| 1. |
- Rohlmann, Patrick, 1986-
(författare)
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Lubrication mechanisms and properties of non-halogenated orthoborate ionic liquids
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One way to reduce energy consumption and waste - a necessity to achieve the UN-mandated limitation of average global temperature in-creases - is to select suitable lubricants so that energy-losses through friction and wear are minimised. In this context, non-halogenated ionicliquids (ILs) are promising candidates to achieve this aim due to their intrinsic ionic properties, low vapour pressure and high thermal stability. These are properties desirable for lubricants. Non-halogenated ILs area relatively new type of chemical compounds in tribology. Therefore, systematic studies are required in order to elaborate understanding oftheir functional properties and to increase their readiness level for use innew and emerging technologies such as battery electric vehicles.This doctoral thesis focuses on the lubrication performance of ILs consisting of phosphonium or imidazolium cations and orthoborate anions. Tribological tests were performed with two different tribological configurations (continuous sliding ball-on-three plates tests and reciprocatingsliding ball-on-disc tests) under different tribological contact conditions(temperature, from 80◦ C to 140 ◦ C; sliding distances of 200 m, 2000 mand 4300 m). In addition, dynamic viscosity, density and ionic conductivity of these ILs were determined for comparative purposes e.g. with commonly used lubricants.The elemental composition and the structure of the anionic and cationic constituents of the ILs determine their lubrication behaviour and their physical properties. The latter are mainly affected by the alkyl chain length of cations and other structural features, such as the presence of aromatic rings in anions. However, the lubricating performance of ILs depends on their elemental composition, their propensity to surface self-assembly and the effects of the breakdown products of these ILs induced by the thermo-mechanical conditions of the tribo-contact. Imidazolium-based ILs outperform phosphonium based ILs in terms of friction-reduction, but the opposite is observed for wear-prevention. This behaviour is attributable to the breakdown products of the imidazolium ILs caused by lubrication tests. Furthermore, contaminants/impurities present in the ILs (such as trace remnants of the precursor moleculesused in the synthesis of ILs) can affect lubrication, either through improved physical properties or through an accelerated breakdown of the ILs under tribo-contact conditions. This is demonstrated with a phosphonium bis(oxalato)-borate IL and the traces of its transition anionic complex (TAC). It is revealed, that there is a delicate balance to be struck between decomposition of the ILs/TAC and the beneficial effects of the decomposition products on friction and wear. This thesis also shows that the non-halogenated phosphonium IL, added to polar and non-polar biodegradable oils, can work as an anti-wear additive by forming boundary films. This effect was only minor in the case of the polar biodegradable oil due to the competition between the ions of the IL and the polar base oil molecules for surface area.In conclusion, this work contributes significantly to the characterisation of non-halogenated ILs as novel lubricants. It does so by expanding the understanding of the influence of structural and elemental variationson their lubricating performance and physical properties. Furthermore, lubrication mechanisms for phosphonium and imidazolium ILs are suggested. As a consequence, non-halogenated ILs appear to be excellent candidates for more energy-efficient lubrication.
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| 2. |
- Hjalmarsson, Nicklas
(författare)
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Ionic liquids : The solid-liquid interface and surface forces
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ionic liquids (ILs) present new approaches for controlling interactions at the solid-liquid interface. ILs are defined as liquids consisting of bulky and asymmetric ions, with a melting point below 373 K. Owing to their amphiphilic character they are powerful solvents but also possess other interesting properties. For example, ILs can self-assemble and are attracted to surfaces due to their charged nature. As a result, they are capable of forming nanostructures both in bulk and at interfaces. This thesis describes how the solid-IL interface responds to external influences such as elevated temperatures, the addition of salt and polarisation. An improved understanding of how these factors govern the surface composition can provide tools for tuning systems to specific applications such as friction.Normal and friction forces are measured for ethylammonium nitrate (EAN) immersed between a mica surface and a silica probe, at different temperatures or salt concentrations. The results demonstrate that an increase in temperature or low concentrations of added salt only induce small changes in the interfacial structure and that the boundary layer properties remain intact. In contrast, at sufficiently large salt concentrations the smaller lithium ion prevails and the surface composition changes. The interfacial layer of a similar IL is also investigated upon the addition of salt and the results reveal that lithium ions affect the surface composition differently depending on the ion structure of the IL. This demonstrates that the surface selectivity strongly depends on the ion chemistry.Remarkably, a repulsive double layer force manifests itself for EAN at 393 K, which is not observed for lower temperatures. This indicates a temperature dependent change in EAN’s microscopic association behaviour and has general implications for how ILs are perceived.A new method is developed based on a quartz crystal microbalance to investigate how the surface compositions of ILs respond to polarisation. The approach demonstrates that interfacial layers of both a neat IL and an IL dissolved in oil can be controlled using potentials of different magnitudes and signs. Furthermore, the method enables two independent approaches for monitoring the charges during polarisation which can be used to quantify the surface composition. The technique also provides information on ion kinetics and surface selectivity.This work contributes to the fundamental understanding of the solid-IL interface and demonstrates that the surface composition of ILs can be controlled and monitored using different approaches.
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| 3. |
- Li, Sichao
(författare)
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Electro-Interfacial Composition Control by Ionic Liquid Technology : Nanostructure, Self-Assembly, and Friction
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Given the potential of ionic liquids (ILs) for batteries, supercapacitors and advanced lubricants, it is crucial to understand how electric fields affect the interfacial behaviour in IL-solvent systems and the intricate relationship between nanostructure and tribotronic properties. This thesis investigates the structural and compositional changes of ILs with different solvents at electrified interfaces.The four papers constituting this thesis can be broadly divided into two studies. The first study outlines the electro-interfacial behaviour of various monocationic (MILs) and dicationic ILs (DILs) dispersed in propylene carbonate. Combining electrochemical quartz crystal microbalance, neutron reflectivity (EC-NR), and atomic force microscopy, a voltage-induced interphase transition from a self-assembled cation bilayer to a conventional electrical double-layer structure has been revealed in bis(oxalato)borate anion MILs. This interphase transition has not been observed in DILs, attributed to the dual charge centres reducing the segregation between polar and apolar domains of dications for self-assembly interaction. The second study explores three MILs sharing the same phosphonium cation with varying orthoborate-based anions dissolved in 2-ethylhexyl laurate (2-EHL). EC-NR measurements reveal a solvent-rich interfacial corona layer and the subtlety of anion architecture in tuning electro-interfacial properties. Meanwhile, EC-NR has been used as a complementary probe to elucidate the nano-scale structural and compositional changes in the boundary films of IL/2-EHL systems with varying potentials, providing a direct link between the molecular controllability and macroscopic tribotronic performance studies.This thesis contributes to the fundamental understanding of electro-interfacial behaviour and controllability of IL-solvent systems and offers valuable molecular insights for deploying these novel ILs as additives in advanced tribological and electrochemical contexts.
