Enhanced performance and functionality of titanium dioxide papermaking pigments with controlled morphology and surface coating

Novel, tailored titanium dioxide pigments with controllable nanoscale morphological features were shown to significantly enhance the optical and strength properties of paper. The opacifying power of synthesized polycrystalline TiO2 particles in a cellulose matrix was found experimentally to be superior to that of a commercial rutile pigment, depending on the crystal structure of the synthesized particles. High aspect ratio polycrystalline rutile pigments composed of a linear linkage of several individual rutile crystals gave 6% more opacity than the commercial rutile pigment. Theoretical light scattering calculations using the T-Matrix Method showed the light scattering efficiency of linearly arranged polycrystalline rutile particles to depend on number and size of crystals composing the particle and confirmed the higher efficiency of the synthesized polycrystalline rutile pigments over commercial rutile. The opacifying power of hollow polycrystalline rutile particles was found experimentally to be superior to that of a commercial rutile pigment in a highly pressed bleached fiber matrix, depending on cavity size, while the opacifying power of silica-rutile titania core-shell particles was found comparable to commercial rutile at constant titania loading. The light scattering efficiency of titania core-shell particles was shown to be dependant on the light scattering efficiency of the core material. The overall particle shape and aspect ratio of titania core-shell and hollow nanoparticles were shown to be tunable by choosing an appropriate template and coating thickness in layer-by-layer or sol-gel templating synthesis. Inorganic-cellulose core-shell and hollow cellulose nanoparticles were prepared by self-encapsulation with regenerated cellulose via precipitation of cellulose in a polyacrylic acid hydrogel layer surrounding inorganic particle templates in 4-Methylmorpholine N-oxide (NMMO) monohydrate solution. This discrete encapsulation of inorganic pigments with a thin, uniform cellulose shell was found to increase the bondability improvement between the particles and a polysaccharide substrate. The crystallinity of several carbohydrate polymers was shown to significantly affect the bondability of encapsulated core-shell particles.Ph.D.Committee Chair: Yulin Deng; Committee Member: Arthur Ragauskas; Committee Member: Jeff Empie; Committee Member: Jeffery Hsieh; Committee Member: Preet Sing

Coherent phonons in plasmonic nanostructures and surface phonon polariton resonators for enhanced light-matter interaction in the mid-IR

Light exhibits a rich set of phenomena when interacting with matter, making it an invaluable tool for fundamental research and also for technological applications. However, in many instances, the size mismatch between matter components and the localization of light with conventional optical elements hampers a more fruitful exploitation of this interaction. The excitation of plasmon polaritons in metals enables us to circumvent the limits in the light localization imposed by far-field diffraction. Nevertheless, the light confinement at optical frequencies in plasmonic systems requires the storage of energy in the motion of free-electrons, which are subject to unavoidable ohmic losses. At lower frequencies, the large negative real permittivity of metals leads to a poor confinement of the near-field radiation. The high losses impede the application of plasmonic systems in the transmission and the guiding of sub-diffraction optical modes. Additionally, the poor confinement at longer wavelengths limits the study and the application of enhanced molecular sensing which requires spatial and spectral overlap between confined modes and vibrational transitions in chemical species. Thus, the search for alternative materials that can provide sub-diffraction light confinement with low losses across the electromagnetic spectrum becomes a major goal in nanophotonics research. In this thesis we explore how the fast electronic relaxation processes related to losses in plasmonic systems can be used to generate coherent acoustic phonons of tailored frequency and amplitude in metallic nanoantennas subject to dielectric mechanical constraints. The damping of coherent phonons through emission of surface acoustic waves (SAWs) is also explored, where narrow-frequency mechanical modulation of plasmonic resonances via the emitted SAWs is shown possible. Finally, we investigate the potential of sub-diffraction surface phonon polariton resonances in polar dielectric materials as an alternative to plasmonic systems for sensing in the mid-infrared range, where the detection of sub-nanometric film thicknesses is achieved.Open Acces

