| 1. |
- Álvarez-Asencio, Rubén, et al.
(författare)
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Nanomechanical properties of human skin and introduction of a novel hair indenter
- 2016
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Ingår i: Journal of The Mechanical Behavior of Biomedical Materials. - : Elsevier. - 1751-6161 .- 1878-0180. ; 54, s. 185-193
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
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| 3. |
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| 4. |
- Das, Prabir Kumar, et al.
(författare)
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Micromechanical investigation ofphase separation in bitumen bycombining atomic force microscopywith differential scanning calorimetryresults
- 2013
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Ingår i: International Journal on Road Materials and Pavement Design. - : Taylor & Francis. - 1468-0629 .- 2164-7402. ; 14:S1, s. 25-37
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Tidskriftsartikel (refereegranskat)abstract
- The thermo-rheological behaviour of bitumen depends largely on its chemical structure and intermolecular microstructures. Bitumen is a complex mixture of organic molecules of different sizes and polarities for which the micro-structural knowledge is still rather incomplete. Knowledge at that level can have great implications for behaviour at a larger scale and will help to optimise the bitumen in its production stage. The present study is focused on understanding the fundamental mechanisms behind the micro-structural phase appearance and the speed or mobility at which they change. To do so, atomic force microscopy was utilised at different temperatures to investigate the phase separation behaviour for four different types of bitumen and co-relate it with the differential scanning calorimetry measurements. Based on the experimental evidences, it was found that the observed phase separation is mainly due to the wax/paraffin fraction presence in bitumen and that the investigated bitumen behaves quite differently. Recommendations are made to continue this research into qualitative information to be used on the asphalt mix design level.
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| 5. |
- Das, Prabir Kumar, et al.
(författare)
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Microscale investigation of thin film surface ageing of bitumen
- 2014
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Ingår i: Journal of Microscopy. - : Wiley. - 2050-5698 .- 0022-2720 .- 1365-2818. ; 254:2, s. 95-107
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Eriksson, Mimmi, et al.
(författare)
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Direct Observation of Gas Meniscus Formation on a Superhydrophobic Surface
- 2019
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 13:2, s. 2246-2252
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Eriksson, Mimmi, et al.
(författare)
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Effects of Gas Layer Thickness on Capillary Interactions at Superhydrophobic Surfaces
- 2024
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 40:9, s. 4801-4810
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 8. |
- Eriksson, Mimmi, et al.
(författare)
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Effects of liquid surface tension on gas capillaries and capillary forces at superamphiphobic surfaces
- 2023
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- 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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| 9. |
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| 10. |
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| 11. |
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| 12. |
- Eriksson, Mimmi, et al.
(författare)
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Wetting Transition on Liquid-Repellent Surfaces Probed by Surface Force Measurements and Confocal Imaging
- 2019
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Ingår i: Langmuir. - : AMER CHEMICAL SOC. - 0743-7463 .- 1520-5827. ; 35:41, s. 13275-13285
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Tidskriftsartikel (refereegranskat)abstract
- Superhydrophobic surfaces in the Cassie-Baxter wetting state retain an air layer at the surface which prevents liquid water from reaching into the porous surface structure. In this work we explore how addition of ethanol, which reduces the surface tension, influences the wetting properties of superhydrophobic and smooth hydrophobic surfaces. Wetting properties are measured by dynamic contact angles, and the air layer at the superhydrophobic surface is visualized by laser scanning confocal microscopy. Colloidal probe atomic force microscopy measurements between a hydrophobic microsphere and the macroscopic surfaces showed that the presence of ethanol strongly affects the interaction forces. When the macroscopic surface is superhydrophobic, attractive forces extending up to a few micrometers are observed on retraction in water and in 20 vol % ethanol, signifying the presence of a large and growing gas capillary. Submicrometer attractive forces are observed between the probe particle and a smooth hydrophobic surface, and in this case a smaller gas capillary is formed. Addition of ethanol results in markedly different effects between superhydrophobic and hydrophobic surfaces. In particular, we show that the receding contact angle on the superhydrophobic surface is of paramount importance for describing the interaction forces.
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| 13. |
- Janhäll, Sara, et al.
(författare)
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A new method and first results for comparing emissions of fumes during construction of asphalt surfaces
- 2024
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Ingår i: Construction and Building Materials. - 0950-0618. ; 422
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Tidskriftsartikel (refereegranskat)abstract
- A novel laboratory methodology for analysing hot asphalt fumes from various paving materials is presented and evaluated. This method facilitates comparative assessments, aiming to enhance occupational safety for asphalt workers and ensure safe implementation of new paving materials. Comparative analyses of emissions to air were conducted on standard asphalt and rubber-modified asphalt at different temperatures. The temperature significantly influences PAH emissions. Rubber-modified asphalt demonstrated higher PAH emissions at equivalent temperatures compared to standard asphalt, predominantly naphthalene. Even heavier PAHs as benzo(a)pyrene were occasionally high. Notably, at recommended working temperatures the standard asphalt resulted in higher emissions, comprising heavier PAHs compared to rubber asphalt.
