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The spatiotemporal organization of complex fluids under flow can be strongly affected by incorporating solid particles. Here, we report that a monolayer of interfacially active microspheres preferentially wetted by the matrix phase can bridge droplets into vorticity-aligned bands in immiscible polymer blends at intermediate particle concentrations and low shear rates. Strong particle bridging ability and the formation of rigid anisotropic droplet bands with a negligible inertia effect in the Newtonian matrix are suggested to be responsible for the vorticity orientation of droplet bands during slow shear flow, which could be understood based on Jeffery orbit theory in the framework of fluid mechanics and strong confinement effect acted by shear walls and adjacent bands. However, increasing the aspect ratio of particles could restrain the formation of anisotropic bands because of reduced particle coverage and promoted droplet coalescence induced by sharp particle corners, increased and uneven distribution of particle aggregates in the matrix phase, and weakened particle bridging ability.

A particle-assembled microstructure in ternary capillary suspensions consisting of polyisobutylene (PIB) as the matrix phase, poly­(ethylene oxide) (PEO) as the minor fluid phase, and silica (SiO2) particles with different aspect ratios (ARs) is probed by an in situ optical-shear technique, scanning electronic microscopy, and confocal laser scanning microscopy as well as rheometry. It is found that the capillary bridging force brought by the presence of the PEO wetting layer between particles can be influenced by the AR of particles and shear rate, which all play decisive roles in determining the microstructure and rheological properties of suspensions. Moreover, two novel aggregation modes of rods and an interesting spatiotemporal organization phenomenon of particle aggregates (vorticity-aligned particle bands) are found under shear flow.

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