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Attractive double-layer forces between neutral hydrophobic and neutral hydrophilic surfaces

Eduardo R. A. Lima, Mathias Boström, Nadine Schwierz, Bo E. Sernelius, and Frederico W. Tavares

Phys. Rev. E 84, 061903 (2011)

The electrostatics of charged particle adsorption (e.g., protein) to surfaces and interaction of dissimilar charged surfaces have been explored in the past. However, our paper addresses the ion-specific double-layer attraction between an uncharged hydrophobic surface and an uncharged hydrophilic surface. Due to opposite signs of the double layers, the ion-specific double-layer pressure between an uncharged hydrophilic surface and an uncharged hydrophobic surface can give a strong attraction that is similar in magnitude to the Hamaker–van der Waals pressure. It is of vital importance to take this effect into account at moderate to medium salt concentrations (0.1–1 M) where, on one hand, the charge due to specific ion adsorption is not too small, and on the other hand, the screening length is not too short. We have found an ion-specific double-layer attraction between unequal surfaces. The attraction between the two asymmetric surfaces increases with increasing size (and polarizability) of the ions. This attraction is bound to be important for the interaction between patchy proteins with hydrophobic and hydrophilic surface patches.

FIG. A schematic of hydrophobic and hydrophilic surfaces interacting across a salt solution. Opposite signs of the double layers can give rise to ion-specific attraction

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Last updated: 01/17/12