POLYMERIC IMPULSIVE ACTUATION MECHANISMS: DEVELOPMENT, CHARACTERIZATION, AND MODELING

Recent advances in the field of biomedical and life-sciences are increasingly demanding more life-like actuation with higher degrees of freedom in motion at small scales. Many researchers have developed various solutions to satisfy these emerging requirements. In many cases, new solutions are made possible with the development of novel polymeric actuators. Advances in polymeric actuation not only addressed problems concerning low degree of freedom in motion, large system size, and bio-incompatibility associated with conventional actuators, but also led to the discovery of novel applications, which were previously unattainable with conventional engineered systems. This dissertation focuses on developing novel actuation mechanisms for soft polymeric gel systems with easily adjustable mechanochemical properties and applicability to various environmental conditions. Inspired by stunning examples in nature which exhibit extremely fast motion in a repeatable manner, termed impulsive motion, we have developed polymeric gel actuators applicable for small-scale, self-contained impulsive systems. In particular, we focused on the effect of geometry and the mechanics of surface-mediated stresses on the dynamic shape-change of polymer gel actuators. We found new opportunities from observation of transient deformations which occur during swelling, or deswelling, of asymmetric gels. We described the development of time-dependent three-dimensional deformation mechanism (4D fabrication) by the utilization of transient inhomogeneous swelling state of the asymmetric polymer gel. We discussed the mechanism and the application of the new deformations mechanism for the development of a novel functionality: chemical gradient sensor. In addition, we developed a high-rate and large-strain reversible actuation mechanism for sub-micrometer scale polymeric gel actuators by utilizing balanced effects of two surface-mediated phenomena, surface diffusion and interfacial-tension, and elasticity of soft and small-scale hydrogels. These new findings were harnessed for developing autonomously controlled power amplified polymeric gel devices. Utilizing deswelling induced transient deformation of gel, we developed design principles for generating meta-stable structures and inducing self-regulating transition forces for repeated snap-through buckling transition of polymeric gel devices. In parallel, we deconvoluted the effect of material properties and geometry on dynamic deformations by establishing simulation models and conducting analyses on the performances of actual synthetic systems. The systematic approach will serve to broaden the application spectrum and manufacturing possibilities of polymeric actuator systems

Thermochemical conversion of biomass in a Swirling Fluidized Bed: a design procedure and numerical simulation

Process intensification of biomass conversion as a route to a low-carbon manufacturing industry pursues novel solutions able to achieve safe, cost-efficient, energy-efficient, and environment-friendly processes. Implementation of process intensification in gas-solid operations enhances mass, heat, and momentum transfer rates, while develops multifunctional equipment to increase production capacity per size of installation. The Swirling Fluidized Bed reactor is a gas-solid contacting device that replaces the Earth's gravitational field with a centrifugal field generating a centrifugal bed that achieves more uniform beds, higher transfer rates, and shorter processing times than conventional fluidized beds. However, there is a gap of research in two points: a binary-phase numerical simulation to study both gas and solid hydrodynamics, and the constructive design of the swirling fluidized bed reactor related to expected operating conditions. In the present work, a design procedure of swirling fluidized beds for thermochemical conversion of biomass is proposed. The study of the swirling fluidized bed reactor comprises three stages: a systematic literature review, a numerical simulation of the reactor, and the development of the design procedure. The simulation gives insight of the SFB reactor operation useful for the decision making during early stages of design. Thermochemical and mechanical models together with technical procedures are used for the reactor design. The proposed design shows good agreement with an operational reactor used for rice husk combustion.MaestríaMagister en Ingeniería Mecánic

