Influence of electrolytes and pH on the phase behaviour of gelatin/maltodextrin aqueous mixtures, for water-in-water emulsion formation

Abstract

The main objective of this work is to study the effect of different electrolytes and pH on the spontaneous formation of water-in-water emulsions. Water-in-water (W/W) emulsions are a less known group of emulsions which are based on the immiscibility of two compounds which are soluble in water. Although they are thermodynamically unstable, W/W emulsions could be kept for some time due to its kinetic metastability, without any surfactant. Subsequently, obtaining microgels from these emulsions could offer a new type of encapsulation with delayed release of active ingredients or drugs. In this work, aqueous mixtures of gelatin and maltodextrin have been studied from its phase diagrams. Initially, the study of electrolytes has been made following the Hofmeister series, thereby, according to the capacity of hydration of ions, studying salts with different free energy of hydration (CsNO3 i LiCl). It was expected that salts had opposite effect on the phase separation of the system, but it was observed that the two salts favour the miscibility of polymers and the precipitation of a coacervate. Then, the effect of pH by adding acetic acid has been studied, observing an interesting result: acid medium favours the miscibility between the polymers, without precipitation. This phenomenon opens a new way: the neutralization of acid medium with sodium hydroxide could favour the spontaneous formation of emulsions. It has been verified that the addition of NaOH produces an instantaneous phase separation, however, obtaining emulsions from this phase separation has not been ensured. Due to the high system instability, many experimental factors could affect the formation of these emulsions. Future further work is required with more detailed studies