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Gebbie MA, Smith AM, Dobbs HA, Lee AA, Warr GG, Banquy X, Valtiner M, Rutland MW, Israelachvili JN, Perkin S, Atkin R. Long range electrostatic forces in ionic liquids. Chem Commun (Camb) 2017; 53:1214-1224. [DOI: 10.1039/c6cc08820a] [Citation(s) in RCA: 231] [Impact Index Per Article: 33.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Experimental evidence for long range surface forces in ionic liquids is collated and examined, key outstanding questions are identified, and possible mechanisms underpinning these long range forces are explored.
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Besharat Z, Wakeham D, Johnson CM, Luengo GS, Greaves A, Odnevall Wallinder I, Göthelid M, Rutland MW. Mixed monolayers of alkane thiols with polar terminal group on gold: Investigation of structure dependent surface properties. J Colloid Interface Sci 2016; 484:279-290. [DOI: 10.1016/j.jcis.2016.08.053] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Revised: 08/19/2016] [Accepted: 08/19/2016] [Indexed: 10/21/2022]
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Nyström L, Álvarez-Asencio R, Frenning G, Saunders BR, Rutland MW, Malmsten M. Electrostatic Swelling Transitions in Surface-Bound Microgels. ACS APPLIED MATERIALS & INTERFACES 2016; 8:27129-27139. [PMID: 27644921 DOI: 10.1021/acsami.6b09751] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Herein, electrostatic swelling transitions of poly(ethyl acrylate-co-methacrylic acid) microgels covalently bound to silica surfaces are investigated. Confined at a solid surface, microgel swelling is anisotropically hindered and the structure is flattened to an extent dictated by pH and microgel composition. Microgel deformation under applied load is also shown to depend on microgel charge density, with the highest deformation observed at intermediate charge densities. Two modes of microgel deformation under load were observed, one elastic and one viscoelastic, related to polymer strand deformation and displacement of trapped water, respectively. Results on polymer strand dynamics reveal that the microgels are highly dynamic, as the number of strand-tip interaction points increases 4-fold during a 10 s contact time. Furthermore, finite element modeling captures these effects qualitatively and shows that stress propagation in the microgel network decays locally at the rim of contact with a solid interface or close to the tip probe. Taken together, the results demonstrate a delicate interplay between the surface and microgel which determines the structure and nanomechanical properties of the latter and needs to be controlled in applications of systems such as pH-responsive surface coatings in biomaterials.
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Hjalmarsson N, Atkin R, Rutland MW. Is the boundary layer of an ionic liquid equally lubricating at higher temperature? Phys Chem Chem Phys 2016; 18:9232-9. [PMID: 26976694 DOI: 10.1039/c5cp05837f] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Atomic force microscopy has been used to study the effect of temperature on normal forces and friction for the room temperature ionic liquid (IL) ethylammonium nitrate (EAN), confined between mica and a silica colloid probe at 25 °C, 50 °C, and 80 °C. Force curves revealed a strong fluid dynamic influence at room temperature, which was greatly reduced at elevated temperatures due to the reduced liquid viscosity. A fluid dynamic analysis reveals that bulk viscosity is manifested at large separation but that EAN displays a nonzero slip, indicating a region of different viscosity near the surface. At high temperatures, the reduction in fluid dynamic force reveals step-like force curves, similar to those found at room temperature using much lower scan rates. The ionic liquid boundary layer remains adsorbed to the solid surface even at high temperature, which provides a mechanism for lubrication when fluid dynamic lubrication is strongly reduced. The friction data reveals a decrease in absolute friction force with increasing temperature, which is associated with increased thermal motion and reduced viscosity of the near surface layers but, consistent with the normal force data, boundary layer lubrication was unaffected. The implications for ILs as lubricants are discussed in terms of the behaviour of this well characterised system.
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Ploss MA, Rutland MW, Glavatskih S. Influence of electric potential on the apparent viscosity of an ionic liquid: facts and artifacts. Phys Chem Chem Phys 2016; 18:26609-26615. [PMID: 27711405 DOI: 10.1039/c6cp02846b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
According to recent findings, the steady shear viscosity of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][Tf2N]) decreases significantly under the influence of electric potential. This implies a causal connection between nanoscale ordering at the electrified interface and a macroscopic change of transport properties. To study this phenomenon in more detail, we reproduced the above-mentioned measurements; however, we find no evidence that the viscosity of [Emim][Tf2N] is a function of electric potential. Additionally, our results show that steady shear measurements can lead to artifacts that, at first glance, may appear to be potential-induced changes in viscosity. We demonstrate that the artifacts result from a sliding electrical contact at the working electrode of the electrochemical cell and we suggest to consider our findings for future viscosity measurements of ionic liquids.