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| 4. |
- Liljeblad, Jonathan F.D. 1978-
(författare)
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Biomimetic Membranes: : Molecular Structure and Stability Studies by Vibrational Sum Frequency Spectroscopy
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the research presented in this licentiate thesis the surface specific technique Vibrational Sum Frequency Spectroscopy, VSFS, combined with the Langmuir trough has been utilized to investigate Langmuir monolayers and Langmuir-Blodgett (LB) deposited mono- and bilayers of phospholipids. Their molecular structure, stability, and hydration were probed to gain additional understanding of important properties aiming at facilitating the use of such layers as model systems for biological membranes. VSFS was applied to in situ studies of the degradation of Langmuir monolayers of 1,2-diacyl-phosphocholines with identical C-18 chains having various degrees of unsaturation. The time-dependent change of the monolayer area at constant surface pressure as well as the sum frequency intensity of the vinyl-CH stretch at the C=C double bonds were measured to monitor the degradation. It was shown that a rapid degradation of the monolayers of unsaturated phospholipids occurred when exposed to the laboratory air compared to the fully saturated lipid, and that the degradation could be inhibited by purging the ambient air with nitrogen. The degradation was attributed to oxidation mediated by reactive species in the air. The molecular structure and order of Langmuir monolayers of 1,2-distearoyl-phosphocholine (18:0 PC) and their hydrating water were investigated at different surface pressures using VSFS. The spectroscopic data indicated a well ordered monolayer at all surface pressures with a more intense signal at higher pressures attributed to the subsequent increase of the number density and more ordered lipid molecules due to the tighter packing. Water molecules hydrating the headgroups or being in contact with the hydrophobic parts were observed and distinguished by their vibrational frequencies, and found to have different average orientations. Additionally, monolayers of 18:0 PC, its fully deuterated analogue, and 1,2-distearoyl-phosphoserine (18:0 PS) were Langmuir-Blodgett (LB) deposited on CaF2 substrates and VSFS was used to investigate the structure and order of the films as well as the hydrating water. The CH-region, water region, and lower wavenumber region containing phosphate, ester, carboxylic acid, and amine signals were probed to obtain a complete picture of the molecule. The data indicates that all deposited monolayers formed a well ordered and stable film and the average orientation of the aliphatic chains was determined using the antisymmetric methyl stretch.
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| 5. |
- Álvarez-Asencio, Rubén, 1978-
(författare)
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Nanotribology, Surface Interactions and Characterization : An AFM Study
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When two surfaces achieve contact, then contact phenomena such as adhesion, friction and wear can occur, which are of great interest in many disciplines, including physics, physical chemistry, material chemistry, and life and health sciences. These phenomena are largely determined by the nature and magnitude of the surface forces such as van der Waals, capillary and hydration forces. Moreover these forces are length-dependent, and therefore when the system scales down, their contribution scales up, dominating the interaction between the surfaces.A goal of my PhD work was to investigate fundamental contact phenomena in terms of the surface forces that regulate their properties. The primary tool applied in this PhD thesis work has been the atomic force microscopy (AFM), which (with all of its sub-techniques) offers the possibility to study such forces with high resolution virtually between all types of materials and intervening media. Therefore, in this work it was possible to study the long ranged interactions presented in air between different industrially relevant materials and how these interactions are shielded when the systems are immersed in an ionic liquid.Also investigated was the influence of microstructure on the tribological properties of metal alloys, where their good tribological properties were related with the vanadium and nitrogen contents for a FeCrVN tool alloy and with the chromium content for a biomedical CoCrMo alloy. Moreover, the effect of the intervening media can significantly affect the surface properties, and when the biomedical CoCrMo alloy was immersed in phosphate buffer saline solution (PBS), repulsive hydration forces decreased the friction coefficient and contact adhesion. On the other hand, with the immersion of the FeCrVN tool alloy in the NaCl solution, small particles displaying low adhesion were generated in specific regions on the surface with low chromium content. These particles are assumed to be related to a prepitting corrosion event in the tool alloy.The mechanical properties of stratum corneum (SC), which is the outermost layer of the skin, were also studied in this work. The SC presents a highly elastic, but stiff surface where the mechanical properties depend on the nanoscale. A novel probe has been designed with a single hair fibre in order to understand how the skin deforms locally in response to the interaction with such a fibre probe. This study revealed that is mostly the lateral scale of the deformation which determines the mechanical properties of the SC.Finally, important achievements in this work are the developments of two new techniques - tribological property mapping and the Hybrid method for torsional spring constant evaluation. Tribological property mapping is an AFM technique that provides friction coefficient and contact adhesion maps with information attributed to the surface microstructure. The Hybrid method is an approach that was originally required to obtain the torsional spring constants for rigid beam shaped cantilevers, which could not be previously determined from their power torsional thermal spectra (conventional method). However, the applicability is shown to be general and this simple method can be used to obtain torsional spring constants for any type of beam shape cantilever.
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| 6. |
- Liljeblad, Jonathan F. D., 1978-
(författare)
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A Spectroscopic Study of Interfacial Films: Internal Structuring, Stability, and Hydration
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Monolayers of molecules are capable of completely changing the nature of surfaces and their interactions with the surroundings despite their almost negligible thickness. In the research presented in this doctoral thesis the surface specific technique Vibrational Sum Frequency Spectroscopy (VSFS) was combined with the Langmuir trough to investigate various manifestations of monolayers, such as biomimetic membranes, mono methyl branched long chain fatty acids in contact with air, and hydrophobic silane monolayers in contact with water.VSFS was applied to in situ studies of the oxidative degradation of Langmuir monolayers of 1,2-diacylphosphocholines with identical C-18 chains featuring various degrees of unsaturation. The monolayer area and vinyl CH signal intensity were probed at constant surface pressure to monitor the degradation. The rapid degradation of the unsaturated lipids in contact with the ambient air is attributed to oxidation of the C=C bonds mediated by reactive species in the air and can be inhibited by purging the compartment surrounding the monolayer with nitrogen.The molecular structure and order of Langmuir monolayers of 1,2-distearoyl-phosphocholine (18:0 PC) and their hydrating water were investigated at different surface pressures using VSFS. The monolayers are conformationally well ordered at all surface pressures and the signal intensity increases due to larger molecular number density at increasing surface pressures. Also, water signals with different vibrational frequencies are observed in different polarization combinations.Additionally, a selection of common phospholipids (18:0 PC, 18:0 PC-D83 and 18:0 PS) were Langmuir-Blodgett (LB) deposited on CaF2 substrates and the CH- and OH-stretching regions as well as lower wavenumber regions were probed using VSFS. The orientation of the conformationally well ordered aliphatic chains was determined to be approximately perpendicular to the sample surface.Monolayers of eicosanoic acid, its iso (19-MEA), and anteiso (18-MEA) analogues were investigated with VSFS, AFM imaging, and the Langmuir trough. The EA forms smooth, featureless monolayers when deposited on silica, while 19-MEA and 18-MEA form 10 -50 nm large domains with homogeneous size distribution. It was not possible to discriminate between the monolayers of racemic and chiral 18-MEA using any of the techniques employedThe influence of the experimental geometry on the SF spectral shape and en-hancement at and near total internal reflection conditions (TIR) were systematically investigated by comparing simulations with recorded data from a hydrophobized silica / water interface. The data agree qualitatively, but not quantitatively, with the simulations, and the reasons were critically discussed.The water structure next to ordered and disordered hydrophobic silane monolayers on silica was investigated using VSFS. The results indicate that the structure of water next to a well ordered hydrophobic monolayer, with the exception of the first layer of water molecules, is not much different from that in the isotropic bulk. This is in contrast to the previous notion where such monolayers were assumed to induce a more ordered interfacial water structure.
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| 7. |
- Reddy, Akepati Bhaskar, 1990-
(författare)
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Sustainable Lubrication and Tribotronics enabled by Ionic Materials
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Developments in machine design play a crucial role in the global endeavor towards sustainability. The potential for energy conservation and emission reduction has pushed lubrication research to the forefront, with the lubricant considered to be a vital machine component. As a result of the need for high machine efficiency and longevity, as well as that of greener lubricants, ionic liquids (ILs) are gaining attention for lubrication applications, especially in combination with biodegradable oils. ILs also present a unique opportunity for developing active lubrication, tribotronic systems. To make them an industrially viable option, however, an in-depth understanding of IL lubrication behavior is required. In this doctoral work, investigations of the tribologically relevant ionic boundary films formed by non-halogenated ILs dispersed in a carrier medium (polar solvent or bio-oil) were conducted using a variety of tribological techniques and neutron reflectance. The effect of external actuation by electric potential on the extent, ionic composition, and tribological relevance of the interfacial boundary films was also studied. The results revealed that the ionic architecture and the condition of IL in the oil play an important role in defining the lubricity of the adsorbed boundary films. Clear electroresponsivity was also observed across methods, with the relative concentration of cations and anions in the interfacial film and the lubricating film thickness changing with the electric potential bias. It was established that the anions, playing an anchor role on the surface, are crucial for the formation of robust load-carrying boundary films. A methodology using electrochemical impedance spectroscopy was developed for measuring and characterizing the electric conductivity of complex lubricating greases with ionic and non-ionic additives. According to these measurements, the electrical characteristics of greases depend on the interactions of IL with the grease matrix. Overall, this work contributes towards the development of sustainable lubrication and tribotronic systems using ILs.
