Visualization and improvement of the physical gelation process during gas phase coagulation through acid–base indicator staining, monitoring and optimization

Gas phase coagulation is a highly efficient method for fabricating physically crosslinked nanochitin-based hydrogels. In this study, a visible and tailorable strategy was developed using phenolphthalein and litmus indicator. The indicator was applied to stain partially deacetylated nanochitin (DEChNs), ensuring that the gelation process occurring during gas phase coagulation was able to be clearly visualized. A semi-gelatinized interface cross-sectional view was obtained, leading to the possibility to monitor and optimize the crosslinking process. Thereafter, a series of optimizations was performed to improve the nanochitin gelation process. Only 16.5 h was required for sufficient physical crosslinking when the molar ratio of ammonia to acetic acid was 3.45. In mixtures containing this proportion, the ammonia solution was completely reduced and the formation process was able to be controlled and improved. A higher concentration of nanochitin led to a slower cross-linking process, but increased the mechanical strength and produced a more uniform structure, which might be due to the formation of a more uniform network at an appropriate gelation rate. The optimization of the physical cross-linking process will improve our understanding of the mechanisms underlying the gas phase coagulation technique and the control of the properties of nanochitin hydrogels and their composites by altering the cross-linking conditions.

The nanochitin gelation process was clearly visualized and optimized with substantially reduces the amount of ammonia solution and the precisely predicts and controls time, while it maintains a homogeneous and stable network structure, a higher specific surface and the same strong mechanical properties of the hydrogel.