title: Anomalous hydrodynamic interaction in a quasi-two-dimensional suspension.
abstract: We study the correlated Brownian motion of micron-sized particles suspended in water and confined between two plates. The hydrodynamic interaction between the particles exhibits three anomalies. (i) The transverse coupling is negative; i.e., particles exert "antidrag" on one another when moving perpendicular to their connecting line. (ii) The interaction decays with interparticle distance r as 1/r(2), faster than in unconfined suspensions but slower than near a single wall. (iii) At large distances, the pair interaction is independent of concentration within the experimental accuracy. The confined suspension thus provides an unusual example of long-range, yet essentially pairwise, correlations even at high concentration. These effects are shown to arise from the two-dimensional dipolar form of the flow induced by single-particle motion.
authors.affiliation: Department of Chemistry and The James Franck Institute, The University of Chicago, Chicago, IL 60637, USA.
authors.forename: Bianxiao
authors.initials: B
authors.lastname: Cui
authors.forename: Haim
authors.initials: H
authors.lastname: Diamant
authors.forename: Binhua
authors.initials: B
authors.lastname: Lin
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Rice