Ioonsete elektromehaaniliselt aktiivsete polümeeride deformatsioonist sõltuv elektroodi impedants

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Elektromehaaniliselt aktiivsed materjalid on polümeeridel põhinevad mitmekihilised komposiitmaterjalid, mis muudavad oma välist kuju, kui neid elektriliselt stimuleerida; tihti nimetatakse neid ka tehislihasteks. Taolistest materjalidest valmistatud täiturid pakkuvad huvi nii mikrolaborseadmetes kui ka loodust matkivas robootikas, sest võimaldavad luua keerukaid ülipisikesi ajameid. Võrreldes tavapäraste elektrimootoritega võimaldavad EAP-d (elektromehaaniliselt aktiivsed polümeerid) helitut liigutust ning neid saab lõigata konkreetse rakenduse jaoks sobivasse suurusesse. EAP-d jagunevad kahte põhiklassi: elektron- ja ioon-EAP. Doktoritöös käsitletakse kahte erinevat ioon-EAP materjali, kus mehaaniline koste on tingitud ioonide ümberpaigutumisest kolmekihilises komposiitmaterjalis. Kuna EAP-de elektromehaanilised omadused sõltuvad lisaks sisendpinge amplituudile ja sagedusele ka tugevasti ümbritseva keskkonna parameetritest (nt niiskus ja temperatuur), siis on nendest materjalidest loodud täiturite juhtimiseks tarvilik kasutada tagasisidet. Täiendav tagasisideallikas võib oma omaduste tõttu aga vähendada EAP-de rakendusvõimalusi ning seetõttu on eesmärgiks luua n-ö isetundlik EAP ajam, mis funktsioneerib samaaegselt nii täituri kui ka liigutusandurina. Doktoritööd esitatakse uuritud materjalide elektroodi impedantsi ja deformatsiooni vaheline seos ning kirjeldatakse vastav elektriline mudel. Eraldamaks andursignaali täituri sisendpingest pakutakse välja elektroodikihi piires täituri ja anduri elektriline eraldamine. Loobudes ainult elektroodimaterjalist säilitab polümeerkarkass täituri ja anduri mehaanilise ühendatuse – seega taolises süsteemis järgib sensor täituri kuju, kuigi need on elektriliselt lahti sidestatud. Elektroodimaterjali valikuliseks eemaldamiseks kasutatakse mitmeid erinevaid meetodeid (freesimine, laserablatsioon jne) ning ühtlasi uuritakse nende kasutusmugavust ja protsessi mõju kogu komposiitmaterjalile.Electromechanically active materials are polymer-based composites exhibiting mechanical deformation under electrical stimulus, i.e. they can be implemented as soft actuators in variety of devices. In comparison to conventional electromechanical actuators, their key characteristics include easy customisation, noiseless operation, straightforward mechanical design, sophisticated motion patterns, etc. Ionic EAPs (electromechanically active polymers) are one of two primary classes of electroactive materials, where actuation is caused mostly by the displacement of ions inside polymer matrix. Mechanical response of ionic EAPs is, in addition to voltage and frequency, dependent on environmental variables such as humidity and temperature. Therefore a major challenge lies in achieving controlled actuation of these materials. Due to their size and added complexity, external feedback devices inhibit the application of micro-scale actuators. Hence, self-sensing EAP actuators—capable for simultaneous actuation and sensing—are desired. In this thesis, sensing based on deformation-dependent electrochemical impedance is demonstrated and modelled for two types of trilayer ionic EAPs—ionic polymer-metal composite and carbon-polymer composite. Separating sensing signal from the input signal of the actuator is achieved by patterning the electrode layers of an IEAP material in a way that different but mechanically coupled sections for actuation and sensing are created. A variety of concepts for pattering the electrode layers (machining, laser ablation, masking, etc.) are implemented and their applicability is discussed

Structure and Functionality of Novel Nanocomposite Granules for a Pressure-Sensitive Ink with Applications in Touchscreen Technologies

