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The dynamics and pair trajectories of two self-propelled (active) colloids in a quiescent fluid for both axisymmetric and asymmetric cases are reported. The autonomous motions of the colloids are due to a catalytic chemical reaction taking place asymmetrically on their surfaces that generates a concentration gradient of interactive solutes around the particles and actuates particle propulsion. A combined analytical-numerical technique was developed to solve the coupled mass conservation equation for the solute and the hydrodynamics between the colloids in the Stokes flow regime. For axisymmetric motions, the translational swimming velocities of the particles in the near field can be enhanced or weakened (compared to their motions when they are far apart) depending on the relative orientations of their active sections. Moreover, it can be shown that different surface activities of two symmetric particles, e.g. an inert versus a catalytic particle or two catalytic particles, can also lead to a propulsion where the far-field swimming velocity for the inert and the catalytic particle attenuate as ∼1/Δ2 and ∼1/Δ5 respectively, Δ is the non-dimensional centre-to-centre distance. For asymmetric motions, our analysis indicates two possible scenarios for pair trajectories of catalytically active particles: either the particles approach, come into contact and assemble or they interact and move away from each other (escape). It is found that the direction of particle rotations is the key factor in determining the escape or assembly scenario due to an interplay between both hydrodynamic and phoretic effects. Based on the analysis, a phase diagram is sketched for the pair trajectory of the catalytically active particles as a function of reacting surface coverages and their initial relative orientations with respect to each other. We believe this study has important implications in elucidation of collective behaviours of autophoretically self-propelled colloids and would be certainly a guide for experimentalists to design and control active systems. [ABSTRACT FROM AUTHOR]

The force and couple that result from the shearing motion of a viscous, unbounded fluid on a Janus drop are the subjects of this investigation. A pair of immiscible, viscous fluids comprise the Janus drop and render it with a ‘perfect’ shape: spherical with a flat, internal interface, in which each constituent fluid is bounded by a hemispherical domain of equal radius. The effect of the arrangement of the internal interface (drop orientation) relative to the unidirectional shear flow is explored within the Stokes regime. Projection of the external flow into a reference frame centred on the drop simplifies the analysis to three cases: (i) a shear flow with a velocity gradient parallel to the internal interface, (ii) a hyperbolic flow, and (iii) two shear flows with a velocity gradient normal to the internal interface. Depending on the viscosity of the internal fluids, the Janus drop behaves as a simple fluid drop or as a solid body with broken fore and aft symmetry. The resultant couple arises from both the straining and swirling motions of the external flow in analogy with bodies of revolution. Owing to the anisotropic resistance of the Janus drop, it is inferred that the drop can migrate lateral to the streamlines of the undisturbed shear flow. The grand resistance matrix and Bretherton constant are reported for a Janus drop with similar internal viscosities. [ABSTRACT FROM PUBLISHER]

Lithium-ion batteries (LIBs) serve as the backbone of modern technologies with ongoing efforts to enhance their performance and sustainability driving the exploration of new electrode materials. This study introduces a new type of alloy-conversion-based gallium ferrite (GFO: GaFeO 3 ) as a potential anode material for Li-ion battery applications. The GFO was synthesized by a one-step mechanochemistry-assisted solid-state method. The powder X-ray diffraction analysis confirms the presence of an orthorhombic phase with the Pc 2 1 n space group. The photoelectron spectroscopy studies reveal the presence of Ga 3+ and Fe 3+ oxidation states of gallium and iron atoms in the GFO structure. The GFO was evaluated as an anode material for Li-ion battery applications, displaying a high discharge capacity of ∼887 mA h g -1 and retaining a stable capacity of ∼200 mA h g -1 over 450 cycles, with a Coulombic efficiency of 99.6 % at a current density of 100 mA g -1 . Cyclic voltammetry studies confirm an alloy-conversion-based reaction mechanism in the GFO anode. Furthermore, density functional theory studies reveal the reaction mechanism during cycling and Li-ion diffusion pathways in the GFO anode. These results strongly suggest that the GFO could be an alternative anode material in LIBs., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)