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| 14. |
- Kraft, Lars, et al.
(författare)
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Experimentalrubber chip concrete mixes for shock absorbent bike lane pavements.
- 2015
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 15. |
- Laurell Lyne, Åsa, et al.
(författare)
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Adhesive surface characteristics of bitumen binders investigated by Atomic Force Microscopy
- 2013
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 113, s. 248-256
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Tidskriftsartikel (refereegranskat)abstract
- Bitumen is a complex hydrocarbon whose composition-structure-property relationship is not well-understood. In this paper, microphase-separated topographic morphologies of unaged penetration grade 70/100 bitumen binders have been visualized by means of AFM QNM, and the relationship to local mechanical properties has been demonstrated. AFM QNM is a surface force mapping technique which measures parameters such as topography, adhesion and elastic modulus simultaneously. The resulting data can then be presented as images representing individual or overlaid parameters, e. g. topographic images with an adhesion overlay or topographic images with a modulus overlay. AFM QNM results show that the adhesive forces measured in the region surrounding (peri phase) the periodic topographic features resembling 'bees' (catana phase) and the region in the 'bee' areas are lower than the adhesive force measured in the smooth matrix (para phase). Likewise it was observed that Young's moduli in the region surrounding (peri phase) the 'bees' (catana phase) and in the 'bees' are higher than Young's modulus of the smooth matrix (para phase).
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| 16. |
- Laurell Lyne, Åsa, et al.
(författare)
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Surface wrinkling : The phenomenon causing bees in bitumen
- 2013
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 48:20, s. 6970-6976
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Tidskriftsartikel (refereegranskat)abstract
- The so called "bee phenomenon" in bitumen has been investigated by means of AFM quantitative nanomechanical property mapping. Bees are a phenomenon that can be observed by topography measurements using AFM. The characteristic "bee" appearance comes from regions with alternating higher and lower bands in the surface topography of bitumen, which are surrounded by a flat area. The proposed mechanism for bee formation is phase separation and differential contraction during cooling from melt temperatures leading to wrinkling due to differences in the elastic modulus of the material phases. Using a laminate wrinkling model, the thickness of the bee laminate was calculated from the wavelengths and Young's moduli of the bee laminate and the matrix. It was found to vary between 70 and 140 nm for the five bitumen samples that contained significant amounts of wax.
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| 17. |
- Makoundou, Christina, et al.
(författare)
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Development of functional rubber-based impact-absorbing pavements for cyclist and pedestrian injury reduction
- 2021
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Ingår i: Sustainability. - : MDPI. - 2071-1050. ; 13:20
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Tidskriftsartikel (refereegranskat)abstract
- Cyclists, pedestrians and elderly people’s specific needs in urban road infrastructures are often neglected. They rarely benefit from safety measures or innovations. Inspired by playgrounds and aiming to reduce vulnerable road users (VRUs) injuries, the development of the rubber-based Impact-Absorbing Pavements (IAP) offers a possibility to rethink the design of urban pavements and address safety on roads, which constitutes a major challenge in terms of attaining more sustain-able, resilient, and safe cities. Therefore, bituminous mixtures with four different crumb rubber con-tents, 0%, 14%, 28%, and 33% (in total weight), were produced by partial aggregates substitution using the dry process. After the assessment of the geometrical and volumetric properties, the mechanical performances were evaluated. Finally, the samples were tested to measure the abrasion and impact attenuation with the well-known Head Injury Criterion (HIC), at different temperatures from −10 to 40 °C, to obtain a wide range of values referring to possible weather conditions. A significant effect of the rubber percentage and layer thickness on impact attenuation was observed. All observations and results confirm the feasibility of the IAP concept and its positive effect on future injury-prevention applications. © 2021 by the authors.
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| 18. |
- Makoundou, Christina, et al.
(författare)
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Functionalization of crumb rubber surface for the incorporation into asphalt layers of reduced stiffness : An overview of existing treatment approaches
- 2021
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Ingår i: Recycling. - : MDPI AG. - 2313-4321. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- The substitution of mineral aggregates with crumb rubber (CR) from waste end‐of‐life tires (ELTs) in the asphalt concretes, has been considered a sustainable paving industry approach. The rubber has been used to construct pavements with proven enhanced resilience and improved durability. However, some issues related to the rubber’s surface adhesion or swelling may arise with these practices and generate complications (binder consumption, temperatures, mixing times). One possible solution to overcome the materials’ compatibility problems is to pre‐treat the CR’s surface before its incorporation into the asphalt mixes to allow a surface functionalization that can enhance coverage and cohesion inside the mixes. The physical treatments using radiations‐based beam are already exploited in the plastic recycling industries avoiding the use of chemicals in con-siderable amounts. Such treatments permit the recovering of large quantities of polymer‐based materials and the enhancement of interfacial properties. This article provides an overview of existing surface treatments of polymers and especially rubber, including gamma ray, UV‐ozone, micro-waves, and plasma. Several studies have shown an overall improvement of the rubber surface’s reactive properties due to contaminant removal or roughness enhancement attributed to cross‐link-ing or scission reactions occurring on the rubber’s surface layer. With those properties, the asphalt mixes’ phase stability properties are increased when the pre‐treated rubber is incorporated. The treatments would permit to increase the CR quantities, yet reduce the layer stiffness, and improve the durability and the sustainability of future advanced road pavements. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
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| 19. |
- Makoundou, Christina, et al.