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Benselfelt T, Cranston ED, Ondaral S, Johansson E, Brumer H, Rutland MW, Wågberg L. Adsorption of Xyloglucan onto Cellulose Surfaces of Different Morphologies: An Entropy-Driven Process. Biomacromolecules 2016; 17:2801-11. [DOI: 10.1021/acs.biomac.6b00561] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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32
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Nyström L, Nordström R, Bramhill J, Saunders BR, Álvarez-Asencio R, Rutland MW, Malmsten M. Factors Affecting Peptide Interactions with Surface-Bound Microgels. Biomacromolecules 2016; 17:669-78. [DOI: 10.1021/acs.biomac.5b01616] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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33
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Li H, Somers AE, Howlett PC, Rutland MW, Forsyth M, Atkin R. Addition of low concentrations of an ionic liquid to a base oil reduces friction over multiple length scales: a combined nano- and macrotribology investigation. Phys Chem Chem Phys 2016; 18:6541-7. [DOI: 10.1039/c5cp07061a] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
The efficacy of ionic liquids (ILs) as lubricant additives to a model base oil has been probed at the nanoscale and macroscale as a function of IL concentration using the same materials.
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Hjalmarsson N, Wallinder D, Glavatskih S, Atkin R, Aastrup T, Rutland MW. Weighing the surface charge of an ionic liquid. NANOSCALE 2015; 7:16039-16045. [PMID: 26370450 DOI: 10.1039/c5nr03965g] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Electrochemical quartz crystal microbalance has been used to measure changes in the composition of the capacitive electrical double layer for 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate, an ionic liquid, in contact with a gold electrode surface as a function of potential. The mass difference between the cation and anion means that the technique can effectively "weigh" the surface charge accurately with high temporal resolution. This reveals quantitatively how changing the potential alters the ratio of cations and anions associated with the electrode surface, and thus the charge per unit area, as well as the kinetics associated with these interfacial processes. The measurements reveal that it is diffusion of co-ions into the interfacial region rather than expulsion of counterions that controls the relaxation. The measured potential dependent double layer capacitance experimentally validates recent theoretical predictions for counterion overscreening (low potentials) and crowding (high potentials) at electrode surfaces. This new capacity to quantitatively measure ion composition is critical for ionic liquid applications ranging from batteries, capacitors and electrodeposition through to boundary layer structure in tribology, and more broadly provides new insight into interfacial processes in concentrated electrolyte solutions.
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Álvarez-Asencio R, Wallqvist V, Kjellin M, Rutland MW, Camacho A, Nordgren N, Luengo GS. Nanomechanical properties of human skin and introduction of a novel hair indenter. J Mech Behav Biomed Mater 2015; 54:185-93. [PMID: 26469630 DOI: 10.1016/j.jmbbm.2015.09.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2015] [Revised: 09/01/2015] [Accepted: 09/14/2015] [Indexed: 11/18/2022]
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 0.4GPa. Force indentation measurements showed permanent deformation of the skin surface only at high applied loads (above 4µN). 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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Wang YL, Sarman S, Glavatskih S, Antzutkin ON, Rutland MW, Laaksonen A. Atomistic Insight into Tetraalkylphosphonium-Bis(oxalato)borate Ionic Liquid/Water Mixtures. I. Local Microscopic Structure. J Phys Chem B 2015; 119:5251-64. [DOI: 10.1021/acs.jpcb.5b00667] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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37
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Li H, Cooper PK, Somers AE, Rutland MW, Howlett PC, Forsyth M, Atkin R. Ionic Liquid Adsorption and Nanotribology at the Silica-Oil Interface: Hundred-Fold Dilution in Oil Lubricates as Effectively as the Pure Ionic Liquid. J Phys Chem Lett 2014; 5:4095-4099. [PMID: 26278938 DOI: 10.1021/jz5021422] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The remarkable physical properties of ionic liquids (ILs) make them potentially excellent lubricants. One of the challenges for using ILs as lubricants is their high cost. In this article, atomic force microscopy (AFM) nanotribology measurements reveal that a 1 mol % solution of IL dissolved in an oil lubricates the silica surface as effectively as the pure IL. The adsorption isotherm shows that the IL surface excess need only be approximately half of the saturation value to prevent surface contact and effectively lubricate the sliding surfaces. Using ILs in this way makes them viable for large-scale applications.
