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Publications (9 of 9) Show all publications
Eriksson, M., Tuominen, M., Järn, M., Claesson, P. M., Wallqvist, V., Butt, H.-J., . . . Swerin, A. (2019). Direct Observation of Gas Meniscus Formation on a Superhydrophobic Surface. ACS Nano, 13(2), 2246-2252
Open this publication in new window or tab >>Direct Observation of Gas Meniscus Formation on a Superhydrophobic Surface
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2019 (English)In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 13, no 2, p. 2246-2252Article in journal (Refereed) Published
Abstract [en]

The formation of a bridging gas meniscus via cavitation or nanobubbles is considered the most likely origin of the submicrometer long-range attractive forces measured between hydrophobic surfaces in aqueous solution. However, the dynamics of the formation and evolution of the gas meniscus is still under debate, in particular, in the presence of a thin air layer on a superhydrophobic surface. On superhydrophobic surfaces the range can even exceed 10 μm. Here, we report microscopic images of the formation and growth of a gas meniscus during force measurements between a superhydrophobic surface and a hydrophobic microsphere immersed in water. This is achieved by combining laser scanning confocal microscopy and colloidal probe atomic force microscopy. The configuration allows determination of the volume and shape of the meniscus, together with direct calculation of the Young-Laplace capillary pressure. The long-range attractive interactions acting on separation are due to meniscus formation and volume growth as air is transported from the surface layer.

Keywords
AFM colloidal probe, capillary forces, laser scanning confocal microscopy, superhydrophobicity, wetting
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-37821 (URN)10.1021/acsnano.8b08922 (DOI)30707561 (PubMedID)
Available from: 2019-03-01 Created: 2019-03-01 Last updated: 2019-06-28Bibliographically approved
Wojas, N., Swerin, A., Wallqvist, V., Järn, M., Schoelkopf, J., Gane, P. & Claesson, P. M. (2019). Iceland spar calcite: Humidity and time effects on surface properties and their reversibility. Journal of Colloid and Interface Science, 541, 42-55
Open this publication in new window or tab >>Iceland spar calcite: Humidity and time effects on surface properties and their reversibility
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2019 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 541, p. 42-55Article in journal (Refereed) Published
Abstract [en]

Understanding the complex and dynamic nature of calcite surfaces under ambient conditions is important for optimizing industrial applications. It is essential to identify processes, their reversibility, and the relevant properties of CaCO3 solid-liquid and solid-gas interfaces under different environmental conditions, such as at increased relative humidity (RH). This work elucidates changes in surface properties on freshly cleaved calcite (topography, wettability and surface forces) as a function of time (≤28 h) at controlled humidity (≤3–95 %RH) and temperature (25.5 °C), evaluated with atomic force microscopy (AFM) and contact angle techniques. In the presence of humidity, the wettability decreased, liquid water capillary forces dominated over van der Waals forces, and surface domains, such as hillocks, height about 7.0 Å, and trenches, depth about −3.5 Å, appeared and grew primarily in lateral dimensions. Hillocks demonstrated lower adhesion and higher deformation in AFM experiments. We propose that the growing surface domains were formed by ion dissolution and diffusion followed by formation of hydrated salt of CaCO3. Upon drying, the height of the hillocks decreased by about 50% suggesting their alteration into dehydrated or less hydrated CaCO3. However, the process was not entirely reversible and crystallization of new domains continued at a reduced rate.

Keywords
Calcium carbonate minerals, Capillary forces, Humidity effects, Iceland spar calcite, Nanomechanical properties, Recrystallization, Reversibility of aging effects, Surface topography, Surface wettability, Van der Waals forces, Atomic force microscopy, Calcite, Calcium carbonate, Contact angle, Crystallization, Humidity control, Hydration, Phase interfaces, Surface properties, Wetting, Aging effects, Capillary force, Iceland spars, Nanomechanical property
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-37696 (URN)10.1016/j.jcis.2019.01.047 (DOI)2-s2.0-85060193864 (Scopus ID)
Note

 Funding details: Vetenskapsrådet, VR, 2015-05080; Funding text 1: Omya International AG provided financial funding of this research. Per M. Claesson acknowledges a grant from the Swedish Research Council (VR) [grant number 2015-05080 ].

