Studies in offset ink setting

The offset printing process is complex and involves the meeting of two essentially complex materials, printing ink and paper, upon which the final product is formed. It can therefore be expected that a multitude of chemical and physical interactions and mechanisms take place at the ink-paper interface. Interactions between ink and paper are of interest to both the papermakers and ink producers, as they wish to achieve better quality in the final product. The objective of this work is to clarify the combined influence of paper coating structure, printing ink and fountain solution on ink setting and the problems related to ink setting. A further aim is to identify the mechanisms that influence ink setting problems, and to be able to counteract them by changing properties of the coating layer or by changing the properties of the ink. The work carried out for this thesis included use of many techniques ranging from standard paper and printability tests to advanced optical techniques for detection of ink filaments during ink levelling. Modern imaging methods were applied for assessment of ink filament remain sizes and distribution of ink components inside pigment coating layers. Gravimetric filtration method and assessment of print rub using Ink-Surface-Interaction-Tester (ISIT) were utilized to study the influence of ink properties on ink setting. The chemical interactions were observed with the help of modified thin layer chromatography and contact angle measurements using both conventional and high speed imaging. The results of the papers in this thesis link the press operational parameters to filament sizes and show the influence of these parameters to filament size distribution. The relative importance between the press operation parameters was shown to vary. The size distribution of filaments is important in predicting the ink setting behaviour, which was highlighted by the dynamic gloss and ink setting studies. Prediction of ink setting behaviour was also further improved by use of separate permeability factors for different ink types in connection to filtration equations. The roles of ink components were studied in connection to ink absorption and mechanism of print rub. Total solids content and ratio of linseed oil to mineral oil were found to determine the degree of print rub on coated papers. Wax addition improved print rub resistance, but would not decrease print rub as much as lowering the total solids content in the ink. Linseed oil was shown to absorb into pigment coating pores by mechanism of adsorption to pore walls, which highlights the need for sufficient pore surface area for improved chromatographic separation of ink components. These results should help press operators, suppliers of printing presses, papermakers and suppliers to papermakers, to better understand the material and operating conditions of the press as it relates to various print quality issues. Even though paper is in competition with electronic media, high quality printed products are still in demand. The results should provide useful information for this segment of the industry.

CFD Modelling of Direct Contact Condensation in Suppression Pools by Applying Condensation Models of Separated Flow

The condensation rate has to be high in the safety pressure suppression pool systems of Boiling Water Reactors (BWR) in order to fulfill their safety function. The phenomena due to such a high direct contact condensation (DCC) rate turn out to be very challenging to be analysed either with experiments or numerical simulations. In this thesis, the suppression pool experiments carried out in the POOLEX facility of Lappeenranta University of Technology were simulated. Two different condensation modes were modelled by using the 2-phase CFD codes NEPTUNE CFD and TransAT. The DCC models applied were the typical ones to be used for separated flows in channels, and their applicability to the rapidly condensing flow in the condensation pool context had not been tested earlier. A low Reynolds number case was the first to be simulated. The POOLEX experiment STB-31 was operated near the conditions between the ’quasi-steady oscillatory interface condensation’ mode and the ’condensation within the blowdown pipe’ mode. The condensation models of Lakehal et al. and Coste & Lavi´eville predicted the condensation rate quite accurately, while the other tested ones overestimated it. It was possible to get the direct phase change solution to settle near to the measured values, but a very high resolution of calculation grid was needed. Secondly, a high Reynolds number case corresponding to the ’chugging’ mode was simulated. The POOLEX experiment STB-28 was chosen, because various standard and highspeed video samples of bubbles were recorded during it. In order to extract numerical information from the video material, a pattern recognition procedure was programmed. The bubble size distributions and the frequencies of chugging were calculated with this procedure. With the statistical data of the bubble sizes and temporal data of the bubble/jet appearance, it was possible to compare the condensation rates between the experiment and the CFD simulations. In the chugging simulations, a spherically curvilinear calculation grid at the blowdown pipe exit improved the convergence and decreased the required cell count. The compressible flow solver with complete steam-tables was beneficial for the numerical success of the simulations. The Hughes-Duffey model and, to some extent, the Coste & Lavi´eville model produced realistic chugging behavior. The initial level of the steam/water interface was an important factor to determine the initiation of the chugging. If the interface was initialized with a water level high enough inside the blowdown pipe, the vigorous penetration of a water plug into the pool created a turbulent wake which invoked the chugging that was self-sustaining. A 3D simulation with a suitable DCC model produced qualitatively very realistic shapes of the chugging bubbles and jets. The comparative FFT analysis of the bubble size data and the pool bottom pressure data gave useful information to distinguish the eigenmodes of chugging, bubbling, and pool structure oscillations.

