Browsing by Author "Ras, Robin"

Filter results by typing the first few letters
Now showing 1 - 20 of 47
  • Aeronautics and Eco-design
    (2020-08-18) Tempelaere, Matthieu
     Perustieteiden korkeakoulu | Master's thesis
    This master thesis report aims to introduce the reader to the basis of the eco-design in aeronautics. In this small guide the reader will understand from where the engineers went through and what the perspectives for this industry are. In order that the largest possible number of people can benefit from this relationship, the basic notions of mechanics, thermodynamics and materials will be developed. Then we will discuss and see how to improve the environmental impact of this industry, which is considered to be polluting.
  • Beyond financial metrics, the place and role of technical and other additional due diligence in the process of Mergers & Acquisitions transactions. Case study in the Engineering Services Industry.
    (2020-08-18) Noell, Pauline
     Perustieteiden korkeakoulu | Master's thesis
    This paper aims at complementing the literature on Mergers & Acquisitions (M&A) with a case study to provide the lecturer with a full insight on the diversity of the challenges inherent to M&A transactions. Especially, a strong emphasis will be made on extra-financial analysis of the target. Indeed, a M&A process always includes a very formal and standardized financial analysis of the target, called the Financial Due Diligences, very often including also a similar Tax & Legal Due Diligences process. However, the collection and analysis of other information relative to the business and its specificities are much less standardized. As regards to the technical capabilities of the target or economic and operational considerations, the level of information available to the purchaser might be significantly variable from an acquisition to another, depending on the availability of the info first, but also on the quality of the analysis of them. This case study will provide concrete examples of what additional analysis to the financial ones can be performed on the target and its environment. It will be then discussed how crucial they might be in the decision-making process of pursuing with the acquisition or not. The discussion will be extended to the place that take each of those analysis (financial and extra-financial ones) in the valuation of the target and the consistency of current valuation methods as regard to the importance of each element.
  • Biomechanical study of roots
    (2019-12-17) Sillanpää, Heikki
     Perustieteiden korkeakoulu | Master's thesis
  • Capillary Transport of Miniature Soft Ribbons
    (2019-10-11) Chang, Bo; Liu, Heng; Ras, Robin; Zhou, Quan
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Manipulation of soft miniature devices is important in the construction of soft robots, wearable devices, and biomedical devices. However, transport of soft miniature devices is still a challenging task, and few studies has been conducted on the subject. This paper reports a droplet-based micromanipulation method for transporting miniature soft ribbons. We show that soft ribbons can be successfully picked up and released to the target location using water droplets. We analyze the forces involved during the process numerically and investigate the influence of the width of the ribbon on the deformation. We verify that the deformation of a soft ribbon caused by elasto-capillary phenomena can be calculated using a well-known equation for calculating the deflection of a cantilever beam. The experimental and theoretical results show that the deformability of a soft miniature device during manipulation depends on its width.
  • Cellulose-based superhydrophobic surfaces and Dynamics of coupled chemical systems
    (2015) Khanjani, Pegah
     School of Science | Licentiate thesis
    Superhydrophobic surfaces can be found in plants, insects, and bird feathers1. Inspired by natural superhydrophobic surfaces, researchers have recently developed and constructed superhydrophobic surfaces in a variety of smart and simple ways. The hydrophilic property of cellulose nanocrystals (CNCs) was modified by the esterification of CNCs with low surface energy chemicals of 2H,2H,3H,3H-Perfluorononanoyl chloride and 2H,2H,3H,3H-Perfluoroundecanoyl chloride, respectively. A stable suspension of nanospherical fluorinated cellulose ester was obtained by using the nanoprecipitation technique. The resulting nanostructured fluorinated cellulose esters was simply coated on a paper surface to gain a superhydrophobic paper surface characterized by a contact angle over 150º. The superhydrophobic paper remained stable even at a high temperature, showing no signs of melting or damage. The hydrophobized paper was characterized by nuclear magnetic resonance (NMR), infrared spectroscopy (IR), and static contact angle (CA) measurement. Further, we investigated the size, shape, and amorphicity of nanostructured fluorinated cellulose esters by light scattering (DLS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) measurements. The development of economically and ecologically viable strategies for the superhydrophobization of surfaces for the introduction of a self-cleaning property offers a vast variety of interesting applications. Examples include packaging materials, textiles, outdoor clothing, and microfluidic devices. The dynamics of oscillation in chemical reactions as a research field has grown dramatically over the past 50 years and produced thousands of studies on about 70 known chemical oscillators. Oscillating chemical reactions find many applications in physics, biology, physiology, geology, and medicine. The dynamics of the bromate-sulfite-ferrocyanide (BSF) reaction is studied in a well-mixed open chemical reactor, called a continuous stirred tank reactor (CSTR). A CSTR system can be used to investigate the dynamics of outof-equilibrium chemical processes, such as oscillation, bistability, and chaos. This BSF reaction exhibits periodic oscillation as a function of [H+], called pH oscillation. The reaction was carried out at 25 ºC, and the flow rate was 1 and 2 mL/min. The pH oscillation occurs only in a specific range of flow rates. Here, we show regular pH oscillation in a BSF system by utilizing different concentrations under a nitrogen atmosphere. Such a pH oscillator system can be coupled or probed with pH-sensitive systems, and it helps to understand new mechanisms may arise by periodic behavior.
