Multiple Volume Scattering in Random Media and Periodic Structures with Applications in Microwave Remote Sensing and Wave Functional Materials

The objective of my research is two-fold: to study wave scattering phenomena in dense volumetric random media and in periodic wave functional materials. For the first part, the goal is to use the microwave remote sensing technique to monitor water resources and global climate change. Towards this goal, I study the microwave scattering behavior of snow and ice sheet. For snowpack scattering, I have extended the traditional dense media radiative transfer (DMRT) approach to include cyclical corrections that give rise to backscattering enhancements, enabling the theory to model combined active and passive observations of snowpack using the same set of physical parameters. Besides DMRT, a fully coherent approach is also developed by solving Maxwell’s equations directly over the entire snowpack including a bottom half space. This revolutionary new approach produces consistent scattering and emission results, and demonstrates backscattering enhancements and coherent layer effects. The birefringence in anisotropic snow layers is also analyzed by numerically solving Maxwell’s equation directly. The effects of rapid density fluctuations in polar ice sheet emission in the 0.5~2.0 GHz spectrum are examined using both fully coherent and partially coherent layered media emission theories that agree with each other and distinct from incoherent approaches. For the second part, the goal is to develop integral equation based methods to solve wave scattering in periodic structures such as photonic crystals and metamaterials that can be used for broadband simulations. Set upon the concept of modal expansion of the periodic Green’s function, we have developed the method of broadband Green’s function with low wavenumber extraction (BBGFL), where a low wavenumber component is extracted and results a non-singular and fast-converging remaining part with simple wavenumber dependence. We’ve applied the technique to simulate band diagrams and modal solutions of periodic structures, and to construct broadband Green’s functions including periodic scatterers.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135885/1/srtan_1.pd

Multiple Volume Scattering in Random Media and Periodic Structures with Applications in Microwave Remote Sensing and Wave Functional Materials

The objective of my research is two-fold: to study wave scattering phenomena in dense volumetric random media and in periodic wave functional materials. For the first part, the goal is to use the microwave remote sensing technique to monitor water resources and global climate change. Towards this goal, I study the microwave scattering behavior of snow and ice sheet. For snowpack scattering, I have extended the traditional dense media radiative transfer (DMRT) approach to include cyclical corrections that give rise to backscattering enhancements, enabling the theory to model combined active and passive observations of snowpack using the same set of physical parameters. Besides DMRT, a fully coherent approach is also developed by solving Maxwell’s equations directly over the entire snowpack including a bottom half space. This revolutionary new approach produces consistent scattering and emission results, and demonstrates backscattering enhancements and coherent layer effects. The birefringence in anisotropic snow layers is also analyzed by numerically solving Maxwell’s equation directly. The effects of rapid density fluctuations in polar ice sheet emission in the 0.5~2.0 GHz spectrum are examined using both fully coherent and partially coherent layered media emission theories that agree with each other and distinct from incoherent approaches. For the second part, the goal is to develop integral equation based methods to solve wave scattering in periodic structures such as photonic crystals and metamaterials that can be used for broadband simulations. Set upon the concept of modal expansion of the periodic Green’s function, we have developed the method of broadband Green’s function with low wavenumber extraction (BBGFL), where a low wavenumber component is extracted and results a non-singular and fast-converging remaining part with simple wavenumber dependence. We’ve applied the technique to simulate band diagrams and modal solutions of periodic structures, and to construct broadband Green’s functions including periodic scatterers.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/137141/1/srtan_1.pd

SMRT: an active–passive microwave radiative transfer model for snow with multiple microstructure and scattering formulations (v1.0)

The Snow Microwave Radiative Transfer (SMRT) thermal emission and backscatter model was developed to determine uncertainties in forward modeling through intercomparison of different model ingredients. The model differs from established models by the high degree of flexibility in switching between different electromagnetic theories, representations of snow microstructure, and other modules involved in various calculation steps. SMRT v1.0 includes the dense media radiative transfer theory (DMRT), the improved Born approximation (IBA), and independent Rayleigh scatterers to compute the intrinsic electromagnetic properties of a snow layer. In the case of IBA, five different formulations of the autocorrelation function to describe the snow microstructure characteristics are available, including the sticky hard sphere model, for which close equivalence between the IBA and DMRT theories has been shown here. Validation is demonstrated against established theories and models. SMRT was used to identify that several former studies conducting simulations with in situ measured snow properties are now comparable and moreover appear to be quantitatively nearly equivalent. This study also proves that a third parameter is needed in addition to density and specific surface area to characterize the microstructure. The paper provides a comprehensive description of the mathematical basis of SMRT and its numerical implementation in Python. Modularity supports model extensions foreseen in future versions comprising other media (e.g., sea ice, frozen lakes), different scattering theories, rough surface models, or new microstructure models.</p