Available from: 2019-02-01 Created: 2019-02-01 Last updated: 2019-06-17Bibliographically approved
Wallqvist, V., Kjell, G., Cupina, E., Kraft, L., Deck, C. & Willinger, R. (2017). New functional pavements for pedestrians and cyclists. Accident Analysis and Prevention, 105, 52-63
Open this publication in new window or tab >>New functional pavements for pedestrians and cyclists
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2017 (English)In: Accident Analysis and Prevention, ISSN 0001-4575, E-ISSN 1879-2057, Vol. 105, p. 52-63Article in journal (Refereed) Published
Abstract [en]

When many fields of pedestrian and cyclist safety have been extensively studied, the surfacing has long been left unquestioned, despite being developed for another mode of transport and being one of the main causes for falls and fall injuries. In this project new surfacing materials for pedestrian and cyclist safety have been produced. Focusing on augmenting previously largely disregarded parameters as impact absorption, comfort and visibility at the same time as avoiding deteriorating of crucial parameters as friction and wear resistance. Rubber content, binder type, and pigment addition have been varied and evaluated. The results demonstrate that by increasing rubber content of the mixtures the head injury criterion (HIC) value and injury risk can be decreased while maintaining frictional properties according to existing criteria. Assembly of test-lanes demonstrate that some developed materials experience lower flow and component separation than standard materials due to rubber addition, calling for further optimisation of construction procedure linked to content development. Initial trials on the test-lanes indicate that a polyurethane (PU) based material has high cycling comfort, visibility and can be modified with phosphorescence properties. For standard asphalt, impact absorption might be inflicted by modification of bitumen alone but is mostly augmented by rubber addition. The results also indicate that rubber content can decrease ice formation on the materials.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
bike lane, cyclist, impact absorption, paving, pedestrian, PPE, rubber, safety
National Category
Composite Science and Engineering Other Materials Engineering Infrastructure Engineering
Identifiers
urn:nbn:se:ri:diva-130 (URN)10.1016/j.aap.2016.04.032 (DOI)2-s2.0-84969160269 (Scopus ID)
Available from: 2016-05-31 Created: 2016-05-31 Last updated: 2018-08-13Bibliographically approved
Álvarez-Asencio, R., Wallqvist, V., Kjellin, M., Rutland, M. W., Camacho, A., Nordgren, N. & Luengo, G. S. (2016). Nanomechanical properties of human skin and introduction of a novel hair indenter. Journal of The Mechanical Behavior of Biomedical Materials, 54, 185-193
Open this publication in new window or tab >>Nanomechanical properties of human skin and introduction of a novel hair indenter
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2016 (English)In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 54, p. 185-193Article in journal (Refereed) Published
Abstract [en]

The mechanical resistance of the stratum corneum, the outermost layer of skin, to deformation has been evaluated at different length scales using Atomic Force Microscopy. Nanomechanical surface mapping was first conducted using a sharp silicon tip and revealed that Young’s modulus of the stratum corneum varied over the surface with a mean value of about 0.4 GPa. Force indentation measurements showed permanent deformation of the skin surface only at high applied loads (above 4 μN). The latter effect was further demonstrated using nanomechanical imaging in which the obtained depth profiles clearly illustrate the effects of increased normal force on the elastic/plastic surface deformation. Force measurements utilizing the single hair fiber probe supported the nanoindentation results of the stratum corneum being highly elastic at the nanoscale, but revealed that the lateral scale of the deformation determines the effective elastic modulus.This result resolves the fact that the reported values in the literature vary greatly and will help to understand the biophysics of the interaction of razor cut hairs that curl back during growth and interact with the skin.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Atomic Force Microscopy, Hair, Mechanical properties, Stratum corneum
National Category
Other Chemistry Topics Biophysics Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:ri:diva-107 (URN)10.1016/j.jmbbm.2015.09.014 (DOI)2-s2.0-84944111754 (Scopus ID)
Available from: 2016-04-28 Created: 2016-04-28 Last updated: 2019-07-01Bibliographically approved
Kraft, L., Rogers, P., Eriksson Brandels, A., Gram, A., Trädgårdh, J. & Wallqvist, V. (2015). Experimentalrubber chip concrete mixes for shock absorbent bike lane pavements.. In: : . Paper presented at 3rd International Conference on Best Practices for Concrete Pavements, 28 - 30 October. 2015. Bonito, Brazil: IBRACON and USP..
Open this publication in new window or tab >>Experimentalrubber chip concrete mixes for shock absorbent bike lane pavements.
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2015 (English)Conference paper, Published paper (Refereed)
Abstract [en]

In Sweden the amount of cyclists being injured in traffic has increased in recent years. Over 23,000 peopleper annum visit an acute care hospital after being injured whilst cycling. Most bicycle accidents are single“vehicle” accidents (82 %) and the most common collision is with another cyclist. Due to increased healthcare costs and the fact that more city dwelling people choose to cycle instead of going by car - due both tomonetary, environmental and personal health reasons - one is devoted to find solutions to make cyclingsafer. Besides efforts to increase helmet usage among cyclists and safer bike lane design separate from cartraffic, another way to reduce injuries may be achieved by modifying the bike lanes’ properties. This wouldresult in safer cycling and not only reducing non-cranial injuries, but also limit the severity of head injuries forcyclists not wearing a helmet. Thus, the pavement and bicycle lane material must be an efficient absorbentof impact energy. The work here presents efforts on modifying a concrete pavement by replacing coarseaggregates and sand with rubber chips and rubber crumbs to increase the shock absorbent capacity.Altogether, eighteen different mixtures with varying proportions of rubber, cement and sand were preparedand evaluated regarding elastic modulus and compressive strength. A fly-ash cement, microsilica and latexsolution were used in the concrete mixes. From the results obtained the mix with the best impact absorbingproperties, with a low E-modulus and sufficient compressive strength, was chosen for further evaluation.