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| 8. |
- Abbott, Andrew, et al.
(författare)
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Ionic liquids at interfaces : general discussion
- 2018
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 206, s. 549-586
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Álvarez-Asencio, Ruben, et al.
(författare)
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Note : Determination of torsional spring constant of atomic force microscopy cantilevers: Combining normal spring constant and classical beam theory
- 2013
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 84:9
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Tidskriftsartikel (refereegranskat)abstract
- A technique has been developed for the calculation of torsional spring constants for AFM cantilevers based on the combination of the normal spring constant and plate/beam theory. It is easy to apply and allow the determination of torsional constants for stiff cantilevers where the thermal power spectrum is difficult to obtain due to the high resonance frequency and low signal/noise ratio. The applicability is shown to be general and this simple approach can thus be used to obtain torsional constants for any beam shaped cantilever.
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| 10. |
- Badal Tejedor, Maria, 1986-
(författare)
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Interfacial and material aspects of powders with relevance to pharmaceutical tableting performance
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tablets are the most common forms of drug administration. They are convenient to administer and easy to manufacture. However, problems associated with the adhesion of the powders to the tableting tools are common. This phenomenon is known as sticking and even though it has been well documented and studied, it remains poorly understood. The many factors that contribute to good performance of the powders make the sticking problem difficult to solve.The goal of this study is to establish a relationship between the properties measured at the nanoscale to the overall tablet mechanical properties, tablet performance and powder pre-processing induced modifications. By using atomic force microscopy (AFM) we aim to develop an analytical method to characterize the mechanical and adhesive properties of the pharmaceutical powders at the nanoscale. Other methodologies such as scanning electron microscopy (SEM), thermal analyses (DSC, TGA) and tablet strength test were also used. The materials used in this study are commonly used excipients, a sticky drug and magnesium stearate (MgSt). Two different approaches offered by AFM were employed: sharp tip imaging and colloidal probe force measurements. Nano-mechanical properties of the materials were evaluated with a sharp tip cantilever showing that higher adhesion correlates with higher tablet cohesion and that both are significantly affected by the presence of MgSt. AFM characterization of the particle surface mechanical properties at the nanoscale was also used to detect the crystallinity and amorphicity levels of the materials. New approaches to presenting such data considering the particle heterogeneity and to track the dynamics of surface recrystallization are revealed. Adhesive interactions between a steel sphere and sticky and non-sticky powders were performed with the colloidal probe technique. Sticky materials presented a higher adhesion against the steel surface, and reveal the mechanism of stickiness.This work thus contributes to the provision of predictability of the performance of formulations at an early stage of the development process.
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| 11. |
- Bergendal, Erik, et al.
(författare)
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3D texturing of the air-water interface by biomimetic self-assembly
- 2020
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Ingår i: Nanoscale Horizons. - : Royal Society of Chemistry. - 2055-6764 .- 2055-6756. ; 5:5, s. 839-846
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Tidskriftsartikel (refereegranskat)abstract
- A simple, insoluble monolayer of fatty acid is shown to induce 3D nanotexturing of the air-water interface. This advance has been achieved through the study of monolayers of a methyl-branched long chain fatty acid, analogous to those found on the surface of hair and wool, directly at the air-water interface. Specular neutron reflectometry combined with AFM probing of deposited monolayers shows pronounced 3D surface domains, which are absent for unbranched analogues and are attributed to hydrocarbon packing constraints. The resulting surface topographies of the water far exceed the height perturbation that can be explained by the presence of capillary waves of a free liquid surface. These have hitherto been considered the only source of perturbation of the flatness of a planar water interface under gravity in the absence of topographical features from the presence of extended, globular or particulate matter. This amounts to a paradigm shift in the study of interfacial films and opens the possibility of 3D texturing of the air-water interface.
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| 12. |
- Bergendal, Erik, et al.
(författare)
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3D texturing of the air–water interface by biomimetic self-assembly
- 2020
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Ingår i: Nanoscale Horizons. - 2055-6764 .- 2055-6756. ; :5, s. 839-846
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Tidskriftsartikel (refereegranskat)abstract
- A simple, insoluble monolayer of fatty acid is shown to induce 3D nanotexturing of the air–water interface. This advance has been achieved through the study of monolayers of a methyl-branched long chain fatty acid, analogous to those found on the surface of hair and wool, directly at the air–water interface. Specular neutron reflectometry combined with AFM probing of deposited monolayers shows pronounced 3D surface domains, which are absent for unbranched analogues and are attributed to hydrocarbon packing constraints. The resulting surface topographies of the water far exceed the height perturbation that can be explained by the presence of capillary waves of a free liquid surface. These have hitherto been considered the only source of perturbation of the flatness of a planar water interface under gravity in the absence of topographical features from the presence of extended, globular or particulate matter. This amounts to a paradigm shift in the study of interfacial films and opens the possibility of 3D texturing of the air–water interface.
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| 13. |
- Bergendal, Erik
(författare)
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Fatty Acid Self-Assembly at the Air–Water Interface : Curvature, Patterning, and Biomimetics: A Study by Neutron Reflectometry and Atomic Force Microscopy
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For more than a hundred years of interfacial science, long chain fatty acids have been the primary system for the study of floating monolayers at the air–water interface due to their amphiphilic nature and system simplicity: an insoluble hydrocarbon chain and a soluble carboxyl group at a flat air–water interface. Despite―or perhaps rather due to―the assumed simplicity of such systems and the maturity of the research field, the seemingly fundamentally rooted notion of a two-dimensional water surface has yet to be challenged.The naturally occurring methyl-branched long chain fatty acid 18-methyleicosanoic acid and one of its isomers form monolayers consisting of monodisperse domains of tens of nanometres, varying in size with the placement of the methyl branch. The ability of domain-forming monolayers to three-dimensionally texture the air–water interface is investigated as a result of hydrocarbon packing constraints owing to the methyl branch.In this work, neutron reflectometry has been used to study monolayers of branched long chain fatty acids directly at the air–water interface, which allowed precise probing of how a deformable water surface is affected by monolayer structure. Such films were also transferred by Langmuir–Blodgett deposition to the air–solid interface, and subsequently imaged by atomic force microscopy. Combined, the results unanimously―and all but unambiguously―show that the self-assembly of branched long chain fatty acids texture the air–water interface, inducing domain formation by a local curvature of the water surface, and thus controverting the preconceived notion of a planar air–water interface. The size and shape of the observed domains are shown to be tuneable using three different parameters: in mixed systems of branched and unbranched fatty acids, with varying hydrocarbon length of the straight chain, and altering subphase electrolyte properties. Each of these factors effectively allows changing the local curvature of the monolayer, much like analogous three-dimensional systems in bulk lyotropic crystals. This precise tuneability opens up for sustainable nanopatterning. Finally, the results lead to a plausible hypothesis of self-healing properties as to why the surface of hair and wool have a significant proportion of branched fatty acid.
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| 14. |
- Bergendal, Erik, et al.