Ambidextrous leadership in customer contact centre organization

In a modern dynamic environment organizations are facing new requirements for success and competitive advantage. This also sets new requirements for leaders. The term of ambidexterity is used in relation with organizations that are able to manage short-term efficiency and long-term innovation simultaneously. Ambidextrous leaders have the same capability at an individual level. They are able to balance between efficiency and flexibility. This study examined the confrontation of these two competing concepts in the leadership perspective. The aim of the study was to understand this recently arisen concept and its antecedents and examine what is currently known about ambidextrous leadership. This was a case study with data collected through theme interviews in a result orientated customer centre organization that has a cultural change at hand when it comes to leadership and empowerment. Organization wants to be efficient and flexible at the same time (a.k.a. ambidextrous) and that requires new type of leadership. In this study the aim was to describe the capabilities and criteria for ambidextrous leader and examine the leadership roles related to ambidextrous leadership in different hierarchical levels. The case organization had also created systematic means to support this cultural change and the effects of the process related to leadership were studied. This study showed that the area is yet widely unexplored and contradictory views are presented. This study contributes to the deprivation of study of ambidexterity in leadership and individuals. The study presents a description of ambidextrous leadership and describes the capabilities of ambidextrous leader. Ambidextrous leaders are able to make cognitive decisions between their leadership style according to situation that requires either leadership related to efficiency such as transactional leadership or leadership related to flexibility such as transformational leadership. Their leadership style supports both short-term and long-term goals. This study also shows that the role of top management is vital and operational leaders rely on their example.

Puuperäisten biomassahydrolysaattien likaamien membraanien pesu

Tässä diplomityössä tutkittiin biomassahydrolysaatilla liattujen ultrasuodatusmembraanien pesua. Työn kirjallisuusosassa käsitellään membraanien likaantumista ja pesua, puuperäistä biomassahydrolysaattia sekä biomassahydrolysaatin suodatusta membraaneilla ja membraanien karakterisointia. Kokeellisessa osassa tutkittiin pesuaineiden vaikutusta koivuhydrolysaatilla liattujen membraanien peseytyvyyteen. Käytetyt ultrasuodatusmembraanit olivat Alfa Lavalin UFX5 ja ETNA01PP. Membraanien pesussa käytettiin Ecolabin entsymaattisia P3-ultrasil 53 ja P3-ultrasil 67 pesuaineita yhdessä emäksisen P3-ultrasil 69 pesuaineen kanssa sekä hapanta P3-ultrasil 75 pesuainetta. Lisäksi emäksisiä P3-ultrasil 110, P3-ultrasil 112 ja P3-ultrasil 115 pesuaineita. Emäksisten pesujen tehokkuutta vertailtiin pelkällä natriumhydroksidilla tehtyyn pesuun. Membraanien likaantumista arvioitiin mittaamalla puhtaan veden vuota ennen ja jälkeen likaantumissuodatuksen ja laskemalla niiden vuoarvojen erotus. Samalla tavalla arvioitiin pesuaineiden vaikutusta membraanin peseytyvyyteen. Lisäksi peseytyvyyttä arvioitiin FTIR–analyyseillä, kontaktikulmamittauksilla ja membraanin sisältämän ligniinin värjäyksellä. Tutkimuksissa havaittiin, että koivuhydrolysaatilla liatuille UFX5 membraaneille vesivuon sekä FTIR–spektrin muuttumisen perusteella sopii parhaiten emäksisen ja happaman pesuaineen kaksivaiheinen pesu. Kontaktikulman palautumisen perusteella parhaiten sopi pelkällä emäksisellä P3-Ultrasil 115 tehty pesu. Ligniiniä parhaiten, mikroskooppiin liitetyllä kameralla otettujen kuvien perusteella, poisti entsymaattinen P3-ultrasil 67, mutta tämä samalla modifioi membraanin pintaa. Tässä tutkimuksessa havaittiin, että emäksinen ja entsymaattinen pesuaine pesevät melko hyvin koivuhydrolysaatilla liattuja membraaneja. Lisäksi havaittiin, että ligniini tunkeutuu suodatuksissa membraanin sisään, joten pelkkä pesuaineen kierrättäminen laitteistossa ei riitä vaan tarvitaan paineellista pesua.

