Published Articles

Microencapsulated Non-aqueous Dispersions

Droplets of oil containing finely dispersed nanoparticles can be encapsulated in natural polymers by leveraging three interesting physical chemical properties of certain polyelectrolytes. Firstly aqueous solutions of gelatin form gels on cooling below ~40°C. Second, gelatin molecules are amphoteric, i.e. negatively charged about pH > ~5 and positively charged at pH < ~4. And lastly, under certain conditions, two oppositely charged polymers dissolved in water can associate by charge neutralization to form fluid droplets of a polymer-rich phase called a coacervate. Gelatin and acacia gum mixed in dilute solution at pH > ~5 forms a clear singlephase solution. If the pH is lowered below ~4, the gelatin molecules become positively charged, and associate with the negatively charged acacia gum molecules to form droplets of the separate coacervate phase containing the hydrated c The phase diagram in figure 1 shows the concentration boundary lines within which the coacervate phase forms from the oppositely charged polymers for four different batches of gelatin (showing the variability in the behavior of different natural materials). The coacervate phase appears for compositions within the boundary lines, while for compositions outside the boundary lines the mixture gelatin / acacia / water remains a single phase. It is of interest to note that the coacervate phase only forms from very dilute solutions (<4% w/w) of each polymer, typical of coacervating mixtures.

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