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  • 1.
    Lundgren, Sarah M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Unsaturated Fatty Acids in Alkane Solution: Adsorption and Tribological Properties2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Fatty acids and blends of fatty acids are used as friction modifiers and anti-wear additives in diesel fuels. A large part of some fatty acid blends are unsaturated fatty acids. Even though fatty acids have been thoroughly investigated, the adsorption and tribological behaviour of unsaturated fatty acids are no fully understood. The aim of this thesis was to investigate the influence of fatty acid unsaturation on the adsorption from alkane solution and the tribological properties, such as friction and wear scar characterization, of such systems.

    To increase the fundamental understanding of the influence of the degree of fatty acid unsaturation the three fatty acids, oleic, linoleic and linolenic acid, have been studied. In boundary lubrication the amount of material and how well the material is bound to the surface can affect the friction and wear of the system. Thus, as a first step the adsorption of fatty acids onto steel surfaces was investigated with the quartz crystal microbalance (QCM). This technique is straight forward to used and is ideal for these samples that are difficult to investigate with optical techniques due to small differences in refractive index between the alkane solvent and fatty acid. To determine the chemical binding to steel surfaces static secondary ion mass spectroscopy (SIMS) has been used.

    Next, the influence of fatty acid unsaturation on the friction and wear was determined. Two different studies were made, one on a molecular level with the tribological surfaces forces apparatus (T-SFA) and the other one with a technique used for determining friction and wear of diesel fuel additives. The T-SFA technique provides data from which the packing of the fatty acids at mica surfaces can be estimated as well as how the friction is altered due to the packing. For determining the friction and wear of steel surfaces the high frequency reciprocating rig (HFRR) and pin on disc apparatus (POD) were used. The HFRR is a standardized technique, where, if the settings specified in the ISO12156 protocol are used, a diesel fuel additive must provide an average wear scar radius less than 0.230 mm to pass. The wear scars received from the two techniques were further analysed with Raman spectroscopy and also a visual rating of the wear scars was performed.

    As the project progressed, there was an increasing interest in the influence of water on the adsorption and lubricating properties of the fatty acids. Moisture uptake of the fatty acids was therefore determined gravimetrically as well as with nuclear magnetic resonance spectroscopy (NMR). The adsorption of the moist fatty acids onto steel surfaces was then investigated with QCM and static SIMS, while HFRR and POD were used for investigate the friction and wear.

  • 2.
    Lundgren, Sarah M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Persson, K.
    Clarke, J.
    Nordstierna, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Claesson, Per Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    The influence of water on the adsorption and the tribological properties of unsaturated fatty acids in alkane solution2011In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 225, no J10, p. 1048-1055Article in journal (Refereed)
    Abstract [en]

    The moisture uptake of the three unsaturated fatty acids, oleic acid, linoleic acid, and linolenic acid has been investigated. The amount of water absorbed by the fatty acids increased with increasing degree of unsaturation. The influence of the water on the adsorption onto steel and lubricating properties of the fatty acid in hexadecane was investigated. The adsorption, as determined with quartz crystal microbalance of 0.1 and 1 wt% of oleic acid onto steel was not affected by the presence of water (1.5 mole% water in fatty acid) while 5.6 mole% water enhanced the adsorbed amount of linolenic acid. Even though this amount of water had a large influence on the adsorption of linolenic acid, it did not affect the friction and wear measured with high frequency reciprocating rig using oleic acid or linolenic acid in hexadecane.

  • 3.
    Lundgren, Sarah M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Persson, Karin
    Clarke, Jim
    Brewer, Mark
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Friction and wear of unsaturated fatty acids in alkane solution under boundary conditions2007In: Wear, ISSN 0043-1648, E-ISSN 1873-2577Article in journal (Other academic)
  • 4.
    Lundgren, Sarah M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Persson, Karin
    Clarke, Jim
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    The influence of water on the adsorption and the wear reducing properties of unsaturated fatty acids in alkane solution2007In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711Article in journal (Other academic)
  • 5.
    Lundgren, Sarah M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Persson, Karin
    YKI, Institute for Surface Chemistry, Stockholm, Sweden.
    Kronberg, Bengt
    YKI, Institute for Surface Chemistry, Stockholm, Sweden.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Adsorption of fatty acids from alkane solution studied with quartz crystal microbalance2006In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 22, no 1, p. 15-20Article in journal (Refereed)
    Abstract [en]

    This paper describes the adsorption of the unsaturated fatty acids, oleic-, linoleic-, and linolenic acid onto steel coated quartz crystal surfaces from 2,2,4,4,6,8,8-heptamethylnonane as monitored by the quartz crystal microbalance (QCM) technique. It is shown that addition of fatty acid to the oil results in changes in bulk density and viscosity and that these changes must be considered before the sensed mass can be evaluated. The change in viscosity of the solution is larger for oleic acid than for linoleic acid and linolenic acid, which results in a larger correction for oleic acid with respect to bulk effects. After considering the effects due to changes in bulk properties, the influence of the viscoelastic properties of the adsorbed layer on the sensed mass was evaluated. The correction for the viscoelastic properties of the adsorbed layer was found to be very small for the systems studied. The sensed mass, at 1.1 weight percent, ranged from 0.5 mg/m(2) for oleic acid to 5 mg/m(2) for linolenic acid.