Characterization of a metal-extracting water-poor microemulsion

Solvent extraction is the key separation method in hydrometallurgy. With proper conditioning of such a system, the transfer of metal-species from an aqueous phase into an organic phase can be triggered, either the enrich a desired metal species or to remove undesired impurities. On a laboratory scale, many powerful extractants have been synthesized that enable to selectively and efficiently select any desired metal species. However, application on an industrial scale is yet out of grasp, as fundamental principles of solvent extraction formulation are yet poorly understood. One key problem that is encountered by engineers is the formation of undesired phases (e.g. liquid crystals, emulsification and third-phase formation) and no model is available that allows to predict the occurrence of these phases. This work is dedicated to elaborate the macroscopic phase behaviour of solvent extraction systems by systematic screening of the macroscopic properties of a reference model. Therefore, we use HDEHP as extractant molecule and its sodium salt represents the extractant engaged in complex formation and how solvent penetration plays a crucial role. Establishing a phase prism, where the Z-axis represents ratio between HDEHP and NaDEHP, we are able to employ different cuts, known from surfactant science. These allow to deduce the properties of the complexes (also referred to as reverse micelles) on a nanoscopic level. The major revelation is that two different types of phase separation have been identified: an emulsification failure, where the interior solvent (water, that is co-solubilized inside the reverse micelles) is rejected from the extracting organic phase. Second, a liquid-gas type of phase separation, where the exterior solvent (the organic diluent) is repelled, resulting in two organic phases, where the heavy one carries all the extractants and the light one is purely the organic diluent. This second type needs to be avoided in solvent extraction formulation. In the second part of this work and based on the phase diagrams determined in the first part, the conductivity profile is extensively screened in monophasic regions. Three limits have been determined to play a major role on the conducting properties of a water-poor microemulsion: the critical aggregation concentration (CAC); the degree to which the head-groups are hydrated: transition from reverse micelles, where water is immobilized as it hydrates the extractant head-groups, towards swollen reverse micelles, exhibiting a liquid water-core; and the percolation threshold. In total, this gives 5 different regions which have dissimilar conducting properties

Electromagnetic Scattering Models for InSAR Correlation Measurements of Vegetation and Snow

Interferometric Synthetic Aperture Radar (InSAR) has proved successful and efficient in measuring the vertical structure of the distributed targets such as vegetation and snow, which are dominated by volume scattering. In particular, the InSAR correlation measurement has been utilized to retrieve the target vertical structural information. One existing and well-known electromagnetic scattering model of the InSAR correlation was first brought forward focusing on the single-pass InSAR observation of a sparse random medium like vegetation. However, the lack of the adaption of this InSAR scattering model for repeat-pass InSAR observation of vegetation as well as for single-pass InSAR observation of snow by considering its dense medium characteristics, essentially constrain fully exploiting InSAR\u27s capability of measuring sparse and dense medium characteristics. In this work, the well-known InSAR scattering model will be adapted to accommodate the two scenarios: 1) repeat-pass InSAR observation of vegetation and 2) single-pass InSAR observation of snow and considering its dense medium characteristics. Theoretical model derivations as well as parameter retrieval approaches are demonstrated for both of the applications, respectively. Both of the simulated and ground validation results are also presented. The InSAR scattering models along with the parameter retrieval analysis described in this work will expand InSAR\u27s capability as well as the range of vegetation and snow characteristics that can be retrieved by single-pass and/or repeat-pass InSAR systems

Structure and molecular dynamics of liquid crystalline / isotropic block copolymers