Rasvankestävät paperit ja kartongit

Rasvankestävyydellä tarkoitetaan sitä, että materiaali hylkii tai kestää rasvaa tietyn ajan läpäisemättä sen pintaa. Rasvankestäviä papereita ja kartonkeja löytyy kaikkialta. Erilaiset ruuanvalmistuspaperit, kuten esimerkiksi leivinpaperi ja voipaperi, ovat rasvankestäviä. Myös pakkauksissa käytetään paljon rasvankestäviä papereita ja kartonkeja. Rasvankestäviltä tuotteilta vaaditaan erilaisia ominaisuuksia riippuen niiden käyttötarkoituksesta. Pakkausmateriaaleilta vaaditaan esimerkiksi lujuutta ja kestävyyttä fyysistä rasitusta, valoa, hajuja ja mikrobeja vastaan. Ruuanvalmistusmateriaaleilta vaaditaan puolestaan lujuutta ja kestävyyttä lämpöä, kosteutta ja fyysistä rasitusta vastaan. Rasvankestäviltä papereilta vaaditaan rasvankestävyyden lisäksi hyvää vetolujuutta, märkälujuutta ja hyviä optisia ominaisuuksia. Neliömassan tulee asettua 20─80 g/m2 välille ja metallipitoisuudet eivät saa olla liian korkeat. Myös tuotteiden kierrätettävyys on nostanut asemaansa viimeaikoina. Tuotteen tuotannon ja itse tuotteen ympäristöystävällisyys ovat todella arvostettuja kuluttajan, tuottajan, Suomen, EU:n ja koko maailman näkökulmista. Jotta tuotteesta saadaan rasvankestävää, vaaditaan siltä erilaisia barrier-ominaisuuksia. Rasvankestävällä paperilla vaaditaan hyviä barrier-ominaisuuksia esimerkiksi rasvan, ilman, veden, vesihöyryn sekä hapen läpäisevyyksissä. Rasvankestäviä papereita ja kartonkeja voidaan valmistaa kemiallisilla ja mekaanisilla tavoilla. Happokäsittely ja fluorokemikaalien lisääminen ovat kemiallisia tapoja, kun taas sellun jauhaminen pitkään matalassa lämpötilassa on mekaaninen tapa valmistaa rasvankestävää paperia. Näiden tapojen lisäksi rasvankestäviä papereita voidaan tehdä erilaisten pinnoitusten avulla. Erilaiset muovit ovat yleisemmin käytettyjä pinnoitemateriaaleja. Esimerkiksi PE- ja PET-päällysteet ovat käytettyjä rasvankestävissä tuotteissa. Viime aikoina on kehitetty paljon erilaisia biomateriaaleja, joista voidaan tehdä rasvankestävä pinnoite. Lipideistä, hydrokolloideista ja erilaisista komposiiteista voidaan luoda uusien tekniikoiden avulla rasvankestäviä pinnoitteita. Rasvankestävyydestä voidaan saada jonkinlainen käsitys WVTR-asteen, Cobb-arvon ja kontaktikulman mittausten avulla. Rasvankestävyyttä voidaan myös mitata erilaisten standarditestien avulla. TAPPI:lla, ISO:lla ja ASTM:llä on useita erilaisia standardeja. Lähes kaikissa rasvankestävyysstandardeissa tuloksen saaminen perustuu visuaaliseen havaintoon, mikä aiheuttaa välillä hankaluuksia tulosten luotettavuuteen, koska tuloksen määrittää ihmissilmä, ja kaikilla testin tekijöillä on erilainen silmä, joka aistii eri tavalla.