Contributions to the Characterization and Mitigation of Rotorcraft Brownout

Rotorcraft brownout, the condition in which the flow field of a rotorcraft mobilizes sediment from the ground to generate a cloud that obscures the pilot's field of view, continues to be a significant hazard to civil and military rotorcraft operations. This dissertation presents methodologies for: (i) the systematic mitigation of rotorcraft brownout through operational and design strategies and (ii) the quantitative characterization of the visual degradation caused by a brownout cloud. In Part I of the dissertation, brownout mitigation strategies are developed through simulation-based brownout studies that are mathematically formulated within a numerical optimization framework. Two optimization studies are presented. The first study involves the determination of approach-to-landing maneuvers that result in reduced brownout severity. The second study presents a potential methodology for the design of helicopter rotors with improved brownout characteristics. The results of both studies indicate that the fundamental mechanisms underlying brownout mitigation are aerodynamic in nature, and the evolution of a ground vortex ahead of the rotor disk is seen to be a key element in the development of a brownout cloud. In Part II of the dissertation, brownout cloud characterizations are based upon the Modulation Transfer Function (MTF), a metric commonly used in the optics community for the characterization of imaging systems. The use of the MTF in experimentation is examined first, and the application of MTF calculation and interpretation methods to actual flight test data is described. The potential for predicting the MTF from numerical simulations is examined second, and an initial methodology is presented for the prediction of the MTF of a brownout cloud. Results from the experimental and analytical studies rigorously quantify the intuitively-known facts that the visual degradation caused by brownout is a space and time-dependent phenomenon, and that high spatial frequency features, i.e., fine-grained detail, are obscured before low spatial frequency features, i.e., large objects. As such, the MTF is a metric that is amenable to Handling Qualities (HQ) analyses

Problems in Scattering and Imaging

Technology advances are always driven by the discovery of new materials, better understanding of their properties and improvements in processing power. This trend is reflected in this work, where I will demonstrate how new science and applications of both scattering and imaging are enabled by these frontiers. This thesis explores a broad spectrum of topics associated with the problems of scattering and imaging. The first topic concerns the fundamental study of the symmetry breaking and the nonlinear light scattering in the system of gold nanorod. In the most recent experiments, the intrinsic electrostatic asymmetry of gold nanorods was investigated by Ji-Young et al. using a variety of microscopy techniques, and the associated optical asymmetry was immediately demonstrated through the nonlinear optical experiments. The understanding of the symmetry breaking of gold nanorods, motivated the development of a model where the second order longitudinal plasmon resonance mode scatters with the electron gas and accounting for the plasmon damping effect. The new microscopic description self-consistently explains all the main features of the nonlinear optical components, and provides a fresh look that beautifully aligns with the recent observations of the nonlinear optical properties of nanorods. Next, we demonstrate an optical system that enables the control of monochromatic light transmission through highly scattering media, with Complex Semi-Definite Programming (SDP) introduced as a novel approach to solve the associated phase retrieval problem. In contrast to the conventional approach that employed an interferometric design which is vulnerable to system vibration, a simple optical setup without the need for a reference beam is proposed by Moussa et al. The SDP algorithm allows computation of the complex transmission matrix of the system from a sequence of intensity speckle patterns generated with phase-modulated wavefronts. We showed that once the transmission matrix is determined, optimal wavefronts can be computed that focuses the incident beam to any position on the far side of the scattering medium, without the need for subsequent measurements or wavefront shaping iterations. Finally, the optical properties and applications of graphene were explored. As a true 2D material, graphene has a unique electronic band structure and has been demonstrated by various research groups to be an interesting photonic building block. At first, we focused on the absorption saturation in optically excited graphene. The microscopic theory that includes Coulomb-scattering as the dominant relaxation mechanism at high carrier densities was developed and then verified by the optical transmission experiment. Then, we showed a novel scheme of a light field camera using a focal stack proposed by a team at the University of Michigan. The key enabling technology is the highly transparent graphene photodetector fabricated by Che-Hung et al., where graphene is used both as the photoconductive gain material and the circuit interconnects. Physically, we built the prototype single-pixel light field camera and demonstrated its operation through optical experiment. Computationally, a synthetic camera system was designed based on the Fourier slice analysis and the framework for the model-based light field reconstruction was provided.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138550/1/mblien_1.pd

Using strain field mining to reveal the spatial distributions of tensile, fatigue, and fracture damage accumulation in paper

