| Abstract
| - Friction properties of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)-supported planar bilayersdeposited on mica were tested in a liquid environment by lateral force microscopy. The presence of thesebilayers was detected by imaging and force measurements with atomic force microscopy. To test how thepresence of NaCl affects the frictional properties of the phospholipid bilayers, four DMPC bilayers wereprepared on mica in saline media ranging from 0 to 0.1 M NaCl. Changes in the lateral vs vertical forcecurves were recorded as a function of NaCl concentration and related to structural changes induced in theDMPC bilayer by electrolyte ions. Three friction regimes were observed as the vertical force exerted bythe tip on the bilayer increased. To relate the friction response to the structure of the DMPC bilayer,topographic images were recorded at the same time as friction data. Ions in solution screened chargespresent in DMPC polar heads, leading to more compact bilayers. As a consequence, the vertical force atwhich the bilayer broke during friction experiments increased with NaCl concentration. In addition, thetopographic images showed that low-NaCl-concentration bilayers recover more easily due to the low cohesionbetween phospholipid molecules.
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