  • Characterization of surface wetting properties using Scanning Droplet Adhesion Microscopy
    (2021-08-24) Sahaoui, Mohamed
     Perustieteiden korkeakoulu | Master's thesis
  • Characterization of surface wetting uniformity in hydrophobic tubes using ferrofluid droplets
    (2019-08-20) Lefranc, Vivien
     Perustieteiden korkeakoulu | Master's thesis
    Hydrophobic surfaces, or water repellent surfaces, have interesting properties for applications on selfcleaning, anti-icing, antifogging and fluid drag reduction. To develop more efficient surfaces, proper characterization methods need to be developed as the current methods available are not sufficient. In this thesis, the theoretical background behind wetting phenomena on hydrophobic surfaces and various techniques for characterizing wetting properties are presented. Furthermore, a new characterization technique applied to hollow, non planar surfaces and more specifically to transparent tubes is proposed. This technique measures wetting inhomogeneities using magnetically controlled water-like droplets over the entire length of the samples. This technique can measure the retentive force, a dissipative force related to the contact angle hysteresis at the three-phase contact line. This technique is used to see differences in wetting properties using reference tubes and their annealed counterparts using two different ferrofluids. As a non-destructive and quantitative characterization method, this technique could readily be used for quality control in academia and industries.
  • Chemical vapor deposition of fluoroalkylsilane self-assembled monolayers.
    (2024-08-29) Koochak, Parham
     Kemian tekniikan korkeakoulu | Master's thesis
    Surface chemistry manipulation by grafting molecular chains of various chemistries has garnered increasing attention in recent decades. By designing molecular-scale surface mono-/multi-layers, many essential surface properties can be achieved, such as anti-stiction, slipperiness, and liquid-repellency. Organosilane-based self-assembled monolayers can be considered more durable alternatives for air-mediated super-liquid-repellent surfaces, as the latter relies on fragile surface structures. Nevertheless, molecular-scale defects can significantly affect the performance of the deposited layers. Contact angle hysteresis, as a measure of surface homogeneity, has been widely utilized as a measure of homogeneity for modified surfaces. Although alkylsilane and silicone-based layers have often exhibited low hysteresis values, the use of more rigid variants, such as fluoroalkylsilanes, results in higher hysteresis. This is because of the lack of self-smoothing behavior observed in more flexible structures, leading local defects to be spontaneously repaired after deposition. Accordingly, fluoroalkylsilanes are much more sensitive to deposition defects. The present thesis investigates the effect of moisture content on the homogeneity of fluoroalkylated surfaces fabricated by chemical vapor deposition. It is shown that high-quality and highly repeatable fluoroalkylated surfaces with hysteresis values comparable to alkylsilanes can be fabricated using a simple, custom-built reactor. For this purpose, trichloro(1H,1H,2H,2H-perfluorooctyl)silane is used as a precursor. Substrates are exposed to various levels of humidity inside the reactor prior to deposition to control the vapor-phase and surface-bound water content. The procedure suggested in this thesis can guide the fabrication of low-defect fluoroalkylated layers showing liquid-like properties regardless of their high molecular rigidity.
