Open AccessOrigin of the long-range attraction between surfactant-coated surfaces
Author(s) -
Emily E. Meyer,
Lin Qi,
Tue Hassenkam,
Emin Oroudjev,
Jacob N. Israelachvili
Publication year - 2005
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.0502110102
Subject(s) - mica , van der waals force , chemical physics , bilayer , surface forces apparatus , monolayer , adsorption , hydrophobic effect , range (aeronautics) , pulmonary surfactant , chemistry , micrometer , electrostatics , surface force , hydrophobe , attraction , nanotechnology , materials science , molecule , membrane , optics , organic chemistry , physics , biochemistry , mechanics , composite material , linguistics , philosophy
We compare the "long-range hydrophobic forces" measured (i) in the "symmetric" system between two mica surfaces that had been rendered hydrophobic by the adsorption of a double-chained cationic surfactant, and (ii) between one such hydrophobic surface and a hydrophilic surface of bare mica ("asymmetric" case). In both cases, the forces were purely attractive, stronger than van der Waals, and of long-range, as previously reported, with those of the asymmetric, hydrophobic-hydrophilic system being even stronger and of longer range. Atomic force microscopy images of these surfaces show that the monolayers transform into patchy bilayers when the surfaces are immersed in water, and that the resulting surfaces contain large micrometer-sized regions of positive charges (bilayer) and negative charges (bare mica) while remaining overall neutral. The natural alignment of oppositely charged domains as two such surfaces approach would result in a long-range electrostatic attraction in water, but the short-range, "truly hydrophobic" interaction is not explained by these results.