| AVS 54th International Symposium | |
| Tribology | Thursday Sessions |
| Session TR2+BI+NS+MN-ThM |
| Session: | Biolubrication, Sensing and Adhesion |
| Presenter: | G. Oncins, University of Barcelona, Spain |
| Authors: | G. Oncins, University of Barcelona, Spain J. Torrent-Burgues, Universitat Politecnica de Catalunya, Spain F. Sanz, Universitat de Barcelona and Center of Nanobioengineering of Catalonia (IBEC), Spain |
| Correspondent: | Click to Email |
Scanning Probe Microscopies development has given biophysics the possibility to deal with the interactions arisen in biological membranes from a nanomentric point of view, revealing that van der Waals, hydrogen bonding and electrostatic interactions play a crucial role in the membrane cohesion. Unfortunately, although interesting experimental conclusions have been reported in the past, these systems are complex and difficult to study.1 In order to isolate the effect of the different cohesive interactions, Langmuir-Blodgett (LB) fatty acid monolayers provide excellent model systems because of the controlled area per molecule, linear hydrocarbon chain geometry, amphiphilic nature, high mechanical stability and the possibility to test solid and liquid phases at room temperature. The nanomechanical properties of arachidic acid LB films extracted at surface pressures of 1, 15 and 35 mN/m and deposited on mica are investigated by Atomic Force Microscopy, Force Spectroscopy and Friction Force Microscopy. It is experimentally demonstrated that the molecular ordering depends on the extraction pressure, while discrete molecular tilting angles of 50°, 34° and 22° are detected and identified as conformations that maximize van der Waals interactions between alkyl chains. The vertical force (Fv) needed to puncture the monolayer strongly depends on the molecular tilting angle, ranging from 13.07±3.24 nN at 1 mN/m to 22.94±5.49 nN at 35 mN/m. The friction force (Ff) measurements performed from low Fv until monolayer disruption reveal three friction regimes corresponding with a low Ff elastic monolayer deformation at low Fv, followed by a sharp increase in Ff due to a sudden plastic deformation of the monolayer. The last regime corresponds with the monolayer rupture and the contact between tip and substrate. Interestingly, as the extraction pressure increases, the friction coefficient of the monolayer reduces while the Fv needed to trigger the monolayer plastic deformation increases, facts that are discussed in terms of sample compactness and monolayer rupture mechanism.2
1 Garcia-Manyes, S.; Oncins, G.; Sanz, F. Biophys. J. 2005, 89, 1812.
2 Oncins, G.; Garcia-Manyes, S.; Sanz, F. Langmuir 2005, 21, 7373.