Effect of unidirectional freezing using a thermal camera on polyvinyl (alcohol) for aligned porous cryogels

Abstract

ABSTRACT Unidirectional freeze casting for polymers and ceramics has been performed extensively; however, the mechanisms involved in unidirectional freezing are not thoroughly understood and therefore, in this study, polyvinyl (alcohol) hydrogels were freeze-thawed by unidirectional freezing and the resultant freezing profile was investigated using thermal imagery to comprehend the physical mechanism involved in the production of these aligned cryogels. The approach used follows a slight variation from what is currently used in literature, by enclosing the mould with insulating materials and leaving one side with a metal encasing for a fast freezing flow from the direction of the desired aligned of the structure. This method was cost-effective and simple; however, it was able to induce unidirectional freezing resulting in two distinct structures. These structures exhibited a cellular region interspersed with a fibrous and porous morphology. The method developed without the need of a freeze-dryer was confirmed to produce a unidirectional freezing which can be used for future studies.