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

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 lambda. 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 sigma(R) similar to 0.03. The average droplet radii (R) over bar(x) parallel and (R) over bar(z) perpendicular to the flow direction are proportional to gamma(-1), with an average aspect ratio <(nu)over bar>(R)=(R) over bar(x)/(R) over bar(z) of 2 independent of gamma 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. (C) 1998 American Institute of Physics.