title: Universal scaling of correlated diffusion in colloidal monolayers.
abstract: Using the techniques of optical microscopy and particle tracking, we measure the correlated diffusion in a monolayer of uniform silica spheres dispersed at a water-air interface. It is found that the correlated motion of the interfacial particles can be well described by two universal response functions, the normalized longitudinal and transverse diffusion coefficients D(∥)(r/r0) and D(⊥)(r/r0), where r is the interparticle distance and r0=a(λS/a)(3/2) is a new scaling length, which depends on both the Saffman length λS and particle radius a. The obtained response functions characterize the crossover behavior of the colloidal monolayers from the subphase-dominated three-dimensional hydrodynamics at low surface coverage to the monolayer-dominated 2D hydrodynamics at high concentrations. The surface viscosity ηs(2) of the colloidal monolayer obtained by two-particle rheology compares well with the one-particle measurements.
authors.affiliation: State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China and Department of Physics, Jinan University, Guangzhou 510632, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhang
authors.forename: Na
authors.initials: N
authors.lastname: Li
authors.forename: Klemen
authors.initials: K
authors.lastname: Bohinc
authors.forename: Penger
authors.initials: P
authors.lastname: Tong
authors.forename: Wei
authors.initials: W
authors.lastname: Chen