Droplet coalescence and clustering behavior in microsphere-filled polymeric emulsions under shear flow: the key role of asymmetric interfacial affinities

Abstract

The flow-induced spatial organization of the droplet phase in ternary polymeric emulsions consisting of two Newtonian fluids, namely polyisobutylene (PIB) and polydimethylsiloxane (PDMS), in the presence of a small amount of solid polystyrene (PS) microspheres are explored by direct flow visualization. The results suggest that the asymmetric affinities of interfacially located PS microspheres to two fluid components lead to diverse flow-induced morphologies in PIB/PDMS blends with different compositions. In 10/90 blends where microspheres are preferentially wetted by the PIB droplets, significantly promoted coalescence of PIB droplets is observed. Increasing the loading of microspheres or changing the shear rate will alter the size and spatial distribution of PIB droplets. In contrast, in the inverse 90/10 blends where microspheres are wetted by the continuous PIB phase, bridging of PDMS droplets is found, leading to the generation of string-like or grape-like clusters. These results indicate that the flow-induced morphology of PIB/PDMS blends in the presence of PS microspheres is not only determined by the experimental conditions such as shear rate but also to a large extent by the asymmetric interfacial affinities of microspheres for fluid components.

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

“…Similar shear banding was not observed in the inverse PDMS/PIB (10/90) blends within all PS microsphere concentrations (0–4 wt %) investigated . In that case, the θ of PS microspheres is 57 ± 6°.…”

“…The addition of 0.1 wt % PS microspheres (Figure b) leads to the formation of grape-like PIB droplet clusters consisting of 3–10 small droplets ( R V = ∼52 μm) and distributed randomly within the PEO matrix, resembling the structure found by Thareja and Velankar . Our previous work with PDMS/PIB (10/90) blends filled with PS microspheres which were preferentially wetted by the PIB matrix phase displayed a similar phenomenon . It is suggested that this process will be facilitated greatly in the presence of the shear flow and by the wall confinement effect.…”

“…Figure shows the corresponding volume average radius R V , droplet size distribution, and capillary number of droplets ( Ca , calculated from eq , the viscosity of the PEO matrix is ∼18.8 Pa·s, and the interfacial tension between PIB and PEO is ∼10.7 mN/m). While the droplet size shifts toward lower values with the increased ϕ PS , droplet size distribution becomes narrower and steeper because of the effective coalescence inhibition due to the enhanced physical barrier effect of particles . The increase of ϕ PS from 0 to 3.0 wt % leads to the reduction of Ca from 0.02 to 0.001.…”

Vorticity Deformation in Polymeric Emulsions Induced by Anisotropic Ellipsoids

“…The PIB droplets in blend filled with PS microspheres appear dark but still acquire a near-spherical shape (Figure b). The droplet size is larger in microsphere-filled blend, which could be interpreted by particle-induced coalescence via the bridging-dewetting mechanism. , In contrast, the droplets in the emulsion containing ellipsoids have distinctly irregular shapes (Figure c). These morphological consequences are ascribed to the fact that particles can be trapped by the fluid interface at an adequately high coverage to jam the interface against coalescence at quiescence or small shear intensities. , Additionally, the bulk elasticity of droplet can also arrest coalescence to form irregular droplets .…”

Particles adsorbed at various non-aqueous liquid-liquid interfaces

“…Mao et al [30,31] reported two studies of blends of polyisobutylene and polydimethylsiloxane in the presence of either spherical or ellipsoid polystyrene particles. They concluded that during shearing, droplets became elongated and rotated periodically about their major axes while aligning along the vorticity direction in ellipsoid-filled emulsions due to both an extremely small Reynolds number that arrested the coalescence and a strong confinement effect.…”