Browsing by master's degree program "Master's Programme in Materials Research"
Now showing items 41-52 of 52
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(2021)Maa-aineksessa fosfori on sitoutunut alkuaineisiin, joista rauta on merkittävässä osassa. Fosfori voi vapautua vedessä tai pohja-aineksessa liuenneeseen muotoon aiheuttaen rehevöitymistä. Fosforin vapautumiseen vesistössä vaikuttavat maa-aineksen koostumus, veden ominaisuudet ja hiilen saatavuus. Raudan pitoisuudet ja esiintymismuodot selittävät osittain vesistöjen välisiä eroja rehevöitymisessä. Röntgenabsorptiospektroskopialla voidaan tutkia alkuaineen atomien hapetustilaa, koordinaatiolukua, koordinaatiokemiaa ja atomien välisiä etäisyyksiä. Menetelmässä mitataan absorptiokerrointa energian funktiona. Näytteiden analysoinnissa käytetään yleensä vertailukohtana hyvin tunnettuja referenssien spektrejä. Tulokset ovat luotettavimmat, kun referenssien spektrit ovat mitattu samoilla asetuksilla yhdessä näytteiden kanssa. Tässä työssä on tutkittu yhtätoista (11) eri maa-ainesta röntgenabsorptiospektroskopialla raudan K-reunan lähiympäristössä. Maa-aineksista tutkittiin; 1. käsittelemätön, 2. oksalaattiuutettu, 3. poltettu sekä 4. oksalaattiuutettu ja poltettu versio. Oksalaattiuuton ja polton tarkoituksena oli selventää maa-ainesten välillä olevia eroja. Uuttaminen tarkoittaa oksalaattiuuttoa, jossa maa-aineksesta poistuu heikosti kiteistä rautaa. Polttaminen tarkoittaa näytteen kuumentamista 700 asteeseen, jolloin maa-aineksen rautaoksidit hapettuvat ja kiteytyvät. Näytteet, 44 kpl, mitattiin kolmeen kertaan. Eri maa-aineksien ja niiden eri käsittelyiden välillä havaittiin eroja absorptioreunan energiassa, joka on yhteydessä raudan hapetustilaan. Polttaminen teki absorptiospektreistä keskenään lähes samanlaisia ja tasoitti käsittelemättömissä näytteissä olleita eroja. Oksalaattiuuttamisella ei havaittu olevan vastaavaa vaikutusta. Näytteiden rautamineraalien spektripainoista voidaan päätellä näytteiden mineraalikoostumuksia. Jotta raudan merkitystä fosforin kierrossa voidaan tarkentaa, tarvitaan lisää tutkimusta.
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(2020)Polysiloxanes are silicon-based polymers consisting of R2SiO repeating units. They are commonly used in many commercial applications, for example, as adhesives, additives, or waterproof coatings. This thesis concentrates on polysiloxanes used as optically clear adhesives, which are needed in display applications to, for instance, bond cover lenses to touch panel sensors. This kind of a material needs to have a high refractive index to match glass or plastic, and it has to be transparent and thermally stable. In addition, it must resist degradation and yellowing from UV exposure and humidity. Anionic ring-opening polymerization was used to synthesize optically transparent polysiloxanes with varying side-groups. These polymers exhibited high refractive index values, which were adjusted by changing the amount of phenyl group -containing monomers or with chain terminating agents. End-functionalization reactions were performed for the synthesized polymers to introduce methacrylate groups to the chain ends, which could later be used in crosslinking trials involving a photoinitiator. The results present an effective synthetic route for the ring-opening polymerization for transparent, high refractive index poly(dimethylsiloxane-co-diphenylsiloxane) and poly(methylphenylsiloxane) that could be used as adhesives after selective chain end functionalization and crosslinking reactions. The properties of the synthesized polysiloxanes were characterized with several different methods, such as size exclusion chromatography, rheology, and NMR spectroscopy. End functionalization reactions were performed for some of the synthesized polymers. These were then further characterized to verify the suitability of the reaction.
