Concentrated emulsions. 2. Effect of the interdroplet film thickness on droplet size and distortion in mono- and bidisperse face centered cubic packings

Abstract

Modeling studies of concentrated emulsions have been extended to include the simultaneous effects of polydispersity and distortion on φ_max (maximum attainable volume fraction) and A_tot(normalized total interfacial area) in bidisperse and tridisperse face centered cubic(fcc) packings, with smaller droplets occupying the interstices formed by large drops. The distortion model considered is the one yielding flat circular faces between interacting drops, the radius of the face increasing with increase indistortion. For constant values of φ and volume average droplet radius, A_tot follows the trend mono > bi > tri. the effect of the interdroplet film thickness t, on emulsion structure has also been considered. it is shown that emulsion droplets get increasingly more distorted as the ration, α, of this film thickness to droplet radius(r) is increased. this distortion becomes especially pronounced when φ exceds 0.9. although the distortion of all droplets in an emulsion increases with increasing φ and α, packing consideration mandate vaiations in the extent of distortion of different sized droplets in a polydisperse matrix. in proportion to their size, amaller droplets in the bidisperse fcc packing would be more distorted than large drops while the opposite might be expected from energetic considerations. Since α varies inversely with r for constant values of t, smaller droplet sizes and higher volume fractions are likely to promote monodispersity, a prediction partially supported freeze fracture scanning electron micrographs of emulsion explosive formulations. the minimum possible size of droplets for given values of φ and t have also been calculated in the present work.