Cryogels preparation

Fig. 45. Pore size distribution of organic oryogels prepared with different fictors and of carbon cryogels prepared from the corresponding organic cryogels at 1273 K. Courtesy of Prof. H. Tamon of...

Examples of the majority of the reported covalent cryogels prepared from macromolecular precursors are given in Table 2. These data show that such cryogels based on natural and synthetic polymers can be synthesized by chemical crosslinking or by irradiation techniques in fi ozen aqueous, organic, or mixed water-organic media. Thus, the chemical structure, physico-chemical properties. 

Table 2 Examples of covalent cryogels prepared by crosslinking of macromolecular precursors in moderately frozen systems... 

Gelatine Formaldehyde Water -28 cryogels Preparation of macroporous carrier [177]... 

Fig. 4 Effect of the thawing rate on (a) the shear modulus and (b) the fusion temperature of PVA cryogels prepared by freezing of aqueous polymer solutions at —20 °C for 18 h. PVA concentrations were 120 (i), 100 (2), and 80 g/L (3). (Plotted based on data from [44])...

Fig. 18 Micrographs of thin sections of PVA cryogels prepared from aqueous solutions of PVA (100 g/L) using (a) single-temperature and (b) two-temperature procedures. The freezing/storage-frozen regimes were -20 °C for 24 h (a) and -20 °C for 1 h and then —2 °C for 23 h (b). The average size of macropores was 2.8 (a) and 2.4 pm (b). The fraction of macropores was 61.3 (a) and 52.5 % (b). Scale bars 20 pm. (From [44] with permission from Springer)...

Fig. 21 Porous morphology of wide-pore PVA cryogels prepared using the feed system water-PVA-GuAr. (a) Photograph of 2-mm-thick disc stained with Congo Red. (b, c) Survey micrographs of the same disc obtained with an optical microscope at two different magnifications, (d) The image of a thin section of the disc. (From [180] with permission from RCS)...

Fig. 22 Optical micrographs at two different magnifications of thin sections of foamed PVA cryogels prepared from the fluid foam produced by whipping of aqueous polymer solutions in the (a, b) absence and (c, d) presence of the surfactant CTAB at a concentration of 0.415 mM. Initial polymer concentration was 120 g/L. Cryotropic gelation conditions fieezing temperature —20 °C freezing duration 18 h, thawing rate 0.03 °C/min. (From [192] with permission from Springer)...

The initial concentration Co of the monomeric or the polymeric precursors is another important parameter in cryogel preparation. Due to the effect of cryo-concentration, cryogels can be prepared at much lower concentrations compared... 

Fig. 3 SEM micrograph of HEC cryogel prepared at a freezing temperature of —20 °C, initial polymer concentration 1 mass%, polymer molar mass 1,300,000 g/mol, 2 mass% BBTMAC, irradiation time 2 min. Reprinted from [12] with permission from Elsevier...

F. 4 Gel fraction yield of cryogels prepared fiom HECs of different molar masses at different polymer eoneentrations. Cryogels were obtained at a freezing temperature of —20 °C,... 

Fig. 14 SEM micrographs of PNIPAAm cryogel prepared from samples immersed in water at 25 °C (left) and 50 °C (right). Cryogel was synthesized from 5 mass% monomer solution, containing H2O2 (5 mass% to monomer) and PEGDA (10 mass%), frozen at —20 °C, and irradiated with UV light for 5 min. Reprinted from [16] with permission from Elsevier...

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