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(2024)One challenge in the research of societal phenomena is to find the balance between realism and tractable models. Molecular dynamics simulations are based on physical theories that use computationally efficient abstractions for interactions. Formulation of human interactions as physical potentials creates an opportunity to apply the computational methods from physics to social sciences. This thesis tries to answer if a simulation model based on physical pair potentials can describe the transgenerational heritance of prenatal alcohol exposure. The society is abstracted to a surface. Individuals can reproduce and die. Their life histories depend on the environment that is presented as a resource lattice with general and alcohol resource particles. The results are promising, showing decent conformity with epidemiological observations. In many cases, an analogical mechanism for societal phenomena can be found from surface physics. Additionally, material physics and epidemiology tackle with similar problems in observation of structures. To this end, this line of research has potential.
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(2021)The plasma-facing materials of future fusion reactors are exposed to high doses of radiation. The characterization of the radiation damage is an essential part in the study of fusion relevant materi- als. Electron microscopy is one of the most important tools used for characterization of radiation damage, as it provides direct observations of the microstructure of materials. However, the char- acterization of defects from electron microscope images remains difficult. Simulated images can be used to bridge the gap between experimental results and models. In this thesis, scanning transmission electron microscope (STEM) images of radiation damage were simulated. Molecular dynamics simulations were employed in order to create defects in tungsten. STEM images were simulated based on the created systems using the multislice method. A data- base of images of h001i dislocation loops and defects produced from collision cascade simulations was generated. The simulated images provide insight into the observed contrast of the defect structures. Differences in the image contrast between vacancy and interstitial h001i dislocation loops were reported. In addition to this, the results were compared against experimental images and used in identification of a dislocation loop. The simulated images demonstrate that it is feasible to simulate STEM images of radiation damage produced from collision cascade simulations.
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(2024)In this master’s thesis, linear zwitterionic poly(ethylene imine) methyl-carboxylates (l-PEI-MCs) were synthesized through a four-step synthesis. The synthesis started with the polymerization of 2-ethyl-2-oxazoline (EtOx) monomers into poly(2-ethyl-2-oxazoline) (PEtOx) homopolymers with polymerization degree of 50 and 100. Living cationic ring-opening polymerization (LCROP) enabled a good control over the molecular weights. Subsequently, the side chains of PEtOxs were cleaved off by acidic hydrolysis. This resulted in linear poly(ethylene imine)s (l-PEIs) bearing a secondary amine group in repeating units of the polymer chain. These amine units were then functionalized with methyl-carboxylate moieties by first introducing tert-butyl ester functionalities to l-PEI chains, and subsequently cleaving off the tert-butyl groups. The final polymer is a polyzwitterion, featuring both an anionic carboxylate and a cationic tertiary amine group within a single repeating unit. Polymers produced in each step were characterized via 1H-NMR and FT-IR spectroscopy and their thermal properties were analyzed by differential scanning calorimetry (DSC). The molecular weights and dispersities (Ð) of PEtOx polymers were additionally estimated by gel permeation chromatography (GPC). Via 1H-NMR, the degree of polymerization for PEtOxs and the hydrolysis degree for l-PEIs were determined. FT-IR gave a further insight into the structures of polymers, successfully confirming the ester functionality of modified l-PEI. The disappearance of the tert-butyl proton signal in 1H-NMR spectrum after deprotection verified the successful removal of tert-butyl groups, resulting in the final product with methyl-carboxylate functionalities. By DSC, different thermal transitions, i.e., glass transition (Tg), melting (Tm) and crystallization (Tc), were observed, and the effects of molar mass and polymer modifications on these transitions were being investigated. The state of the art explores the literature regarding synthesis and properties of poly(2-oxazoline)s (POx), poly(ethylene imine)s (PEIs), and polyzwitterions. The theory behind living cationic ring-opening polymerization of 2-oxazolines and acidic hydrolysis of POxs is described. Different post-polymerization modification strategies to functionalize PEIs are being discussed. In addition, possible applications for each of these polymer classes are shortly outlined.