  • Controllable fabrication of periodic arrays of magnetically actuated polymeric microstructures
    (2015-02-04) Tupasela, Topi
     Perustieteiden korkeakoulu | Bachelor's thesis
  • Cooperative colloidal self-assembly of metal-protein superlattice wires
    (2017-09-22) Liljeström, Ville; Ora, Ari; Hassinen, Jukka; Rekola, Heikki; Nonappa, Nonappa; Heilala, Maria; Hynninen, Ville; Joensuu, Jussi J.; Ras, Robin; Törmä, Päivi; Ikkala, Olli; Kostiainen, Mauri
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Material properties depend critically on the packing and order of constituent units throughout length scales. Beyond classically explored molecular self-assembly, structure formation in the nanoparticle and colloidal length scales have recently been actively explored for new functions. Structure of colloidal assemblies depends strongly on the assembly process, and higher structural control can be reliably achieved only if the process is deterministic. Here we show that self-assembly of cationic spherical metal nanoparticles and anionic rod-like viruses yields well-defined binary superlattice wires. The superlattice structures are explained by a cooperative assembly pathway that proceeds in a zipper-like manner after nucleation. Curiously, the formed superstructure shows right-handed helical twisting due to the right-handed structure of the virus. This leads to structure-dependent chiral plasmonic function of the material. The work highlights the importance of well-defined colloidal units when pursuing unforeseen and complex assemblies.
  • Design of robust superhydrophobic surfaces
    (2020-06-04) Wang, Dehui; Sun, Qiangqiang; Hokkanen, M.J.; Zhang, Chenglin; Lin, Fan-Yen; Liu, Qiang; Zhu, Shun-Peng; Zhou, Tianfeng; Chang, Qing; He, Bo; Zhou, Quan; Chen, Longquan; Wang, Zuankai; Ras, Robin; Xu, Deng
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The ability of superhydrophobic surfaces to stay dry, self-clean and avoid biofouling is attractive for applications in biotechnology, medicine and heat transfer 1–10. Water droplets that contact these surfaces must have large apparent contact angles (greater than 150 degrees) and small roll-off angles (less than 10 degrees). This can be realized for surfaces that have low-surface-energy chemistry and micro- or nanoscale surface roughness, minimizing contact between the liquid and the solid surface 11–17. However, rough surfaces—for which only a small fraction of the overall area is in contact with the liquid—experience high local pressures under mechanical load, making them fragile and highly susceptible to abrasion 18. Additionally, abrasion exposes underlying materials and may change the local nature of the surface from hydrophobic to hydrophilic 19, resulting in the pinning of water droplets to the surface. It has therefore been assumed that mechanical robustness and water repellency are mutually exclusive surface properties. Here we show that robust superhydrophobicity can be realized by structuring surfaces at two different length scales, with a nanostructure design to provide water repellency and a microstructure design to provide durability. The microstructure is an interconnected surface frame containing ‘pockets’ that house highly water-repellent and mechanically fragile nanostructures. This surface frame acts as ‘armour’, preventing the removal of the nanostructures by abradants that are larger than the frame size. We apply this strategy to various substrates—including silicon, ceramic, metal and transparent glass—and show that the water repellency of the resulting superhydrophobic surfaces is preserved even after abrasion by sandpaper and by a sharp steel blade. We suggest that this transparent, mechanically robust, self-cleaning glass could help to negate the dust-contamination issue that leads to a loss of efficiency in solar cells. Our design strategy could also guide the development of other materials that need to retain effective self-cleaning, anti-fouling or heat-transfer abilities in harsh operating environments.
