Bridge-to-drain: How nanoparticles can promote coalescence in model polymer blends

Despite negligible effects on rheology and interfacial energy, the nanoparticles significantly promote coalescence. Analysis of hundreds of coalescence events revealed that the nanoparticles bridge colliding droplets and keep them in contact long enough to allow drainage of the matrix film even when the collisions occur at unfavorable angles where bare droplets do not coalesce. This novel "bridge-to-drain" mechanism requires that (i) the droplets are only partially covered by the particles and (ii) the latter have the ability to bridge droplets. A dimensionless critical surface coverage fraction was defined, above which the nanoparticles stop promoting coalescence and start stabilizing the microstructure.