Direct Observation of Hydrodynamic Rotation-Translation Coupling between Two Colloidal Spheres

Abstract

By combining optical tweezers with polarization microscopy, the hydrodynamic coupling between position and orientation fluctuations in a pair of colloidal spheres has been measured. Imaging of birefringent particles under crossed polarizers allows for the simultaneous determination of the positions and orientations of both particles. The temporal cross-correlation function between random displacements of one particle and orientation fluctuations of its neighbor allows for the quantification of the hydrodynamic rotation-translation coupling between the spheres. Our results are in good agreement with predictions for the hydrodynamic mobility tensors calculated in the creeping-flow limit of the Navier-Stokes equation.

Propagation of hydrodynamic interactions between particles in a compressible fluid

“…While the parallel correlation γ 12 (t) is positive at all times, the perpendicular correlation γ ⊥ 12 (t) is initially negative and subsequently becomes positive. Comparable results have been reported in experimental studies [3][4][5] where the difference between the parallel and perpendicular correlations was attributed to the flow field around the particle 4,7 . We discuss the time dependence of the velocity cross-relaxation functions in more detail below.…”

“…In recent years, the temporal evolution of hydrodynamic interactions between two particles has been directly observed [3][4][5][6] . In these experimental studies, particles were trapped by optical tweezers, and the correlations between the positional fluctuations of particles were measured.…”

Dynamical Density Functional Theory with Hydrodynamic Interactions and Colloids in Unstable Traps

“…Second, we apply the theory to the dynamics of colloidal particles confined in an unstable optical trap which switches periodically in time from a stable to unstable confining potential. This situation can in principle be realized, e.g., by combining two laser tweezers or by scanning around a single laser tweezer quickly [3,19,20]. The response to this oscillating trap is a time-dependent radial-symmetric one-particle density profile which we call -in analogy to trapped Bose gases [21] -a driven breathing mode.…”

A Numerical Model for Brownian Particles Fluctuating in Incompressible Fluids

“…This is not a bad approximation for large/heavy particles, but it is insufficient for particles whose size is on the order of a micrometer or smaller; the coupling of TF and HI becomes crucial in these systems. Owing to some new experimental techniques that enable direct examination of the properties of Brownian particles fluctuating in a host fluid, several interesting phenomena have recently been reported, including the non-diffusive behavior of Brownian particles 10) and the rotational-translation coupling of a pair of spherical particles 11) where the coupling of TF and HI plays an essential role.…”