(författare)
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Rubber- and emulsion-based impact-absorbing paving material produced with cold and dry processes : Laboratory and in-situ study
- 2023
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Ingår i: Construction and Building Materials. - : Elsevier Ltd. - 0950-0618 .- 1879-0526. ; 408
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Tidskriftsartikel (refereegranskat)abstract
- Impact-absorbing pavements (IAPs) may be used as novel sidewalks and bike lanes surface layers to decrease fall-related injuries among vulnerable road users (VRUs). Therefore, a cold-made, highly rubberised asphalt mixture (56% recycled rubber in the total volume of the mix) was developed in the laboratory, and the process was then upscaled, permitting its construction on a trial site. Both laboratory and on-site tests facilitated the evaluation of the material’s mechanical properties, impact-absorption capabilities, and frictional behaviour. The field trial enabled a comprehensive assessment of the material’s performance after six months of usage by pedestrians and cyclists on a hybrid segment. Additionally, evaluations were conducted after six, fifteen, and twenty months. The results confirmed the possibility to produce and lay a cold, highly rubberised paving material with valuable impact-attenuation performances. The mechanical analysis has shown the material’s elastic behaviour and its capability to carry uniaxial compression stress leading to a 5% strain of the total height without losing its properties. Furthermore, the critical fall height (CFH) values exhibited a sixfold increase compared to conventional asphalt, thereby reducing the severity of potential injuries. In terms of durability, the pavement’s overall effectiveness remained significant even after six, fifteen, and twenty months of use. The study demonstrated the capability to cover and fill holes and damaged portions using the same rubberised and cold mixture, a crucial aspect concerning the material’s future and maintenance considerations.
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| 20. |
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| 21. |
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| 22. |
- Sahandifar, Pooya, 1991-, et al.
(författare)
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A rubberized impact absorbing pavement can reduce the head injury risk in vulnerable road users : A bicycle and a pedestrian accident case study
- 2022
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Ingår i: Traffic Injury Prevention. - : Taylor and Francis Ltd.. - 1538-9588 .- 1538-957X. ; 23:5, s. 315-320
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Vulnerable Road Users (VRU), including pedestrians and cyclists, are generally the least protected road users and are frequently missed in the planning process of preventive measures. Rubberized asphalt mixtures were originally developed as a possible environmentally friendly solution to recycle the End-of-Life Tires while making the pavements more durable. The objective of the current study was to explore the effects of increasing the rubber content of the common rubberized asphalt mixtures in reducing the head injuries risk for VRUs. Method: To achieve this purpose, four different sample series with 0, 14, 28, and 33 weight percent rubber in each were tested. A compressive test without permanent deformation and one with failure were performed on each sample series. The mechanical behavior of each set was modeled using a MAT_SIMPLIFIED_RUBBER material model in LS-Dyna and validated against a standard Head Injury Criterion (HIC) drop test. Ultimately, previously low-speed accident reconstructed cases, a bicycle and a pedestrian one, were used to assess the effect of varying the rubber content on reducing the head injury risk. Results: In the bicycle accident case, the risk of skull fracture was reduced from 0.99 to 0.29 when comparing the non-rubberized asphalt mixture with the 33% rubber mixture. In the same accident case, the risk of concussion, evaluated using the logistic regression method, was reduced from 0.97 in the non-rubberized mixture to 0.81 in the 33% rubber mixture. The initial conditions, linear and rotational velocities, were lower for the pedestrian case compared to the bicycle case (the bicycle case was more severe compared to the pedestrian case), which led to lower strains in the pedestrian case. In the pedestrian accident case, the risk of skull fracture was reduced from 1.00 in the non-rubberized mixture to 0.63 in the 33% rubber mixture, while the risk of concussion was reduced from 0.64 to 0.07. Conclusion: The rubberized asphalt mixtures could reduce the head injury risk for the studied cases when the rubber content in the asphalt mixture increases. © 2022 The Author(s).
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| 23. |
- Sahandifar, Pooya, et al.
