Thisprocessresultsfromexternalforcesusuallygravitationalorcentrifugal.When such forces exceed the thermal motion of the droplets (Brownain motion), a concentration gradient builds up in the system with the larger droplets moving faster to the top (if their density is lower than that of the medium) or to the bottom (if their density is larger than that of the medium) of the container. In the limiting cases, the droplets may form a close-packed (random or ordered) array at thetop or bottomofthesystemwiththeremainderofthevolumeoccupiedbythecontinuous liquid phase.