  • 6.
    Lundgren, Sarah M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Persson, Karin
    YKI, Institute for Surface Chemistry.
    Mueller, Gregor
    ThyssenKrupp Steel AG, Center of Materials Excellence, Surface Analysis.
    Kronberg, Bengt
    YKI, Institute for Surface Chemistry.
    Clarke, Jim
    Arizona Chemical B.V., European Technical Center.
    Chtaib, Mohammed
    Laboratories of LUXCONTROL SA.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Erratum: Unsaturated fatty acids in alkane solution: Adsorption to steel surfaces (Langmuir (2007) 23 (10598-10602))2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 17, p. 9922-9922Article in journal (Refereed)
  • 7.
    Lundgren, Sarah M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Persson, Karin
    YKI, Institute for Surface Chemistry.
    Mueller, Gregor
    ThyssenKrupp Steel AG, Center of Materials Excellence, Surface Analysis.
    Kronberg, Bengt
    YKI, Institute for Surface Chemistry.
    Clarke, Jim
    Arizona Chemical B.V., European Technical Center.
    Chtaib, Mohammed
    Laboratories of LUXCONTROL SA.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Unsaturated fatty acids in alkane solution: adsorption to steel surfaces2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 21, p. 10598-10602Article in journal (Refereed)
    Abstract [en]

    The adsorption of the unsaturated fatty acids oleic, linoleic, and linolenic acid on steel surfaces has been investigated by means of a quartz crystal microbalance (QCM). Two different solvents were used, n-hexadecane and its highly branched isomer. viz.. 2.2,4,4,6,8,8-heptamethylnonane. The area occupied per molecule of oleic acid at 1 wt % corresponds to what is needed for adsorption parallel to the surface. At the same concentration, the adsorbed amount of linoleic acid and linolenic acid indicates that they adsorb in multilayers. The chemisorbed amount estimated from static secondary ion mass spectroscopy (SIMS) measurements was found to be similar for the three unsaturated fatty acids. In the case of linolenic acid, it was found that the presence of water significantly alters the adsorption, most likely because of the precipitation of fatty acid/water aggregates. Furthermore, static SIMS results indicate that the amount of water used here inhibits the chemisorption of linolenic acid.

  • 8.
    Lundgren, Sarah M.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Ruths, M.
    Department of Chemistry, University of Massachusetts Lowell.
    Danerlöv, K.
    YKI, Institute for Surface Chemistry.
    Persson, K.
    YKI, Institute for Surface Chemistry.
    Effects of unsaturation on film structure and friction of fatty acids in a model base oil2008In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 326, no 2, p. 530-536Article in journal (Refereed)
    Abstract [en]

    The normal and friction forces between layers of three fatty acids (stearic, oleic, and linoleic acid) and a rosin acid (dehydroabietic acid) have been measured in n-hexadecane with a surface forces apparatus. Stearic, oleic, and dehydroabietic acid form loose-packed monolayers on mica surfaces when adsorbed from dry n-hexadecane. Linoleic acid forms an additional dimer layer between monolayer-covered surfaces, where it is stabilized by interactions between the double-bond-rich regions of the molecules. The monolayers formed by linoleic and dehydroabietic acid are thinner than the ones formed by stearic and oleic acid, but are not as easily removed from between the mica surfaces when the load or pressure is increased. The friction force increased linearly with load in all systems, and the friction coefficient increased with increasing unsaturation. Linoleic acid showed two regimes of linear friction with increasing load, corresponding to two different film thicknesses. its friction was sensitive to sliding speed and adsorption time, and the thinner film observed at higher load had a lower friction coefficient. Such features were not observed for stearic and oleic acid, where the monolayers were removed and the friction coefficient changed to that of pure n-hexadecane at a pressure of 3.5 MPa.

  • 9. Ruths, M.
    et al.
    Lundgren, Sarah M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Danerlöv, K.
    Persson, K.
    Friction of fatty acids in nanometer-sized contacts of different adhesive strength2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 4, p. 1509-1516Article in journal (Refereed)
    Abstract [en]

    The effects of adhesion, contact area, and pressure on the lubricating properties of self-assembled monolayers on steel have been investigated with friction force microscopy. The adsorbed molecules were fatty acids with varying degrees of unsaturation (0-2 double bonds; stearic, oleic, and linoleic acid) and a rosin acid (dehydroabietic acid), adsorbed from n-hexadecane solution. The friction of these loose-packed monolayers was studied in dry N-2 gas and in ethanol. Low adhesion (in ethanol) resulted in a linear increase in friction force at low loads, that is, F = mu L, whereas higher adhesion (in N-2 gas) gave an apparent area-dependence at low loads of the form F = S(c)A, where S-c is the critical shear stress. A recent model for the contact mechanics of a compliant elastic film confined between stiffer substrates was applied to the data obtained in dry N-2. Using this approach, we obtained interfacial energies of the compliant monolayers in good agreement with van der Waals-Lifshitz theory. With a low monolayer elastic modulus of E-1' = 0.2 GPa, we obtained a slightly higher value of S, for stearic acid than that established for more close-packed stearic acid monolayers. An increase of p and Sc was found with increasing degree of unsaturation of the fatty acid.

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