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Sweeney J, Webber GB, Rutland MW, Atkin R. Effect of ion structure on nanoscale friction in protic ionic liquids. Phys Chem Chem Phys 2014; 16:16651-8. [DOI: 10.1039/c4cp02320j] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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39
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Ghalgaoui A, Shimizu R, Hosseinpour S, Alvarez-Asencio R, McKee C, Johnson CM, Rutland MW. Monolayer study by VSFS: in situ response to compression and shear in a contact. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:3075-3085. [PMID: 24547702 DOI: 10.1021/la4042474] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Self-assembled octadecyltrichlorosilane ((OTS), CH3(CH2)17SiCl3) layers on hydroxyl-terminated silicon oxide (SiO2) were prepared. The monolayers were characterized with atomic force microscopy (AFM) and contact angle measurements; their conformation was studied before, during, and after contact with a polymer (either PDMS or PTFE) surface using the vibrational sum frequency spectroscopy (VSFS) technique. During contact, the effect of pressure was studied for both polymer surfaces, but in the case of PTFE, the effect of shear rate on the contact was simultaneously studied. The VSFS response of the monolayers with pressure was almost entirely due to changes in the real area of contact with the polymer and therefore the Fresnel factors, whereas sliding caused disorder in the previously all-trans monolayer, as evidenced by a significant increase in the population of gauche defects.
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Li H, Wood RJ, Rutland MW, Atkin R. An ionic liquid lubricant enables superlubricity to be “switched on” in situ using an electrical potential. Chem Commun (Camb) 2014; 50:4368-70. [DOI: 10.1039/c4cc00979g] [Citation(s) in RCA: 133] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
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41
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Liljeblad JFD, Tyrode E, Thormann E, Dublanchet AC, Luengo G, Magnus Johnson C, Rutland MW. Self-assembly of long chain fatty acids: effect of a methyl branch. Phys Chem Chem Phys 2014; 16:17869-82. [DOI: 10.1039/c4cp00512k] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The morphology and molecular conformation of monolayers of straight chain and methyl-branched fatty acids have been investigated by VSFS and AFM, revealing domains in the latter case, due to inverse micellar packing constraints.
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Álvarez-Asencio R, Thormann E, Rutland MW. Note: Determination of torsional spring constant of atomic force microscopy cantilevers: combining normal spring constant and classical beam theory. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2013; 84:096102. [PMID: 24089877 DOI: 10.1063/1.4820345] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
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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Mizuno H, Luengo GS, Rutland MW. New insight on the friction of natural fibers. Effect of sliding angle and anisotropic surface topography. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:5857-5862. [PMID: 23565816 DOI: 10.1021/la400468f] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The friction anisotropy of human hair has been investigated as a function of angle using AFM fiber probe measurements to evaluate the role of cuticle alignment. It is found that friction hysteresis, the difference in friction coefficients between sliding with or against the cuticle direction, is essentially nonexistent for native human hair. For damaged human hair, however, a clear friction hysteresis is observed, which appears to be a periodic function of the angle between the fibers. The implication is that antiparallel sliding is not in itself sufficient for friction isotropy but that lifting of the cuticle edges is required. A methodology to perform friction analysis independently for trace and retrace was therefore developed, which is applicable to any type of AFM lateral force measurement. It explicitly accounts for roll, noncircular cross section, and off-axis alignment as well as baseline drift, which allows real anisotropy in the friction coefficient to be deconvoluted from these artifacts.
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Nordgren N, Carlsson L, Blomberg H, Carlmark A, Malmström E, Rutland MW. Nanobiocomposite Adhesion: Role of Graft Length and Temperature in a Hybrid Biomimetic Approach. Biomacromolecules 2013; 14:1003-9. [DOI: 10.1021/bm301790b] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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45
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Li H, Rutland MW, Atkin R. Ionic liquid lubrication: influence of ion structure, surface potential and sliding velocity. Phys Chem Chem Phys 2013; 15:14616-23. [DOI: 10.1039/c3cp52638k] [Citation(s) in RCA: 126] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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46
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Elbourne A, Sweeney J, Webber GB, Wanless EJ, Warr GG, Rutland MW, Atkin R. Adsorbed and near-surface structure of ionic liquids determines nanoscale friction. Chem Commun (Camb) 2013; 49:6797-9. [DOI: 10.1039/c3cc42844c] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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47
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Skedung L, Arvidsson M, Chung JY, Stafford CM, Berglund B, Rutland MW. Feeling small: exploring the tactile perception limits. Sci Rep 2013; 3:2617. [PMID: 24030568 PMCID: PMC3771396 DOI: 10.1038/srep02617] [Citation(s) in RCA: 95] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Accepted: 08/22/2013] [Indexed: 11/25/2022] Open
Abstract
The human finger is exquisitely sensitive in perceiving different materials, but the question remains as to what length scales are capable of being distinguished in active touch. We combine material science with psychophysics to manufacture and haptically explore a series of topographically patterned surfaces of controlled wavelength, but identical chemistry. Strain-induced surface wrinkling and subsequent templating produced 16 surfaces with wrinkle wavelengths ranging from 300 nm to 90 μm and amplitudes between 7 nm and 4.5 μm. Perceived similarities of these surfaces (and two blanks) were pairwise scaled by participants, and interdistances among all stimuli were determined by individual differences scaling (INDSCAL). The tactile space thus generated and its two perceptual dimensions were directly linked to surface physical properties - the finger friction coefficient and the wrinkle wavelength. Finally, the lowest amplitude of the wrinkles so distinguished was approximately 10 nm, demonstrating that human tactile discrimination extends to the nanoscale.
