pH/temperature-responsive salt-tolerant Pickering emulsion formed by PNIPAM-modified chitosan particles

Natural polymer chitosan (CS) has been widely used as emulsifier due to its good stability, salt-resistant, and stimuli-responsive demulsification. However, chitosan is a hydrocarbon structure molecule containing -NH3+ and -OH with low surface activity, which is mainly suitable for some specific oil-water systems such as corn oil and sunflower oil. Appropriate hydrophilic-hydrophobic modification of chitosan by PNIPAM not only increases its surface activity but also introduces a temperature response on chitosan. Pickering emulsions (O/W) formed by CS-PNIPAM were prepared. The stability and response performance of the emulsions were investigated by observing the macroscopic states, microscopic images, droplet size distributions, emulsion emulsification indices, water partition rates, etc. Molecular dynamics and dissipative particle dynamics simulations were used to reveal the distribution pattern of the emulsifiers at the water-oil interface and clarify the stabilization and pH/temperature response mechanism of the emulsions. CS-PNIPAM performs excellent emulsification in various oil phases. The addition of salt ions enhances the stability performance of the emulsion. At low pH, CS will be protonated to break the emulsion, while increasing the pH will deprotonate CS and reform the emulsion. Also, the increase of temperature to 80 °C leads to emulsion breakage due to the agglomeration of PNIPAM.