Zusammenfassung Mikrophasen separierte Blockcopolymere stellen einen wichtigen Bestandteil der modernen Nanotechnologie dar. Sie kombinieren zwei Polymere mit unterschiedlichen physikalischen Eigenschaften und zeigen eine Domänenbildung im Nanobereich. In dieser Dissertation wurden Morphologie, Molekulardynamik und Phasenübergänge von neuartigen seitenketten-flüssigkristallinen / Polystyren (PSLC) Diblockcopolymeren mit gut definierter chemischer Struktur, breitem Zusammensetzungsbereich und einer engen Molekulargewichtsverteilung studiert. Die Morphologie der mikrophasenseparierten Blockcopolymere wurde mittels Röntgenkleinwinkelstreuung (SAXS) untersucht. Es wurden vier Typen von Strukturen gefunden: Polystyren-(PS)-Zylinder in einer flüssigkristallinen (LC)- Matrix, alternierende Lamellen, LC-Zylinder in einer PS-Matrix und LC-Kugeln in einer PS-Matrix. Die Größenordnung der Domänen lag zwischen 9 und 26 nm, die der Gitterkonstanten zwischen 27 und 47 nm. Das Phasendiagramm verhielt sich in einem Temperaturbereich von 25 bis 170 °C stabil, d.h. die Morphologie der Proben änderte sich nicht. Dennoch unterschied es sich auf Grund des Einflusses der nematischen LC Phase sehr stark vom Phasendiagramm der isotrop/isotropen (I/I) Blockcopolymere. Im Gegensatz zum Phasendiagramm der I/I Blockcopolymere, wies das der untersuchten PSLC Proben eine starke Asymmetrie auf. Die Molekulardynamik wurde mit dielektrischer Spektroskopie (DS) untersucht. Vier Relaxationsprozesse wurden dabei festgestellt – zwei segmentale ({alpha}- Relaxation und {delta}-Relaxation) und zwei lokale ({beta}-Relaxation und {gamma}-Relaxation). Die {alpha}-Relaxation bezieht sich auf die segmentale Bewegung der Hauptkette zusammen mit der Seitenkette. Die {delta}-Relaxation korrespondiert mit der Bewegung der Seitenkette als ganze. Die {beta}-Relaxation der Rotation der Biphenyl Mesogene um ihre Längsachse. Die {gamma}-Relaxation entspricht der Bewegung der Alkylspacer in der Seitenkette des LC Blocks. Während {alpha}- und {delta}-Relaxationen kooperativen Charakter aufweisen, verhält sich die {beta}-Relaxation teilweise kooperativ und {gamma}-Relaxation rein local. PSLC mit eine LC Phase, die eine eingeschränkte Geometrie aufweisen, zeigen einen zusätzlichen Relaxationsprozess bei niedrigen Frequenzen: die sogenannte Maxwell-Wagner (MW) Polarisation. Diese zeigt sich aufgrund der Polarisation am Interface zwischen dem LC und PS Block. Die räumliche Einschränkung des LC Blocks in 1D (Lamellen) und 2D (Zylinder) Domänen hat unterschiedlichen Einfluss auf die dielektrischen Parameter der {alpha}, {delta}, {beta} und {gamma}-Relaxationen, abhängig von der Kooperationslänge für den jeweiligen Prozess. Es wurde festgestellt, dass die Relaxationszeit {tau} für {delta}- und {alpha}-Relaxationensprozesse in eingeschränkter Geometrie signifikant abnimmt. Die Abnahme in {tau} ist bei 2D Begrenzung (zylindrische LC Domänen) stärker ausgeprägt. Die Abhängigkeit der Ralaxationszeit des {beta}-Prozesses von der Einschränkung ist ähnlich der der {alpha}- und {delta}-Relaxationen, wenn auch weniger stark ausgeprägt. Die Relaxationszeit der {gamma}-Relaxation wird nicht durch die Domänenform oder Dimension beeinflusst. Die Ergebnisse dieser Dissertation tragen zu einem besseren Verständnis der Morphologie und Molekulardynamik von seitenketten- flüssigkristallinen / isotropen (SCLC/I) Blockcopolymeren bei. Sie geben auch Aufschluss über die Molekulardynamik in eingeschränkter Geometrie. Die hier präsentierten Ergebnisse bilden damit eine Basis für einerseits weiterführende Entwicklungen im Polymer-LC Design für technische Anwendungen und andererseits für Verbesserungen der aktuell existierenden Theorien über SCLC/I Blockcopolymere.Microphase separated block copolymers are an important part of modern nanotechnology. These block copolymers combine two polymers with different physical properties, which are separated by nanoscale domains. This dissertation investigated the morphology, molecular dynamics and phase transitions of novel side-chain liquid crystalline / polystyrene (PSLC) block copolymers with well defined chemical structure, broad composition range and narrow molecular weight distributions. The domain structure of the microphase separated block copolymers was determined by small angle X-ray scattering (SAXS). Four types of structures were found to occur: polystyrene (PS) cylinders in liquide crystalline (LC) matrix, alternating lamellae, LC cylinders in PS matrix and LC spheres in PS matrix. The domain dimensions vary between 9 and 26 nm and the lattice constants between 27 and 47 nm. The phase diagram remains stable in a temperature range of 25°C-170°C, i.e. the morphology of the samples does not change. However, it differs strongly from the phase diagram of isotropic / isotropic (I/I) block copolymers; due to the influence of the nematic LC phase it is strongly asymmetric. The molecular dynamics, studied by dielectric spectroscopy (DS), detected four relaxation processes: two segmental ({alpha}- relaxation and {delta}-relaxation) and two local ({beta}-relaxation and {gamma}-relaxation) relaxations. They correspond to the segmental motion of the main chain together with the side chain ({alpha}), to the motion of the side-chain as a whole ({delta}), to the rotation of the biphenyl mesogen around its long axis ({beta}) and to the motion of the alkyl spacer in the side-chain of the LC block ({gamma}). While the {alpha}- and {delta}-relaxations show cooperative character, {beta}-relaxation behaves as partially cooperative and {gamma}-relaxation shows purely local behaviour. The PSLC with a LC phase, confined in domains exhibit an additional relaxation process at low frequencies, namely the Maxwell-Wagner (MW) polarization, which appears due to polarization at the interface between the LC and PS block. The spatial confinement of the LC block in 1D- (lamellae) and 2D- (cylindrical) domains has an influence on the dielectric parameters of the {alpha}-, {delta}-, {beta}- and {gamma}-relaxations, depending on the cooperativity length for each process. It was found that the relaxation time {tau} for {delta}- and {alpha}-relaxation processes decreases significantly in a restricted geometry. The decrease of relaxation time {tau} is more pronounced for the 2D confinement (cylindrical LC domains). The dependence of the relaxation time of the {beta}-process on the constraint is similar to that of {alpha}- and {delta}-relaxations, although the variation is less pronounced. The relaxation time of the {gamma}-relaxation is not influenced by the domain shape and dimensions. The results in this dissertation contribute to a better understanding of the morphlogy and molecular dynamic of side-chain liquid crystal / isotropic (SCLC/I) block copolymers as well as of the molecular dynamics in a confined geometry. This work forms a basis for further development in polymer-LC design leading to the improvement of up to date existing theories for SCLC/I block copolymers as well as future technological applications