(författare)
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Assessing the Impact of Rubberized Asphalt on Reducing Hip Fracture Risk in Elderly Populations Using Human Body Models
- 2024
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Ingår i: SAE International Journal of Transportation Safety. - : SAE International. - 2327-5626 .- 2327-5634. ; 12:1, s. 87-94
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Tidskriftsartikel (refereegranskat)abstract
- Compared to other age groups, older adults are at more significant risk of hip fracture when they fall. In addition to the higher risk of falls for the elderly, fear of falls can reduce this population’s outdoor activity. Various preventive solutions have been proposed to reduce the risk of hip fractures ranging from wearable hip protectors to indoor flooring systems. A previously developed rubberized asphalt mixture demonstrated the potential to reduce the risk of head injury. In the current study, the capability of the rubberized asphalt sample was evaluated for the risk of hip fracture for an average elderly male and an average elderly female. A previously developed human body model was positioned in a fall configuration that would give the highest impact forces toward regular asphalt. Three different rubber contents with 14, 28, 33 weight percent (% wt.) were implemented as the ground alongside one regular non-rubberized (0%) asphalt mixture, one baseline, and one extra-compliant playground rubber-composite material. The whole-body model was simulated to fall on the rubberized asphalt mixtures with an initial vertical velocity of 3 m/s with a 10° trunk angle and +10° anterior pelvis rotation. The impact forces were measured on the femoral head, and a previously developed hip fracture risk function was used to compare the rubberized asphalt mixtures. It was found that the rubberized asphalt mixture with 33% wt. rubber can reduce the impact forces up to 10% for the elderly male and female model compared to regular asphalt. The impact forces were most reduced for the extra-compliant playground material, with a 23% reduction for the female model. The risk of injury for the asphalt mixture with 33% wt. rubber was reduced up to 18% for elderly females and 20 for elderly males, compared to regular asphalt. The extra-compliant playground material had the most reduction of hip fracture risk for both sexes, 39 and 43% for elderly females and males, respectively.
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| 24. |
- Sahandifar, Pooya, 1991-, et al.
(författare)
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Assessing the Impact of Rubberized Asphalt on Reducing Hip Fracture Risk in Elderly Populations Using Human Body Models
- 2024
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Ingår i: SAE International Journal of Transportation Safety. - : SAE International. - 2327-5626 .- 2327-5634. ; 12:1, s. 87-94
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Tidskriftsartikel (refereegranskat)abstract
- Compared to other age groups, older adults are at more significant risk of hip fracture when they fall. In addition to the higher risk of falls for the elderly, fear of falls can reduce this population's outdoor activity. Various preventive solutions have been proposed to reduce the risk of hip fractures ranging from wearable hip protectors to indoor flooring systems. A previously developed rubberized asphalt mixture demonstrated the potential to reduce the risk of head injury. In the current study, the capability of the rubberized asphalt sample was evaluated for the risk of hip fracture for an average elderly male and an average elderly female. A previously developed human body model was positioned in a fall configuration that would give the highest impact forces toward regular asphalt. Three different rubber contents with 14, 28, 33 weight percent (% wt.) were implemented as the ground alongside one regular non -rubberized (0%) asphalt mixture, one baseline, and one extra -compliant playground rubber -composite material. The whole -body model was simulated to fall on the rubberized asphalt mixtures with an initial vertical velocity of 3 m/s with a 10 degrees trunk angle and +10 degrees anterior pelvis rotation. The impact forces were measured on the femoral head, and a previously developed hip fracture risk function was used to compare the rubberized asphalt mixtures. It was found that the rubberized asphalt mixture with 33% wt. rubber can reduce the impact forces up to 10% for the elderly male and female model compared to regular asphalt. The impact forces were most reduced for the extra -compliant playground material, with a 23% reduction for the female model. The risk of injury for the asphalt mixture with 33% wt. rubber was reduced up to 18% for elderly females and 20 for elderly males, compared to regular asphalt. The extra -compliant playground material had the most reduction of hip fracture risk for both sexes, 39 and 43% for elderly females and males, respectively.