Tactile sensors are now ubiquitous within human-computer interactions, where mouse and keyboard functionality can be replaced with a trackpad or touchscreen sensor. In most technologies the sensor can detect the touch location only, with no information given on the force of the touch. In this thesis, functional components of a novel nanocomposite ink are developed, which when printed, form a pressure-sensitive interface which can detect both touch location and touch force. The physical basis of the force-sensitive response is investigated for the touchscreen sensor as a whole, as well as the intrinsic force-sensitivity of the ink components. In an earlier form the nanocomposite ink, that was the starting point of this study, contained agglomerates of conductive nanoparticles which were formed during blending of the ink, and provided the electrical functionality of the sensor. Here, novel nanocomposite granules were pre-fabricated prior to inclusion in the ink. The granules were designed such that they exhibited well-defined size, structure and strength. Control of these parameters was achieved through selection of the granule constituents, as well as the energy and duration of the granulation process. When incorporated into the ink and screen-printed to form a pressure-sensitive layer in a touchscreen test device, the functional performance could be assessed. Sensors containing pre-formed granules showed improved optical transmission, compared to sensors containing the same mass loading of nanoparticles forming spontaneous agglomerates. Agglomerates tend to create a larger number of small scattering centres which scatter light to larger angles. The spatial variation in the force-resistance response, as well as the sensitivity of this response, was also linked to the distribution of the granules within the pressure-sensitive layer. The physical basis of the force-resistance response is two-fold. Firstly, mathematical simulations showed that deflection of the upper electrode increased the number of granules contacted with increasing applied force and therefore decreased the resistance through the sensor. Secondly, a force-sensitive resistance of the granules themselves was also observed at high forces. Analysis of the non-linear current-voltage characteristics suggested the presence of non-linear conduction pathways within the granules. Using a random resistor network model, the non-linear current contribution decreased after approximately 0.7 N force. To understand this effect, a model based on the physical basis of quantum tunnelling mechanisms was also applied, however this provided a poor fit to the data and no further understanding could be gained

Textile materials

In this specialised publication, the reader will find research results and real engineering developments in the field of modern technical textiles. Modern technical textile materials, ranging from ordinary reinforcing fabrics in the construction and production of modern composite materials to specialised textile materials in the composition of electronics, sensors and other intelligent devices, play an important role in many areas of human technical activity. The use of specialized textiles, for example, in medicine makes it possible to achieve important results in diagnostics, prosthetics, surgical practice and the practice of using specialized fabrics at the health recovery stage. The use of reinforcing fabrics in construction can significantly improve the mechanical properties of concrete and various plaster mixtures, which increases the reliability and durability of various structures and buildings in general. In mechanical engineering, the use of composite materials reinforced with special textiles can simultaneously reduce weight and improve the mechanical properties of machine parts. Fabric- reinforced composites occupy a significant place in the automotive industry, aerospace engineering, and shipbuilding. Here, the mechanical reliability and thermal resistance of the body material of the product, along with its low weight, are very relevant. The presented edition will be useful and interesting for engineers and researchers whose activities are related to the design, production and application of various technical textile materials

A study of emission of nanoparticles during physical processing of aged polymer-matrix nanocomposites

