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Utilization of active colloids to transport both biological and inorganic cargo has been widely examined in the context of applications ranging from targeted drug delivery to sample analysis. In general, carriers are customized to load one specific target via a mechanism distinct from that driving the transport. Here we unify these tasks and extend loading capabilities to include on-demand selection of multiple nano/micro-sized targets without the need for pre-labelling or surface functionalization. An externally applied electric field is singularly used to drive the active cargo carrier and transform it into a mobile floating electrode that can attract (trap) or repel specific targets from its surface by dielectrophoresis, enabling dynamic control of target selection, loading and rate of transport via the electric field parameters. In the future, dynamic selectivity could be combined with directed motion to develop building blocks for bottom-up fabrication in applications such as additive manufacturing and soft robotics.

Previously, metallodielectric Janus particles have been shown to travel with their dielectric hemisphere forward under low frequency applied electric fields as a result of asymmetric induced-charge electroosmotic flow. Here, it is demonstrated that at high frequencies, well beyond the charge relaxation time of the electric double layer induced around the particle, rather than the velocity decaying to zero, the Janus particles reverse direction, traveling with their metallic hemisphere forward. It is proposed that such motion is the result of a surface force, arising from localized nonuniform electric field gradients, induced by the dual symmetry-breaking of an asymmetric particle adjacent to a wall, which act on the induced dipole of the particle to drive net motion even in a uniform AC field. Although the field is external, since the driving gradient is induced on the particle level, it may be considered an active colloid. We have thus termed this propulsion mechanism "self-dielectrophoresis", to distinguish from traditional dielectrophoresis where the driving nonuniform field is externally fixed and the particle direction is restricted. It is demonstrated theoretically and experimentally that the critical frequency at which the particle reverses direction can be characterized by a nondimensional parameter which is a function of electrolyte concentration and particle size.

We study the electro-osmotic flow through a T-junction of microchannels whose dielectric walls are weakly polarizable. The present global analysis thus extends earlier studies in the literature concerning the local flow of an unbounded electrolyte solution around nearly insulated wedges. The velocity field is obtained via superposition of an irrotational part associated with the equilibrium zeta potential and the induced-charge electro-osmotic flow originating from the interaction of the externally applied electric field and the charge cloud it induces owing to field leakage through the polarizable dielectric channel walls. Along the channel walls the latter component gives rise to fluid velocities converging toward the corner which dominate the flow in its immediate vicinity. Recent experimental observations in the literature regarding the appearance and subsequent expansion of flow reversal and vortices downstream ͑initially͒ and upstream ͑subsequently͒ of the junction, are both rationalized in terms of the growing relative importance of this induced contribution to the global velocity field with increasing intensity of the externally applied electric field.

The effective conductivity of composite media with ellipsoidal inhomogeneities and highly conducting interfaces is studied. At such interfaces the temperature field is continuous, but the normal component of the heat flux undergoes a discontinuity which is proportional to the local surface Laplacian of the temperature field. The dilute approximation for the case of ellipsoidal inhomogeneities in such circumstances is derived. The derivation involves the solution of an auxiliary problem of a single particle embedded in an infinite medium and employs ellipsoidal harmonics. This solution is also used to derive a mean-field approximation for non-dilute concentrations.

The impulsively starting motion of a circular cylinder submerged horizontally below a free surface is studied analytically using a small-time expansion. The series expansion is taken as far as necessary to include the leading gravitational effects for two cases: constant velocity and constant acceleration, both commencing from rest. The hydrodynamic force on the cylinder and the surface elevation are calculated and expressed in terms of bipolar coordinates. Comparisons are also made with earlier theoretical and experimental work. The theory is valid for arbitrary value of submergence depth to cylinder radius.

We study the induced-charge electro-osmotic flow around a stationary polarizable dielectric spheroid in the presence of a uniform arbitrarily oriented external electric field. A Robin-type condition connecting the respective electric potentials within the dielectric solid and the bulk electro-neutral solution is highlighted in formulating the macroscale description for the limit of thin electric double layers and low potentials. The results illustrate symmetry breaking phenomena in the ensuing flow and demonstrate qualitative differences associated with variations of the dielectric constant. We briefly discuss the potential impact of these differences on the rotation of freely suspended spheroids.The standard description of electro-osmotic flows in the presence of thin electric double layers ͑EDL's͒ utilizes a macroscale approach which avoids the need to resolve the details of the double layer. This, in turn, is effectively represented by appropriate boundary conditions imposed on the electric potential within the bulk electro-neutral fluid. Incorporating the solution of the resulting electrostatic problem with a prescribed electrokinetic surface charge density or, equivalently, a prescribed zeta potential into the HelmholtzSmoluchowski relation 1 yields the fluid slip velocity, thereby providing the appropriate boundary condition for the macroscopic hydrodynamic problem. For a uniform prescribed zeta potential the resulting flow is irrotational. At polarizable surfaces where the external electric field acts on the diffuse ionic charge cloud induced by the field itself, the interaction gives rise to a slip velocity which is nonlinear in the external field. The resulting induced-charge electro-osmosis ͑ICEO, Ref. 2͒ is thus no longer irrotational. This mechanism has been studied extensively for ideally polarizable ͑i.e., conducting͒ solids 2-6 and to a lesser extent for dielectrics. [7][8][9] The present contribution aims at illustrating the combined effects of nonisotropic body shapes and nonideal electrical material properties on the ICEO around a dielectric solid immersed in an unbounded electrolyte solution in the presence of a uniform external electric field. Recent analyses of induced-charge electro-osmosis and electrophoresis ͑ICEP͒ have focused on the hydrodynamic interaction 10 and the translational and rotational motion 11 of rod-like ideally polarizable ͑conducting͒ particles modeled as slender prolate spheroids. The effects of body geometry on the resulting flows have explicitly been presented 6 for nearly symmetric bodies. It has been demonstrated that slight deviations from a perfect ͑spherical or cylindrical͒ symmetry are sufficient for the appearance of symmetry-breaking phenomena. We examine here these features for dielectric prolate spheroids potentially spanning the entire spectrum from spherical through slender rod-like shapes. Spheroidal shapes are common in colloidal science. Thus, they are often used as models in the context of manipulation of biological cells as well as in the electrodynami...