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Ice-templating is a simple, practical kind of template synthesis which consists of sol-gel polycondensation, unidirectional freezing of hydrosols or hydrogels, and pore-preserving drying method, such as freeze drying, thereby resulting in desirable porous materials. The unidirectional freezing may be achieved by either immersion freezing or contact freezing. Freeze-dried materials contain porous microstructures that are replicas of the ice crystals formed during the unidirectional freezing process. Two similar but slightly different applications of ice-templating will be investigated here. Fabrication of macroporous foam materials by unidirectional freezing of an aqueous suspension of carbon nanotubes (CNTs) dispersed by chitosan is a concrete example of functionalization of an electroconductive foam, which is a composite material made from a polymer and CNTs. As expected, their electroconductive properties can be controlled by the fabrication method and condition. Additional examples of porous materials synthesized by ice-templating are porous microfibers and microhoneycombs of silica, titania, silica-alumina, titania-silica, and even carbon. In the preparation, the morphology and porous structure can be controlled by the freezing conditions and synthesis conditions of the corresponding hydrogels, respectively.

Cryogel based oil encapsulation was attempted with a ternary system of colloidal chitosan, κ-carrageenan, and carboxymethylcellulose sodium salt (NaCMC). Favourable formulations of this ternary system that caused irreversible sol-gel transition by freezing (cryogelation) were found in this study, and the oil phase that contained a selected model food ingredient (curcumin) was successfully encapsulated in this prepared cryogel matrix. The encapsulation yields were found to vary from ca 89 to 99%, and the values were influenced by the cooling protocol used during freezing, thereby indicating that the gel formation kinetics was intimately related to the degree of encapsulation. The release behaviours of the ingredient were investigated in aqueous systems. The release curves showed that both a burst release and a first order release were achieved simply by changing the freezing condition. Freezing could modify the gel formation of the present cryogel, and the resulting structural modification evidently controlled the oil encapsulation manner. The prepared cryogels were found to be sensitive to the ambient pH. It was suggested that the ternary system of chitosan, κ-carrageenan, and NaCMC is an interesting matrix for designing controlled release system.

Polyimide (PI) films containing dispersed ZnO nanoparticles were prepared from both zinc nitrate hexahydrate (designated as Zn(NO3)2/PI) and ZnO nanopar- ticles, 2-nm average primary size (ZnO/PI). This work shows how the origin of ZnO affects both the photolumines- cence and thermal decomposition of the film. The presence of ZnO derived from Zn(NO3)2� 6H2 Ow as conf irmed by X- ray diffraction technique. The fluorescent intensities from Zn(NO3)2/PI and ZnO/PI were much higher than that from pure PI films. When the ZnO concentration exceeded a cer- tain saturation level, the emission intensity decreased due to the undesirable aggregation of ZnO. At the same concentra- tion, ZnO/PI exhibited higher emission intensity than Zn(NO3)2/PI. All samples prepared under nitrogen emitted higher intensity than their counterparts prepared under ar- gon. The ZnO/PI film was thermally more stable than the Zn(NO3)2/PI one. From TEM images of 117.6 mol% ZnO/PI films, the ZnO aggregates, whose average size was 17- 90 nm, were well distributed throughout the film but poorly dispersed in nanometer range. 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 1921-1928, 2008