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 around 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.

In situpoly(urea-formaldehyde) microencapsulation of dicyclopentadiene

“…Mean diameter and standard deviation were determined from data sets of at least 250 measurements. The size distribution was biased toward small microcapsule diameters as discussed by Ovez et al (1997). However, the mean and standard deviation captured the dominant mode of the distribution.…”

“…In situ encapsulation of water-immiscible liquids by the reaction of urea with formaldehyde at acid pH is outlined by Dietrich et al (1989). Tan et al (1991), Yan et al (1993), Alexandridou and Kiparissides (1994) and Ovez et al (1997) have all shown that microcapsule size can be controlled by adjusting the agitation rate during microencapsulation.…”

Control of the morphology and the size of complex coacervate microcapsules during scale‐up

“…Most of these studies were mainly focussing on the identification of new polymer systems (other than gum arabic/gelatin) suitable for the food industry requirements (milk/plant proteins, fish gelatin, and so on), on the effects of the system chemical properties (such as pH, ionic strength, polymer ratio or concentration2, 3, 4), on the coacervate phase properties (such as rheology, yield2), and on the encapsulation of specific compounds 2, 5–9. However, only few studies have been published to describe the effect of processing parameters (shear, temperature, residence time, and so on) on the final product characteristics 6, 9, 10. As a result, scaling‐up was almost always achieved empirically (trial and errors setup) at the expense of cost and resources.…”

Functional hydrogel microspheres: Parameters affecting electrostatic assembly of biopolymer particles fabricated from gelatin and pectin

“…At high shear rates (> 300 rpm), the size of the hydrogel particles was relatively small because the mixing of the acid with the biopolymer solution was rapid and uniform, and because the particle breakup mechanism dominated (Kim & Berg, 2000;Laneuville et al, 2005;Norton et al, 1999). An inverse relationship between shear rate and particle size has also been reported in several other studies (Garrec & Norton, 2012;Kim & Berg, 2000;Norton et al, 1999;Övez et al, 1997;Xiao et al, 2014). At low shear rates (< 300 rpm), we postulate that the size of the hydrogel particles was relatively small (Figures 8 and 9) because of poor mixing conditions related to the flow profile generated by the magnetic stirrer i.e., vortex flow (Halász et al, 2007).…”