Control of mean diameter and size distribution during formulation of microcapsules with cellulose nitrate membranes

Abstract

Microcapsules were prepared by forming a cellulose nitrate (collodion) membrane around emulsified aqueous droplets within an organic continuous phase. The control of mean diameter and size distribution of the microcapsules was achieved by varying the conditions of emulsification. Distribution data were shown to fit the log-normal distribution function. A lattice impeller permitted a greater variation of particle distribution parameters (35 to 225 μm mean diameter for a decreasing range of rev min −1 from 600 to 150) than was possible with a turbine impeller (72 to 91 μm for a similar range of rotational speed). Increasing emulsification time lowers the microcapsule mean diameter (from 130 to 70 μm for 1 to 3 min, respectively) and the geometric standard deviation (from 2.0 to 1.5 for 3 to 9 min, respectively). The addition of a surfactant (1% to 4% v/v) promotes the formation of smaller droplets (mean diameter from 85 to 70 μm) and leads to unimodally distributed microcapsules even at low rotational speed and duration. Finally, increasing phase ratio of internal emulsified aqueous to organic external (from 5% to 20% v/v) decreases the geometric standard deviation (from 1.7 to 1.5).