Formation of droplets with a very narrow size distribution in mixtures subjected to shear flow. I. Shear rate dependence

Abstract

The phase-separated structures of a semidilute solution of off-critical polymer mixtures composed of polystyrene (PS) and polybutadiene (PB) in a common solvent of dioctylphthalate (DOP) under steady shear flow are investigated by light scattering as a function of shear rate γ̇. Light scattering patterns show multiple-order scattering maxima up to the 13th order or more in a weak shear regime, revealing formation of droplets with surprisingly uniform size having a relative standard deviation of droplet radius σR∼0.03. The average droplet radii R̄x parallel and R̄z perpendicular to the flow direction are proportional to γ̇−1, with an average aspect ratio v̄R≡R̄x/R̄z of 2 independent of γ̇ in the weak shear regime. The result obtained in the average particle size is in good agreement with that predicted by Taylor’s theory for a single droplet case, but the extreme uniformity in size distribution would not be trivial and be worth it for future theoretical considerations.