Written language provides a snapshot of linguistic, cultural, and current events information for a given time period. Aggregating these snapshots by studying many texts over time reveals trends in the evolution of language, culture, and society. The ever-increasing amount of electronic text, both from the digitization of books and other paper documents to the increasing frequency with which electronic text is used as a means of communication, has given us an unprecedented opportunity to study these trends. In this dissertation, we use hundreds of thousands of books spanning two centuries scanned by Google, and over 100 billion messages, or ‘tweets’, posted to the social media platform, Twitter, over the course of a decade to study the English language, as well as study the evolution of culture and society as inferred from the changes in language. We begin by studying the current state of verb regularization and how this compares between the more formal writing of books and the more colloquial writing of tweets on Twitter. We find that the extent of verb regularization is greater on Twitter, taken as a whole, than in English Fiction books, and also for tweets geotagged in the United States relative to American English books, but the opposite is true for tweets geotagged in the United Kingdom relative to British English books. We also find interesting regional variations in regularization across counties in the United States. However, once differences in population are accounted for, we do not identify strong correlations with socio-demographic variables. Next, we study stretchable words, a fundamental aspect of spoken language that, until the advent of social media, was rarely observed within written language. We examine the frequency distributions of stretchable words and introduce two central parameters that capture their main characteristics of balance and stretch. We explore their dynamics by creating visual tools we call ‘balance plots’ and ‘spelling trees’. We also discuss how the tools and methods we develop could be used to study mistypings and misspellings, and may have further applications both within and beyond language. Finally, we take a closer look at the English Fiction n-gram dataset created by Google. We begin by explaining why using token counts as a proxy of word, or more generally, ‘n-gram’, importance is fundamentally flawed. We then devise a method to rebuild the Google Books corpus so that meaningful linguistic and cultural trends may be reliably discerned. We use book counts as the primary ranking for an n-gram and use subsampling to normalize across time to mitigate the extraneous results created by the underlying exponential increase in data volume over time. We also combine the subsampled data over a number of years as a method of smoothing. We then use these improved methods to study linguistic and cultural evolution across the last two centuries. We examine the dynamics of Zipf distributions for n-grams by measuring the churn of language reflected in the flux of n-grams across rank boundaries. Finally, we examine linguistic change using wordshift plots and a rank divergence measure with a tunable parameter to compare the language of two different time periods. Our results address several methodological shortcomings associated with the raw Google Books data, strengthening the potential for cultural inference by word changes.

The electronics industry is shifting its emphasis from reducing transistor size and operational frequency to increasing device integration, reducing form factor and increasing the interface of electronics with their surroundings. This new emphasis has created increased demands on the electronic package. To accomplish the goals to increase device integration and interfaces will undoubtedly require new materials with increased functionality both electrically and mechanically. This thesis focuses on developing new interconnect and printable conductive materials capable of providing power, ground and signal transmission with enhanced electrical performance and mechanical flexibility and robustness. More specifically, we develop: 1.) A new understanding of the conduction mechanism in electrically conductive composites (ECC). 2.) Develop highly conductive stretchable silicone ECC (S-ECC) via in-situ nanoparticle formation and sintering. 3.) Fabricate and test stretchable radio frequency devices based on S-ECC. 4.) Develop techniques and processes necessary to fabricate a stretchable package for stretchable electronic and radio frequency devices. In this thesis we provide convincing evidence that conduction in ECC occurs predominantly through secondary charge transport mechanism (tunneling, hopping). Furthermore, we develop a stretchable silicone-based ECC which, through the incorporation of a special additive, can form and sinter nanoparticles on the surface of the metallic conductive fillers. This sintering process decreases the contact resistance and enhances conductivity of the composite. The conductive composite developed has the best reported conductivity, stretchability and reliability. Using this S-ECC we fabricate a stretchable microstrip line with good performance up to 6 GHz and a stretchable antenna with good return loss and bandwidth. The work presented provides a foundation to create high performance stretchable electronic packages and radio frequency devices for curvilinear spaces. Future development of these technologies will enable the fabrication of ultra-low stress large area interconnects, reconfigurable antennas and other electronic and RF devices where the ability to flex and stretch provides additional functionality impossible using conventional rigid electronics.