(författare)
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Tuneable interfacial surfactant aggregates mimic lyotropic phases and facilitate large scale nanopatterning
- 2021
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 13:1, s. 371-379
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that the air-liquid interface can be made to display the same rich curvature phenomena as common lyotropic liquid crystal systems. Through mixing an insoluble, naturally occurring, branched fatty acid, with an unbranched fatty acid of the same length, systematic variation in the packing constraints at the air-water interface could be obtained. The combination of atomic force microscopy and neutron reflectometry is used to demonstrate that the water surface exhibits significant tuneable topography. By systematic variation of the two fatty acid proportions, ordered arrays of monodisperse spherical caps, cylindrical sections, and a mesh phase are all observed, as well as the expected lamellar structure. The tuneable deformability of the air-water interface permits this hitherto unexplored topological diversity, which is analogous to the phase elaboration displayed by amphiphiles in solution. It offers a wealth of novel possibilities for the tailoring of nanostructure
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| 15. |
- Bergendal, Erik, et al.
(författare)
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Unveiling Texture and Topography of Fatty Acid Langmuir Films : Domain Stability and Isotherm Analysis
- 2024
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 40:20, s. 10468-10476
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Tidskriftsartikel (refereegranskat)abstract
- 3D texturing by self-assembly at the air-water interface has recently been proposed. The hypothesis of this work is that, if this is true, such domain formation should be inferable directly from pressure-area isotherms and be thermodynamically stable. Monolayers of branched fatty acid mixtures with straight chain analogues and their stability are thus studied using a combination of pressure-area isotherms, thermodynamic analysis, in situ Brewster angle microscopy, and atomic force microscopy of both LB-deposited and drop-cast films on silicon wafers. Isotherms reflecting the behavior of monodisperse 3D domains are shown to be independent of compression rate and display long-term stability. Gibbs analysis further confirms the thermodynamic rather than kinetic origin of such novel species by revealing that deviations from ideal mixing can be explained only a priori by differences in the topography of the water surface, thus also indirectly confirming the self-assembly deformation of the water interface. The intrinsic self-assembly curvature and miscibility of the two fatty acids is confirmed by drop-casting, which also provides a rapid, tunable thin-film preparation approach. Finally, the longevity of the nanostructured films is extraordinary, the long-range order of the deposited films increases with equilibration time at the water interface, and the integrity of the nanopatterns remains intact on the scale of years.
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| 16. |
- Bergendal, Erik, et al.
(författare)
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Unveiling Texture and Topography of Fatty Acid Langmuir Films : Domain Stability and Isotherm Analysis
- 2024
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Ingår i: Langmuir. - : American Chemical Society. - 0743-7463 .- 1520-5827. ; 40:20, s. 10468-10476
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Tidskriftsartikel (refereegranskat)abstract
- 3D texturing by self-assembly at the air-water interface has recently been proposed. The hypothesis of this work is that, if this is true, such domain formation should be inferable directly from pressure-area isotherms and be thermodynamically stable. Monolayers of branched fatty acid mixtures with straight chain analogues and their stability are thus studied using a combination of pressure-area isotherms, thermodynamic analysis, in situ Brewster angle microscopy, and atomic force microscopy of both LB-deposited and drop-cast films on silicon wafers. Isotherms reflecting the behavior of monodisperse 3D domains are shown to be independent of compression rate and display long-term stability. Gibbs analysis further confirms the thermodynamic rather than kinetic origin of such novel species by revealing that deviations from ideal mixing can be explained only a priori by differences in the topography of the water surface, thus also indirectly confirming the self-assembly deformation of the water interface. The intrinsic self-assembly curvature and miscibility of the two fatty acids is confirmed by drop-casting, which also provides a rapid, tunable thin-film preparation approach. Finally, the longevity of the nanostructured films is extraordinary, the long-range order of the deposited films increases with equilibration time at the water interface, and the integrity of the nanopatterns remains intact on the scale of years.
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| 17. |
- Besharat, Zahra
(författare)
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Adsorption of molecular thin films on metal and metal oxide surfaces
- 2016
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Konstnärligt arbete (övrigt vetenskapligt/konstnärligt)abstract
- Metal and metal oxides are widely used in industry, and to optimize their performance their surfaces are commonly functionalized by the formation of thin films. Self-assembled monolayers (SAMs) are deposited on metals or metal oxides either from solution or by gas deposition. Thiols with polar terminal groups are utilized for creating the responsive surfaces which can interact electrostatically with other adsorbates. Surface charge effects wetting and adhesion, and many other surface properties. Polar terminal groups in thiols could be used to modify these factors. Mixed SAMs can provide more flexible surfaces, and could change the resulting surface properties under the influence of factors such as pH, temperature, and photo-illumination. Therefore, in order to control these phenomena by mixed polar-terminated thiols, it is necessary to understand the composition and conformation of the mixed SAMs and their response to these factors. In this work, mixtures of thiols with carboxylic and amino terminal groups were studied. Carboxylic and amino terminal groups of thiol interact with each other via hydrogen bonding in solution and form a complex. Complexes adsorb to the surface in non-conventional orientations. Unmixed SAMs from each type, either carboxylic terminated thiols or amino terminated thiols are in standing up orientation while SAMs from complexes are in an axially in-plane orientation. Selenol is an alternative to replace thiols for particular applications such as contact with biological matter which has a better compatibility with selenol than sulfur. However, the Se-C bond is weaker than the S-C bond which limits the application of selenol. Understanding the selenol adsorption mechanism on gold surfaces could shed some light on Se-C cleavage and so is investigated in this work. Se-C cleavage happens in the low coverage areas on the step since atoms at steps have lower coordination making them more reactive than atoms on the terraces. Another area where the self-assembly of molecules is of importance is for dye sensitized solar cells, which are based on the adsorption of the dye onto metal oxides surfaces such as TiO2.The interface between the SAM of dye and the substrate is an important factor to consider when designing dyes and surfaces in dye sensitized solar cells (DSSCs). The quality of the self-assembled monolayers of the dye on the TiO2 surface has a critical influence on the efficiency of the DSSCs. Creation of just a monolayer of dye on the surface could lead to an efficient current of photo-excited electrons to the TiO2 and degeneration of the dye by redox. This work, T-PAC dye showed island growth with some ad-layer that is not in contact with the surface, whereas the MP13 dye adsorption is laminar growth. Cuprite (Cu2O) is the initial and most common corrosion product for copper under atmospheric conditions. Copper could be a good replacement for noble metal as catalysts for methanol dehydrogenation. Knowledge about the structure of Cu2O(100) and Cu2O(111) surfaces could be used to obtain a deeper understanding of methanol dehydrogenation mechanisms with respect to adsorption sites on the surfaces. In this work, a detailed study was done of Cu2O(100) surface which revealed the possible surface structures as the result of different preparation conditions. Studies of the structure of Cu2O(100) and Cu2O(111) surfaces show that Cu2O(100) has a comparatively stable surface and reduces surface reactivity. As a consequence, dehydrogenation of methanol is more efficient on the Cu2O(111) surface. The hydrogen produced from methanol dehydrogenation is stored in oxygen adatom sites on both surfaces.
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| 18. |
- Hammond, Oliver S., et al.
