Volume 79, Number 1, July 2007
Article Number 18003
Number of page(s) 6
Section Interdisciplinary Physics and Related Areas of Science and Technology
Published online 19 June 2007
EPL, 79 (2007) 18003
DOI: 10.1209/0295-5075/79/18003

Counterion distribution near a monolayer of variable charge density

K. Giewekemeyer and T. Salditt

Institut für Röntgenphysik - Friedrich-Hund Platz 1, 37077 Göttingen, Germany

received 14 February 2007; accepted in final form 21 May 2007; published July 2007
published online 19 June 2007

We study the bromide counterion distribution near a solid-supported monolayer in the case of vanishing bulk electrolyte concentration by resonant X-ray reflectivity. The surface charge density of the monolayer was varied by using different molar ratios of the cationic Di-Octadecyl-Di-methyl-Ammonium-Bromide (DODAB) and the neutral Di-Palmitoyl-Glycero-Phosphocholine (DPPC). The analysis, either based on a conventional box model with an additional counterion contribution, or based on an independent unbiased global optimization approach, yields a good agreement with the classical Poisson-Boltzmann theory for the salt-free case.

87.16.Dg - Membranes, bilayers, and vesicles.
83.85.Hf - X-ray and neutron scattering.
68.08.-p - Liquid-solid interfaces.

© Europhysics Letters Association 2007