Browsing by Author "Virtanen, Sannakaisa"

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  • Dissolution Control of Mg by Cellulose Acetate–Polyelectrolyte Membranes
    (2014) Yliniemi, Kirsi; Wilson, Benjamin. P.; Singer, Ferdinand; Höhn, Sarah; Kontturi, Eero; Virtanen, Sannakaisa
     School of Chemical Technology | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Cellulose acetate (CA)-based membranes are used for Mg dissolution control: the permeability of the membrane is adjusted by additions of the polyelectrolyte, poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA). Spin-coated films were characterized with FT-IR, and once exposed to an aqueous solution the film distends and starts acting as a membrane which controls the flow of ions and H2 gas. Electrochemical measurements (linear sweep voltammograms, open-circuit potential, and polarization) show that by altering the CA:PDMAEMA ratio the dissolution rate of Mg can be controlled. Such a control over Mg dissolution is crucial if Mg is to be considered as a viable, temporary biomedical implant material. Furthermore, the accumulation of corrosion products between the membrane and the sample diminishes the undesirable effects of high local pH and H2 formation which takes place during the corrosion process.
  • From Waste to Valuable Resource: Lignin as a Sustainable Anti-Corrosion Coating
    (2018-12-08) Dastpak, Arman; Yliniemi, Kirsi; Cecilio de Oliveira Monteiro, Mariana; Höhn, Sarah; Virtanen, Sannakaisa; Lundström, Mari; Wilson, Benjamin P.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this study, a waste of biorefinery—lignin—is investigated as an anticorrosion coating on stainless steel. Corrosion behavior of two lignin types (hardwood beech and softwood spruce) was studied by electrochemical measurements (linear sweep voltammetry, open circuit potential, potentiostatic polarization, cyclic potentiodynamic polarization, and electrochemical impedance measurements) during exposure to simulated body fluid (SBF) or phosphate buffer (PBS). Results from linear sweep voltammetry of lignin-coated samples, in particular, demonstrated a reduction in corrosion current density between 1 and 3 orders of magnitude cf. blank stainless steel. Furthermore, results from cross cut adhesion tests on lignin-coated samples demonstrated that the best possible adhesion (grade 0) of ISO 2409 standard was achieved for the investigated novel coatings. Such findings suggest that lignin materials could transform the field of organic coatings towards more sustainable alternatives by replacing non-renewable polymer coatings.
  • Long-term stability of aerophilic metallic surfaces underwater
    (2023-12) Tesler, Alexander B.; Kolle, Stefan; Prado, Lucia H.; Thievessen, Ingo; Böhringer, David; Backholm, Matilda; Karunakaran, Bhuvaneshwari; Nurmi, Heikki A.; Latikka, Mika; Fischer, Lena; Stafslien, Shane; Cenev, Zoran M.; Timonen, Jaakko V.I.; Bruns, Mark; Mazare, Anca; Lohbauer, Ulrich; Virtanen, Sannakaisa; Fabry, Ben; Schmuki, Patrik; Ras, Robin H.A.; Aizenberg, Joanna; Goldmann, Wolfgang H.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Aerophilic surfaces immersed underwater trap films of air known as plastrons. Plastrons have typically been considered impractical for underwater engineering applications due to their metastable performance. Here, we describe aerophilic titanium alloy (Ti) surfaces with extended plastron lifetimes that are conserved for months underwater. Long-term stability is achieved by the formation of highly rough hierarchically structured surfaces via electrochemical anodization combined with a low-surface-energy coating produced by a fluorinated surfactant. Aerophilic Ti surfaces drastically reduce blood adhesion and, when submerged in water, prevent adhesion of bacteria and marine organisms such as barnacles and mussels. Overall, we demonstrate a general strategy to achieve the long-term stability of plastrons on aerophilic surfaces for previously unattainable underwater applications.
  • Ruostumattoman kompound-levyn käyttö jäänmurtajan vedenalaisissa osissa
    (1984) Virtanen, Sannakaisa
     Helsinki University of Technology | Master's thesis
  • Time-Dependent Behavior of Cation Transport through Cellulose Acetate-Cationic Polyelectrolyte Membranes
    (2018-02-02) Hakanpää, Janina; Yliniemi, Kirsi; Wilson, Benjamin; Putkonen, Matti; Höhn, Sarah; Kontturi, Eero; Virtanen, Sannakaisa; Murtomäki, Lasse
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Cation transport through a cellulose acetate-poly(N,N-dimethylaminoethyl methacrylate) membrane (CA:PDMAEMA) was studied with scanning electrochemical microscope (SECM) and the thickness increase of the membrane was monitored with ellipsometry. Upon addition of the polyelectrolyte PDMAEMA, the permeability of the probe cation (ferrocenium methanol, FcMeOH) was increased as much as 40-fold. Soaking membranes in an electrolyte solution doubled the permeability in plain CA membranes, whereas for PDMAEMA containing membranes the opposite was observed and the permeability was reduced by 20–40%. This time-dependent behavior is shown to be a result of the presence of PDMAEMA within the membrane matrix, thus providing an interesting platform for controllable membrane permeability.