(författare)
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Molecular Architecture Effects on Bulk Nanostructure in Bis(Orthoborate) Ionic Liquids
- 2023
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Ingår i: Small. - : John Wiley and Sons Inc. - 1613-6810 .- 1613-6829. ; 29
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Tidskriftsartikel (refereegranskat)abstract
- A series of 19 ionic liquids (ILs) based on phosphonium and imidazolium cations of varying alkyl-chain lengths with the orthoborate anions bis(oxalato)borate [BOB]−, bis(mandelato)borate, [BMB]− and bis(salicylato)borate, [BScB]−, are synthesized and studied using small-angle neutron scattering (SANS). All measured systems display nanostructuring, with 1-methyl-3-n-alkyl imidazolium-orthoborates forming clearly bicontinuous L3 spongelike phases when the alkyl chains are longer than C6 (hexyl). L3 phases are fitted using the Teubner and Strey model, and diffusely-nanostructured systems are primarily fitted using the Ornstein-Zernicke correlation length model. Strongly-nanostructured systems have a strong dependence on the cation, with molecular architecture variation explored to determine the driving forces for self-assembly. The ability to form well-defined complex phases is effectively extinguished in several ways: methylation of the most acidic imidazolium ring proton, replacing the imidazolium 3-methyl group with a longer hydrocarbon chain, substitution of [BOB]− by [BMB]−, or exchanging the imidazolium for phosphonium systems, irrespective of phosphonium architecture. The results suggest there is only a small window of opportunity, in terms of molecular amphiphilicity and cation:anion volume matching, for the formation of stable extensive bicontinuous domains in pure bulk orthoborate-based ILs. Particularly important for self-assembly processes appear to be the ability to form H-bonding networks, which offer additional versatility in imidazolium systems. © 2023 The Authors.
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| 19. |
- Hammond, Oliver S., et al.
(författare)
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Small-Angle Neutron Scattering Insights into 2-Ethylhexyl Laurate : A Remarkable Bioester
- 2024
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 12:5, s. 1816-1821
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Tidskriftsartikel (refereegranskat)abstract
- Commercial (protiated) samples of the "green" and biodegradable bioester 2-ethylhexyl laurate (2-EHL) were mixed with D-2-EHL synthesized by hydrothermal deuteration, with the mixtures demonstrating bulk structuring in small-angle neutron scattering measurements. Analysis in a polymer scattering framework yielded a radius of gyration (R (g)) of 6.5 angstrom and a Kuhn length (alternatively described as the persistence length or average segment length) of 11.2 angstrom. Samples of 2-EHL dispersed in acetonitrile formed self-assembled structures exceeding the molecular dimensions of the 2-EHL, with a mean aggregation number (N-agg) of 3.5 +/- 0.2 molecules across the tested concentrations. We therefore present structural evidence that this ester can function as a nonionic (co)-surfactant. The available surfactant-like conformations appear to enable performance beyond the low calculated hydrophilic-lipophilic balance value of 2.9. Overall, our data offer an explanation for 2-EHL's interfacial adsorption properties via self-assembly, resulting in strong emolliency and lubricity for this sustainable ester-based bio-oil.
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| 20. |
- Harris, Kathryn L, et al.
(författare)
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A Sticky Situation or Rough Going? : Influencing Haptic Perception of Wood Coatings Through Frictional and Topographical Design
- 2021
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Ingår i: Tribology letters. - : Springer. - 1023-8883 .- 1573-2711. ; 69:3
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Tidskriftsartikel (refereegranskat)abstract
- Improving the tactile aesthetics of products that can be described as touch intensive is an increasing priority within many sectors, including the furniture industry. Understanding which physical characteristics contribute to the haptic experience of a surface, and how, is therefore highly topical. It has earlier been shown that both friction and topography affect tactile perception. Thus, two series of stimuli have been produced using standard coating techniques, with systematic variation in (physical) friction and roughness properties. This was achieved through appropriate selection of matting agents and resins. The stimuli sets were then evaluated perceptually to determine the extent to which discrimination between pairs of surfaces followed the systematic materials variation. In addition to investigating the role of the physical properties in discrimination of the surfaces, their influence on perceived pleasantness and naturalness was also studied. The results indicate that changes in tactile perception can be understood in terms of friction and roughness, and that varying the matting agents (topography) and resins (material properties) in the coatings provide the controlling factors for furniture applications. Perceived pleasantness is associated with low friction and smoother topography, whilst perceived naturalness is found to be described by an interaction between tactile friction and the average maximum peak height of the surface features. Graphic Abstract: [Figure not available: see fulltext.] © 2021, The Author(s).
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| 21. |
- Jin, R., et al.
(författare)
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Bioinspired Self-Assembled 3D Patterned Polymer Textures as Skin Coatings Models : Tribology and Tactile Behavior
- 2020
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Ingår i: Biotribology. - : Elsevier Ltd. - 2352-5738. ; 24
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that during evolution, specific surface patterns emerged (e.g., on lotus leaves and butterfly wings) endowed with many remarkable surface properties (superhydrophobicity, vibrant structural color, delicate textures, etc.). In order to obtain these natural effects in cosmetics, we look for ways to transfer topographic patterns in coatings and treatments. Textured polymer surfaces were studied to explore their friction properties on the microscale and possible correlations with human tactile friction on the macroscale. We have chosen self-assembling block and random copolymers as model systems to prepare reliable biomimetic films with different micrometer and nanometer scale randomly patterned and randomly rough surfaces. The surface texture of the films was characterized by atomic force microscopy (AFM), and their tribological (friction) properties were studied with a surface forces apparatus (SFA) at a low sliding speed of 3 μm/s and at a speed of 10 cm/s relevant to realistic applications. The results are evaluated in terms of polymer segment mobility, interpenetration, entanglement and relaxation at interfaces, surface texture as described by roughness parameters, and interlocking of asperities. A stiction spike (static friction) was commonly found for the randomly patterned glassy polymer films. Random roughness patterns made from semi-crystalline polymers above their Tg gave high friction at low speed, but their friction coefficients were reduced at high speed due to less time for local entanglement and relaxations. The friction response of one of them was also affected differently by humidity than that of glassy polymer films. Tactile friction measurements with a human finger sliding against the polymer films revealed that the textures also provided differences at the macroscale, although the dynamic changes possibly due to lipid transfer, occlusion of moisture and/or damage of the films makes it difficult to draw robust conclusions. Finally, as an example, it is shown that these textures can be transferred to a soft elastomeric skin mimic substrate. This study introduces the concept of surface patterning by self-assembly to deliver tactile sensorial properties in coatings.
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| 22. |
- Li, Sichao, et al.
(författare)
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Anion Architecture Controls Structure and Electroresponsivity of Anhalogenous Ionic Liquids in a Sustainable Fluid
- 2024
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society. - 1520-6106 .- 1520-5207. ; 128:17, s. 4231-4242
-
Tidskriftsartikel (refereegranskat)abstract
- Three nonhalogenated ionic liquids (ILs) dissolved in 2-ethylhexyl laurate (2-EHL), a biodegradable oil, are investigated in terms of their bulk and electro-interfacial nanoscale structures using small-angle neutron scattering (SANS) and neutron reflectivity (NR). The ILs share the same trihexyl(tetradecyl)phosphonium ([P6,6,6,14]+) cation paired with different anions, bis(mandelato)borate ([BMB]−), bis(oxalato)borate ([BOB]−), and bis(salicylato)borate ([BScB]−). SANS shows a high aspect ratio tubular self-assembly structure characterized by an IL core of alternating cations and anions with a 2-EHL-rich shell or corona in the bulk, the geometry of which depends upon the anion structure and concentration. NR also reveals a solvent-rich interfacial corona layer. Their electro-responsive behavior, pertaining to the structuring and composition of the interfacial layers, is also influenced by the anion identity. [P6,6,6,14][BOB] exhibits distinct electroresponsiveness to applied potentials, suggesting an ion exchange behavior from cation-dominated to anion-rich. Conversely, [P6,6,6,14][BMB] and [P6,6,6,14][BScB] demonstrate minimal electroresponses across all studied potentials, related to their different dissociative and diffusive behavior. A mixed system is dominated by the least soluble IL but exhibits an increase in disorder. This work reveals the subtlety of anion architecture in tuning bulk and electro-interfacial properties, offering valuable molecular insights for deploying nonhalogenated ILs as additives in biodegradable lubricants and supercapacitors.
