Browsing by Author "Tuominen, Mikko"

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    Effects of Gas Layer Thickness on Capillary Interactions at Superhydrophobic Surfaces
    (American Chemical Society, 2024-03-05) Eriksson, Mimmi; Claesson, Per M.; Järn, Mikael; Wallqvist, Viveca; Tuominen, Mikko; Kappl, Michael; Teisala, Hannu; Vollmer, Doris; Schoelkopf, Joachim; Gane, Patrick A.C.; Mäkelä, Jyrki M.; Swerin, Agne; Department of Bioproducts and Biosystems; KTH Royal Institute of Technology; RISE Research Institutes of Sweden AB; Nordtreat Oy; Max Planck Institute for Polymer Research; Omya International AG; Tampere University
    Strongly attractive forces act between superhydrophobic surfaces across water due to the formation of a bridging gas capillary. Upon separation, the attraction can range up to tens of micrometers as the gas capillary grows, while gas molecules accumulate in the capillary. We argue that most of these molecules come from the pre-existing gaseous layer found at and within the superhydrophobic coating. In this study, we investigate how the capillary size and the resulting capillary forces are affected by the thickness of the gaseous layer. To this end, we prepared superhydrophobic coatings with different thicknesses by utilizing different numbers of coating cycles of a liquid flame spraying technique. Laser scanning confocal microscopy confirmed an increase in gas layer thickness with an increasing number of coating cycles. Force measurements between such coatings and a hydrophobic colloidal probe revealed attractive forces caused by bridging gas capillaries, and both the capillary size and the range of attraction increased with increasing thickness of the pre-existing gas layer. Hence, our data suggest that the amount of available gas at and in the superhydrophobic coating determines the force range and capillary growth.
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    Effects of liquid surface tension on gas capillaries and capillary forces at superamphiphobic surfaces
    (Nature Publishing Group, 2023-04-26) Eriksson, Mimmi; Claesson, Per M.; Järn, Mikael; Wallqvist, Viveca; Tuominen, Mikko; Kappl, Michael; Teisala, Hannu; Vollmer, Doris; Schoelkopf, Joachim; Gane, Patrick A.C.; Mäkelä, Jyrki M.; Swerin, Agne; Department of Bioproducts and Biosystems; KTH Royal Institute of Technology; RISE Research Institutes of Sweden AB; Max Planck Institute for Polymer Research; Omya International AG; Tampere University
    The formation of a bridging gas capillary between superhydrophobic surfaces in water gives rise to strongly attractive interactions ranging up to several micrometers on separation. However, most liquids used in materials research are oil-based or contain surfactants. Superamphiphobic surfaces repel both water and low-surface-tension liquids. To control the interactions between a superamphiphobic surface and a particle, it needs to be resolved whether and how gas capillaries form in non-polar and low-surface-tension liquids. Such insight will aid advanced functional materials development. Here, we combine laser scanning confocal imaging and colloidal probe atomic force microscopy to elucidate the interaction between a superamphiphobic surface and a hydrophobic microparticle in three liquids with different surface tensions: water (73 mN m-1), ethylene glycol (48 mN m-1) and hexadecane (27 mN m-1). We show that bridging gas capillaries are formed in all three liquids. Force-distance curves between the superamphiphobic surface and the particle reveal strong attractive interactions, where the range and magnitude decrease with liquid surface tension. Comparison of free energy calculations based on the capillary menisci shapes and the force measurements suggest that under our dynamic measurements the gas pressure in the capillary is slightly below ambient.
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    Global stability of composite bridge during construction
    (2011) Tuominen, Mikko; Luokkakallio, Jussi; Rakenne- ja rakennustuotantotekniikan laitos; Insinööritieteiden korkeakoulu; School of Engineering; Salokangas, Lauri
    The stability of the I-shaped twin girder system can be lost by the global buckling of the entire system or by the buckling of an individual girder between cross frames. These failure modes are most likely to take place during incremental launching or during casting of the concrete deck. Once the deck has hardened, global lateral-torsional buckling (LTB) of the twin girder system is not an issue. Global LTB of twin girder system is possible on systems with no lateral trusses between the girders. The objective of this thesis is to offer closed form solutions to address the problem of instability in the twin girder system. Both individual girder LTB between cross frames and system LTB were studied. Identified solutions were verified by finite-element analysis (FEAs) using Lusas software. To determine suitable loads for use in the design of the construction phase in Finland, Euro code had to be carefully studied. In addition, the compulsory Finnish documentation on construction phase design was studied in this thesis. As a result, a new field, calculations was found relevant to add to the documentation. The main results of the thesis are two-fold: first, the thesis presents ways of how to calculate the global LTB of twin girder systems; second, the thesis describes how to improve the capacity of the global LTB.
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    Teräsrakenteisen rakennusrungon jäykistäminen
    (2008) Tuominen, Mikko; Mäkeläinen, Pentti; Insinööritieteiden ja arkkitehtuurin tiedekunta; Aalto, Jukka