Hydrodynamic couplings of colloidal ellipsoids diffusing in channels

The hydrodynamic interactions (HIs) of two colloidal spheres characterized by the translation–translation (T–T) couplings have been studied under various confinements, but little is known regarding the HIs of anisotropic particles and rotational motions, which are common in nature and industry. Here, we study the T–T, rotation–rotation (R–R) and translation–rotation (T–R) hydrodynamic couplings of two colloidal ellipsoids sediment on the bottoms of channels in experiment, theory and simulation. We find that the degree of confinement and the particle shape anisotropy are critical tuning factors resulting in anomalous hydrodynamic and diffusive behaviours. The negative R–R coupling reflects the tendency of opposite rotations of two neighbouring ellipsoids. The positive T–R coupling reflects that an ellipsoid rotates away from the channel axis as another ellipsoid approaches. As the channel width increases, the positive T–T coupling changes to an abnormal negative coupling, indicating that the single-file diffusion can exist even in wide channels. By contrast, only positive T–T couplings were observed for spheres in channels. The T–T coupling increases with the aspect ratio p. The R–R coupling is the maximum at a moderate p ~ 2.8. The T–R coupling is the maximum at a moderate degree of confinement. The spatial range of HIs is longer than that of spheres and increases with p. We propose a simple model which reproduces some coupling phenomena between two ellipsoids, and it is further confirmed by low-Reynolds-number hydrodynamic simulation. These findings shed new light on anisotropic particle diffusion in porous media, transport through membranes, microfluidics and microrheology.

Green chemical synthesis for well-defined and sharply distributed SiO2@FexOy particles

Using a non-toxic precursor, we created a green chemical synthesis for colloidal spheres with a core@shell structure having a silica core and an iron oxide shell (SiO2@FexOy). Our synthesis pathway enabled an iron oxide shell formation with a 9 ± 6 nm thick shell onto colloidal silica spheres (ca. 700 nm). SiO2@FexOy particles reduced A549 cell viability and induced DNA damage. SiO2@FexOy particles showed the potential for removing fluoride from water.

Magnetic assembly and manipulation of Janus photonic crystal supraparticles from a colloidal mixture of spheres and ellipsoids

Photonic crystal supraparticles (PCSs) obtained by self-assembly of colloidal building blocks hold promise for applications in various areas. The majority of PCSs are based on isotropic colloidal spheres, fundamentally limiting...

Gauge invariant and gauge dependent aspects of topological walking colloidal bipeds

Paramagnetic colloidal spheres assemble to colloidal bipeds of various length in an external magnetic field and walk on a magnetic pattern.

In-situ growth of an opal-like TiO2 electron transport layer by atomic layer deposition for perovskite solar cells

Orderly-arranged photonic crystal structure can produce trapping effect to improve light utilization. Herein, atomic layer deposition system and different sizes of polystyrene colloidal spheres were employed to in-situ prepare the...