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| 23. |
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| 24. |
- Li, Sichao, et al.
(författare)
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Tuneable interphase transitions in ionic liquid/carrier systems via voltage control
- 2023
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 652, s. 1240-1249
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Tidskriftsartikel (refereegranskat)abstract
- The structure and interaction of ionic liquids (ILs) influence their interfacial composition, and their arrangement (i.e., electric double-layer (EDL) structure), can be controlled by an electric field. Here, we employed a quartz crystal microbalance (QCM) to study the electrical response of two non-halogenated phosphonium orthoborate ILs, dissolved in a polar solvent at the interface. The response is influenced by the applied voltage, the structure of the ions, and the solvent polarizability. One IL showed anomalous electro-responsivity, suggesting a self-assembly bilayer structure of the IL cation at the gold interface, which transitions to a typical EDL structure at higher positive potential. Neutron reflectivity (NR) confirmed this interfacial structuring and compositional changes at the electrified gold surface. A cation-dominated self-assembly structure is observed for negative and neutral voltages, which abruptly transitions to an anion-rich interfacial layer at positive voltages. An interphase transition explains the electro-responsive behaviour of self-assembling IL/carrier systems, pertinent for ILs in advanced tribological and electrochemical contexts.
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| 25. |
- Liu, Xiaoyan, et al.
(författare)
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Low friction and high load bearing capacity layers formed by cationic-block-non-ionic bottle-brush copolymers in aqueous media
- 2013
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 9:22, s. 5361-5371
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Tidskriftsartikel (refereegranskat)abstract
- Efficient lubricants should be able to build surface layers that result in low friction and high load bearing capacity. In this work we show how this can be achieved in aqueous media by means of adsorption of a diblock copolymer consisting of a cationic anchor block without side chains and an uncharged and hydrophilic bottle-brush block that protrudes into solution. Surface and friction forces were measured between negatively charged silica surfaces coated with adsorbed layers of the cationic diblock copolymer, utilizing the atomic force microscope colloidal probe technique. The interactions between the surfaces coated with this copolymer in water are purely repulsive, due to a combination of steric and electrostatic double-layer forces, and no hysteresis is observed between forces measured on approach and separation. Friction forces between the diblock copolymer layers are characterized by a low friction coefficient, μ ≈ 0.03-0.04. The layers remain intact under high load and shear due to the strong electrostatic anchoring, and no destruction of the layer was noted even under the highest pressure employed (about 50 MPa). Addition of NaCl to a concentration of 155 mM weakens the anchoring of the copolymer to the substrate surface, and as a result the friction force increases.
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| 26. |
- Munavirov, Bulat, et al.
(författare)
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The effect of anion architecture on the lubrication chemistry of phosphonium orthoborate ionic liquids
- 2021
-
Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
-
Tidskriftsartikel (refereegranskat)abstract
- Phosphonium ionic liquids with orthoborate anions have been studied in terms of their interfacial film formation, both physisorbed and sacrificial from chemical breakdown, in sheared contacts of varying harshness. The halogen-free anion architecture was varied through (i) the heteronuclear ring size, (ii) the hybridisation of the constituent atoms, and (iii) the addition of aryl functionalities. Time of Flight-Secondary Ion Mass Spectrometry analysis revealed the extent of sacrificial tribofilm formation allowing the relative stability of the ionic liquids under tribological conditions to be determined and their breakdown mechanisms to be compared to simple thermal decomposition. Overall, ionic liquids outperformed reference oils as lubricants; in some cases, sacrificial films were formed (with anion breakdown a necessary precursor to phosphonium cation decomposition) while in other cases, a protective, self-assembly lubricant layer or hybrid film was formed. The salicylate-based anion was the most chemically stable and decomposed only slightly even under the harshest conditions. It was further found that surface topography influenced the degree of breakdown through enhanced material transport and replenishment. This work thus unveils the relationship between ionic liquid composition and structure, and the ensuing inter- and intra-molecular interactions and chemical stability, and demonstrates the intrinsic tuneability of an ionic liquid lubrication technology.
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| 27. |
- Naranjo, Teresa, et al.
(författare)
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Hydrogen-bonded host–guest systems are stable in ionic liquids
- 2020
-
Ingår i: Scientific Reports. - : Nature Research. - 2045-2322. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- We show that H-bonded host–guest systems associate in ionic liquids (ILs), pure salts with melting point below room temperature, in which dipole–dipole electrostatic interactions should be negligible in comparison with dipole-charge interactions. Binding constants (Ka) obtained from titrations of four H-bonded host–guest systems in two organic solvents and two ionic liquids yield smaller yet comparable Ka values in ionic liquids than in organic solvents. We also detect the association event using force spectroscopy, which confirms that the binding is not solely due to (de)solvation processes. Our results indicate that classic H-bonded host–guest supramolecular chemistry takes place in ILs. This implies that strong H-bonds are only moderately affected by surroundings composed entirely of charges, which can be interpreted as an indication that the balance of Coulombic to covalent forces in strong H-bonds is not tipped towards the former. © 2020, The Author(s).
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| 28. |
- Pilkington, Georgia, et al.
(författare)
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Effect of water on the electroresponsive structuring and friction in dilute and concentrated ionic liquid lubricant mixtures
- 2020
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 22:48, s. 28191-28201
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Tidskriftsartikel (refereegranskat)abstract
- The effect of water on the electroactive structuring of a tribologically relevant ionic liquid (IL) when dispersed in a polar solvent has been investigated at a gold electrode interface using neutron reflectivity (NR). For all solutions studied, the addition of small amounts of water led to clear changes in electroactive structuring of the IL at the electrode interface, which was largely determined by the bulk IL concentration. At a dilute IL concentration, the presence of water gave rise to a swollen interfacial structuring, which exhibited a greater degree of electroresponsivity with applied potential compared to an equivalent dry solution. Conversely, for a concentrated IL solution, the presence of water led to an overall thinning of the interfacial region and a crowding-like structuring, within which the composition of the inner layer IL layers varied systematically with applied potential. Complementary nanotribotronic atomic force microscopy (AFM) measurements performed for the same IL concentration, in dry and ambient conditions, show that the presence of water reduces the lubricity of the IL boundary layers. However, consistent with the observed changes in the IL layers observed by NR, reversible and systematic control of the friction coefficient with applied potential was still achievable. Combined, these measurements provide valuable insight into the implications of water on the interfacial properties of ILs at electrified interfaces, which inevitably will determine their applicability in tribotronic and electrochemical contexts.
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| 29. |
- Pilkington, Georgia, et al.
(författare)
-
Electroresponsive structuring and friction of a non-halogenated ionic liquid in a polar solvent : effect of concentration
- 2020
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 22:34, s. 19162-19171
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Tidskriftsartikel (refereegranskat)abstract
- Neutron reflectivity (NR) measurements have been employed to study the interfacial structuring and composition of electroresponsive boundary layers formed by an ionic liquid (IL) lubricant at an electrified gold interface when dispersed in a polar solvent. The results reveal that both the composition and extent of the IL boundary layers intricately depend on the bulk IL concentration and the applied surface potential. At the lowest concentration (5% weight/weight), a preferential adsorption of the IL cation at the gold electrode is observed, which hinders the ability to electro-induce changes in the boundary layers. In contrast, at higher IL bulk concentrations (10 and 20% weight/weight), the NR results reveal a significantly larger concentration of the IL ions at the gold interface that exhibit significantly greater electroresponsivity, with clear changes in the layer composition and layer thickness observed for different potentials. In complementary at. force microscopy (AFM) measurements on an electrified gold surface, such IL boundary layers are demonstrated to provide excellent friction reduction and electroactive friction (known as tribotronics). In agreement with the NR results obtained, clear concentration effects are also observed Together such results provide valuable mol. insight into the electroactive structuring of ILs in solvent mixtures, as well as provide mechanistic understanding of their tribotronic behaviors.
