Variation of droplet sizes during the formation of microcapsules from emulsions

Abstract

The size distributions of microcapsules are important in determining the surface area over which the contents of the microcapsules are released. The size distribution is generally not normal arournd the mean, but biased toward smaller capsule sizes, forming a mode around some characteristic diameter. In order to assess the factors effective in determining this characteristic drop size, size distribution analyses were carried out photographically at each stage of the complex coacervation process. In addition, the emulsion drop size distributions were investigated as a function of stirring rate, stirring time and phase ratio. The results agreed qualitatively with the theory of isotropy but were an order of magnitude smaller. This theory is valid for Newtonian liquids. Elongational stresses could be operative with large-sized macromolecules and a mechanism was proposed based on variation of elongational stresses with velocity and rates of extension. Elongational viscosities measured for the gelatin solutions supported the proposed mechanism.

Key Words:

• Size distribution
• Microcapsules
• Elongational stresses
• Gelatin emulsions
• Coacervation