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Sweeney J, Hausen F, Hayes R, Webber GB, Endres F, Rutland MW, Bennewitz R, Atkin R. Control of nanoscale friction on gold in an ionic liquid by a potential-dependent ionic lubricant layer. PHYSICAL REVIEW LETTERS 2012; 109:155502. [PMID: 23102330 DOI: 10.1103/physrevlett.109.155502] [Citation(s) in RCA: 119] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Indexed: 06/01/2023]
Abstract
The lubricating properties of an ionic liquid on gold surfaces can be controlled through application of an electric potential to the sliding contact. A nanotribology approach has been used to study the frictional behavior of 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py(1,4)]FAP) confined between silica colloid probes or sharp silica tips and a Au(111) substrate using atomic force microscopy. Friction forces vary with potential because the composition of a confined ion layer between the two surfaces changes from cation-enriched (at negative potentials) to anion-enriched (at positive potentials). This offers a new approach to tuning frictional forces reversibly at the molecular level without changing the substrates, employing a self-replenishing boundary lubricant of low vapor pressure.
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Thormann E, Mizuno H, Jansson K, Hedin N, Fernández MS, Arias JL, Rutland MW, Pai RK, Bergström L. Embedded proteins and sacrificial bonds provide the strong adhesive properties of gastroliths. NANOSCALE 2012; 4:3910-3916. [PMID: 22653376 DOI: 10.1039/c2nr30536d] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The adhesive properties of gastroliths from a freshwater crayfish (Cherax quadricarinatus) were quantified by colloidal probe atomic force microscopy (AFM) between heavily demineralized gastrolith microparticles and gastrolith substrates of different composition. Combined AFM and transmission electron microscopy studies demonstrated that the sequential detachment and large adhesion energies that characterise the adhesive behaviour of a native gastrolith substrate are dominated by sacrificial bonds between chitin fibres and between chitin fibres and CaCO(3). The sacrificial bonds were shown to be strongly related to the gastrolith proteins and when the majority of these proteins were removed by ethylenediaminetetraacetic acid (EDTA), the sequential detachment disappeared and the adhesive energy was reduced by more than two orders of magnitude.
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Asencio RÁ, Cranston ED, Atkin R, Rutland MW. Ionic liquid nanotribology: stiction suppression and surface induced shear thinning. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012; 28:9967-9976. [PMID: 22676253 DOI: 10.1021/la3010807] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The friction and adhesion between pairs of materials (silica, alumina, and polytetrafluoroethylene) have been studied and interpreted in terms of the long-ranged interactions present. In ambient laboratory air, the interactions are dominated by van der Waals attraction and strong adhesion leading to significant frictional forces. In the presence of the ionic liquid (IL) ethylammonium nitrate (EAN) the van der Waals interaction is suppressed and the attractive/adhesive interactions which lead to "stiction" are removed, resulting in an at least a 10-fold reduction in the friction force at large applied loads. The friction coefficient for each system was determined; coefficients obtained in air were significantly larger than those obtained in the presence of EAN (which ranged between 0.1 and 0.25), and variation in the friction coefficients between systems was correlated with changes in surface roughness. As the viscosity of ILs can be relatively high, which has implications for the lubricating properties, the hydrodynamic forces between the surfaces have therefore also been studied. The linear increase in repulsive force with speed, expected from hydrodynamic interactions, is clearly observed, and these forces further inhibit the potential for stiction. Remarkably, the viscosity extracted from the data is dramatically reduced compared to the bulk value, indicative of a surface ordering effect which significantly reduces viscous losses.
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