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| 25. |
- Sahandifar, Pooya, 1991-
(författare)
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Biomechanical Analysis of Fall Injuries using Finite Element Modeling
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A fall is a serious health issue for the elderly. Among different fall types, the sideways fall is considered to be more severe concerning the injury outcome. When elderlies experience an unintentional sideways fall, they can either resist the impact forces with the soft tissue force attenuation capacity and femoral strength or need external protections to reduce the injury risk. In this thesis, these two aspects were investigated. Finite element whole-body models are valuable tools for analyzing fall biomechanics and investigating the possible preventive measures more conveniently. The whole-body models were developed to investigate traffic accidents; however, a sideways fall has different kinematics than the other types of accidents. Consequently, it is necessary to enhance the whole-body models according to the major fall parameters leading to severe injury cases before assessing the external protection capabilities.The current thesis attempted to advance these two critical aspects regarding fall-induced injuries. A finite element whole-body model was chosen to study three critical parameters in fall biomechanics: body posture, soft tissue, and femoral strength. The whole body model was positioned in different body configurations relevant for the sideways fall to evaluate the body posture that could lead to the highest internal forces on the femoral head. Next, different soft tissue constitutive material models and soft tissue thicknesses were investigated to find a material model that could accurately reproduce the experimental results according to an objective rating method named CORrelation and Analysis (CORA). Finally, the separate and combined effects of geometrical and mechanical properties change due to aging on femoral strength were assessed for the elderly males and females. In the second aspect of the thesis, the shock-absorbing rubberized asphalt pavements' preventive capacity was examined. First, different rubberized asphalt mixtures were implemented in a bicycle and a pedestrian accident reconstruction cases to evaluate the head injury risks. Later, the asphalt mixtures were studied in a sideways fall scenario to evaluate the hip fracture risk in an elderly male and female.The first aspect of the thesis presented the results and methods to improve the sideways fall analysis, and the second aspect of the thesis focused on assessing the rubberized asphalt mixtures for injury prevention purposes. The sideways fall with the upright trunk and a slightly forward-tilted pelvis could lead to the highest internal forces. A nonlinear Ogden material model for muscle tissue and a Mooney-Rivlin material model for adipose tissue scored better among different soft tissue material models in the side impacts to the hip segments. The geometrical and mechanical properties change due to aging leading to a different behavior for males and females, where females experience a higher rate of strength loss due to aging. Moreover, it was indicated that a rubberized asphalt mixture could reduce the head injury risk for pedestrians and cyclists and the hip fracture risk for the elderly. The amount of rubber in the asphalt mixtures needs to exceed a specific limit to observe rubberized asphalts' preventive effects. Consequently, it is necessary to optimize the mixtures' rubber content to improve its prevention capacity.In summary, the current thesis presented a method to improve the whole-body models according to the sideways fall requirements and assessed the protective capacity of the rubberized asphalt mixtures against head and hip injuries.
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| 26. |
- Skedung, Lisa, et al.
(författare)
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FINE-TUNING THE TACTILE PERCEPTION OF COATINGS
- 2021
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Ingår i: European Coatings Journal. - 0930-3847. ; 6, s. 32-37
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Human tactile evaluations were combined with tactile friction measurements to quantify the perceptual experience of touching coated panels. Monosized beads of nine different polymer compositions were added to a soft-touch waterborne two-component PUR coating. Introducing beads of different composition affected tactile perception.
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| 27. |
- Wallqvist, Viveca, et al.
(författare)
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Fluid transport in compacted porous talc blocks
- 2008
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Ingår i: Fluid Dynamics & Materials Processing. - 1555-256X .- 1555-2578. ; 4:2, s. 85-98
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Tidskriftsartikel (refereegranskat)abstract
- It has been shown that talc powder can be compacted into tablets with a preferred orientation of the platelets. The tablets can be obtained with different controlled porosity depending on pressing methods and applied pressure. The tablets can be obtained with or without additives, which may, in turn, be adsorbed. The orientation of the high aspect ratio platy talc, the surface chemistry imparted by the additives and the transported fluid influence the imbibition and permeation rates. Non-polar hexadecane displays a higher imbibition and permeability than water for all particulate orientations during short timescale absorption, likely due to the oleophilic nature of talc, and thus a more complete filling of the pores for non-polar liquids is to be expected. At longer timescales water is imbibed either at a similar rate to hexadecane or faster depending on the surface chemistry generated by additives leading to hydrophilicity. The swelling of the added polymers used to create wettability leads to break-up of the structure and exposure of hydrophilic surfaces for more rapid imbibition. It is not possible, therefore, to measure reliably the water uptake parameters when talc is fully dispersed with surfactants. Furthermore, dispersing agents tend to contribute to the blocking of pores and throats in the swollen state, and so a limitation in total imbibed volume occurs. The permeability under pressure is also inhibited by additives, which supports the suggestion of partial blockage of the pores and throats. When the individual talc crystal c axes, defining the perpendicular to the [001] planes, are oriented 90° to the primary average liquid flow direction, i.e. are oriented in a planar configuration to the flow, imbibition and permeation of wetting liquid are increased. This is assumed to be due to decreased tortuosity, provided the liquid is wetting in respect to the oriented edge surface. However, non-wetting liquids in respect to all, or geometrically dependent, orientations are subject also to the surface chemistry presented by the orientation, i.e. whether the talc is primarily displaying OH-groups or not, or adsorbed species aiding wetting by the liquid. Measurements where additives are not strongly adsorbed are complicated by the solubility of some wetting and dispersing agents.
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| 28. |
- Wallqvist, Viveca, et al.
(författare)
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Hamaker constants for talc minerals using spectral ellipsometric data
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Measurements of refractive indices over a large wavelength span for talc minerals using spectral ellipsometry allow more accurate determinations of Hamaker constants than previously reported, or otherwise calculated from literature data. We report that for the birefringent talc minerals different Hamaker constants are obtained for samples cut in different crystallographic orientations. In water, very small differences, from 1.710-20 to 1.910-20 J is obtained for nanocrystalline talc samples cut in different directions, whereas a microcrystalline sample from another source give considerably higher value of the Hamaker constant, 4.210-20J. The difference is explained by a significant difference in the refractive index. Implications for interactions relevant in connection to the use of talc as a pitch control agent, in the action of wetting and dispersing additives used as processing aids, and in combinations of talc with cellulose, calcite and polystyrene are indicated.