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(2020)In this thesis, synthesis and solution properties of the polyampholyte poly(acrylic acid)-b-poly[(vinylbenzyl)trimethylammonium chloride], PAA-PVBTMA-Cl, were investigated in aqueous solutions. First, the diblock copolymer was synthesized via RAFT polymerization where poly(acrylic acid), PAA was used as a chain transfer agent (CTA). In addition, the homopolymer poly[(vinylbenzyl)trimethylammonium chloride], PVBTMA-Cl, was synthesized via RAFT polymerization to compare the solution properties with the block copolymer. Molar masses of the polymers were determined using several methods such as NMR, UV-Vis spectroscopy and SEC. The experimental molar masses were close to theoretical values and block ratio in diblock copolymer from NMR was 30% of AA and 70% of VBTMA-Cl. Furthermore, the solution properties of the polyampholyte were studied under external stimuli such as pH and temperature. UCST type of behaviour was observed for aqueous PAA-PVBTMA-Cl solutions when the hydrophobic trifluoromethanesulfonate (OTf) anion was introduced. In addition, self-assembly of the diblock copolymer was confirmed by zeta potential measurements in different pH conditions. The expected reverse of the micelle structure with changing pH was not observed. However, aqueous PAA-PVBTMA-Cl showed UCST behaviour and micellization induced by the hydrophobic counterion.
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(2024)One of the main goals of materials research is to find the link between the properties of materials and their fundamental structures. The distinct properties of thin films, categorized as materials from a few single layers of atoms to some hundreds of nanometers, have enjoyed an unparalleled demand in modern device manufacturing, and thus the investigation of factors which determine thin film structure and morphology is a vital area of research. In the case of thin films, their final structures can often be connected back to the initial film formation stages, such as in the crystallographic growth competition during island growth and coalescence. In this thesis, thin film growth stages are studied from the perspective of how they are affected by impurities. From the initial diffusion of adatoms on a bare substrate; to the formation of islands, their growth and coalescence; to the mobility of grain boundaries and bulk diffusion leading to the formation of a fully continuous layer; impurities influence each of these thin film growth processes in a multifaceted way, either acting as growth inhibitors, promoters or potentially neutral agents. To this end, Ag and Cu thin films were synthesized by magnetron sputtering onto SiO_2/Si substrates, with thicknesses ranging from 3 nm to 30 nm using varied deposition conditions, with the addition of a 3 nm amorphous carbon layer to limit further restructuring and oxidation. Impurities were let into the deposition atmosphere via a controlled opening of a leak valve, corresponding to a step-wise increase of base pressure from 10^(-8) Torr to 10^(-6) Torr and finally 10^(-5) Torr. The full range of thin films was deposited with each base pressure (except for 10^(-5) Torr for Cu) using two deposition rates, around 0.1 Ås^(-1) and 2 Ås^(-1). Each film was characterized ex situ with ellipsometry, 4PP, XRD and AFM to map the morphological and microstructural evolution during film growth. It is found that impurities tend to inhibit island coalescence and initial grain growth, resulting in a reduction of continuous film formation thickness and average grain size, leading to the formation of flatter films with, in most cases, less surface roughness. In later stages, it is found that impurities may allow for more grain growth by their incorporation into the growing facets. In terms of crystal structure, it is shown that impurities have a more pronounced effect on (111) oriented grains, inhibiting their growth, thus altering the preferred growth orientations of Ag and Cu by allowing (200) grains to grow larger. Grain radii and equivalent ellipse distributions showed the different responses of Ag and Cu to impurities. Ag films showed more prominent effects when a lower deposition rate was used, highlighting the impact of impurities on diffusive processes, while Cu films exhibited more effects with the use of higher deposition rates, indicating that the role of impurities, in this case, was more significant after the formation of a continuous layer.
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(2020)In this thesis, thermoresponsive poly(N-acryloyl glycinamide-co-methacrylic acid) (P(NAGA-co-MAA)) microgels were synthesized via surfactant stabilized free radical precipitation polymerization. Also, PNAGA microgel was synthesized as reference. The upper critical solution temperature (UCST) behavior of the microgels was tuned by changing the molar ratio of the monomers in the copolymer. The phase transition behavior of the formed microgel particles were characterized with NMR spectroscopy, microcalorimetry, turbidimetry and light scattering. It was observed that both PNAGA and P(NAGA-co-MAA) microgels display UCST type temperature response. However, in neutral pH, the phase transition of the copolymer gels was prevented due to the deprotonated acid groups of MAA. Hence, all the measurements were made in pH 3, below the pKa of MAA. The phase transition became sharper when the amount of MAA repeating units was increased in the copolymer. Also, the phase transition temperature of the copolymer gels increased when the amount of MAA was increased. In addition to phase transition behavior studies, the reactivity ratios of the monomers were studied during polymerization to analyze the structure of the forming copolymer gels. It was concluded that, as the both monomers had similar reactivity rates, statistical random copolymer gels are formed.
