Hydrodynamic orienting of asymmetric microobjects under gravity

Abstract

It is shown that nonsymmetric microobjects orient while settling under gravity in a viscous fluid. To analyze this process, a simple shape is chosen: a non-deformable 'chain'. The chain consists of two straight arms, made of touching solid spheres. In the absence of external torques, the spheres are free to spin along the arms. The motion of the chain is evaluated by solving the Stokes equations with the use of the multipole method. It is demonstrated that the spinning beads speed up sedimentation by a small amount, and increase the orientation rate significantly in comparison to the corresponding rigid chain. It is shown that chains orient towards the V-shaped stable stationary configuration. In contrast, rods and star-shaped microobjects do not rotate. The hydrodynamic orienting is relevant for efficient swimming of non-symmetric microobjects, and for sedimenting suspensions.

Engineering particle trajectories in microfluidic flows using particle shape

“…These also tumble with no net migration. However, self-alignment has recently been predicted for asymmetric objects in bulk sedimentation, with a dynamical equation similar to ours when the object is initially oriented in a vertical plane 25 .…”

Fibrinogen conformations and charge in electrolyte solutions derived from DLS and dynamic viscosity measurements

“…Such a scheme has been used in numerous applications, including evaluation of sedimentation, collective diffusion, translational and rotational self diffusion, and viscosity coefficients for suspensions in the whole range of volume fractions [34,51], as well as calculation of the dynamics, mobility, and diffusion tensors for rigid and flexible bead aggregates forming various conformations [35,52] or groups of non-touching particles [53,54], in an unbounded fluid or a fluid in a confined geometry.…”

Streaming potential studies of colloid, polyelectrolyte and protein deposition

“…Obviously for solid spheres 〈R H 〉 is equal to the sphere radius a. For a solid sphere doublet 〈R H 〉 = 1.39a [78], for a triplet (linear aggregate) 〈R H 〉 = 1.73a [79,80] and for a linear aggregate composed of n s equal sized spheres one has [81] 〈R H 〉 = n s ln2n s −0:25 a = 1 ln2λ−0:25…”