Electronic devices are used for tasks such as keeping people connected, figuring out the contents of a package or detecting impurities in the air. The use of electronic sensors in short life cycle products has also begun to increase with the field of smart packaging. For example, RFID tags are used everyday in sorting facilities to identify packages and then discarded when the packaging is thrown away. Every year the world generates millions of tons of E-waste and most of it is exported, incinerated, or put in landfills. To mitigate the impact of electronics on the environment, it is essential that the next generation of disposable electronic devices are fabricated using environmentally friendly materials. For these materials to be considered for high throughput fabrication they need to be solution processable and biodegradable, all while having the necessary mechanical and electrical properties. This thesis focuses on the development of novel environmentally friendly dielectrics that can be used in capacitors and thin film transistors. A common environmentally friendly and biodegradable material used as a polymer dielectric is poly(vinyl alcohol) (PVA). Although PVA has a high capacitance it also has its drawbacks. Being mostly processed from aqueous solutions it is hard to form uniform thin films of PVA and it is sensitive to moisture which changes its capacitance. PVA is also a polar material which can cause charge trapping at the semiconductor/dielectric interface when used as a dielectric in the fabrication of organic thin film transistors (OTFTs). In this thesis we use different strategies such as blending dielectrics and stacking them to help improve the performance of PVA as a dielectric in OTFTs. In the first study, I demonstrate how low weight percentages of cellulose nanocrystals can be used to increase the viscosity of PVA without negatively impacting its dielectric properties. This led to better film uniformity and a larger number of functioning OTFTs. The second study focused on using a toluene diisocyanate terminated polycaprolactone (TPCL) polymer as a low-k barrier between PVA and the semiconductor. The TPCL led to an increase in OTFT performance and a large reduction in moisture sensitivity. For the third study, I improved the shelf life of the TPCL materials by replacing the toluene diisocyanate end units with UV crosslinking end units. The UV end units were protected unlike the TPCL end units allowing the polymer to remain stable under ambient conditions. The UV-PCL demonstrates similar resistance to moisture and dielectric properties to TPCL while being more stable and easier to use in traditional printing processes. My last study, investigates the use of a poly(lactic acid) (PLA) layer as a third layer in the TPCL/PVA/PLA dielectric system. The PLA layer acted as an intermediate between the substrate and PVA increasing the adhesion of PVA. Further the PLA layer improved OTFT performance and allowed for n-type single walled carbon nanotube transistors under ambient conditions. Finally, this work has demonstrated ways to improve the performance of PVA so that it can be used as an environmentally friendly dielectric in thin film, flexible and printed electronic applications.

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<p> Effects of electron correlations on a two dimensional quantum spin Hall system are studied. We examine possible phases of a generalized Hubbard model on a bilayer honeycomb lattice with a spin-orbit coupling and short range electron-electron repulsions at half filling, based on the slave rotor mean-field theory. The phase diagram of the model is found for a special case where the interlayer Coulomb repulsion is comparable to the intralayer Coulomb repulsion.</p> <p> Besides the conventional quantum spin Hall phase and a broken-symmetry insulating phase, we find a new phase, a fractionalized quantum spin Hall phase, where the quantum spin Hall effect arises for fractionalized spinons which carry only spin but not charge. Experimental manifestations of the exotic phase and effects of fluctuations beyond the saddle point approximation are also discussed.</p> <p> We finally study a toy Bose-Hubbard model for the charge sector of the theory to gain some insight into the phase diagram away from the special Coulomb repulsion values.</p> / Thesis / Master of Science (MSc)