Side peaks in Nb and NbTi point-contact spectra

Superconductor – normal metal point contacts were investigated, using different combinations of Cu, brass, Nb and NbTi. The resulting spectra contained side peaks. The currents at which these side peaks appeared, depended on the radii of the contacts. For contacts with Nb this dependence was quadratic, while for contacts with NbTi it was linear. Based on this, we argue that the side peaks in the case of the Nb contacts are due to the critical current density being exceeded. In contrast, side peaks of the NbTi contacts are caused by the self-magnetic field exceeding the lower critical field of NbTi. The NbTi contacts did not show the expected contribution from the vanishing Maxwell resistance of the superconductor, a question which remained open.

A Soft Contact Collision Method For Real-Time Simulation of Triangularized Geometries in Multibody Dynamics

When modeling machines in their natural working environment collisions become a very important feature in terms of simulation accuracy. By expanding the simulation to include the operation environment, the need for a general collision model that is able to handle a wide variety of cases has become central in the development of simulation environments. With the addition of the operating environment the challenges for the collision modeling method also change. More simultaneous contacts with more objects occur in more complicated situations. This means that the real-time requirement becomes more difficult to meet. Common problems in current collision modeling methods include for example dependency on the geometry shape or mesh density, calculation need increasing exponentially in respect to the number of contacts, the lack of a proper friction model and failures due to certain configurations like closed kinematic loops. All these problems mean that the current modeling methods will fail in certain situations. A method that would not fail in any situation is not very realistic but improvements can be made over the current methods.

Probabilistic contact preferences in protein-ligand and protein-protein complexes

