Control of ice crystal growth and its effect on porous structure of chitosan cryogels

We presented an improved preparation method to generate cryogels with controllable pore size. It included 5 stages: pre-cooling, pre-crystallization, crystal growth, freezing, and thawing (PPCFT); crystal growth was the key step. Chitosan (CS) cryogels with uniform and honeycomb-like structures were prepared with the method, and then the properties of these cryogels were studied. The results demonstrated that the mean pore diameters of CS cryogels were successfully controlled in a wide range (approximately 60–240 μm, by scanning electron microscope) by simply varying the temperature and time of crystal growth. The crystal growth law of this process was described by an empirical equation based on the classical theory for Ostwald ripening by Lifshitz, Slyozov, and Wagner (LSW). Furthermore, the hydrodynamics performance (permeability and column efficiency) of CS cryogel columns clearly varied with crystal growth conditions, while both the accessible porosity and water absorption ratio remained at a high level.