Abstract In this thesis flexible electronics composite materials were developed and utilized in pressure sensors. Additionally, stretchable materials based on piezoresistive structures were fabricated and their feasibility for printed electronics switches and stretchable strain sensors was investigated. In the first part of the thesis two types of composite materials were developed based on polyurethane foam with added carbon powder and on liquid crystal polymer with ceramic powder. The first developed composite was utilized in piezoresistive and capacitive hybrid sensors and the latter one for an additive manufactured piezoelectric sensor strip suitable for operation at elevated temperatures. The formable hybrid sensor achieved a maximum pressure sensitivity of 0.338 kPa-1 with response and recovery times less than 200 ms at pressures over 200 kPa and also showed a linear response. The sensor could be utilized, for example, in wearable electronics and robotics. The new type of piezoelectric material showed piezoelectric coefficients of d33 > 14 pC/N and g33 > 108 mVm/N at pressure below 10 kPa with a wide pressure sensing range up to 4.5 MPa. This was higher than that previously achieved for materials fabricated using traditional printing techniques. The piezoelectric sensor would be suitable for industrial process control at elevated temperatures. In the second part of the thesis the stretchable materials were utilized in a new type of piezoresistive structure to fabricate one of the first stretchable switches and a machine washable self-adherable strain sensor. The developed stretchable switch could be actuated with either stretching or vibration with a minimum movement of < 2 μm. The versatile strain sensor with a tunable resistance-strain characteristic achieved the currently highest reported gauge factor (>105) at > 70% stretching. The strain sensor could be utilized for sensing human body movements and physiological signals. / Tiivistelmä Väitöstyössä kehitettiin joustavan elektroniikan komposiittimateriaaleja, joita hyödynnettiin paineantureissa sekä käytettiin venytettäviä materiaaleja painettavan elektroniikan kytkimen ja venymäanturin valmistukseen. Työn ensimmäisessä osassa kehitettiin kahdenlaisia komposiittimateriaaleja, joista ensimmäinen pohjautui polyuretaanivaahtoihin, joihin sisällytettiin hiilijauhetta, sekä toinen nestekidepolymeeriin, johon lisättiin keraamijauhetta. Ensimmäistä kehitettyä komposiittia hyödynnettiin pietsoresistiivisessä ja -kapasitiivisessa hybridianturissa ja jälkimmäistä lisäaine valmistettavassa pietsosähköisessä anturinauhassa, joka soveltui kohotettuihin lämpötiloihin. Muovattavalla hybridianturilla saavutettiin herkkyyden maksimiarvoksi 0.338 kPa-1, alle 200 ms vaste- ja palautumisajat yli 200 kPa paineessa ja lineaarinen vaste. Anturia voitaisiin monipuolisesti hyödyntää mm. puettavassa elektroniikassa ja robotiikassa. Uudenlaisella pietsosähköisellä materiaalilla saavutettiin pietsosähköiset kertoimet (d33 > 14 pC/N ja g33 > 108 mVm/N < 10 kPa paineessa), jotka olivat korkeammat kuin perinteisin tulostusmenetelmin valmistetuilla materiaaleilla. Pietsosähköinen anturi soveltuisi mm. teolliseen prosessivalvontaan kohotetuissa lämpötiloissa. Toisessa osassa hyödynnettiin venytettäviä materiaaleja uudentyyppisissä pietsoresistiivisissä rakenteissa ensimmäisten venytettävän painettavan elektroniikan kytkimen sekä konepestävän itsekiinnityttävän venymäanturin valmistamiseksi. Tulokset on esitetty kahdessa julkaisussa, joista ensimmäinen keskittyi kytkimen valmistamiseen ja toimintaan sekä toinen venymäanturin toimintaan ihmiskehon liikkeen ja signaalien mittaamiseksi. Kehitettyä kytkintä voitiin aktuoida monipuolisesti esim. venytyksen tai värinän avulla alle 2 μm liikkeellä. Monipuolisella venymäanturilla saavutettiin säädettävä resistanssi-venymä suhde korkeimmalla tähän asti ilmoitettu herkkyydellä (>105) yli 70% venytyksellä. Venymäanturia voitiin hyödyntää ihmiskehon liikkeiden ja fysiologisten signaalien mittaamiseen.