Impact of morphology and scale on the physical properties of periodic/quasiperiodic micro- and nano- structures

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 130-147).A central pillar of real-world engineering is controlled molding of different types of waves (such as optical and acoustic waves). The impact of these wave-molding devices is directly dependent on the level of wave control they enable. Recently, artificially structured metamaterials have emerged, offering unprecedented flexibility in manipulating waves. The design and fabrication of these metamaterials are keys to the next generation of real-world engineering. This thesis aims to integrate computer science, materials science, and physics to design novel metamaterials and functional devices for photonics and nanotechnology, and translate these advances into realworld applications. Parallel finite-difference time-domain (FDTD) and finite element analysis (FEA) programs are developed to investigate a wide range of problems, including optical micromanipulation of biological systems [1, 2], 2-pattern photonic crystals [3], integrated optical circuits on an optical chip [4], photonic quasicrystals with the most premier photonic properties to date [5], plasmonics [6], and structure-property correlation analysis [7], multiple-exposure interference lithography [8], and the world's first searchable database system for nanostructures [9].by Lin Jia.Ph.D

Understanding The Dynamic And Mechanical Properties Of Polymers Under Nanoconfinement

The physical properties e.g. dynamics, mechanics, etc., of polymers can change drastically under nanoconfinement. For example, confinement to free-standing thin films leads to an enhancement in the segmental dynamics, and changes in the chain conformation lead to changes in the entanglement density in confined polymers. Understanding the impact of confinement on the physical properties of polymers is helpful to guide the development of new polymer materials. For the first part of my thesis, we investigate the conformations and dynamics of polymer melts under porous-like confinement and compare the behaviors of rings with linear melts under planar confinement. By simulating linear melts confined in a diamond network geometry with two characteristic length scales mimicking porous confinement, we find chain disentanglement increases diffusivity of entangled polymers along confined channels compared to the bulk and there is competing effects between the local friction near the wall and chain disentanglement. In the study of ring melts under planar confinement, we demonstrate that the chain dynamics of rings are primarily affected by the friction from walls based on monomeric friction coefficient analysis. For the second part, we investigate the role of both segmental dynamics and changes in entanglement density on the mechanical response of glassy polymer films under uniaxial tension using molecular dynamics simulations. We demonstrate that not all entanglements carry significant load at large deformation, and our analysis allows the development of a model to describe the number of load-bearing entanglements per chain as a function of blend ratio. The film strength measured experimentally, and the simulated film toughness are quantitatively described by a new model that only accounts for load-bearing entanglements. Varying the film thickness uncovers competing effects between the reduction in entanglement density and changes in the segmental dynamics. From the mechanical study of diblock copolymer films, we notice that the toughness of the films with fingerprint morphologies is larger compared to homopolymers due to increase in the randomness of domain orientations and entanglements. Our studies of the film mechanics provide molecular insight into how segmental mobility and entanglements interplay with position and morphology to control the mechanics of thin polymer films