High sensitivity temperature sensor based on a helically twisted photonic crystal fiber

Helically twisted photonic crystal fibers (HT-PCFs) provide additional opportunities for controlling the light propagation characteristics and improving the sensing performances. In this paper, a toluene and gold wire-filled HT-PCF was proposed and designed for high sensitivity temperature sensing. The influences of the structure parameters on the confinement loss, sensitivity, and resolution of the proposed HT-PCF were investigated. For the optimized HT-PCF, the average sensitivity is as high as 14.35 and 17.29 nm/℃ in the temperature range of −20 to 20 ℃ and 20 to 70 ℃, respectively. Moreover, the proposed HT-PCF-based temperature sensor is insensitive to the hydrostatic pressure. Finally, the detailed fabrication process of the toluene and gold wire-filled HT-PCF temperature sensor is proposed. It is believed that the proposed HT-PCF temperature sensor has potential applications in the fields of the environmental monitoring, medical diagnostics, etc

Cellulose Filaments for Responsive and Functional Materials

Cellulosic filaments, found in plants, are crucial structural elements for their survival and are a great source of inspiration to obtain new functional materials. The work performed out in this thesis aimed for the isolation, physical characterization, study of the morphology and shape, as well as the mechanical behaviour of cellulosic filaments obtained from the leaves of Agapanthus africanus and Ornithogalum thyrsoides and from the filaments that form the ribbons existing on the awns of the Erodium plants. These cellulosic filaments and filament networks were chosen due to the fundamental role that they play in the plant kingdom and their ability to change shape in the presence of an external stimuli. The study of the chosen systems served as an inspiration for the preparation and production of new membranes formed by non-woven networks of micro/nano filaments. A prototype, which allows for the selective removal of oil micro droplets from aqueous emulsions, was developed. This dissertation begins with a general introduction, based on two review papers, which the author of this thesis is the first author, in which the main concepts used in the following chapters are addressed and interconnected. The original part of the work is in chapters II, III and IV. In chapter II, the study of microfilaments from the leaves tracheary of two plants, Agapanthus africanus and Ornithogalum thyrsoides, is made. These microfilaments belong to plants of the same order and have identical shapes (left helices), chemical composition and skeletons, but different mechanical properties. For the first time, micrometric droplets of a nematic liquid crystal were used as sensors to reveal the morphology of the filaments. In order to obtain quantitative characteristics on the surface of the microfilaments, photos of the textures of pierced droplets were obtained by Polarized Optical Microscopy (POM). These textures were compared with simulated optical microphotographs obtained by numerical modelling for the nematic droplets. Homeotropic anchoring at the air, and different anchoring conditions, at the interfaces with the filaments were considered for the nematic structure. This study allowed the establishment of relationships between the physical properties/morphology of the filaments and to determine their interactions with other filaments and with the environment. In chapter III, cellulosic networks existing on dead tissues of the Erodium awns were isolated and characterized. An interesting feature of these cellulosic networks is that they form ribbons that change reversibly the shape in the presence of moisture. When dried these ribbons are right-handed helices, that uncoil remaining taut, in the presence of moisture. The work performed allowed the preparation of helical ribbons that can change the shape from right- to lefthanded helices in the presence of moisture. The behaviour observed was explained using computational simulations, considering filaments that contract and expand asymmetrically. Birefringent transparent ribbons were also isolated. The asymmetric arrangement of cellulosic fibres allows the material to be stimuli-responsive without the use of complicated lithography and intricate deposition techniques, making it suitable for a diverse range of applications, such as the production of intelligent textiles and environmental friendly micro components. In chapter IV, non-woven membranes obtained from cellulosic materials and cellulose nanocrystals were prepared and characterized. Different patterns were designed using the screenprinting technique. The adhesion between the different types of cellulosic fibres was promoted through a heat treatment. The non-woven membranes produced allowed the development of a prototype that selectively removes oil droplets from aqueous emulsions with an efficiency of approximately 80%. Throughout this thesis (chapters II and III), the complexity of the systems increases. The work begins by studying the morphology of a filament and its mechanical behaviour in the presence of other filaments. After a much more complex system, in which anisotropic filament networks, produced by the Erodium plant were addressed. The stimuli-responsive behaviour of these