Direct Measurement of Sub-Debye-Length Attraction between Oppositely Charged Surfaces

Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot 76100, Israel.
Physical Review Letters (Impact Factor: 7.51). 09/2009; 103(11):118304. DOI: 10.1103/PhysRevLett.103.118304
Source: PubMed


Using a surface force balance with fast video analysis, we have measured directly the attractive forces between oppositely charged solid surfaces (charge densities sigma(+), sigma(-)) across water over the entire range of interaction, in particular, at surface separations D below the Debye screening length lambda(S). At very low salt concentration we find a long-ranged attraction between the surfaces (onset ca. 100 nm), whose variation at D<lambda(S) agrees well with predictions based on solving the Poisson-Boltzmann theory, when due account is taken of the independently-determined surface charge asymmetry (sigma(+) not equal to |sigma(-)|).

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