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(2021)Pipe fouling is a challenging problem in many industrial applications. Established cleaning techniques require that the production is aborted during the cleaning phase. These techniques are unable to focus cleaning power, even though fouling often is localized to certain areas inside the pipeline. This study introduces an effective method to clean fouling inside complex structures. We use finite-element modelling (FEM) -based time-reversed signals to focus ultrasound power onto a predetermined pipe residing inside a Plexiglas container. We compare the cleaning effect obtained by this method with the cleaning obtained with standard ultrasound cleaning when using the same input electric power and cleaning time. Our results indicate that the proposed time-reversal based technique removes more fouling compared to when using the standard technique. Moreover, we demonstrate ability to relocate the focus including changing the target from one pipe to another one inside the container.
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(2020)Two different bio transfer standards (BTS), composed of fatty acid bilayers, NanoRuler and NanoStar were developed. NanoRuler consists of a nanometer scale staircase with eight steps that are 5 nm tall each and NanoStar is designed to have topological structure with sharp edge and three height planes 5 nm elevated with respect to each other. With NanoRuler nanometer vertical calibration from 5 nm to 40 nm is possible and NanoStar allows the evaluation of the instrument transfer function (ITF). Due to the soft nature of the standards, the topographical stability was researched. Thus, an investigation of the topographical stability of three NanoRulers and one NanoStar across 24 months was done by measuring the surface topography with a custom-built Scanning White Light Interferometer (SWLI). The BTS were measured over 100 times during the experiments and were stored in laboratory conditions. The step heights of the structures were calculated with a histogram method and the surface roughness of the samples was evaluated using the Sq parameter. The step height analysis method was compared to the standard method (ISO 5436-1) where applicable and no notable differences were found. In both roughness and step height data no linear or non-linear trends were found, and the step heights compared well with the literature values. For NanoRuler the step heights were 4.9 nm, 10.1 nm, 15.1 nm, 20.1 nm, 25 nm, 30.1 nm, 35.1 nm and 40.2 nm and the respective stabilities were 0.3 nm, 0.3 nm, 0.6 nm, 0.9 nm, 1.3 nm, 1.6 nm, 2.1 nm, and 2.5 nm. For NanoStar the step heights were -5.1 nm and 5.2 nm with stabilities 0.3 nm and 0.4 nm respectively. The NanoRuler had a surface roughness stability of 0.02 nm whereas NanoStar had a roughness stability of 0.01 nm. After 24 months both BTS types preserved their topographical structure and no issues with surface topographical stability were observed.
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(2023)High-entropy alloys (HEAs), esteemed for their exceptional resistance to radiation damage, carry considerable potential for deployment within fusion reactors. Nonetheless, due to their compositional complexity, comprehending the diffusion behaviour in these multifaceted alloys continues to be a daunting task. This thesis proposes a novel approach to modelling vacancy diffusion in body-centred cubic (BCC) HEAs, particularly Mo-Nb-Ta-V-W. The methodology involves the tactical application of collective variable-driven hyperdynamics (CVHD) to procure data for training a Gaussian process regression (GPR) and feed-forward neural network (FNN) model. The trained FNN model is subsequently employed within kinetic Monte Carlo (KMC) simulations for accurately predicting jump rates, whereas the GPR model is used to elucidate experimental findings related to the behaviour of vacancies in \mbox{Mo-Nb-Ta-V-W}. The robustness of the FNN model is manifested by its capacity to generalise to unseen data, whilst the efficacy of the overall method is corroborated by Monte Carlo molecular dynamics (MCMD) simulations. The CVHD methodology, uniquely capable of functioning at finite temperatures, can capture the entropic contribution to the free energy and model kinematics explicitly. This singular ability facilitates a more comprehensive understanding of the system's behaviour under authentic conditions. The findings presented in this thesis signify a considerable stride forward in the study of HEAs, providing a robust framework for the design of advanced materials. These results underscore the potential of the CVHD-trained FNN-KMC methodology in exploring complex environments, thereby establishing a firm foundation for future investigations and emphasising the need for its continued refinement and augmentation.
