Friction of fatty acids in nanometer-sized contacts of different adhesive strength
2008 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 4, 1509-1516 p.Article in journal (Refereed) Published
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.
Place, publisher, year, edition, pages
2008. Vol. 24, no 4, 1509-1516 p.
SELF-ASSEMBLED MONOLAYERS, INTERFACIAL SHEAR-STRENGTH, LATERAL FORCE MICROSCOPY, LANGMUIR-BLODGETT-FILMS, BOUNDARY LUBRICATION, TRIBOLOGICAL PROPERTIES, MOLECULAR-DYNAMICS, ORGANIC MONOLAYERS, SLIDING FRICTION, ALKANE SOLUTION
IdentifiersURN: urn:nbn:se:kth:diva-34110DOI: 10.1021/la7023633ISI: 000253130900048ScopusID: 2-s2.0-40449083945OAI: oai:DiVA.org:kth-34110DiVA: diva2:419107
QC 201105252011-05-252011-05-252011-05-25Bibliographically approved