'ils apparaissent simultanément pendant une mission spatiale. L'étude des effets de synergie est alors le thème principal de cette thèse.Sur un amplificateur opérationnel bipolaire, la réponse de sortie du composant due à un événement transitoire est directement liée aux paramètres internes du composant, qui varient sous l’effet des radiations. A l’aide d’une comparaison entre trois amplificateurs opérationnels différents partageant la même référence, l'impact du design sur la dégradation due aux radiation est étudié.Récemment, des défaillances imprévues ont été reportées pour lesquelles le mode de défaillance semblait indiquer qu'une structure de protection contre les décharges électrostatiques (ESD) était en cause. Par conséquent, pour comprendre si ces protections peuvent causer des défaillances inattendues, la dégradation des « Gate Grounded n-MOSFET » (GGnMOS) est également étudiée. / Any system sent to space is submitted to many constraints (radiations, temperature) which may lead to a failure of the whole system. In a close future, these constraints will become more and more critical as the space agencies are developing missions aiming at others planets such as Jupiter for which the radiative constraint is extremely harsh. In this work, two types of radiation effects are studied: the cumulative effects and the transient effects. One corresponds to the radiation-induced degradation over time, while the other corresponds to a punctual event that can happen at any time when the system is in space. To ensure a proper functioning of a system sent to space, qualifications standards for electronic components have been developed by different space agencies. All of these standards specify that the components must be tested for cumulative and transient effects, using pristine components for each test. Therefore, cumulative effects are treated separately from transient effects, while there is a significant probability that they will appear simultaneously during a space mission. The study of the synergistic effects is then the main frame of this thesis.On a bipolar operational amplifier, the output response of the component due to a transient event is directly related to the internal parameters of the component, which vary over time once in space. Through a comparison between three different operational amplifier sharing the same reference, the impact of the design over the degradation is explained.Lately, some unexpected failures were reported for which the failure mode seemed to indicate that an Electrostatic Discharge (ESD) protection structure was involved. Therefore, to understand if those protections may cause some unexpected failures, the degradation of gate grounded n-MOSFET (GGnMOS) will be investigated next.