anisotropic networks was investigated after being released by the plant. Based on the understanding of the systems formed by cellulosic filaments, studied in chapters II and III, functional non-woven membranes were produced, printed, and characterized. The non-woven membranes led to the development of a prototype, which allows the selective removal of micro droplets of oil form aqueous emulsions. At the end, a summary of the main scientific results and future work including a technological application, which was developed in the framework of this thesis, are presented.Os filamentos celulósicos, existentes nas plantas, são elementos estruturais cruciais para a sua sobrevivência e fontes de inspiração para a obtenção de novos materiais funcionais. O trabalho realizado nesta tese visou o isolamento, caracterização física, estudo da morfologia e forma, assim como do comportamento mecânico de filamentos celulósicos obtidos a partir das folhas das plantas Agapanthus africanus e Ornithogalum thyrsoides e de filamentos que formam fitas existentes nas hastes da planta Erodium. Estes filamentos e redes de filamentos celulósicos foram escolhidos devido ao papel fundamental que desempenham no reino vegetal e à resposta que podem apresentar na presença de estímulos externos. O estudo dos sistemas escolhidos serviu de inspiração para a preparação e fabrico de novas membranas formadas por redes não tecidas de filamentos micro/nanométricos e o desenvolvimento de um protótipo, que permite a remoção seletiva de microgotas de óleo de emulsões aquosas. Inicia-se com uma introdução de caracter geral, baseada em dois artigos de revisão, dos quais a autora desta tese é primeira autora, na qual se abordam e interligam os conceitos principais, que são utilizados nos capítulos seguintes. A parte original do trabalho reparte-se pelos capítulos II, III e IV. No capítulo II é feito o estudo de microfilamentos existentes nos sistemas vasculares das folhas de duas plantas, Agaphantus africanus e Ornithogalum thyrsoides. Estes microfilamentos pertencem a plantas da mesma ordem e possuem formas (hélices esquerdas), composições químicas e esqueletos idênticos, mas apresentam propriedades mecânicas distintas. Pela primeira vez foram utilizadas gotas micrométricas de um cristal líquido nemático como sensores da morfologia dos filamentos isolados. De modo a obter características quantitativas sobre a superfície dos microfilamentos, fotos de texturas obtidas por microscopia com luz polarizada foram comparadas com microfotografias óticas simuladas a partir de modelação numérica de um meio contínuo das estruturas das gotas nemáticas, com ancoragem homeotrópica na superfície com o ar suspensas nos microfilamentos com diferentes ancoragens. O estudo realizado permitiu estabelecer relações entre as propriedades físicas/morfologia dos filamentos e determinar as suas interações com outros filamentos e com o meio ambiente. No capítulo III foram isoladas e caracterizadas redes celulósicas existentes nas hastes de tecidos mortos da planta Erodium. Uma característica interessante destas redes celulósicas é a de formarem fitas que mudam reversivelmente de conformação na presença de humidade. Quando secas estas fitas são hélices direitas, que na presença de humidade desenrolam para fitas esticadas, sem torção nem flexão. Este trabalho permitiu induzir uma inversão de quiralidade nas fitas que foi explicada pelo uso de simulações computacionais considerando que as fitas contraem e esticam de modo assimétrico. Fitas birrefringentes transparentes também foram isoladas. A disposição assimétrica das fibras celulósicas permite a resposta do material não envolvendo o uso de técnicas complicadas de litografia nem de deposição, podendo ser aplicado, por exemplo, no fabrico de têxteis inteligentes e de microcomponentes amigos do ambiente. No capítulo IV foram preparadas e caracterizadas membranas não tecidas obtidas a partir de soluções de derivados celulósicos e de celulose nano cristalina. Foram desenhadas diferentes geometrias pela utilização da técnica de “screenprinting” e promovida a adesão entre os diferentes tipos de fibras celulósicas através de tratamento térmico. As membranas não tecidas produzidas permitiram o desenvolvimento de um protótipo que remove, de forma seletiva, microgotas de óleo de emulsões aquosas com uma eficiência de cerca de 80%. Ao longo desta tese (capítulo II e III), a complexidade dos sistemas estudados aumenta, isto é, começa-se por estudar a morfologia de um filamento e o seu comportamento mecânico na presença de outros filamentos, para depois se passar para um sistema muito mais complexo em que redes anisotrópicas de filamentos, impressas pela planta Erodium, permitem a resposta a estímulos externos da estrutura formada, mesmo após esta ter abandonado a planta. Tendo por base a compreensão dos sistemas formados por filamentos celulósicos, estudados nos capítulos II e III, foram produzidas, impressas e caracterizadas, no laboratório, membranas funcionais tecidas de filamentos micro/nano celulósicos. As membranas não tecidas originaram o desenvolvimento de um protótipo, que permite a remoção seletiva de micro gotas de óleo existentes em emulsões aquosas. No final é apresentado um sumário dos principais resultados científicos e perspetivas de avanço tecnológico alcançadas por este trabalho