The most common nonwoven fiber composite material, paper, has a porous, heterogeneous fiber network structure and complicated mechanical properties. The mechanical properties of commercial, machine made papers are orthotropic and are sensitive to loading rate, moisture content, and temperature. Thus, defining the constitutive relationship of paper has remained as a challenge due to the stochastic nature of the structure and countless variables that affect the mechanics of paper. Moreover, the technology to non-destructively characterize the three-dimensional network topography at the fiber length scale is not readily available. This presents a critical barrier to establishing the structure-property relationships of paper. Here, I approached the problem with a fundamentally different strategy and used the structure of the strain fields as a proxy for the network topography. The strain fields of paper from tensile, fatigue, tearing experiments revealed new information about each damage mechanisms. During the tensile deformation, the interplay between the axial and the transverse motions in the fiber network resulted in specimen-orientation-dependent (MD and CD) parameters such as Poisson's ratio, hot spot length scales, and the degree of nonaffinity, D. These metrics were direct manifestation of the anisotropic fiber network in paper. Next, I used strain field mining to track the fatigue crack lengths and quantified crack growth rates during cyclic and constant loading conditions. The fracture profiles and the crack growth rates revealed that there was a unique fatigue damage mechanism in paper which induced the fiber fracture rather than the fiber pull-out. Moreover, I found that the pre-applied creep damage in paper can significantly reduce the fatigue crack growth rate and extend paper's high cycle fatigue life. Lastly, from the strain fields of tearing specimens, I was able to characterize paper's crack tip process zone and the zone of active plasticity (ZAP) whose shape depended on the orientation of the fiber network. Although paper has a completely different structure and failure mechanism from metals, I found that tearing of paper also followed a steady-state process, which was previously observed in thin sheet aluminum foils.Ph.D

Volume 21, Summer 1994 Communication and Theater Association of Minnesota Journal

Complete digitized volume (volume 21, Summer 1994) of Communication and Theater Association of Minnesota Journal

Rigorous direct and inverse design of photonic-plasmonic nanostructures

Designing photonic-plasmonic nanostructures with desirable electromagnetic properties is a central problem in modern photonics engineering. As limited by available materials, engineering geometry of optical materials at both element and array levels becomes the key to solve this problem. In this thesis, I present my work on the development of novel methods and design strategies for photonic-plasmonic structures and metamaterials, including novel Green’s matrix-based spectral methods for predicting the optical properties of large-scale nanostructures of arbitrary geometry. From engineering elements to arrays, I begin my thesis addressing toroidal electrodynamics as an emerging approach to enhance light absorption in designed nanodisks by geometrically creating anapole configurations using high-index dielectric materials. This work demonstrates enhanced absorption rates driven by multipolar decomposition of current distributions involving toroidal multipole moments for the first time. I also present my work on designing helical nano-antennas using the rigorous Surface Integral Equations method. The helical nano-antennas feature unprecedented beam-forming and polarization tunability controlled by their geometrical parameters, and can be understood from the array perspective. In these projects, optimization of optical performances are translated into systematic study of identifiable geometric parameters. However, while array-geometry engineering presents multiple advantages, including physical intuition, versatility in design, and ease of fabrication, there is currently no rigorous and efficient solution for designing complex resonances in large-scale systems from an available set of geometrical parameters. In order to achieve this important goal, I developed an efficient numerical code based on the Green’s matrix method for modeling scattering by arbitrary arrays of coupled electric and magnetic dipoles, and show its relevance to the design of light localization and scattering resonances in deterministic aperiodic geometries. I will show how universal properties driven by the aperiodic geometries of the scattering arrays can be obtained by studying the spectral statistics of the corresponding Green’s matrices and how this approach leads to novel metamaterials for the visible and near-infrared spectral ranges. Within the thesis, I also present my collaborative works as examples of direct and inverse designs of nanostructures for photonics applications, including plasmonic sensing, optical antennas, and radiation shaping

Development of a compact wireless SAW Pirani vacuum microsensor with extended range and sensitivity