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| 29. |
- Wallqvist, Viveca, et al.
(författare)
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Influence of Surface Topography on Adhesive and Long-Range Capillary Forces between Hydrophobic Surfaces in Water
- 2009
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:16, s. 9197-9207
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Tidskriftsartikel (refereegranskat)abstract
- We report oil the interactions between a hydrophobic probe particle and surfaces with nanoscopic surface features, These surfaces have been prepared by spin-coating of nanoparticles and by polishing. The surface topography was characterized by AFM, using the methods of high-resolution imaging, low-resolution imaging using the probe particle, and by the rolling ball method. The spin-coated surfaces can be characterized as nanostructured due to the high density of nanoparticles that oil a short length scale provides a regular pattern of crevices and hills. Oil these surfaces a larger waviness is also distinguished. In contrast, the polished surfaces display sharp nanoscopic peaks and hardly any crevices. I n all cases the dominant force at short separations was found to be a capillary attraction due to the formation of an air/ vapor condensate. Our data show that the large-scale waviness of the surface does not significantly influence the range and magnitude of the capillary attraction, but large local variations in these quantities are found. The large variation in on force corresponds to a small variation in local contact angle of the capillary condensate It the surfaces. The adhesion report discusses how the nature of the surface topographical features influences the capillary attraction by influencing the local contact angle and by pinning of the three-phase contact line. The effect is clearly dependent on whether the surface features exist in the form of crevices or as extending ridges.
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| 30. |
- Wallqvist, Viveca, et al.
(författare)
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Influence of Wetting and Dispersing Agents on the Interaction between Talc and Hydrophobic Particles
- 2009
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:12, s. 6909-6915
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between a natural talc surface and a model hydrophobic particle have been investigated in aqueous solutions by employing the atomic force microscopy (AFM) colloidal probe technique. The results demonstrate the presence of long-range attractive forces due to bridging via preadsorbed or induced bubbles/cavities. Due to the natural heterogeneity of talc, and the stochastic nature of the bubble bridging process, the variability in the range and magnitude of the attraction is larger than that for cases when other interactions predominate or than that when only model surfaces are used. Addition of poly(acrylic acid), a common dispersing agent, did not affect the measured forces. Thus, we conclude that poly(acrylic acid) does not adsorb to the basal plane of talc. In sharp contrast, addition of Pluronic PE6400, a nonionic triblock polymer used as wetting agent, resulted in complete removal of the bubble-induced attractive force. Instead, a short-range steric repulsion is the dominating feature. Clearly, Pluronic PE6400 is able to displace air bubbles from the surface and prevent their formation when the particles come into contact. These are suggested to be important features of efficient wetting agents.
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| 31. |
- Wallqvist, Viveca, et al.
(författare)
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Interaction forces between talc and hydrophobic particles probed by AFM
- 2006
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 277:03-jan, s. 183-190
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between cleaved talc surfaces and hydrophobic probe particles, silanized silica and thiolized gold, has been investigated employing the atomic force microscopy (AFM) colloidal probe technique. These model systems have hydrophobicities similar to some of the talc-pitch combinations present during pulp and paper manufacture. The talc surfaces used in this study, in the [0 0 1] plane, show a micro-roughness with sharp peaks of up to 3 nm in height. The force profiles obtained demonstrate the predominance of a long-range attractive force. However, the range and magnitude of the attractive force show large variability. The variability of the attractive force, and the frequent observations of clear steps in the force curve demonstrate that it is caused by gas/vapor cavities bridging the Surfaces once the surfaces are brought sufficiently close together. The results suggest that the same mechanism is of importance in applications where talc is used as a collector for pitch.
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| 32. |
- Wallqvist, Viveca, et al.
(författare)
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Interaction forces between talc and pitch probed by atomic force microscopy
- 2007
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:8, s. 4248-4256
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal wood resin components present in pulp are collectively called pitch. The presence of pitch may cause severe problems due to deposits in and on the paper machine. There is thus a need for controlling pitch aggregation and adsorption. To be able to develop more efficient pitch control systems, one needs to develop the understanding of pitch-pitch interactions and of the interactions between pitch and other materials. With this general goal in mind, we present methods for preparing geometrically well-defined pitch particles attached to atomic force microscopy tips. This has enabled us to investigate the interactions between pitch and talc, an additive commonly used for pitch control. We have used model pitch particles consisting of one component only (abietic acid), a mixture of components (collophonium), and particles prepared from real pitch deposits. We show that the forces acting between pitch and talc are attractive and, once the initial approach is made, exert this attraction out to large distances of separation. We present evidence that the formation of bridging air bubbles or cavities is responsible for this interaction.
