Vorticity-Aligned Droplet Bands in Sheared Immiscible Polymer Blends Induced by Solid Particles

Abstract

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.

Coalescence Suppression in Flowing Polymer Blends Using Silica Rods with Different Surface Chemistries

“…3c′). A similar phenomenon has also been reported in our previous studies with PS ellipsoids and microspheres [17,38,39] and interpreted by using the Jeffery orbits theory [40] in the framework of fluid mechanics. It is suggested that only when oriented in the vorticity direction can these rigidized droplets rotate around their long axes under slow shear flow with a minimized energy dissipation.…”

Shear-induced vorticity aligned flocs in a temperature responsive colloid-polymer mixture

“…Of the plethora of anisotropic shear-induced structures observed, a subset feature log-rolling flocs, whose formation strongly depends on the degree of confinement. These vorticity-aligned log-rolling flocculated structures have been observed in emulsions [19]; particleloaded polymer blends [20]; carbon nanotube suspensions [21,22]; carbon black suspensions [23][24][25]; mud samples [26]; and other suspensions of attractive particles [27,28]. A complete understanding of such log-rolling floc formation is crucial for applications where complex fluids might flow through confined geometries (e.g., 3D printing) and for scalable methods of producing anisotropic materials (e.g., films with anisotropic conductivity [29,30]).…”

Morphology of Anisotropic Banded Structures in an Emulsion under Simple Shear

“…Its vast applications are directed to microfluidics, the food industry, and granular materials, among other possibilities. Some band formation studies have been reported in the literature for different types of samples, such as granular materials [1,2], stiff particle suspensions [3,4], liquid crystals [5], polymer solutions [6], in surfactant wormlike micelles [7,8], and attractive emulsions [9,10]. The arrangement of bands in emulsions is reported mainly for the concentric cylinder geometry [11], where band formation can occur in all three directions (the directions of the flow, the velocity gradient, or the direction of vorticity).…”