Vakuumsensoren haben nach wie vor einen begrenzten Messbereich und erfordern eine aufwendige Verkabelung sowie eine komplexe Integration in Vakuumkammern. Ein kompakter Sensor, der in der Lage ist, den Erfassungsbereich zwischen Hochvakuum und Atmosphärendruck zu erweitern und dabei drahtlos zu arbeiten, ist äußerst wünschenswert. Der Schwerpunkt dieser Arbeit liegt auf dem Entwurf, der Simulation, der Herstellung und der experimentellen Validierung eines drahtlosen kompakten Vakuum-Mikrosensors mit erweiterter Reichweite und Empfindlichkeit. Zunächst wurde ein neuer Sensor unter Verwendung vorhandener und neu entwickelter Komponenten entworfen. Zweitens wurden die Sensorkomponenten simuliert, um ihre Parameter zu optimieren. Drittens wurde ein Prototyp unter Verwendung der verfügbaren Mikrobearbeitungs- und Halbleitertechnologien hergestellt und montiert. Viertens wurde der Prototyp unter Umgebungs- und Vakuumbedingungen charakterisiert, um seine Leistungen zu validieren. Für das Wandlerprinzip wurden zwei Techniken kombiniert, nämlich Pirani-Sensorik und akustische Oberflächenwellen. Das Design der Sensorkomponenten bestand aus vier Einheiten: Sensoreinheit, Heizeinheit, Abfrageeinheit und Gehäuse. Alle Einheiten wurden in einen kompakten Würfel eingebaut. Einige Komponenten wurden neu entwickelt, während andere gekauft, modifiziert und dann miteinander verbunden wurden. Die Sensoreinheit besteht aus einem neuen Chip mit verbesserter Sensorleistung dank eines optimierten Verhältnisses von Oberfläche zu Volumen. Die Heizeinheit wurde aus zwei induktiv gekoppelten Spulen und der zugehörigen Konditionierungselektronik zusammengesetzt. Die Abfrageeinheit wurde mit einer Mikro-Patch-Antenne hergestellt. Ein würfelförmiges Polymergehäuse wurde entwickelt, um alle Komponenten in einer Vakuumkammer unterzubringen. Zweitens wurde die Simulation des Verhaltens der Sensorkomponenten behandelt. Die für die Druckmessung verantwortliche Wärmeübertragung des Sensorchips wurde vom Hochvakuum bis zum Atmosphärendruck untersucht, um seine Abmessungen zu optimieren. Die Verwendung eines hängenden Lithium-Niobat-Chips mit Y-Z-Schnitt und einem TCF von 94 ppm/K führte zu einer verbesserten Leistung in einem Messbereich zwischen \num{d-4}~Pa und \num{e5}~Pa. Die elektronische Kopplung der Heizspulen wurde ebenfalls simuliert, um die Leistungsübertragung und den Kopplungsabstand zu optimieren. Der dritte Teil betrifft die Herstellungs- und Montageschritte des Prototyps unter Verwendung der verfügbaren Halbleitertechnologien und -ausrüstung. Ein SAW Chip wurde mit einer 100~nm dicken Goldschicht an der Unterseite gesputtert, um den Heizwiderstand zu bilden, und mit Hilfe von Drahtbonding elektrisch mit dem Rest des Sensors verbunden. Es wurde eine Leiterplatte vorbereitet, die die Heiz- und Sensoreinheit enthält. Ein kubisches Gehäusewurde aus PTFE hergestellt. Viertens wurden die Sensorkomponenten zunächst separat charakterisiert, um ihre Leistungen zu überprüfen, und dann zusammen unter Umgebungsbedingungen. Später wurde der Sensor im Vakuum integriert, und es wurde ein druckabhängiges Verhalten des Sensorchips beobachtet. Die Relevanz eines drahtlosen Übertragungsverfahrens wurde den herkömmlichen drahtgebundenen Methoden gegenübergestellt. Die Ergebnisse der experimentellen Arbeiten außerhalb und innerhalb des Vakuums zeigten die Machbarkeit und Relevanz des neuen Konzepts

Volume 22, Summer 1995 Communication and Theater Association of Minnesota Journal

Complete digitized volume (volume 22, Summer 1995) of Communication and Theater Association of Minnesota Journal

Framing, control-related beliefs and outsourcing of decision making: a study of management consulting interventions

Outsourcing of decision-making refers to the delegation of management’s responsibility to make decisions to external organizational agents. These include consultants. This thesis elaborates a theoretical framework for the analysis of outsourcing of decision-making, testing empirically its adaptive value for the self-regulation system. It explores why managers outsource decision-making and what consequences follow if they do not do so in situations framed as threat. A qualitative study suggested that two cognitive concepts, framing of the decision event and control-related beliefs, lead to outsourcing of decision-making. A quasi-experiment and an experiment using computer-simulation examined empirically their relevance to the propensity of managers to outsource strategic decision-making. Results showed that framing as opportunity led to a perception of enhanced control. Consequently, individuals were inclined to remain proactive and to shape their environment according to their wishes. This type of control has been conceived of in the literature as primary control. Threat, on the other hand, led to a perception of loss of control, and individuals tried to adapt internally, rather than change the environment. This cognitive strategy is called secondary control. The thesis reports the development of a scale of primary and secondary control in the field of management and confirms the following model: Framing as threat reduces the perception of primary control, which in turn makes outsourcing of decision-making more likely. Outsourcing of decision-making is accompanied by a transition from primary to secondary control. A failure to shift to secondary control under conditions of threat has negative impact on personal well-being. This research found empirical evidence that secondary control is a coping mechanism rather than a type of control. It is argued that management education should create awareness of its adaptive value. Two strategies could help to avoid high degrees of outsourcing of decision-making: influencing either the framing of the situation or the perception of control