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| 33. |
- Wallqvist, Viveca, 1977-
(författare)
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Interactions between non-polar surfaces in water: Fokus on talc, pitch and surface roughness effects
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis work was to gain understanding of the interactions between talc mineral and surfaces, liquids and chemicals relevant for industrial applications, such as pulp and paper. Talc is used in the pulp and paper industry as a filler pigment, in control of pitch (lipophilic extractives) deposits and as a coating pigment. A deeper understanding of talc interactions will be beneficial in optimizing its use. Long-range attractive interactions between talc and hydrophobic model probes, as well as pitch probes, have been measured using the atomic force microscope (AFM) colloidal probe method. Two procedures for preparation of pitch colloidal probes were developed to allow these studies. Model hydrophobic, nanorough surfaces with surface energy characteristics similar to talc have also been prepared and their interactions with hydrophobic model probes compared to interactions between hydrophobic model probes and talc. It is demonstrated that talc mineral interacts with model hydrophobic particles, as well as with pitch, by long-range attractive forces, considerably stronger than the expected van der Waals force. The possible origin of the measured interaction forces is discussed, and the conclusion is that the main cause is an attractive capillary force due to formation of a gas/vapor capillary between the surfaces. Force measurements using model hydrophobic, nanorough surfaces show that a large-scale waviness does not significantly influence the range and magnitude of the capillary attraction, but large local variations in these quantities are found. It is demonstrated that a large variation in adhesion force corresponds to a small variation in local contact angle of the capillaries at the surfaces. The nature of the surface topographical features influences the capillary attraction by affecting the local contact angle and by pinning of the three-phase contact line. The effect is clearly dependent on the size of the surface features and whether they exist in the form of crevices or as extending ridges. Entrapment of air also affects the imbibition of water in pressed talc tablets. The effects of wetting and dispersion agents on the interactions between talc and hydrophobic probes have also been investigated. It is demonstrated that a common dispersing agent used for talc, poly(acrylic acid), does not affect the capillary attraction between talc and non-polar probes. In fact, the results strongly suggest that poly(acrylic acid) does not adsorb on the basal plane of talc. From this finding it is inferred that the stabilizing effect of this additive most likely is due to adsorption to the edges of talc. In contrast, a wetting agent (the non-ionic triblock copolymer Pluronic PE6400) removes the long-range capillary attraction. It is suggested that such an ability to replace air at the talc surface is of great importance for an efficient wetting agent. The Hamaker constant for talc has also been estimated by using optical data obtained from spectroscopic ellipsometry. It is demonstrated that a nanocrystalline talc mineral, cut in different directions displays very small differences in Hamaker constant between the different crystallographic orientations, whereas a microcrystalline sample displays a significantly higher value. The estimated Hamaker constants are discussed for different material combinations of relevance for the pulp- and paper industry, such as cellulose and calcium carbonate.
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| 34. |
- Wallqvist, Viveca, et al.
(författare)
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New functional pavements for pedestrians and cyclists
- 2017
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Ingår i: Accident Analysis and Prevention. - : Elsevier. - 0001-4575 .- 1879-2057. ; 105, s. 52-63
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 35. |
- Wallqvist, Viveca, et al.
(författare)
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Prototype bike lanes - placement practices and properties
- 2015
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Ingår i: 57º Congresso Brasileiro do Concreto, Bonito/MS [CBC 2015]. - : IBRACON.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- AstaZero, a unique environment to build any scenario in order to develop, test or certifynew traffic safety solutions was opened 2014 in Sweden. In this environment a testingarena for vulnerable road users has been developed. Among with the solutions testedbelongs impact absorbing surfaces for cyclists, one which has been made of rubbermodified concrete. The study involved testing of different compositions and examining newproperties in the fresh state, which affected the production process to different extents. Forexample, due to difference in density between aggregate and rubber the segregation maybe a problem. Regarding the materials properties, the head injury criterion (HIC) was usedfor evaluation of the pavements shock absorbing capability. In the laboratory tests themodified concrete demonstrated a decrease in HIC-value by 85% compared to standardbitumen material. In the AstaZero test-lane, measured at -1°C, the decrease in HIC-valuecompared to reference was 79%. The frictional properties were approved according toexisting criteria. Future tests will determine the new materials’ durability, maintenance andcycling comfort.
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| 36. |
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| 37. |
- Wojas, Natalia, et al.
