Antiwear performance of ionic liquid+graphene dispersions with anomalous viscosity-temperature behavior

New dispersions of few-layers graphene (G) in 1-ethyl-3-methylimidazolium ([EMIM]) ionic liquids (ILs) with dicyanamide ([DCA]) or bis(trifluoromethylsulfonyl)imide ([TFSI]) anions have been obtained by mechanical mixing and sonication. IL+0.5 wt% G dispersions show constant viscosity values from 357K (for IL = [EMIM][DCA]) or from 385K (for IL = [EMIM][TFSI]) to 393K. IL + G dispersions with G > 0.5 wt% show linear viscosity increases with increasing temperature, from 306K (for [EMIM][DCA]+1 wt%G) and from 330K to 393K (for [EMIM][TFSI]+0.75 wt%G and [EMIM][TFSI]+1 wt%G). Addition of graphene improves the poor wear reducing performance of [EMIM][DCA], and prevents surface damage on steel when added to [EMIM][TFSI]. Graphene increases the load-carrying ability of ILs, forms a surface layer on the sliding path and retains wear debris, preventing the formation of large abrasive particles.Ministerio de Economía, Industria y Competitividad (MINECO, Spain), EU FEDER Program (Grant # MAT2017-85130-P) Este trabajo es resultado de la actividad desarrollada en el marco del Programa de Ayudas a Grupos de Excelencia de la Región de Murcia, de la Fundación Séneca, Agencia de Ciencia y Tecnología de la Región de Murcia (Grant # 19877/GERM/15) M.D. Avilés ha recibido una beca del MINECO (BES-2015-074836)

Synthesis and exploration of the lubricating behavior of nanoparticulated Mo15S19 in linseed oil

Producción CientíficaMolybdenum chalcogenides present interesting properties beyond their superconducting critical temperatures and upper critical magnetic fields, making them suitable for potential applications in tribology, batteries, catalysis, or thermopower. In this study, Mo15S19 nanoparticles with an average diameter of 10 nm were synthesized via the reaction of ammonium molybdate with hydrochloric acid and elemental sulfur as reducers at 245 °C. The oxidation to MoO3 in air was efficiently avoided by using linseed oil as a reaction medium and dispersant. Scanning electron microscopy (SEM) micrographs of the as-prepared samples revealed the presence of few-micron-size aggregates, while transmission electron microscopy (TEM) characterization evidenced that the samples were polynanocrystalline with a high degree of homogeneity in size (standard deviation of 2.7 nm). The absence of the first-order (00l) reflection in the X-ray diffraction pattern was also indicative of the absence of Mo3S4 stacking, suggesting that it was a non-layered material. A dispersion of the nanoparticles in linseed oil has been studied as a lubricant of steel–steel sliding contacts, showing the formation of a surface layer that reduces wear and mean friction coefficients with respect to the base oil.QREN-Mais Centro (project ICT-2009-02-012-1980

Synthesis and Characterization of New Layered Double Hydroxide-Polyolefin Film Nanocomposites with Special Optical Properties

In this study, we have synthesized new double layered hydroxides to be incorporated to low density polyethylene thermoplastic matrix. These new composites present promising applications as materials to build greenhouses due to the enhancement of their optical properties. A characterization of the modified nanoclay has been performed by means of X-ray fluorescence (XRF), X-ray Diffraction (XRD), Thermogravimetric analysis (TGA), and Fourier-transform infrared spectroscopy (FTIR). We have prepared a series of polyolefin-based films to evaluate the effect of the addition of a whitening agent (disodium 2,20 -((1,10 -biphenyl)-4,40 -diyldivinylene)bis(benzenesulfonate)), the modified hydrotalcite-like material and a commercial dispersant. The rheological and mechanical characterization of the films have proved that the inclusion of the modified-layered double hydroxides (LDHs) do not substantially affect the processing and mechanical performance of the material. On the other hand, optical properties of the nanocomposites are improved by reducing the transmission in the UVA region.This research was funded by CETEC (Project 5865/19IMMF-C) and “Este trabajo es resultado de la actividad desarrollada en el marco del Programa de Ayudas a Grupos de Excelencia de la Región de Murcia, de la Fundación Séneca, Agencia de Ciencia y Tecnología de la Región de Murcia (grant #19877/GERM/15)”. Authors thank Carlos Gracia from TA Instruments for technical support

Effect of temperature on geopolymer and Portland cement composites modified with Micro-encapsulated Phase Change materials

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Protic ammonium bio-based ionic liquid crystal lubricants

Bis(2-hydroxyethyl) ammonium stearate (DES) protic ionic liquid crystal (PILC) has been added in 1 wt% and 2 wt% proportion to di-bis(2-hydroxyethyl) ammonium succinate (DSU) protic ionic liquid (PIL) to obtain (DSU+1%DES) and (DSU+2%DES) lubricant blends. The new blends are non-Newtonian fluids with liquid crystalline domains. Addition of (DES) PILC to (DSU) PIL reduces running-in friction coefficient in more than 70% and prevents surface damage, decreasing wear rate in more than one order of magnitude. Optical profilometry, optical and scanning electron microscopy (SEM), energy dispersive (EDX) and X-ray photoelectron spectroscopy (XPS) have been used to analyze surfaces after the tribological tests.This research was funded by Spanish Ministerio de Ciencia e Innovación, Agencia Estatal de Investigación (AEI) , and the European Union FEDER Program (Grant # MAT2017–85130-P ). “Este trabajo es resultado de la actividad desarrollada en el marco del Programa de Ayudas a Grupos de Excelencia de la Región de Murcia, de la Fundación Seneca, Agencia de Ciencia y Tecnología de la Región de Murcia (Grant # 19877/GERM/15 )”