  • Developing a measuring system for cryogenic droplets in inert atmosphere
    (2017-05-09) Nurmi, Heikki
     Perustieteiden korkeakoulu | Master's thesis
  • Developing the Scanning Droplet Tribometer
    (2021-10-19) Vieillescazes-Delrieu, Tanguy
     Perustieteiden korkeakoulu | Master's thesis
    This thesis reviews the needs of the research and industry for surface wetting characterization, as well as the different wetting characterization methods available. The thesis puts in evidence the arising need for a method of fast surface wetting scanning. The Scanning Droplet Tribometer (SDT) offers a solution to this need. This instrument scans the friction and adhesion forces of a magnetically controlled water-like droplet on a surface. However, the original design of the SDT requires further development. The sources of errors are investigated, and we suggest improvements to the SDT, to make it more reliable and adapted to a wider range of samples.
  • Droplet movement on superhydrophilic patterned superhydrophobic surface
    (2018-05-11) Kivinen, Oskari
     Perustieteiden korkeakoulu | Bachelor's thesis
  • Droplet slipperiness despite surface heterogeneity at molecular scale
    (2024-04) Lepikko, Sakari; Morais Jaques, Ygor; Junaid, Muhammad; Backholm, Matilda; Lahtinen, Jouko; Julin, Jaakko; Jokinen, Ville; Sajavaara, Timo; Sammalkorpi, Maria; Foster, Adam; Ras, Robin
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Friction determines whether liquid droplets slide off a solid surface or stick to it. Surface heterogeneity is generally acknowledged as the major cause of increased contact angle hysteresis and contact line friction of droplets. Here we challenge this long-standing premise for chemical heterogeneity at the molecular length scale. By tuning the coverage of self-assembled monolayers (SAMs), water contact angles change gradually from about 10° to 110° yet contact angle hysteresis and contact line friction are low for the low-coverage hydrophilic SAMs as well as high-coverage hydrophobic SAMs. Their slipperiness is not expected based on the substantial chemical heterogeneity of the SAMs featuring uncoated areas of the substrate well beyond the size of a water molecule as probed by metal reactants. According to molecular dynamics simulations, the low friction of both low- and high-coverage SAMs originates from the mobility of interfacial water molecules. These findings reveal a yet unknown and counterintuitive mechanism for slipperiness, opening new avenues for enhancing the mobility of droplets.
  • Droplet splitting on superhydrophobic wires
    (2015-02-20) Jokela, Aleksi
     Perustieteiden korkeakoulu | Bachelor's thesis
  • Dynamic life cycle assessment to compare conventional and bio-based building construction impact on global warming
    (2019) Zieger, Vladimir
     Perustieteiden korkeakoulu | Master's thesis
    In a context of climate emergency, storing temporarily carbon in biogenic construction materials seems a particularly attractive strategy to mitigate important building sector impact on global warming. Usually, environmental impacts are assessed using standard Life Cycle Assessment (LCA), a product-based method that gives notably the global warming potential (GWP). In LCA, all greenhouse gas emissions linked to the product are assumed to be released in the first year even if they are emitted at different times within the chosen time horizon. Their GWP is calculated at this time horizon, which is usually 100 years. Moreover, biogenic carbon is often excluded of the calculation assuming a balance between captured and emitted carbon. On the other hand, new global warming impact calculation methods such as dynamic LCA propose to include timing in the calculation and to assess the value of temporarily storing carbon in long-lived products such as building structures. The aim of this study was to investigate the impact of these hypotheses on the estimated GWP of building materials, by comparing the static and a dynamic LCA approach. Two types of exterior walls were compared: one made with conventional materials (concrete and glass wool), the other mostly composed of bio-based materials such as straw and timber. Several parameters are discussed in detail: the real lifespan of buildings in France, carbon storage by forests and annual crops, the time horizon used to calculate GWP, the different greenhouse gases emitted, the accuracy of CO2 equivalent as an indicator of global warming. Finally, the overall impact on the global warming of different building construction and renovation materials is estimated under different scenarios applied to the French context.
  • Eco-design
    (2020-08-18) Melkebeke, Clément
     Perustieteiden korkeakoulu | Master's thesis
  • Effect of hydrophobicity and surface material on electrical breakdown at the microscale
    (2022-12-16) Zenuni, Gentrit
     Perustieteiden korkeakoulu | Bachelor's thesis
  • Experimental analysis of magnetic field-induced splitting of ferrofluid droplets
    (2016-09-16) Ballesio, Alberto
     Perustieteiden korkeakoulu | Master's thesis