abstract: In engineering, buckling is mechanical instability of walls or columns under compression and usually is a problem that engineers try to prevent. In everyday life buckles (wrinkles) on different substrates are ubiquitous -- from human skin to a rotten apple they are a commonly observed phenomenon. It seems that buckles with macroscopic wavelengths are not technologically useful; over the past decade or so, however, thanks to the widespread availability of soft polymers and silicone materials micro-buckles with wavelengths in submicron to micron scale have received increasing attention because it is useful for generating well-ordered periodic microstructures spontaneously without conventional lithographic techniques. This thesis investigates the buckling behavior of thin stiff films on soft polymeric substrates and explores a variety of applications, ranging from optical gratings, optical masks, energy harvest to energy storage. A laser scanning technique is proposed to detect micro-strain induced by thermomechanical loads and a periodic buckling microstructure is employed as a diffraction grating with broad wavelength tunability, which is spontaneously generated from a metallic thin film on polymer substrates. A mechanical strategy is also presented for quantitatively buckling nanoribbons of piezoelectric material on polymer substrates involving the combined use of lithographically patterning surface adhesion sites and transfer printing technique. The precisely engineered buckling configurations provide a route to energy harvesters with extremely high levels of stretchability. This stiff-thin-film/polymer hybrid structure is further employed into electrochemical field to circumvent the electrochemically-driven stress issue in silicon-anode-based lithium ion batteries. It shows that the initial flat silicon-nanoribbon-anode on a polymer substrate tends to buckle to mitigate the lithiation-induced stress so as to avoid the pulverization of silicon anode. Spontaneously generated submicron buckles of film/polymer are also used as an optical mask to produce submicron periodic patterns with large filling ratio in contrast to generating only ~100 nm edge submicron patterns in conventional near-field soft contact photolithography. This thesis aims to deepen understanding of buckling behavior of thin films on compliant substrates and, in turn, to harness the fundamental properties of such instability for diverse applications. / Dissertation/Thesis / Ph.D. Mechanical Engineering 2014

Orientador: Carlos Cesar Bof Bufon / Resumo: Materiais de carbono obtidos por pirólise de celulose e biopolímeros sintéticos têm sido am-plamente investigados para aplicações no desenvolvimento de dispositivos eletrônicos. Eles apresentam excelentes propriedades elétricas, mas são extremamente frágeis. Então uma alter-nativa seria integrar esses materiais em elastômeros. Assim, para a contornar a fragilidade e a questão de adesão de materiais condutores em substratos alongáveis, neste trabalho é proposto um novo método de fabricação para desenvolvimento de dispositivos eletroquímicos. Inspira-do no sistema redox eficiente das plantas e que está firmemente aderido ao solo pela estrutura das raízes, foi desenvolvido um processo de retardo do fluxo capilar do polidimetilsiloxano (PDMS) na estrutura pirolisada modificada, de forma que fibras pirolisadas integradas no elas-tômero possam garantir adesão e estabilidade mecânica, e que parte delas fique exposta para possibilitar atividade eletroquímica na interface. Baseado no modelo matemático de Lucas-Washburn, as mudanças na superfície das fibras de papel por conta da adição de acetato de celulose e a diminuição do raio dos poros resulta no retardo do fluxo da solução polimérica viscosa na estrutura porosa. Como resultado foi obtida uma superfície de eletrodo de carbono altamente ativa para reações redox. Além disso, testes mecânicos com o dispositivo flexiona-do, dobrado, e alongado, demonstraram que uma deformação linear de até 75% do tamanho inicial não tem efeitos nas pr... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Cellulose and synthetic biopolymers derived carbon materials are extensively used for application in electronic field. They show excellent electrical properties but are extremely fragile and prone to crack. Then an alternative to address this challenge and the adhesion problem reported on literature, a new fabrication route for a flexible and stretchable electrochemical device is proposed. Inspired by trees redox system that is highly adhered on the ground and based on Lucas Wash-Burn model, the pyrolyzed paper is modified with cellulose acetate. Then, in a process named delayed capillary flow of elastomers the surface changes in paper fibers and the decrease in pore radius results in a delay on capillary flow of viscous polymer polydimethylsiloxane (PDMS) solution on its porous structure. As a result, a highly active carbon surface exposed on the top for redox reactions is produced, which shows a remarkable performance and is similar to tree leaves. Also, mechanical deformation studies on the new bendable, twistable, flexible, and stretchable device reveal a linear stretch up to 75%, without effects on its electrochemical properties. These mechanical properties are similar to tree roots highly adhered on the ground. The electrode working area was nanofunctionalized with polydopamine (PDA) that is used for anchoring redox mediators and improvement of wettability with unprecedent homogeneous spreading of liquids and development of self-collection liquid samples. This system is... (Complete abstract click electronic access below) / Mestre

Die Etablierung der Telemedizin stellt neue Herausforderungen an die Aufbau- und Verbindungstechnik der Elektronik. Neue medizintechnische Anwendungen für die breite Gesellschaft erfordern biokompatible, flexible und dehnbare Elektronik, die zugleich kostengünstig und individuell hergestellt werden kann. Einen vielversprechenden Ansatz bietet die Verwendung additiver Herstellungsverfahren. Gegenstand dieser Arbeit ist die Materialauswahl für flexible und dehnbare Mikrosysteme vor dem Hintergrund der Anforderungen für zukünftige biomedizinische Anwendungen und unter Verwendung ausschließlich additiver Verfahren. Der grundlegende Aufbau gedruckter Elektronik, bestehend aus Leiterzügen verschiedener Nanopartikeltinten und polymeren Substraten, wird hinsichtlich biologischer und mechanischer Eigenschaften untersucht. Diese Charakterisierung beinhaltet die Evaluation der Zytotoxizität, Haftfestigkeit, Biegebelastung und Dehnungsbelastung der Materialkombinationen. Im Fokus steht der Inkjetdruck von Platintinte auf flexiblen Polyimid- und dehnbaren Polyurethansubstraten. Aufgrund der Inkompatibilität zwischen der erforderlichen Sintertemperatur der Platintinte und der Erweichungstemperatur des Polyurethans, wird das photonische Sintern untersucht. Dafür kommen Lasersintern und Blitzlampensintern zum Einsatz. Die Platintinte zeigt ausgezeichnete Eigenschaften im Zytotoxizitätstest durch 98 %ige Zellvitalität im Vergleich zur biokompatiblen Referenz. Die bestimmten Haftfestigkeiten liegen zwischen 0,5N/mm2 und 2,5N/mm2 und entsprechen damit aktuellen Literaturwerten. Weiterhin zeigt das Ergebnis von Biegetests vielversprechende flexible Eigenschaften. Der Widerstand nach 180 000 Biegezyklen erhöht sich bei einem Biegeradius von 5mm um maximal 9,5% und bei 2mm um maximal 42 %. Die Dehnungstests mit Horseshoestrukturen aus Silbertinte zeigen ca. 400 Dehnungszyklen bei 10% Dehnung und ca. 400 Zyklen bei 20% Dehnung bis zur vollständiger Leiterzugunterbrechung. Zwei Demonstratoren validieren das Potential der ausschließlichen Nutzung von additiven Prozessen zur Herstellung biomedizinischer Mikrosysteme. Der erste Demonstrator ist eine Hautelektrode, welche sich durch temporären Elektroden-Hautkontakt zur Hautleitwertmessung eignet. Der zweite Demonstrator beinhaltet eine miniaturisierte, gedruckte Interdigitalelektrode, die durch die Anwendung von Nanosekundenimpulsen in der Lage ist, Zellen zu manipulieren. Die Erkenntnisse aus dieser Arbeit zeigen das große Potential der Nutzung additiver Prozesse für die Herstellung von Medizinprodukten.