Anyone who has eaten spicy foods has experienced the adverse effects of capsaicin, the pungent chemical found in hot chili that causes a burning sensation. The specific action of capsaicin occurs by the activation of receptors in sensory neurons. This thesis investigates the interaction of capsaicin with model cell membranes representing the structure of neurons. In particular, we are interested in the changes induced by capsaicin to the structure and dynamics of membranes. Molecular dynamics simulations are used to study the molecular interactions. The first part of this study evaluates different molecular representations for capsaicin in an 1-octanol/water system. This inhomogeneous system is commonly used to determine the partition of compounds between hydrophilic and hydrophobic environments, as that found in biological membranes. The results of these simulations validate the OPLS united-atom force field as a reasonable molecular representation of capsaicin, as it describes the behavior of capsaicin both quantitatively and qualitatively in 1-octanol/water mixtures. In the second part, simulations are performed for capsaicin and model cell membranes consisting of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylethanolamine, two of the most commonly found lipids. Simulations investigated capsaicin in the aqueous and lipid phases. The results provide insight into the changes to the bilayers caused by capsaicin. Bilayers containing dipalmitoylphosphatidylethanolamine showed lower permeabilities to capsaicin than those composed of pure dipalmitoylphosphatidylcholine. Temperature is found to be an important factor in the permeability of capsaicin in the bilayer. Capsaicin in the bilayer concentrated in a region beneath the lipid/water interface, in which favorable hydrophilic and lipophilic interactions occur. The structure of the bilayer is not significantly changed at the concentrations of capsaicin considered. One important result from the simulations indicates that the interfacial density decreases with increasing capsaicin concentration in the bilayer, supporting the experimental observations of increased permeability in bilayers exposed to capsaicin. / Master of Science

Within the vestibular system are otolith organs, both the utricle and saccule. The primary function of these organs is to transduce linear head accelerations and static head tilts into afferent signals that are sent to the central nervous system for the utilization of image fixation, muscle posture control, and the coordination of musculoskeletal movement in dynamic body motion. The utricle of the red ear slider turtle was studied in this dissertation. The turtle's utricle is composed of several layers. The base layer contains a set of neural receptor cells, called hair cells, and supporting cells. The three layers above the base layer compose the utricle's otoconial membrane (OM) and are: 1.) a saccharide gelatinous layer, 2.) a column filament layer, and 3.) a calcite and aragonite otoconial crystal layer. The primary goal of this research was to study the dynamic response of the turtle's OM to a variety of natural inertial stimuli in order to characterize its inherent mechanical properties of natural frequency ("n), damping ("), and shear modulus (G). The medial-lateral (ML) and anterior-posterior (AP) anatomical axes parameters were measured for the utricle. The ML axis median with 95% confidence intervals was found to be "n = 374 (353, 396) Hz, " = 0.50 (0.47, 0.53), and G = 9.42 (8.36, 10.49) Pa. The AP axis median with 95% confidence intervals was found to be "n = 409 (390, 430) Hz, " = 0.53 (0.48, 0.57), and G = 11.31 (10.21, 12.41). Nonlinearites were not found to occur in the OM for the tested inertial stimuli and no significant difference was found between the mechanical properties for the ML and AP axes. Additionally, this research presents the initial steps to form a novel bio-inspired accelerometer based on the morphology of the utricle. The primary transducer element for this possible otolith organ inspired accelerometer design is a droplet interface bilayer (DIB). A DIB is a lipid bilayer that is formed when the interface of two aqueous droplets, that contain free-floating lipids, are joined. The aqueous droplets are suspended in a nonpolar environment (oil) and the oil/water interface forms a lipid monolayer. This research developed and used an experimental test setup to characterize the mechanoelectrical characteristics of a micron-sized DIB. This information, along with examples in the text, could be used to further design the aforementioned accelerometer. / Ph. D.

This dissertation investigates the behavior of the Escherichia Coli mechanosensitive (MS) channel MscL, when incorporated within a droplet interface bilayer (DIB). The activity of MscL channels in an artificial DIB system is demonstrated for the first time in this document. The DIB represents a building block whose repetition can form the basis to a new class of smart materials. The corresponding stimuli-responsive properties can be controlled by the type of biomolecule incorporated into the lipid bilayer, which is in the heart of this material. In the past decade, many research groups have proven the capability of the DIB to host a wide collection of natural and engineered functional biomolecules. However, very little is known about the mechano-electrical transduction capabilities of the DIB. The research present herein specifically seeks to achieve three direct goals: 1) exploring the capabilities of the DIB to serve as a platform for mechano-electrical transduction through the incorporation of bacterial MscL channels, 2) understanding the physics of mechano-electrical transduction in the DIB through the development of theoretical models, and 3) using the developed science to regulate the response of the DIB to a mechanical stimulus. MscL channels, widely known as osmolyte release valves and fundamental elements of the bacterial cytoplasmic membrane, react to increased tension in the membrane. In the event of hypo-osmotic shocks, several channels residing in the membrane of a small cell can generate a massive permeability response to quickly release ions and small molecules, saving bacteria from lysis. Biophysically, MscL is well studied and characterized primarily through the prominent patch clamp technique. Reliable structural models explaining MscL's gating mechanism are proposed based on its homolog's crystal structure modeling, which lead to extensive experimentation. Under an applied tension of ~10 mN/m, the closed channel which consists of a tight bundle of transmembrane helices, transforms into a ring of greatly tilted helices forming an ~8 A water-filled conductive pore. It has also been established that the hydrophobicity of the tight gate, positioned at the intersection of the inner TM1 domains, determines the activation threshold of the channel. Correspondingly, it was found that by decreasing the hydrophobicity of the gate, the tension threshold could be lowered. This property of MscL made possible the design of various controllable valves, primarily for drug delivery purposes. For all the aforementioned properties and based on its fundamental role of translating cell membrane excessive tensions into electrophysiological activities, MscL makes a great fit as a mechanoelectrical transducer in DIBs. The approach presented in this document consists of increasing the tension in the lipid bilayer interface through the application of a dynamic mechanical stimulus. Therefore, a novel and simple experimental apparatus is assembled on an inverted microscope, consisting of two micropipettes (filled with PEG-DMA hydrogel) containing Ag/AgCl wires, a cylindrical oil reservoir glued on top of a thin acrylic sheet, and a piezoelectric oscillator actuator. By using this technique, dynamic tension can be applied by oscillating one droplet, producing deformation of both droplets and area changes of the DIB interface. The tension in the artificial membrane will cause the MS channels to gate, resulting in an increase in the conductance levels of the membrane. The increase in bilayer tension is found to be equal to the sum of increase in tensions in both contributing monolayers. Tension increase in the monolayers occurs due to an increase in surface area of the constant volume aqueous droplets supporting the bilayer. The results show that MS channels are able to gate under an applied dynamic tension. Interestingly, this work has demonstrated that both electrical potential and surface tension need to be controlled to initiate mechanoelectric coupling, a property previously not known for ion channels of this type. Gating events occur consistently at the peak compression, where the tension in the bilayer is maximal. In addition, the experiments show that no activity occurred at low amplitude oscillations (< 62.5um). These two findings basically present an initial proof that gating is occurring and is due to the mechanical excitation, not just a random artifact. The role of the applied potential is also highlighted in this study, where the results show that no gating happens at potentials lower that 80 mV. The third important observation is that the frequency of oscillation has an important impact of the gating probability, where no gating is seen at frequencies higher than 1 Hz or lower than 0.1 Hz. Each of the previous observations is addressed separately in this research. It was found that the range of frequencies to which MscL would respond to in a DIB could be widened by using asymmetrical sinusoidal signals to stimulate the droplets. By increasing the relaxation time and shorting the compression time, a change in the monolayer's surface area is achieved, thus higher tension increase in the bilayer. It was also found that a high membrane potential assists in the opening of MscL as the droplets are stimulated. This is due to the sensitivity of MscL to the polarity of the signal. By using the right polarity the channel could be regulated to become more susceptible to opening, even at tensions lower than the threshold. Finally, it was demonstrated, for the first time, that MscL would gate in asymmetric bilayers without the need to apply a high external potential. Asymmetric bilayers, which are usually composed from different lipids in each leaflet, generate an asymmetric potential at the membrane. This asymmetric potential is proven to be enough to cause MscL to gate in DIBs upon stimulation. / Ph. D.