The continuous dispersed phase constitutes the solid skeleton of the gel, the continuous dispersion medium forms the fluid part of the gel, and the particle size that constitutes the colloid makes the gel have a capillary microstructure. Capillary phenomenon refers to the phenomenon that the liquid rises or falls in the vertical capillary due to the difference between the adhesion between the liquid and the tube wall and the cohesion of the liquid itself. The action between these two forces is the action of capillary force.
The capillary structure of the fresh gel is filled with liquid dispersion medium. As the gel dries, the gel will change from liquid-solid two-phase to liquid-solid-gas three-phase. Finally, the liquid phase will be completely replaced by the gas phase and become a dry gel. It can be seen that the air permeability of the shell is determined by the capillary microstructure of the gel; at the same time, it can be seen that the drying process is a very critical and important link in the gel formation process, and factors related to the gel drying speed will ultimately affect the microstructure of the gel capillaries.