Structure formation in pH-sensitive hydrogels composed of sodium caseinate and N,O-carboxymethyl chitosan

• A novel smart hydrogel was prepared induced by DGL.
• Surface characteristics of the hydrogel were examined by AFM.
• Gelation process was characterized using structure formation parameters.
• The temperature effects on the kinetics of gelation were analyzed by a non-isothermal kinetic model.
• The smart hydrogel exhibited an outstanding sol-gel transition induced by H+/OH−.

The pH-sensitive hydrogels composed of sodium caseinate (SC) and N,O-carboxymethyl chitosan (NOCC) were prepared and a new method to characterize the gelation process was presented in this work. Reological tests suggested that RSC/NOCC = 3/7 (the weight ratio of SC and NOCC) was the best ratio of hydrogel. The well-developed three-dimensional network structures in the hydrogel were confirmed by AFM. Two structural parameters, tIS and tCS, denoted as the initial and critical structure formation time, respectively, were used to provide an exact determination of the start of structure formation and description of gelation process. The gelation process strongly depended on temperature changes, a high temperature resulted in an early start of gelation. The non-kinetic model suggested the higher activation energy in the higher temperatures was disadvantageous to structure formation, and vice versa. Due to the smart gel reported here was very stable at room temperature, we believed that the gel is required for applications in drug delivery or could be exploited in the development of potential application as molecular switches in the future.