Chiral Auxiliaries and Chirogenesis II

This Reprint Book highlights and overviews the most important and novel aspects of chiral auxiliary and chirogenesis in different natural/physical sciences and in modern technologies. In particular, some newly emerging classes of molecules used for these purposes have been described. Furthermore, some important experimental and theoretical issues associated with the chirality field have been addressed. This book consists of one review article and six research papers and is of interest for general chemistry readership, including graduate and post-graduate students, and for researchers specializing in the fields of chirality and stereochemistr

Optical angular momentum in air core fibers

As data consumption continues to grow, the backbone of the internet, comprising single mode fiber (SMF)-based infrastructure, is fundamentally limited by nonlinear optical effects. One strategy to address this bottleneck, space division multiplexing (SDM), utilizes multiple modes in a single fiber as independent data channels. Orbital Angular Momentum (OAM) carrying modes, which have twisting phase fronts tracing out helices as the beams propagate, have recently received tremendous attention as a means of achieving low-crosstalk, digital signal processing (DSP)-free transmission with enhanced capacity. Terabit-scale transmission using 4 OAM modes over 1.1km has been demonstrated, but questions remain – how many OAM modes can fibers support, and how stable is propagation over longer lengths? In this thesis, we investigate angular momentum carrying modes in a novel class of fibers featuring an air core. We find that high-order OAM states, although arising in degenerate pairs, counterintuitively resist mode coupling due to OAM conservation, pointing to a unique stability inherent to OAM modes in fibers. We achieve OAM propagation up to 13.4km lengths, and achieve mode purities greater than 15dB at data-center length-scales. We use these fibers to transmit wavelength-division multiplexed data with 25 GHz channel spacing, 10 GBaud rates and quadrature-phase-shift keyed modulation formats in 12 modes simultaneously, over 1.2km, and over a large number of wavelengths across the C-band (1530-1565nm). However, transmission over every mode in every channel of the C-band was prevented by the accidental degeneracy of OAM states with undesired modes. To achieve a larger ensemble of stable modes over a larger wavelength range, we study new fiber designs that avoid this accidental degeneracy problem. We find that the most scalable modal eigenbasis is a set of states that carry non-integer amounts of average OAM, also called spin-orbit coupled modes in analogy with similar effects observed in atomic physics. We demonstrate excitation and transmission of 24 such modes over device lengths (10m). The achievement of a record number of uncoupled modes in fibers confirms the viability of angular momentum states as data carriers, and potential applications include links in data centers, high capacity optical amplifiers, and quantum communications links.2017-09-09T00:00:00

Development and characterization of novel indigoid chromophores, photoswitches and molecular machinery

The photochemistry and photophysical properties of hemiindigo based photoswitches and indigo based molecular machines were examined. It could be shown that hemiindigos are a class of virtually unexplored, potent photoswitches supporting high photoisomerization ratios with blue over green to yellow and red light, high thermal bistabilities, good quantum yields and high tolerance of the photoreactions towards solvent polarity changes. The introduction of a chiral acyl or aryl axis on the hemiindigo chromophore at the indoxyl nitrogen was tested with various substitution patterns to explore the influence of electronics and sterics on the photophysical properties, electronic circular dichroism spectra and the motion of the passive chiral axes. Introduction of two chiral axes to the well-known indigo chromophore was carried out. The potential of these molecules as prospective molecular motors and -machines was demonstrated, giving insights into novel photoinduced- and thermal motions, which is crucial for the design of nanomachines and molecular robots. Also, addressability within the biooptical window was achieved, as all photosteps can be driven with low energy, 625 nm LED light, making the application of likewise systems available on biological tissues in vitro and in vivo. Three permanently charged, thermally bistable hemiindigos were synthesized and their photochemical properties in the gas phase and in solution were investigated. Several permanently charged hemiindigo photoswitches were tested in water and their photophysical properties as well as their ability to bind to DNA/RNA was scrutinized. Furthermore, the measurement procedures and automatization of photophysical measurements were improved

Magnetic Hybrid-Materials

Externally tunable properties allow for new applications of suspensions of micro- and nanoparticles in sensors and actuators in technical and medical applications. By means of easy to generate and control magnetic fields, fluids inside of matrices are studied. This monnograph delivers the latest insigths into multi-scale modelling, manufacturing and application of those magnetic hybrid materials

Magnetic Hybrid-Materials

Externally tunable properties allow for new applications of suspensions of micro- and nanoparticles in sensors and actuators in technical and medical applications. By means of easy to generate and control magnetic fields, fluids inside of matrices are studied. This monnograph delivers the latest insigths into multi-scale modelling, manufacturing and application of those magnetic hybrid materials

Bibliography of Lewis Research Center technical publications announced in 1993

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1993. All the publications were announced in the 1993 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses