The effects of salt and pH on coacervates formed by PDMAEMA (Poly [2 (Dimethylamino)ethyl Methacrylate]) and Gum Arabic

Abstract

Complex coacervates are dense, polymer-rich droplets resulted from the electrostatic complexation of oppositely charged polyelectrolytes. Interest in coacervates has been established long ago for use in encapsulation, particularly in the food and pharmaceutical industries. Complex coacervates formation is influenced by many parameters such as ionic strength, pH, temperature, and polyelectrolyte charge ratio due to the electrostatic interactions. The effects of these parameters are important to evaluate the stability of the complex coacervates in a complex ionic environment of various applications.The study aimed to evaluate the effects of salt and pH on the formation of complex coacervates between positively charged PDMAEMA and negatively charged Gum Arabic. Turbidity measurements were used to investigate the coacervation process as a function of different salt concentrations and types. Different charge ratios of the polymers and pH were tested and optimised for maximum complex coacervates formation. The ratio of 8:2 molar (Gum Arabic: PDMAEMA) at a pH 5.8 with saltfree conditions was found to be the optimal condition to form complex coacervates. The effects of salt types and ions were conducted at different concentrations to obtain the maximum turbidity for the complex coacervates system using critical salt concentration as the criteria. Monovalent and divalent salts were used to analyse the effects of these salts on the coacervation process, whether it enhances or prevents coacervates from being formed. To investigate the relationship of the Hofmeister series and hydration energies with the coacervation process, anions effects were investigated using sodium halides and monovalent salts, whereas cations effects were also investigated using chlorides salts. Overall, the results aligned with the Hofmeister series where the chaotropics tend to increase polymer solubility and prevent complex coacervates formation. The opposite effect holds for the kosmotropics. The divalent salts were found to have a higher inhibitory effect than the monovalent salts.