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- Deep Eutectic Solvents (DES) based on sulphur for silicon surfaces as alternative lubricantsPublication . Antunes, Mónica; Martins, Anne-Sophie; Freire, Mariana de Sá; Caetano, Fernando J. P.; Diogo, Herminio; Colaco, Rogério; Branco, Luís C.; Saramago, BenildeDeep eutectic mixtures composed of hydrogen-bond donors and hydrogen-bond acceptors, the so-called DESs, have recently being proposed as possible “green” alternatives to mineral oils and ionic liquids (ILs) in the lubrication of steel surfaces. DESs have similar physical properties to ILs but have the advantage of being cheaper and easier to prepare. In this work, new DESs containing sulphur units in their structure were prepared and tested in the lubrication of silicon surfaces which are relevant for nano/microelectromechanical systems (NEMS/MEMS). The following new DESs were prepared: dibutil-ethyl sulfonium ethylsulfate: polyethylene glycol ([S4,4,2][EtSO4]:PEG), ethyl-tetrahydrothiophenium ethylsulfate: polyethylene glycol ([C2-THT][EtSO4]:PEG, cis-1-ethyl-3methylimidazolium canforsulfonate: polyethylene glycol ([C2MIM][(S)-CSA]:PEG), and 1,3-dimethylpiridinium methyl sulfate: polyethylene glycol ([C1-3-pic][MeSO4]:PEG). Other DES, already known, were tested for comparison purposes: tetrabutylammonium bromide: tetrahydrothiophene 1,1-dioxide ([N4,4,4,4][Br]:Sulfolane), choline chloride: polyethylene glycol (ChCl:PEG), and tetrabutylammonium bromide: polyethylene glycol ([N4,4,4,4][Br]:PEG). All DESs were characterized in terms of their water content, viscosity, wettability, and tribological properties. The friction coefficients were measured in a nanotribometer using steel spheres against Si surfaces. The new DES prepared from ILs based on the sulfur-containing anions showed good tribological performance, but the best results were obtained with [C2MIM][(S)-CSA]:PEG and [C1-3-pic][MeSO4]:PEG which reduced the friction coefficients to values < 0.1, typical of excellent lubrication conditions.
- Improving the lubrication of silicon surfaces using ionic liquids as oil additives: the effect of sulfur-based functional groupsPublication . Antunes, Mónica; Donato, Mariana T.; Paz, Victória; Caetano, Fernando J. P.; Santos, Luís; Colaco, Rogério; Branco, Luís C.; Saramago, BenildeThe performance of micro/nanoelectromechanical systems (MEMS/NEMS) relies on efficient lubrication. In the present work, new sulfur-based organic salts were tested as additives in a polyethylene glycol to lubricate silicon surfaces used in the manufacture of MEMS/NEMS. Seven salts were tested: 1-butylsulfonic-3-methylimidazolium triflate [(C4SO3H)MIM][TfO], thiamine triflate [Thiamine][TfO]2, 1-ethyl-3-methylimidazolium camphorsulfonate [C2MIM][CSA] [isomers (R) and (S)], 1,3-dimethylpiridinium methylsulfate [C1-3pic][MeSO4], methylimidazolium methanesulfonate [HMIM][MeSO3], and tetramethylguanidine methanesulfonate [TMG][MeSO3]. A nanotribometer was used to determine the friction coefficients using steel spheres as counter bodies. Excellent tribological properties were achieved with the additives containing the anions [MeSO4]− and [MeSO3]−. The films formed on the Si substrates were studied by FTIR, ellipsometry and AFM. A mixed lubrication mechanism was proposed where additive adsorption avoids contact between sliding surfaces.
- Deep eutectic solvents (DES) based on sulfur as alternative lubricants for silicon surfacesPublication . Antunes, Mónica; Campinhas, Anne-Sophie; Freire, Mariana de Sá; Caetano, Fernando J. P.; Diogo, Herminio; Colaço, Rogério; Branco, Luís C.; Saramago, BenildeDeep eutectic mixtures composed of hydrogen-bond donors (HBDs) and hydrogen-bond acceptors (HBAs), the so-called DESs, have recently being proposed as possible “green” alternatives to mineral oils and ionic liquids (ILs) in the lubrication of steel surfaces. DESs have similar physical properties to ILs but have the advantage of being cheaper and easier to prepare. In this work, new DESs containing sulfur units in their composition were prepared and tested in the lubrication of silicon surfaces which are relevant for nano/microelectromechanical systems (NEMS/MEMS). The following new DESs were prepared: ethyldibutyl sulfonium ethylsulfate: polyethylene glycol ([S4,4,2][EtSO4]:PEG), 1-ethyl-tetrahydrothiophenium ethylsulfate: polyethylene glycol ([C2-THT][EtSO4]:PEG), 1-ethyl-3-methylimidazolium (S)-camphorsulfonate: polyethylene glycol ([C2MIM][(S)CSA]:PEG), and 1-methyl-3-picolinium methyl sulfate: polyethylene glycol ([C1-3-pic][MeSO4]:PEG). Other DES, already reported, were tested for comparison purposes: tetrabutylammonium bromide: sulfolane ([N4,4,4,4][Br]:Sulf), choline chloride: polyethylene glycol (ChCl:PEG), and tetrabutylammonium bromide: polyethylene glycol ([N4,4,4,4][Br]:PEG). All DESs were characterized in terms of their water content, viscosity, wettability, and tribological properties. The friction coefficients were measured in a nanotribometer using steel spheres against Si surfaces. The new DES prepared from salts based on the sulfur-containing anions showed good tribological performance, but the best results were obtained with [C2MIM][(S)-CSA]:PEG and [C1-3-pic][MeSO4]:PEG which reduced the friction coefficients to values <0.1, typical of excellent lubrication conditions.
- Picolinium‐based hydrophobic ionic liquids as additives to PEG200 to lubricate steel‐silicon contactsPublication . Donato, Mariana T.; Caetano, Fernando J. P.; Colaco, Rogério; Branco, Luís C.; Saramago, BenildeNew ionic liquids (ILs) based on picolinium, [C6-x-pic][TfO] where x=2, 3 and 4, were successfully synthesized using microwave process. The performance of these ILs as additives to model lubricant oil PEG200 was evaluated and compared with that of other ILs sharing the same hydrophobic anion, using the tribological pair steel sphere/Si surface. [C6-4-pic][TfO] was the most efficient additive, which may be attributed to the symmetry of the cation leading to an ordered adsorbed layer.