摘要 : A comprehensive simulation of the coarsening mechanism coalescence-induced coalescence (CIC) is developed to predict the growth rate of inviscid droplets in a viscous matrix fluid. In CIC, the shape relaxations of coalescing dropl... 展开 A comprehensive simulation of the coarsening mechanism coalescence-induced coalescence (CIC) is developed to predict the growth rate of inviscid droplets in a viscous matrix fluid. In CIC, the shape relaxations of coalescing droplets establish flow fields that drive other droplets into contact, thus creating a cascade of coalescence events. It is believed that CIC is responsible for droplet growth in some demixed polymer solutions, such as isotactic polypropylene (iPP) and diphenyl ether (DPE). A cascade of coalescence events is simulated using a three-dimensional molecular dynamics-like simulation of a dispersed two-phase isopycnic fluid system. The coalescence-induced flow is driven mostly by the strong gradients in curvature at the neck of a coalescing pair of droplets, and the flow is modeled analytically by approximating it as due to a ring of point forces. The resultant velocity of each droplet in the suspension is calculated by superimposing all of the coalescence-induced flow fields and applying Faxen's Law. The mean droplet size [a] grows like t(xi), where t is the coarsening time and xi a growth exponent that increases with increasing minority phase volume fraction to. Good agreement with experimental values of xi (0.22 < <xi> < 0.47) is obtained for a phase-separated iPP-DPE solution for <phi> greater than or equal to 0.23. It is also shown that the droplet size distribution broadens for semidilute suspensions (phi less than or equal to 0.42) but remains relatively narrow for highly concentrated suspensions (phi greater than or equal to 0.54). A phenomenological kinetic theory of coalescence is proposed. It is believed that in nondilute emulsions, CIC can account for coarsening that has been attributed previously to more traditional coalescence mechanisms. (C) 2000 Academic Press. [References: 61] 收起