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| 30. |
- Reddy, Akepati Bhaskar, Dr. 1990-, et al.
(författare)
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Ionic liquids enhance electrical conductivity of greases: an impedance spectroscopy study
- 2024
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Ingår i: Colloids and Surfaces A. - : Elsevier. - 0927-7757 .- 1873-4359. ; 683
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Tidskriftsartikel (refereegranskat)abstract
- Ionic liquids (ILs) have emerged as viable solutions for developing new-age lubricants, both as neat lubricants and lubricant additives. Enabled by the presence of discrete ions, ILs have the possibility to render electrically conductive lubricants, which is a feasible strategy for developing lubricant systems compatible with modern e-drive conditions. However, this requires the characterization of the electrical properties of lubricants, which is a bottleneck for developing electrically conductive greases, given their complex architecture. This work introduces an electrochemical impedance spectroscopy measurement methodology to evaluate grease samples' electrical properties. Compared to the commonly used conductivity meters, this method, through its multi-frequency alternating current (AC) impedance approach, can effectively distinguish the individual contributions of the bulk and the sample-electrode interface to the measured electrical response. Impedance spectra of grease samples are obtained using an electrochemical cell with parallel plate electrodes, mounted on a temperature-controlled cell stand and coupled with a potentiostat. The grease's bulk conductivity is extracted by fitting the impedance data to relevant equivalent electrical circuits. The bulk conductivity of lithium complex grease doped with ILs is evaluated and compared to greases with conventional conductivity additives (copper powder and conductive carbon black). The analysis of temperature-dependent conductivity reveals the rather different conductivity mechanisms for different additives. For greases doped with ILs, a comparison against the electrical conductivity of neat ILs reveals that, in addition to the ion dissociation, the interaction of the ions with the different grease components (base oil, thickener) is crucial in defining the grease conductivity.
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| 31. |
- Reddy, Akepati Bhaskar, et al.
(författare)
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Micro- To Nano- To from Surface to Bulk : Influence of Halogen-Free Ionic Liquid Architecture and Dissociation on Green Oil Lubricity
- 2021
-
Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society. - 2168-0485. ; 9:40, s. 13606-13617
-
Tidskriftsartikel (refereegranskat)abstract
- Four nonhalogenated ionic liquids (ILs) based on the same phosphonium cation are investigated in terms of the anion suitability for enhancing the lubricity of a biodegradable oil. For all test conditions, typical for industrial machine components, the lubrication is shown to be governed by nonsacrificial films formed by the physisorption of ionic species on the tribo-surfaces. The anionic structure appears to have an important role in the formation of friction modifying films. The orthoborate ILs exhibit the formation of robust ionic boundary films, resulting in reduced friction and better wear protection. On the contrary, the surface adsorption of phosphinate and phosphate ILs appears to antagonistically disrupt the intrinsic lubrication properties of the biodegradable oil, resulting in high friction and wear. Through additional investigations, it is postulated that the higher dissociation of orthoborate ILs in the biodegradable oil allows the formation of hierarchical and electrostatically overscreened layer structures with long-range order, whereas the ILs with phosphate and phosphinate anions exhibit low dissociation in biodegradable oil, possibly due to the ion pairs being surrounded by a hydrocarbon halo, which presumably results in weak adsorption to form a mixed interfacial layer with no long-range order. © 2021 The Authors.
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| 32. |
- Reddy, Akepati Bhaskar, et al.
(författare)
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Tribotronic control of an ionic boundary layer in operando extends the limits of lubrication
- 2022
-
Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 12:1
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of electric potential on the lubrication of a non-halogenated phosphonium orthoborate ionic liquid used as an additive in a biodegradable oil was studied. An in-house tribotronic system was built around an instrument designed to measure lubricant film thickness between a rolling steel ball and a rotating silica-coated glass disc. The application of an electric field between the steel ball and a set of customized counter-electrodes clearly induced changes in the thickness of the lubricant film: a marked decrease at negative potentials and an increase at positive potentials. Complementary neutron reflectivity studies demonstrated the intrinsic electroresponsivity of the adsorbate: this was performed on a gold-coated silicon block and made possible in the same lubricant system by deuterating the oil. The results indicate that the anions, acting as anchors for the adsorbed film on the steel surface, are instrumental in the formation of thick and robust lubricating ionic boundary films. The application of a high positive potential, outside the electrochemical window, resulted in an enormous boost to film thickness, implicating the formation of ionic multi-layers and demonstrating the plausibility of remote control of failing contacts in inaccessible machinery, such as offshore wind and wave power installations.
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| 33. |
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| 34. |
- Rohlmann, Patrick, et al.
(författare)
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Boundary lubricity of phosphonium bisoxalatoborate ionic liquids
- 2021
-
Ingår i: Tribology International. - : Elsevier. - 0301-679X .- 1879-2464. ; 161
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Tidskriftsartikel (refereegranskat)abstract
- The lubricating performance of trihexyl(tetradecyl)phosphonium bis-(oxalato)-orthoborate (P-BOB) ionic liquid is analysed at 80°C and 140°C, together with an ionic liquid containing partially hydrated version of the anion. The reduction of the anions produces oxalate complexes that contribute synergistically to lower friction. To confirm the role of oxalate in enhancing lubricity, two ionic liquids, at different stages of the synthesis were used. One of the batches contained precursor orthoborate anions complexed with oxalic acid and consequently showed the lowest friction at 80°C. Upon heating the precursor was converted into [BOB]- and displayed the same friction at 140°C as the fully synthesised species. The mechanisms of the breakdown of the [BOB]- anion and formation of the tribofilm are elucidated.
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| 35. |
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| 36. |
- Rohlmann, Patrick, et al.
(författare)
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Tribochemistry of imidazolium and phosphonium bis(oxalato)borate ionic liquids: Understanding the differences
- 2023
-
Ingår i: Tribology International. - : Elsevier Ltd. - 0301-679X .- 1879-2464. ; 181
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Tidskriftsartikel (refereegranskat)abstract
- Lubrication properties of imidazolium and phosphonium bis(oxalato)borate ionic liquids (ILs) are compared in a reciprocating sliding contact at 80 °C and 140 °C. Both the influence of the alkyl chain length and the cation architecture on friction, wear and lubricant breakdown are investigated. Imidazolium ILs showed lower friction than phosphonium ILs though only phosphonium-based ILs reduced wear. A longer alkyl chain reduced friction only in the case of the imidazolium-based ILs. Analysis of the wear scars was consistent with chemical breakdown solely of the anion. Chemical changes in the ILs after the tribotests were more pronounced for imidazolium-based ILs, and comparison of breakdown and tribofilm formation implicated catalysis by the imidazolium center, which, in turn, had a strong dependence on the surface self-assembly.
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| 37. |
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| 38. |
- Skedung, Lisa, et al.
(författare)
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A Curly Q : Is Frizz a Matter of Friction?
- 2021
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Ingår i: Perception. - : SAGE Publications. - 0301-0066 .- 1468-4233. ; 50:8, s. 728-732
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Tidskriftsartikel (refereegranskat)abstract
- The oft discussed and fretted over environmental influences on hair have led to a popular consensus which suggests that elevated temperature and humidity lead to frizzier, wilder hair. However, few attempts at actually quantifying these effects have been made. Although frizziness is usually perceived visually, here the influence of variations in temperature and humidity on the tactile perception and friction of curly and straight hair were investigated. It is shown that changes in humidity may disproportionately affect perceived frizziness of curly hair by touch due to concurrent changes in the tactile friction.
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| 39. |
- Skedung, Lisa, et al.