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(2019)Rehevöityminen on yksi merkittävimmistä vesistöjen ekologista tilaa heikentävistä tekijöistä. Järvivesissä fosfori on useimmiten levien kasvua rajoittava tekijä, jolloin fosforin määrän kasvu vastaanottavassa vesistössä lisää kasvillisuuden perustuotantoa ja kiihdyttää näin ollen vesistön rehevöitymistä. Fosforia päätyy vesistöihin valumavesien mukana liuenneessa muodossa ja eroosion ansiosta hiukkasmaisessa muodossa sitoutuneena esimerkiksi erodoituneessa maa-aineksessa oleviin raudan oksideihin. Erodoitunut maa-aines laskeutuu vesistöjen pohjalle, päätyy osaksi pohjasedimenttiä ja lopulta kohtaa hapettomat olosuhteet. Pohjasedimentteihin varastoituneet ravinteet voivat hapettomissa olosuhteissa vapautua takaisin vesistön tuottavaan kerrokseen ja näin ollen kiihdyttää rehevöitymistä. Hiukkasmaisen fosforin vapautuminen liuenneeseen, leville käyttökelpoiseen muotoon tunnetaan huonosti, joten erodoituneen maa-aineksen mukana kulkeutuvan fosforin merkitys vesistöjen rehevöitymisessä ei ole täysin selvä. Tässä työssä tutkitaan maa-aineksen matkaa pelloilta järvien pohjasedimentteihin käyttäen raudan K-reunan röntgenabsorptiospektroskopiaa lähireuna-alueella. Keskipisteessä on raudan kemiallisen tilan muutos siirryttäessä hapellisista olosuhteista hapettomiin olosuhteisiin sekä mahdollisesti järvien sedimenteissä muodostuva raudan fosfaattimineraali vivianiitti, jolla voi olla merkittävä rooli fosforin pidättämisessä sedimenttiin. Lisäksi tutustutaan röntgenabsorptiospektroskopian teoriaan sekä tutkimuksessa käytettävän spektrometrin toimintaan. Erilaisten maa-ainesten päätymistä järvien sedimentteihin simuloitiin valmistamalla järviveden ja maa-ainesten seoksia, joista osaan lisättiin myös orgaanista hiiltä. Seoksista valmistettiin näytteet röntgenabsorptiomittauksia varten vuorokauden aerobisen sekä neljän kuukauden anaerobisen inkuboinnin jälkeen. Mittaustuloksista havaitaan selvästi raudan pelkistyminen anaerobisissa olosuhteissa, ja että pelkistymistä edesauttaa orgaanisen hiilen läsnäolo. Vertailemalla järvivesi-maanäytteiden spektrejä mitattuun vivianiittimineraalista valmistetun näytteen spektriin, havaitaan että raudan pelkistyminen anaerobisessa ympäristössä suosii Fe(II)-mineraalien muodostumista. Mitattuja spektrejä verrattiin vivianiitin spektriin ja vertailun perusteella vivianiittia muodostui neljän kuukauden anaerobisen inkuboinnin aikana hiilettömissä näytteissä 12 - 22 % ja hiilellisissä näytteissä 31 - 50 % verrattuna hapelliseen alkutilanteeseen. Prosenttiluvut ovat todennäköisesti yliarvioita vivianiitin muodostumiselle, mutta tuloksista voidaan kuitenkin päätellä, että raudan voimakkaampi pelkistyminen edesauttaa vivianiitin tai muiden Fe(II)-mineraalien muodostumista ja että vivianiitin muodostumisella saattaa olla vaikutus fosforin pidättämisessä sedimenttiin.
Now showing items 41-52 of 52