Nanotechnology research and its commercial applications have experienced an exponential rise in the recent decades. Although there are a lot of studies with regards to toxicity of nanoparticles, the exposure to nanoparticles, both in terms of quality and quantity, during the life cycle of nanocomposites is very much an unknown quantity and an active area of research. Unsurprisingly, the regulations governing the use and disposal of nanomaterials during its life cycle are behind the curve. This work aims to assess the quantity of nanoparticles released along the life cycle of nanocomposites. Machining operations such as milling and drilling were chosen to simulate the manufacturing of nanocomposites parts, and impact testing to recreate the end-of-life of the materials. Several studies have tried to simulate different release scenarios, however these experiments had many variables and in general were not done in controlled environments. In this study, a reliable method was developed to assess the release of nanoparticles during machining and low velocity impact of nanocomposites. The development and validation of a new prototype used for measurement and monitoring of nanoparticles in a controlled environment is presented, as along with release experiments on different nanocomposites. Every sample tested was found to release nanoparticles irrespective of the mechanical process used or the type of material tested. Even neat polymers released nanoparticles when subjected to mechanical forces. The type of matrix was identified to play a major role on the quantity of nanoparticles release during different process. Thermoset polymers (and especially polyester) were found to release a higher number concentration of particles, mainly due to their brittle properties. A polyester sample was found to release up to 48 times more particles than a polypropylene one during drilling. The nanofiller type and percentage used to reinforce the polymer is also a key point. For example, the addition of 2 wt.% of nano-alumina into polyester increases the number concentration of particles by 106 % following an impact. The nanofiller chosen and its quantity affect the mechanical properties and machinability of the composites and therefore its nanoparticles release potential. The mechanical process and the process parameters chosen were also found to be crucial with regards to the nanoparticles released with different trends observed during drilling and impact of similar materials. Finally, thermal ageing of nanocomposites increases the number concentration of nanoparticles released (by 8 to 17 times after 6 weeks)

Functional Nanostructure Synthesis and Properties

The dissertation addressed challenges in the nanostructure synthesis, applied the materials to engineering fields, such as lithium battery material, fluorescent and magnetic drug deliveries; and developed new characterization methods to better understand particle properties and formation mechanisms

Emerging Functions of Nano-Organized Polysaccharides

Natural polysaccharides, such as cellulose and chitin, possess unique hierarchical nanoarchitectures that can never be artificially reconstructed, and their nano-organized structures are involved in the hidden materials functions with great potential. Pioneering the emerging functions of nano-organized polysaccharides will break through to achieve the Sustainable Development Goals

Smoke Aerosol Characterization for Spacecraft Fire Detection Systems

Appropriate design of fire detection systems requires knowledge of both the expected fire signature and the background aerosol levels. Terrestrial fire detection systems have been developed based on extensive study of terrestrial fires. Unfortunately there is no corresponding data set for spacecraft fires and consequently the fire detectors in current spacecraft were developed based upon terrestrial designs. There are a number of factors that affect the smoke particle size distribution in spacecraft fires. In low gravity, buoyant flow is negligible which causes particles to concentrate at the smoke source, increasing their residence time, and increasing the transport time to smoke detectors. Microgravity fires have significantly different structure than those in 1-g which can change the formation history of the smoke particles. Finally the materials used in spacecraft are different from typical terrestrial environments where smoke properties have been evaluated. It is critically important to detect a fire in its early phase before a flame is established, given the fixed volume of air on any spacecraft. Consequently, the primary target for spacecraft fire detection is pyrolysis products rather than soot. This dissertation is a compilation of experimental investigations performed at three different NASA facilities which characterize smoke aerosols from overheating common spacecraft materials. The earliest effort consists of aerosol measurements in low gravity, called the Smoke Aerosol Measurement Experiment (SAME), and subsequent ground-based testing of SAME smoke in 55-gallon drums with an aerosol reference instrument. The feasibility of the moment method for characterizing smoke from limited data, including the lognormal assumption, is explored. Experiments in low gravity are very rare and expensive, so detailed studies to exploit every possible aspect of the data to increase the science outcome are warranted. Another set of experiments were performed at NASA’s Johnson Space Center White Sands Test Facility (WSTF), with additional fuels and an alternate smoke production method. Measurements of these smoke products include mass and number concentration, and a thermal precipitator was designed for this investigation to capture particles for microscopic analysis. Smoke particle morphology and chemical composition are analyzed for various fuels. The final data presented are from NASA’s Gases and Aerosols from Smoldering Polymers (GASP) Laboratory, with selected results focusing on realistic fuel preparations and heating profiles with regards to early detection of smoke. Additional research on ambient air quality in the International Space Station (ISS) is presented which sheds light on background aerosols that may interfere with smoke detection in spacecraft

Süsinikmaterjalist elektroodidega ioonsed ja mahtuvuslikud elektroaktiivsed laminaadid sensorite ning energiakogumisseadmetena

