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| - Rupture of Hydrophobic Microcontacts in Water: Correlation of Pull-Off Force with AFM Tip Radius
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| Abstract
| - The purpose of this work was to investigate the functional dependence of the adhesion (pull-off) forceon probe radius in AFM force measurements. Pull-off forces for hydrophobic AFM probes in contact withhydrophobic substrates were measured in water. Chemical functionalization of probes and substrates wasaccomplished by self-assembly of octadecanethiol on Au. Average pull-off forces for 10 SAM/Au-coatedprobes were measured and found to depend linearly on the probe tip radii, which were determined byscanning electron microscopy (SEM). Using the JKR contact mechanics model, the thermodynamic workof adhesion (Wad) determined from the pull-off forces was 110 ± 10 mJ/m2 which compares favorably withestimates of Wad based on reported interfacial energies. These results verify the linear dependence of theadhesive force on probe radius, as expected from contact mechanics models. They also verify that SEMcan provide self-consistent and reproducible estimates of the probe radius.
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