(författare)
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Calcite Surfaces Modified with Carboxylic Acids (C2 to C18) : Layer Organization, Wettability, Stability, and Molecular Structural Properties
- 2023
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 39:42, s. 14840-14852
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Tidskriftsartikel (refereegranskat)abstract
- A fundamental understanding of the interactions between mineral surfaces and amphiphilic surface modification agents is needed for better control over the production and uses of mineral fillers. Here, we controlled the carboxylic acid layer formation conditions on calcite surfaces with high precision via vapor deposition. The properties of the resulting carboxylic acid layers were analyzed using surface-sensitive techniques, such as atomic force microscopy (AFM), contact angle measurements, angle resolved X-ray photoelectron spectroscopy (XPS), and vibrational sum-frequency spectroscopy. A low wettability was achieved with long hydrocarbon chain carboxylic acids such as stearic acid. The stearic acid layer formed by vapor deposition is initially patchy, but with increasing vapor exposure time, the patches grow and condense into a homogeneous layer with a thickness close to that expected for a monolayer as evaluated by AFM and XPS. The build-up process of the layer occurs more rapidly at higher temperatures due to the higher vapor pressure. The stability of the deposited fatty acid layer in the presence of a water droplet increases with the chain length and packing density in the adsorbed layer. Vibrational sum frequency spectroscopy data demonstrate that the stearic acid monolayers on calcite have their alkyl chains in an all-trans conformation and are anisotropically distributed on the plane of the surface, forming epitaxial monolayers. Vibrational spectra also show that the stearic acid molecules interact with the calcite surface through the carboxylic acid headgroup in both its protonated and deprotonated forms. The results presented provide new molecular insights into the properties of adsorbed carboxylic acid layers on calcite.
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| 38. |
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| 39. |
- Wojas, Natalia, et al.
(författare)
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Iceland spar calcite : Humidity and time effects on surface properties and their reversibility
- 2019
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 541, s. 42-55
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 40. |
- Wojas, Natalia, et al.
(författare)
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Nanoscale Wear and Mechanical Properties of Calcite : Effects of Stearic Acid Modification and Water Vapor
- 2021
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 37:32, s. 9826-9837
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the wear of mineral fillers is crucial for controlling industrial processes, and in the present work, we examine the wear resistance and nanomechanical properties of bare calcite and stearic acid-modified calcite surfaces under dry and humid conditions at the nanoscale. Measurements under different loads allow us to probe the situation in the absence and presence of abrasive wear. The sliding motion is in general characterized by irregular stick-slip events that at higher loads lead to abrasion of the brittle calcite surface. Bare calcite is hydrophilic, and under humid conditions, a thin water layer is present on the surface. This water layer does not affect the friction force. However, it slightly decreases the wear depth and strongly influences the distribution of wear particles. In contrast, stearic acid-modified surfaces are hydrophobic. Nevertheless, humidity affects the wear characteristics by decreasing the binding strength of stearic acid at higher humidity. A complete monolayer coverage of calcite by stearic acid results in a significant reduction in wear but only a moderate reduction in friction forces at low humidity and no reduction at 75% relative humidity (RH). Thus, our data suggest that the wear reduction does not result from a lowering of the friction force but rather from an increased ductility of the surface region as offered by the stearic acid layer. An incomplete monolayer of stearic acid on the calcite surface provides no reduction in wear regardless of the RH investigated. Clearly, the wear properties of modified calcite surfaces depend crucially on the packing density of the surface modifier and also on the air humidity.
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| 41. |
- Wojas, Natalia, et al.
(författare)
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Surface-Modified and Unmodified Calcite : Effects of Water and Saturated Aqueous Octanoic Acid Droplets on Stability and Saturated Fatty Acid Layer Organization
- 2021
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Ingår i: Langmuir. - : American Chemical Society. - 0743-7463 .- 1520-5827. ; 37:48, s. 14135-
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Tidskriftsartikel (refereegranskat)abstract
- A profound understanding of the properties of unmodified and saturated fatty acid-modified calcite surfaces is essential for elucidating their resistance and stability in the presence of water droplets. Additional insights can be obtained by also studying the effects of carboxylic acid-saturated aqueous solutions. We elucidate surface wettability, structure, and nanomechanical properties beneath and at the edge of a deposited droplet after its evaporation. When calcite was coated by a highly packed monolayer of stearic acid, a hydrophilic region was found at the three-phase contact line. In atomic force microscopy mapping, this region is characterized by low adhesion and a topographical hillock. The surface that previously was covered by the droplet demonstrated a patchy structure of about 6 nm height, implying stearic acid reorganization into a patchy bilayer-like structure. Our data suggest that during droplet reverse dispensing and droplet evaporation, pinning of the three-phase contact line leads to the transport of dissolved fatty carboxylic acid and possibly calcium bicarbonate Ca(HCO3)2 molecules to the contact line boundary. Compared to the surface of intrinsically hydrophobic materials, such as polystyrene, the changes in contact angle and base diameter during droplet evaporation on stearic acid-modified calcite are strikingly different. This difference is due to stearic acid reorganization on the surface and transport to the water-air interface of the droplet. An effect of the evaporating droplet is also observed on unmodified calcite due to dissolution and recrystallization of the calcite surface in the presence of water. In the case where a water droplet saturated with octanoic acid is used instead of water, the stearic acid-coated calcite remains considerably more stable. Our findings are discussed in terms of the coffee-ring effect. © 2021 The Authors.
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| 42. |
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