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Kaasaegses elektroonika- ja robootikatööstuses valitseb suundumus miniatuursete, autonoomsete ja läbinisti pehmete seadmete väljatöötamisele, mis ühtlasi tingib huvi sobivate materjalide arenduse vastu. Käesolevas töös käsitletakse antud valdkonnale huvipakkuvat pehmet ioonset elektroaktiivset polümeerset laminaatmaterjali (IEAP), mis koosneb suure-eripinnalistest süsinikelektroodidest, poorsest polümeermembraanist ning ioonvedelikust, mis täidab nii elektroodi kui polümeermembraani poore. Antud laminaatmaterjal on väga multifunktsionaalne – varasemalt on tuntud selle energiasalvestus- ja täituriomadused. Käesolevas töös uuritakse antud materjaliklassi uudset omadust – elektrilaengu genereerimise võimet. Esmalt rakendati IEAP laminaati konfiguratsioonis, mis vastab selle kasutamisele elektromehaanilise täiturina, kuid seda painutati välise jõuga. Painutamise tulemusena genereeris IEAP elektrilaengut proportsionaalselt painutuse ulatusega. Seega on võimalik sama IEAP-i kasutada vaheldumisi nii pehme täituri kui liigutussensorina. IEAP-d iseloomustab suur tundlikkus õhuniiskuse suhtes, sest IEAP koosneb ülihügroskoopsetest koostisosadest. Elektrokeemilise impedantsspektroskoopia meetodil selgus, et õhuniiskuse pöörduva absorptsiooni tõttu võivad IEAP elektrilised omadused muutuda enam kui ühe suurusjärgu ulatuses. Antud töös rakendati IEAP materjali kõrget niiskustundlikkust uudses, ootamatus konfiguratsioonis – hügroelektrilise rakuna. Kui IEAP paigutada kahe erineva suhtelise õhuniiskusega keskkonna eralduspiirile, tekib IEAP elektroodidel elektrilaeng. IEAP hügroelektriline rakk võimaldab koguda elektrienergiat ümbritsevast õhuniiskusest, kusjuures õhuniiskusest genereeritav elektrilaeng ületab enam kui suurusjärgu võrra painutussensorit. Siinkohal on määrava tähtsusega ka IEAP-i energiasalvestiomadused – IEAP hügroelektriline rakk ei vaja välist energiasalvestuselementi, vaid genereeritud elektrilaeng salvestatakse samasse materjaliossa, mis antud laengu genereeris.The modern electronics and robotics industry is interested in development of miniature, autonomous, and fully soft devices; consequently, the research on compatible materials is promoted. This work considers one class of materials – ionic electroactive polymer laminate (IEAP), perspective for the given field. An IEAP consists of carbonaceous electrodes with high specific surface area, a porous polymeric separator, and ionic liquid, which fills the pores in electrode and separator. IEAP is a multifunctional material – it is known for its energy storage and actuation capability. The work at hand explores a novel property of IEAP – generation of electric charge. First, an IEAP laminate was employed in a configuration that corresponds to its use as an electromechanical actuator, but it was bent using an external force. The IEAP generated electric charge proportional to the bending magnitude. Consequently, the same IEAP could be used intermittently as a soft actuator and as a motion sensor. IEAP consists of highly hygroscopic materials, which is expressed in its high sensitivity to ambient humidity. Electrochemical impedance spectroscopy revealed that reversible absorption of ambient humidity changes the electrical properties of IEAP over one order of magnitude. In this work, humidity-sensitive IEAP is employed in a novel, unexpected configuration – as a hygroelectrical cell. If an IEAP is placed between environments with unequal relative humidities, electric charge is formed between the IEAP’s electrodes. An IEAP can be used to harvest electric energy from the ambient humidity, whereas the magnitude of the generated charge is more than one order of magnitude higher than in the case of the same material as a motion sensor. At this point, the energy storage properties of IEAP are essential – an IEAP hygroelectrical cell does not require additional energy storage units; instead, the generated electric charge is stored in the same part of the material, where it was generated