8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Fri 911:10-14:00P1.43Van der Waals interactions between bodies of classicaldipolesJoakim Stenhammar, 1 Martin Trulsson, 2 Håkan Wennerström, 2 Per Linse, 2 andGunnar Karlström 21 Lund University, Physical Chemistry, P. O. Box 124 22100, Lund, Sweden2 Lund University, Lund, SwedenThe term ”van der Waals (vdW) interactions” denotes three mechanistically distinct kinds of intermolecularinteractions, all decaying as r −6 between two molecules. Traditionally, vdW interactionsbetween (macroscopic) bodies are described using Lifshitz theory [1], which treats the three differentcontributions to the interaction on equal grounds through the use of the frequency-dependentdielectric properties of the interacting materials. In the present work, we have derived analyticalexpressions specifically describing the classical, i. e. rotationally averaged dipole-dipole, partof the vdW interaction free energy between two spherical bodies characterized by their static dielectricconstants [2]. Our approach accurately reproduces the classical limit of Lifshitz theory,but takes into account the spherical geometry in a more straightforward manner. Furthermore, itpartly avoids the linear-response assumption inherent in Lifshitz theory. The analytical dielectriccontinuum results are compared to a simple molecular model system consisting of Lennard-Jonesparticles with embedded point dipoles. The interaction between two spherical bodies of such afluid is calculated using a combination of Monte Carlo simulations and classical perturbation theory.The results obtained from the molecular model are shown to agree remarkably well with thosefrom the dielectric continuum model down to separations of sub-molecular length scale [3]. Thisagreement is partly explained through the cancellation between two errors coming from the neglectof the discrete nature of the fluid within the dielectric continuum description. References [1]I. E. Dzyaloshinskii, E. M. Lifshitz, and L. P. Pitaevskii, Adv. Phys. 10, 165-209 (1961) [2] J.Stenhammar, P. Linse, H. Wennerström, and G. Karlström, J. Phys. Chem. B 114, 13372-13380(2010) [3] J. Stenhammar and M. Trulsson, Submitted manuscript43