Nanoparticle-Shelled Bubbles for Lightweight Materials

Lightweight materials that are mechanically robust are of great interest in automotive, aerospace, and construction industries. However due to the nature of materials, it is challenging to obtain materials that have high strength, stiffness and toughness, and light weight simultaneously. One approach that tries to address this limitation is the use of composite materials containing hollow microparticles, also known as syntactic foams. The incorporation of hollow microparticles decreases the density of the material at the same time that increases its specific strength. Conventional methods of fabrication of hollow particles involving bulk reactions result in high heterogeneity in geometry as well as mechanical properties, and little or no control over the shell nanostructure. This variability in the structure and properties of the hollow microparticles adversely affects the macroscopic properties of the syntactic foams and hinders the understanding of the structure-property relationship. The use of microfluidics for the generation of shelled-bubbles addresses these limitations. This microfluidic technique, in contrast to bulk methods, is based on single droplet formation, allowing for the generation of highly uniform bubbles, and enabling the assembly of nanoparticles at the interface forming stable nanoparticle-shelled bubbles. Microfluidics allow a precise control over the geometry, nanostructure and properties of the shelled-bubbles, further enabling the functionalization of the shell surface to present amphiphilicity, or the modification of the shell structure with thermal processes to enhance their mechanical behavior. These versatile nanoparticle-shelled bubbles are optimal candidates to form hierarchically assembled lightweight composites with targeted mechanical properties. In composites, the precise control over the structure and properties of the fillers allows the determination of the structure-property relationship, and enables a better understanding of the effect of the nanostructure on the macroscopic mechanical response

Development of a low damping MEMS resonator

MEMS based low damping inertial resonators are the key element in the development of precision vibratory gyroscopes. High quality factor (Q factor) is a crucial parameter for the development of high precision inertial resonators. Q factor indicates how efficient a resonator is at retaining its energy during oscillations. Q factor can be limited by different types of energy losses, such as anchor damping, squeeze-film damping, and thermoelastic damping (TED). Understanding the energy loss-mechanism can show a path for designing high Q resonator. This thesis explores the effects of different design parameters on Q factor of 3D inertial resonators. TED loss mechanisms in a 3D non-inverted wineglass (hemispherical) shell resonator and a disk resonator were investigated. Both the disk and shell share the same vibration modes, and they are widely used as a vibratory resonator shape. Investigation with loss-mechanism shows that robust mechanical materials such as fused silica can offer ultra-low damping during oscillation. TED loss resulting from the effects of geometric parameters (such as thickness, height, and radius), mass imbalance, thickness non-uniformity, and edge defects were investigated. Glassblowing was used to fabricate hemispherical 3D shell resonators and conventional silicon based dry etching was used to fabricate micro disk resonators. The results presented in this thesis can facilitate selecting efficient geometric and material properties for achieving a higher Q-factor in 3D inertial resonators. Enhancing the Q-factor in MEMS based 3D resonators can further enable the development of high precision resonators and gyroscopes

Applications of Marangoni Forces in Actuating Solid Phase Objects.

The Marangoni effect develops due to surface tension variations at the liquid/gas interface caused by temperature gradient in the liquid. Spatially localized temperature rise reduces the localized surface tension, resulting in surface flows away from the heat source and subsurface flows in opposite direction. This phenomenon shows potential in droplet/particle manipulation for microfluidic applications. In this work, a series of experiments is performed to address several important questions to further evaluate the utility of this effect. The questions address how to spatially localize suspension particles on blank substrates, sort floating particles according to size, and actuate millimeter-sized solid objects. Using a heater array suspended about 500 micrometer above the liquid, Marangoni flows are shown to spatially localize sedimentations of microscale suspended particles. The sedimentation patterns and accumulation levels depend on the temperature gradient at the liquid surface, number of active heaters and type of liquid used. For example, a single active heater is used to generate a temperature elevation of 6.9 K at the surface of silicone oil DC-704, resulting in the localized sedimentation of suspended 25 micrometer pollen over a region of 2.9 squared millimeter beneath the active heater. Marangoni flows in evaporating liquid droplets can be utilized to sort cenospheres with sizes in a continuous spectrum from 5-200 micrometer. By heating the droplets from below, spheres 100-200 micrometer are deposited at the center and <50 micrometer spheres at the droplet periphery. The physical separation of large and small spheres is possible by using perforated metal plates. Cenospheres about 200 micrometer in diameter are subsequently modified by a focused ion beam to form hemispherical shells, and the fundamental wine glass mode resonance is investigated. Activating the suspended heater array in a certain configuration rotates a millimeter-scale rotary structure mounted on a hub and completely immersed in the liquid. With a maximum temperature gradient of 36.6 K/mm at the surface of a liquid with viscosity 5 cSt, the structure takes 28 s to make a complete rotation. The angular velocity of the structure depends on the temperature gradient and viscosity of the liquid.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/99924/1/erwinh_1.pd