Modeller för intermolekulär växelvärkan utnyttjas brett inom biologin. Analys av kontakter mellan proteiner och läkemedelsforskning representerar typiska tillämpningsområden för dylika modeller. En modell som beskriver sådana molekylära växelverkningar kan utformas med hjälp av biofysisk teori, vilket tenderar att resultera i ytterst tung beräkningsbörda även för enkla tillämpningar. Ett alternativt sätt att formulera modeller är att utnyttja stora databaser som innehåller strukturmätningar gjorda med hjälp av till exempel röntgendiffraktion. Då man använder sig av empiriska mätdata direkt, möjliggör en statistisk modell att osäkerheten och inexaktheten i datat tas till hänsyn på ett adekvat sätt, samtidigt som beräkningsbördan håller sig på en rimligare nivå jämfört med kvantmekaniska metoder som i princip borde ge de optimala resultaten. I avhandlingen utvecklades en 3D modell för numerisk undersökning av intermolekulär växelverkan baserad på Bayesiansk statistik. Modellens syfte är att åstadkomma prognoser för det hurdana eller vilka molekylstrukturer prefereras i en given kontext, d.v.s. är mer sannolika inom ramen för interaktion. Modellen testades i essentiella molekyläromgivningar - en liten molekyl vid sin bindningsplats hos ett protein och en gränsyta mellan proteinerna i ett komplex. De erhållna numeriska resultaten motsvarar väl experimentella resultat som tidigare rapporterats i litteraturen, exempelvis kvalitativa bindningsaffiniteter och kemisk kännedom av vissa aminosyrors rumsliga förmågor att utgöra bindningar. I avhandlingen gjordes ytterligare preliminära tester av den statistiska ansatsen för modellering av den centrala molekylära strukturella anpassningsbarheten. I praktiken är den utvecklade modellen ämnad som ett led i en mer omfattande analysmetod, så som en s.k. farmakofor modell. Molekyylivuorovaikutusten mallintamista hyödynnetään laajasti biologisten kysymysten tarkastelussa. Tyypillisiä esimerkkejä sovelluskohteista ovat proteiinien väliset kontaktit ja lääkesuunnittelu. Vuorovaikutuksia kuvaavan mallin lähtökohta voi olla molekyyleihin liittyvä teoria, jolloin soveltamiseen liittyvä laskenta saattaa olla erityisen raskasta, tai suuri havaintojoukko joka on saatu aikaan esimerkiksi mittaamalla rakenteita röntgendiffraktio menetelmällä. Tilastollinen malli mahdollistaa havaintoaineistossa olevan epätarkkuuden ja epävarmuuden huomioimisen, samalla pitäen laskennallisen kuorman pienempänä verrattuna periaatteessa parhaan tuloksen antavaan kvanttimekaaniseen mallinnukseen. Väitöstyössä kehitettiin bayesiläiseen tilastotieteeseen perustuva 3D malli molekyylien välisten vuorovaikutusten laskennalliseen tarkasteluun. Mallin tehtävä on tuottaa ennusteita sen suhteen, minkä tai millaisten molekyylirakenteiden väliset kompleksit ovat etusijalla, toisin sanoen todennäköisempiä, vuorovaikutustilanteessa. Työssä kehitetyn menetelmän toimivuutta testattiin käyttötarkoituksen suhteen olennaisissa molekyyliympäristöissä - pieni molekyyli sitoutumiskohdassaan proteiinissa sekä rajapinta kahden proteiinin välilllä proteiinikompleksissa. Saadut laskennalliset tulokset vastasivat hyvin vertailuun käytettyjä kirjallisuudesta saatuja kokeellisia tuloksia, kuten laadullisia sitoutumisaffiniteetteja, sekä kemiallista tietoa esimerkiksi tiettyjen aminohappojen avaruudellisesta sidoksenmuodostuksesta. Väitöstyössä myös alustavasti testattiin tilastollista lähestymistapaa tärkeän molekyylien rakenteellisen mukautuvuuden mallintamiseen. Käytännössä malli on tarkoitettu osaksi jotakin laajempaa analyysimenetelmää, kuten farmakoforimallia.

The role of emotional state, sexual arousal, and alcohol intoxication as situational factors associated with adults’ online sexual contact with children and adolescents

In the present study we explored whether and how the situational factors; emotional states, sexual arousal, and alcohol intoxication influenced the propensity in adults to engage in online sexual contact with children (13 or younger) and adolescents (14 – 17 year olds). The results were compared to a group of adults that had engaged in online sexual contact with adults only (18 or older). We also looked at the variation over time within these situational factors during the online sexual contact with a child, an adolescent, or an adult. The present study was an online self-report survey to the adult populations in Finland, Sweden, and Germany, with a final sample (N = 776) of women and men who were active on the Internet. The participants were asked to report whether, how, and with whom they had engaged in online sexual contact. The results showed that more men than women reported online sexual contact with persons of all age groups, and that the situational factors; emotional states and sexual arousal influenced the propensity in both women and men to engage in online sexual contact with children and adolescents. However, the effects of alcohol intoxication were small and significant only for men. These results indicate that higher levels of emotional state and sexual arousal might increase the propensity to go against social norms and contact children and adolescents online for sexual purposes, but it can also imply that that those who look for online sexual contact online with children and adolescents, are more emotionally and/or sexually aroused than the group that only seek adult company or that these are post-hoc explanations for such sexual activities.

