Dresden 2006 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 12: POSTER Colloids, Nanoparticles and Self-Organizing Systems
CPP 12.18: Poster
Tuesday, March 28, 2006, 17:00–19:00, P3
Importance of boundary conditions for fluctuation forces between colloids — •Hartwig Lehle1,2 and Martin Oettel1,2 — 1Max Planck Institut für Metallforschung, Heisenbergstraße 3, 70569 Stuttgart — 2ITAP, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart
We consider rotationally symmetric colloids trapped at a fluid interface and subjected to thermal movement. Due to the constraints the colloids impose on the spectrum of the capillary waves the free energy becomes dependent on colloid-colloid separation leading to a thermal Casimir force. The free energy is calculated in a functional integral approach. We present two distinct schemes to calculate the partition function elucidating the importance of the various boundary-type dependent contributions to the Casimir force. The long-range behaviour of the Casimir force can be expressed in terms of multipole interactions of auxiliary “charge fields” on the colloids. The resulting force is shown to be long-range, F ∼ −1/(d log(d)) in the case of fixed colloids and a pinned contact line. If the colloid position or the contact line are also fluctuating, additional competing terms induce a cancellation of the leading terms. For a pinned contact line and fluctuating colloid heights the leading contribution to the interaction is of dipole-dipole (∼ −1/d4), for a fluctuating contact line of quadrupole-quadrupole (∼ −1/d8) character.