Series
IBRACON, ISSN 2175-8182
Keywords
Rubber chips, rubber crumbs, rubber modified concrete, bike lane
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-39891 (URN)
Conference
3rd International Conference on Best Practices for Concrete Pavements, 28 - 30 October. 2015. Bonito, Brazil: IBRACON and USP.
Available from: 2019-09-06 Created: 2019-09-06 Last updated: 2019-09-06Bibliographically approved
Kumar Das, P., Kringos, N., Wallqvist, V. & Birgisson, B. (2014). Microscale investigation of thin film surface ageing of bitumen (ed.). Journal of Microscopy, 254(2), 95-107
Open this publication in new window or tab >>Microscale investigation of thin film surface ageing of bitumen
2014 (English)In: Journal of Microscopy, ISSN 2050-5698, Vol. 254, no 2, p. 95-107Article in journal (Refereed) Published
Abstract [en]

This paper investigates the mechanism of bitumen surface ageing, which was validated utilizing the atomic force microscopy and the differential scanning calorimetry. To validate the surface ageing, three different types of bitumen with different natural wax content were conditioned in four different modes: both ultraviolet and air, only ultraviolet, only air and without any exposure, for 15 and 30 days. From the atomic force microscopy investigation after 15 and 30 days of conditioning period, it was found that regardless the bitumen type, the percentage of microstructure on the surface reduced with the degree of exposure and time. Comparing all the four different exposures, it was observed that ultraviolet radiation caused more surface ageing than the oxidation. It was also found that the combined effect was not simply a summation or multiplication of the individual effects. The differential scanning calorimetry investigation showed that the amount of crystalline fractions in bitumen remain constant even after the systematic conditioning. Interestingly, during the cooling cycle, crystallization of wax molecules started earlier for the exposed specimens than the without exposed one. The analysis of the obtained results indicated that the ageing created a thin film upon the exposed surface, which acts as a barrier and creates difficulty for the wax induced microstructures to float up at the surface. From the differential scanning calorimetry analysis, it can be concluded that the ageing product induced impurities in the bitumen matrix, which acts as a promoter in the crystallization process.

Keywords
Atomic force microscopy, Bitumen, DSC, Oxidation, Surface ageing, UV radiation, Microscale investigation of thin film surface ageing of bitumen
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-27037 (URN)10.1111/jmi.12122 (DOI)2-s2.0-84897963787 (Scopus ID)
Note

A3442

Available from: 2016-12-08 Created: 2016-12-08 Last updated: 2019-08-09Bibliographically approved
Wallqvist, V. (2013). Adhesive surface characteristics of bitumen binders investigated by Atomic Force Microscopy (ed.). Fuel, 113, 248-256
Open this publication in new window or tab >>Adhesive surface characteristics of bitumen binders investigated by Atomic Force Microscopy
2013 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 113, p. 248-256Article in journal (Refereed) Published
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-6555 (URN)23840 (Local ID)23840 (Archive number)23840 (OAI)
Available from: 2016-09-08 Created: 2016-09-08 Last updated: 2018-08-13Bibliographically approved
Wallqvist, V. (2013). Micromechanical investigation of phase separation in bitumen by combining atomic force microscopy with differential scanning calorimetry results (ed.). International Journal on Road Materials and Pavement Design, 14(Suppl 1), 25-37
Open this publication in new window or tab >>Micromechanical investigation of phase separation in bitumen by combining atomic force microscopy with differential scanning calorimetry results
2013 (English)In: International Journal on Road Materials and Pavement Design, ISSN 1468-0629, E-ISSN 2164-7402, Vol. 14, no Suppl 1, p. 25-37Article in journal (Refereed) Published
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-6587 (URN)23886 (Local ID)23886 (Archive number)23886 (OAI)
Available from: 2016-09-08 Created: 2016-09-08 Last updated: 2018-08-13Bibliographically approved
Wallqvist, V., Rutland, M. & Claesson, P. (2013). Surface wrinkling: The phenomenon causing bees in bitumen (ed.). Journal of Materials Science, 48(20), 6970-6976
Open this publication in new window or tab >>Surface wrinkling: The phenomenon causing bees in bitumen
2013 (English)In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 48, no 20, p. 6970-6976Article in journal (Refereed) Published
National Category
Natural Sciences
Identifiers
urn:nbn:se:ri:diva-6556 (URN)23841 (Local ID)23841 (Archive number)23841 (OAI)
Available from: 2016-09-08 Created: 2016-09-08 Last updated: 2018-08-13Bibliographically approved
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1634-6789

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