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Biological systems are composed of complex materials which are responsible for performing various functions, such as providing structural support, mobility, functional adaptation to the environment, damage repair, and self-healing. These complex materials display excellent mechanical properties and can rapidly adapt to external stimuli. Thus, nature inspires in terms of source materials, functions, and designs to develop new-generation structural and functional materials. Polymers (natural or synthetic) are excellent sources of developing materials to mimic the functions of soft segments in biological systems. This dissertation focuses on synthesizing and characterizing two different materials with tunable structures and properties: complexes from natural polysaccharides or polyelectrolytes and bioinspired hydrogels from synthetic polymers. Oppositely charged polyelectrolytes can form polyelectrolyte complexes (PECs) due to the electrostatic interactions. The structure and properties of PECs can be tuned by varying the salt concentration, as the addition of salt can facilitate associative phase separation. PECs were prepared from two biopolymers, positively charged chitosan and negatively charged alginate. Rheological experiments for the complexes displayed a tunable shear modulus with changing salt concentrations. The microstructural study conducted using small-angle X-ray scattering provided insights regarding the length scales of these complexes, and the results follow the observed rheological and phase behavior. Elastic biopolymers such as resilin display remarkable mechanical properties, including high stretchability and resilience, which many species exploit in nature for mechanical energy storage to facilitate their movement. Such properties of resilin have been attributed to the balanced combination of hydrophilic and hydrophobic segments present in the chain. In this work, we synthesized hydrogels with hydrophilic and hydrophobic components to mimic the properties of resilin. With this system, we determined the tensile, retraction (ability to revert to the original state after stretching), and swelling properties when (i) the concentration of the hydrophobic polymer was varied and (ii) additional hydrophobic components were included. The stretchability, stiffness, and strength of the gels varied as the compositions were altered. The fundamental understanding of the structure-property-function relationship for materials presented in this work provides insights into engineering materials for applications such as tissue engineering, drug delivery, wound healing, artificial muscles, soft robotics, and power amplification.

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Current cardiac monitoring devices are rigid, bulky, and integrate poorly with the human skin, obstructing health monitoring for longer periods. With the miniaturization of electronics, soft and stretchable polymer substrate-based cardiac monitoring device is being developed at Mycronic AB to overcome the aforementioned issues and replacing the traditional rigid electronics-based cardiac monitoring devices. Manufacturing of stretchable cardiac monitoring device includes new materials and manufacturing techniques as well as different end-of-life treatments. The sustainability of this kind of stretchable device is often enquired by curious customers and environment enthusiasts. Without a comprehensive scientific study on the environmental performance of this device, it is difficult for the manufacturer to answer such inquiries. Hence, this study aims to carry out a comparative Life Cycle Assessment (LCA) of rigid and stretchable cardiac monitoring devices. The LCA for both the devices was based on ISO 14044:2006 standards. The impact assessment method used was ReCiPe 2016 (Hierarchist). The LCA results showed that the stretchable cardiac monitor had significantly lower impacts than its rigid counterpart. Lower usage of Printed Circuit Board (PCB) in the stretchable device was the main reason for its better environmental performance. The PCB was identified as the major environmental hotspot in both the devices. / Nuvarande hjärtövervakningsanordningar är styva, skrymmande och dåligt integrerade med människans hud och hindrar övervakning under längre perioder. Inom ramen för det europeiska forskingsprojektet SINTEC har Mycronic bidragit till att utveckla en ny design och tillverkningsmetod för en mjuk och töjbar polymersubstratbaserad övervakningsanordning för att övervinna de ovan nämnda hindren med de traditionella alternativ. Tillverkning av töjbar hjärtövervakningsanordning inkluderar nya material och tillverkningstekniker som ger en ökad hållbarhet som ofta efterfrågas av nyfikna kunder och miljöentusiaster. Men utan en omfattande vetenskaplig studie om enhetens miljöprestanda är det dock svårt för tillverkaren att besvara sådana frågor, och därför syftar denna studie till att utföra en jämförande livscykelanalys (LCA) av styva och töjbara hjärtövervakningsanordningar. LCA för båda enheterna baseras på ISO 14044: 2006-standarder. Den konsekvensbedömning som användes var ReCiPe 2016 (Hierarchist). LCA-resultaten visade att den töjbara hjärtmonitorn hade signifikant lägre påverkan än dess styva motsvarighet. Lägre användning av kretskort (PCB) i den töjbara enheten var den främsta anledningen till dess bättre miljöprestanda och just PCB identifierades som den viktigaste miljöhotspoten i båda enheterna.