Surface characterization of chemically modified fiber, wood and paper

Inorganic-organic sol-gel hybrid coatings can be used for improving and modifying properties of wood-based materials. By selecting a proper precursor, wood can be made water repellent, decay-, moisture- or UV-resistant. However, to control the barrier properties of sol-gel coatings on wood substrates against moisture uptake and weathering, an understanding of the surface morphology and chemistry of the deposited sol-gel coatings on wood substrates is needed. Mechanical pulp is used in production of wood-containing printing papers. The physical and chemical fiber surface characteristics, as created in the chosen mechanical pulp manufacturing process, play a key role in controlling the properties of the end-use product. A detailed understanding of how process parameters influence fiber surfaces can help improving cost-effectiveness of pulp and paper production. The current work focuses on physico-chemical characterization of modified wood-based materials with surface sensitive analytical tools. The overall objectives were, through advanced microscopy and chemical analysis techniques, (i) to collect versatile information about the surface structures of Norway spruce thermomechanical pulp fiber walls and understand how they are influenced by the selected chemical treatments, and (ii) to clarify the effect of various sol-gel coatings on surface structural and chemical properties of wood-based substrates. A special emphasis was on understanding the effect of sol-gel coatings on the water repellency of modified wood and paper surfaces. In the first part of the work, effects of chemical treatment on micro- and nano-scale surface structure of 1st stage TMP latewood fibers from Norway spruce were investigated. The chemicals applied were buffered sodium oxalate and hydrochloric acid. The outer and the inner fiber wall layers of the untreated and chemically treated fibers were separately analyzed by light microscopy, atomic force microscopy and field-emission scanning electron microscopy. The selected characterization methods enabled the demonstration of the effect of different treatments on the fiber surface structure, both visually and quantitatively. The outer fiber wall areas appeared as intact bands surrounding the fiber and they were clearly rougher than areas of exposed inner fiber wall. The roughness of the outer fiber wall areas increased most in the sodium oxalate treatment. The results indicated formation of more surface pores on the exposed inner fiber wall areas than on the corresponding outer fiber wall areas as a result of the chemical treatments. The hydrochloric acid treatment seemed to increase the surface porosity of the inner wall areas. In the second part of the work, three silane-based sol-gel hybrid coatings were selected in order to improve moisture resistance of wood and paper substrates. The coatings differed from each other in terms of having different alkyl (CH3–, CH3-(CH2)7–) and fluorocarbon (CF3–) chains attached to the trialkoxysilane sol-gel precursor. The sol-gel coatings were deposited by a wet coating method, i.e. spraying or spreading by brush. The effect of solgel coatings on surface structural and chemical properties of wood-based substrates was studied by using advanced surface analyzing tools: atomic force microscopy, X-ray photoelectron spectroscopy and time-of-flight secondary ion spectroscopy. The results show that the applied sol-gel coatings, deposited as thin films or particulate coatings, have different effects on surface characteristics of wood and wood-based materials. The coating which has a long hydrocarbon chain (CH3-(CH2)7–) attached to the silane backbone (octyltriethoxysilane) produced the highest hydrophobicity for wood and wood-based materials.

Michelson interferometer with porch swing bearing for portable FTIR spectrometer

The interferometer for low resolution portable Fourier Transform middle infrared spectrometer was developed and studied experimentally. The final aim was a concept for a commercial prototype. Because of the portability, the interferometer should be compact sized and insensitive to the external temperature variations and mechanical vibrations. To minimise the size and manufacturing costs, Michelson interferometer based on plane mirrors and porch swing bearing was selected and no dynamic alignment system was applied. The driving motor was a linear voice coil actuator to avoid mechanical contact of the moving parts. The driving capability for low mirror driving velocities required by the photoacoustic detectors was studied. In total, four versions of such an interferometer were built and experimentally studied. The thermal stability during the external temperature variations and the alignment stability over the mirror travel were measured using the modulation depth of the wide diameter laser beam. Method for estimating the mirror tilt angle from the modulation depth was developed to take account the effect from the non-uniform intensity distribution of the laser beam. The spectrometer stability was finally studied also using the infrared radiation. The latest interferometer was assembled for the middle infrared spectrometer with spectral range from 750 cm−1 to 4500 cm−1. The interferometer size was (197 × 95 × 79) mm3 with the beam diameter of 25 mm. The alignment stability as the change of the tilt angle over the mirror travel of 3 mm was 5 μrad, which decreases the modulation depth only about 0.7 percent in infrared at 3000 cm−1. During the temperature raise, the modulation depth at 3000 cm−1 changed about 1 . . . 2 percentage units per Celsius over short term and even less than 0.2 percentage units per Celsius over the total temperature raise of 30 °C. The unapodised spectral resolution was 4 cm−1 limited by the aperture size. The best achieved signal to noise ratio was about 38 000:1 with commercially available DLaTGS detector. Although the vibration sensitivity requires still improving, the interferometer performed, as a whole, very well and could be further developed to conform all the requirements of the portable and stable spectrometer.