Rheological study of new dispersions of Carbon Nanotubes in the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide

Dispersions of three different types of carbon nanotubes in a 1 wt.% proportion in the low viscosity 1-ethyl-3-methylimidazolium ([EMIM][DCA]) ionic liquid have been obtained. The neat ionic liquid presents Newtonian behavior, but the addition of carbon nanotubes increases the viscosity with respect to [EMIM][DCA] in the following order: Single-Walled Carbon Nanotubes (SWCNTs) > aligned Multi-Walled Carbon Nanotubes (aligned-MWCNTs) > Multi-Walled Carbon Nanotubes (MWCNTs), and the resulting fluids show non-Newtonian behavior. SWCNTs and MWCNTs dispersions present shear thinning with increasing shear rate, but a shear thickening effect for aligned-MWCNTs at intermediate shear rate values at room temperature has been observed. This effect disappears at 100 ºC. The thermal response of the viscosity of [EMIM][DCA] and the CNTs-IL dispersions can be fitted to the Arrhenius model. For[EMIM][DCA] and the dispersion with MWCNTs the viscous behavior prevails at low frequencies, with a cross point at a critical frequency value which decreases with increasing temperature. However, the dispersions of SWCNTs and aligned-MWCNTspresent storage modulus values higher than loss modulus in the whole range of frequency.The authors acknowledge the Ministerio de Economía, Industria y Competitividad (MINECO, Spain), the EU FEDER Program (Grants # MAT2014-55384-P and # MAT2017-85130-P), and Fundación Séneca - Agencia de Ciencia y Tecnología de la Región de Murcia “Ayuda a las Unidades y Grupos de Excelencia Científica de la Región de Murcia (Programa Séneca 2014)” (Grant # 19877/GERM/14), for financial support. M.D. Avilés acknowledges a research fellowship (Grant # BES-2015-074836) to MINECO

Physicochemical characterisation of graphene-ammonium lactate ionic liquid nanofluid.

A new series of nanofluids based on graphene dispersed in 2-hydroxyethylammonium lactate (ML) ionic liquid was developed. Concentrations of 0.1, 0.5 and 1 wt% of graphene were studied and these dispersions were stable after 2 months. Raman spectra showed a strong interaction between ML and graphene. The effect of the concentration of graphene and temperature on the viscoelastic behaviour and conductivity of the nanofluids was studied. An unexpected decrease in the viscosity was found with a low concentration of graphene due to the suppression of hydrogen bonding of the ionic liquid. Shear thinning effects appeared with higher concentrations of graphene and Ostwald and Herschel-Bulkley equations were used to describe the steady-state viscosity results. Creep-recovery tests were also performed, and the data were fitted to a complex Burgers model for the nanofluid with 1 wt% of graphene, with a 47 % of elastic response. The complexity of the model was related to the presence of different molecular arrangements in the nanofluid. An enhancement of the conductivity was observed with increasing values of the graphene concentration. The effect of temperature on viscosity and electrical conductivity was successfully modelled by using both Vogel-Fulcher-Tammann and Power Law equations. Electrochemical characterisation at room temperature was also carried out, finding an irreversible oxidation at 1 V only for the highest concentration (1 wt%). The concentration of percolation was estimated in the range of 0.5 to 1 wt% of graphene.The authors acknowledge the financial support of Ministerio de Economía y Competitividad and Agencia Estatal de Investigación (MINECO and AEI, Spain), EU-FEDER (MAT2017-85130-P, and PID2021-122169NB) and the Fundación Seneca, Agencia de Ciencia y Tecnología de la Región de Murcia (‘Ayuda a las Unidades y Grupos de Excelencia Científica de la Región de Murcia’; Grant # 19877/GERM/15). P.M. M.-R. is grateful to Fundación Séneca for FPI research grant (21574/FPI/21)

The effect of microencapsulated phase change materials on the rheology of geopolymer and Portland cement mortars

The effect of microencapsulated phase‐change materials (MPCM) on the rheological properties of pre‐set geopolymer and Portland cement mortars was examined. Microcapsules with hydrophilic and hydrophobic shells were compared. The shear rate dependency of the viscosities fitted well to a double Carreau model. The zero shear viscosities are higher for geopolymer mortar, illustrating poorer workability. The time evolution of the viscosities was explored at shear rates of 1 and 10 s−1. New empirical equations were developed to quantify the time‐dependent viscosity changes. The highest shear rate disrupted the buildup of the mortar structures much more than the lower shear rate. Microcapsules with a hydrophobic shell affect the rheological properties much less than the microcapsules with a hydrophilic shell, due to the higher water adsorption onto the hydrophilic microcapsules. Shear forces was found to break down the initial structures within geopolymer mortars more easily than for Portland cement mortars, while the geopolymer reaction products are able to withstand shear forces better than Portland cement hydration products. Initially, the viscosity of geopolymer mortars increases relatively slowly during due to formation of geopolymer precursors; at longer times, there is a steeper viscosity rise caused by the development of a 3D‐geopolymer network. Disruption of agglomerates causes the viscosities of portland cement mortars to decrease during the first few minutes, after which the hydration process (increasing viscosities) competes with shear‐induced disruption of the structures (decreasing viscosities), resulting in a complex viscosity behavior.publishedVersio

Effect of freeze-thaw cycles on the mechanical behavior of geopolymer concrete and Portland cement concrete containing micro-encapsulated phase change materials

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