(författare)
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Feeling smooth : Psychotribological probing of molecular composition
- 2018
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Ingår i: Tribology letters. - : Springer. - 1023-8883 .- 1573-2711. ; 66:4, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to evaluate whether smooth surfaces varying in surface chemistry could be perceptually distinguished with the sense of touch. A set of ten glass surfaces was prepared which varied systematically in terms of the molecular composition of a thin coating of low topography. The contact angle, contact angle hysteresis, and surface energy were evaluated as objective physical parameters characterizing each coating. Additionally, the interaction forces between a human finger and the different coatings were quantified and compared in terms of tactile friction coefficients. The surfaces were evaluated psychophysically in terms of perceived similarities and were then ranked according to pleasantness. The participants could perceptually distinguish between surfaces varying in surface chemistry and a primary and secondary perceptual dimension were identified as sufficient to distinguish them. The primary dimension correlates with surface free energy, but both tactile friction and surface energy contribute to this dimension depending on whether the coatings are organic or inorganic. The secondary dimension could not be identified explicitly in terms of a physical quantity but is discussed in terms of recent developments in the literature. Coated glass is characterized by high friction coefficient upon interaction with a human finger as well as significant hysteresis in the stroking directions (lower applied load and higher friction in the backward stroke). Despite the complexity of the tribology, pleasantness can be clearly linked to it, where low friction (high contact angle) materials receive a higher ranking. © The Author(s) 2018.
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| 40. |
- Skedung, Lisa, et al.
(författare)
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The finishing touches : the role of friction and roughness in haptic perception of surface coatings
- 2020
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Ingår i: Experimental Brain Research. - : Springer Nature. - 0014-4819 .- 1432-1106. ; 238:6, s. 1511-1524
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Tidskriftsartikel (refereegranskat)abstract
- Humans are extraordinarily skilled in the tactile evaluation of, and differentiation between, surfaces. The chemical and mechanical properties of these surfaces are translated into tactile signals during haptic exploration by mechanoreceptors in our skin, which are specialized to respond to different types of temporal and mechanical stimulation. Describing the effects of measurable physical characteristics on the human response to tactile exploration of surfaces is of great interest to manufacturers of household materials so that the haptic experience can be considered during design, product development and quality control. In this study, methods from psychophysics and materials science are combined to advance current understanding of which physical properties affect tactile perception of a range of furniture surfaces, i.e., foils and coatings, thus creating a tactile map of the furniture product landscape. Participants' responses in a similarity scaling task were analyzed using INDSCAL from which three haptic dimensions were identified. Results show that specific roughness parameters, tactile friction and vibrational information, as characterized by a stylus profilometer, a Forceboard, and a biomimetic synthetic finger, are important for tactile differentiation and preferences of these surface treatments. The obtained dimensions are described as distinct combinations of the surface properties characterized, rather than as 'roughness' or 'friction' independently. Preferences by touch were related to the roughness, friction and thermal properties of the surfaces. The results both complement and advance current understanding of how roughness and friction relate to tactile perception of surfaces.
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| 41. |
- Sun, Kangdi, et al.
(författare)
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Insight into the assembly of lipid-hyaluronan complexes in osteoarthritic conditions
- 2023
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Ingår i: Biointerphases. - : American Institute of Physics Inc.. - 1934-8630 .- 1559-4106. ; 18:2
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Tidskriftsartikel (refereegranskat)abstract
- Interactions between molecules in the synovial fluid and the cartilage surface may play a vital role in the formation of adsorbed films that contribute to the low friction of cartilage boundary lubrication. Osteoarthritis (OA) is the most common degenerative joint disease. Previous studies have shown that in OA-diseased joints, hyaluronan (HA) not only breaks down resulting in a much lower molecular weight (MW), but also its concentration is reduced ten times. Here, we have investigated the structural changes of lipid-HA complexes as a function of HA concentration and MW to simulate the physiologically relevant conditions that exist in healthy and diseased joints. Small angle neutron scattering and dynamic light scattering were used to determine the structure of HA-lipid vesicles in bulk solution, while a combination of atomic force microscopy and quartz crystal microbalance was applied to study their assembly on a gold surface. We infer a significant influence of both MW and HA concentrations on the structure of HA-lipid complexes in bulk and assembled on a gold surface. Our results suggest that low MW HA cannot form an amorphous layer on the gold surface, which is expected to negatively impact the mechanical integrity and longevity of the boundary layer and could contribute to the increased wear of the cartilage that has been reported in joints diseased with OA. © 2023 Author(s).
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| 42. |
- Watanabe, Seiya, et al.
(författare)
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Interfacial structuring of non-halogenated imidazolium ionic liquids at charged surfaces : effect of alkyl chain length.
- 2020
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:16, s. 8450-8460
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Tidskriftsartikel (refereegranskat)abstract
- Control of the interfacial structures of ionic liquids (ILs) at charged interfaces is important to many of their applications, including in energy storage solutions, sensors and advanced lubrication technologies utilising electric fields. In the case of the latter, there is an increasing demand for the study of non-halogenated ILs, as many fluorinated anions have been found to produce corrosive and toxic halides under tribological conditions. Here, the interfacial structuring of a series of four imidazolium ILs ([CnC1Im]) of varying alkyl chain lengths (n = 5, 6, 7, 10), with a non-halogenated borate-based anion ([BOB]), have been studied at charged interfaces using sum frequency generation (SFG) spectroscopy and neutron reflectivity (NR). For all alkyl chain lengths, the SFG spectra show that the cation imidazolium ring responds to the surface charge by modifying its orientation with respect to the surface normal. In addition, the combination of SFG spectra with electrochemical NR measurements reveals that the longest alkyl chain length (n = 10) forms a bilayer structure at all charged interfaces, independent of the ring orientation. These results demonstrate the tunability of IL interfacial layers through the use of surface charge, as well as effect of the cation alkyl chain length, and provide valuable insight into the charge compensation mechanisms of ILs.
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| 43. |
- Wolff, Max, et al.
(författare)
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Grazing incidence neutron scattering for the study of solid–liquid interfaces
- 2023
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Ingår i: Encyclopedia of Solid-Liquid Interfaces. - : Elsevier. ; , s. 1-1
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Neutrons are characterized by a low absorption in many engineering materials. At the same time the scattering cross section of light elements, such as hydrogen and deuterium, may be large. These properties make neutron scattering experiments performed under grazing incidence geometry an excellent tool for the study of solid–liquid interfaces. In this review we describe the basic concepts of neutron reflection and grazing incidence scattering experiments as well as experimental procedures and sample cells. The full power of the method is exemplified on a range of science areas, including polymers, bio- and ionic liquid lubricants, electrolytes as well as bio-membranes or magnetic liquids.
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| 44. |
- Zhang, Yunxiao, et al.
(författare)
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Potential-Dependent Superlubricity of Ionic Liquids on a Graphite Surface
- 2021
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 125:7, s. 3940-3947
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Tidskriftsartikel (refereegranskat)abstract
- The lubricities of four quaternary phosphonium ionic liquids-trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate ([P6,6,6,14][(iC8)2PO2]), trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate ([P6,6,6,14][BEHP]), trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([P6,6,6,14][TFSI]), and tributylmethylphosphonium bis(trifluoromenthylsulfonyl)imide ([P4,4,4,1][TFSI])-were measured as a function of potential on highly oriented pyrolytic graphite (HOPG) by using atomic force microscopy (AFM). The shear strength and surface contact radius values fitted from JKR model indicate the AFM probe slides on an IL boundary layer rather than bare HOPG. Frictions change as the compositions of the boundary layers switch from cation enriched to anion enriched when the potential changes from negative to positive. Superlubricity, which refers to near zero increase in friction with load, is achieved for the [P6,6,6,14]+ cation at-1.0 V and the [TFSI]- anion at +1.0 V. The lubricities of ILs are mainly influenced by three factors: The alkyl chain length, chemical composition, and ion sizes.
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