Reverse osmosis membrane surface modification: effects on membrane performance

The aim of this thesis was to study the surface modification of reverse osmosis membranes by surfactants and the effect of modification on rejection and flux. The surfactants included anionic and nonionic surfactants. The purpose of membrane modification was to improve pure water permeability with increasing salt rejection. The literature part of the study deals with the basic principles of reverse osmosis technology and factors affecting the membrane performance. Also the membrane surface modification by surfactants and their influence on membrane’s surface properties and efficiency (permeability and salt rejection) were discussed. In the experimental part of the thesis two thin-film composite membranes, Desal AG and LE-4040, were modified on-line with three different surfactants. The effects of process parameters (pressure, pH, and surfactant concentration) on surface modification were also examined. The characteristics of the modified membranes were determined by measuring the membranes’ contact angle and zeta potentials. The zeta potential and contact angle measurements indicate that the surfactants were adsorbed onto the both membranes. However, the adsorption did not effect on membrane’s pure water permeability and salt rejection. Thereby, the surface modification of the Desal AG and LE-4040 membranes by surfactants was not able to improve the membrane’s performance.

Reducing contact resistance in graphene devices

In this thesis, the contact resistance of graphene devices was investigated because high contact resistance is detrimental to the performance of graphene field-effect transistors (GFET). Method for increasing so-called edge-contact area was applied in device fabrication process, as few nanometers thick Ni layer was used as a catalytic etchant during the annealing process. Finally, Ni was also used as a metal for contact. GFETs were fabricated using electron beam lithography using graphene fabricated by chemical vapor deposition (CVD). Critical part of the fabrication process was to preserve the high quality of the graphene channel while etching the graphene at contact areas with Ni during the annealing. This was achieved by optimizing the combination of temperature and gas flows. The structural properties of graphene were studied using scanning electron microscopy, scanning confocal μ-Raman spectroscopy and optical microscopy. Evaluation of electric transport properties including contact resistance was carried out by transmission line method and four-probe method. The lowest contact resistance found was about at 350 Ωμm. In addition, different methods to transfer CVD graphene synthesized on copper were studied. Typical method using PMMA as a supporting layer leaves some residues after its removal, thus effecting on the performance of a graphene devices. In a metal assisted transfer method, metal is used as an interfacial layer between PMMA and graphene. This allows more effective removal of PMMA. However, Raman spectra of graphene transferred by metal assisted method showed somewhat lower quality than the PMMA assisted method

Membrane development for oil contaminated water treatments

The aim of this Master’s thesis study was to develop a membrane for oil contaminated water treatments. Oily wastewaters are a big problem to environment and therefore it is important to find an efficient method for their treatment. There are several treatment methods, but one of the most promising methods is membrane filtration. In the theoretical part of this study the membrane technology and polymeric membrane preparation with phase inversion and membrane modification methods was discussed. It was also told about the most important properties of the membranes. Oily waters, their treatment methods and oily wastewater sources were discussed more specifically. In the experimental part membranes from cellulose acetate were prepared and membranes were modified with two different methods. Modification methods were surface modification and polymer mixing. The modification purpose was to make membranes more hydrophilic and increase surface charge, which can reduce fouling. Membranes were characterized by determining zeta potential, contact angle, oil retention, pure water permeability, pressure-normalized flux and fouling. It were used both synthetic and real spent oil-water emulsion in membrane filtration. Surface modification resulted membranes, which had better properties than unmodified membrane. The amount of substance used in surface modification affected a lot to membrane properties, so it would be necessary to try different amounts of substance to develop the best membrane for oil-water emulsion treatment.