Experimental and Novel Analytic Results for Couplings in Ordered Submicroscopic Systems: from Optomechanics to Thermomechanics

Theoretical modelling of challenging multiscale problems arising in complex (and sometimes bioinspired) solids are presented. Such activities are supported by analytical, numerical and experimental studies. For instance, this is the case for studying the response of hierarchical and nano-composites, nanostructured solid/semi-fluid membranes, polymeric nanocomposites, to electromagnetic, mechanical, thermal, and sometimes biological, electrical, and chemical agents. Such actions are notoriously important for sensors, polymeric films, artificial muscles, cell membranes, metamaterials, hierarchical composite interfaces and other novel class of materials. The main purpose of this project is to make significant advancements in the study of such composites, with a focus on the electromagnetic and mechanical performances of the mentioned structures, with particular regards to novel concept devices for sensing. These latter ones have been studied with different configuration, from 3D colloidal to 2D quasi-hemispherical micro voids elastomeric grating as strain sensors. Exhibited time-rate dependent behavior and structural phenomena induced by the nano/micro-structure and their adaptation to the applied actions, have been explored. Such, and similar, ordered submicroscopic systems undergoing thermal and mechanical stimuli often exhibit an anomalous response. Indeed, they neither follow Fourier’s law for heat transport nor their mechanical time-dependent behavior exhibiting classical hereditariness. Such features are known both for natural and artificial materials, such as bone, lipid membranes, metallic and polymeric “spongy” composites (like foams) and many others. Strong efforts have been made in the last years to scale-up the thermal, mechanical and micro-fluidic properties of such solids, to the extent of understanding their effective bulk and interface features. The analysis of the physical grounds highlighted above has led to findings that allow the describing of those materials’ effective characteristics through their fractional-order response. Fractional-order frameworks have also been employed in analyzing heat transfer to the extent of generalizing the classical Fourier and Cattaneo transport equations and also for studying consolidation phenomenon. Overall, the research outcomes have fulfilled all the research objectives of this thesis thanks to the strong interconnection between several disciplines, ranging from mechanics to physics, from structural health monitoring to chemistry, both from an analytical and numerical point of view to the experimental one

Use of rotary kilns for solar thermal applications: Review of developed studies and analysis of their potential

Rotary kilns have a long history of use in classical industries. They are able to achieve high temperatures with higher thermal efficiencies than other reactor types. Their performance has been widely studied and classified according to different parameters. Since it is a well-known technology, rotary kilns have been selected for high temperature solar processes. This article initially presents a brief review of the rotary kiln technology and it focuses on the employment of these devices for thermal and thermochemical processes conducted by concentrating solar energy. Among the solar devices, a novel rotary kiln prototype for thermochemical processes is presented and compared with a static solar reactor. Finally, some practical conclusions on the design and operation of solar rotary kilns are remarked and an analysis of their main limitations is presented.The authors acknowledge the financial support provided by the FONDECYT project number 3150026 of CONICYT (Chile), the Education Ministry of Chile Grant PMI ANT 1201, as well as CONICYT/FONDAP/ 15110019 ‘‘Solar Energy Research Center” SERC-Chile. Also, the second author wish to thank to the Plataforma Solar de Almería and the University of Almería for the collaboration and assistance devoted to the development of his Ph.D research