Cryogels gelation temperature

Fig. 19 Thermally induced collapse of poly(A, Af-diethylacrylamide) hydrogel (curve 1) and cryogel samples (curve 2) upon increasing the temperature from room temperatiffe to 60 °C. The variation in the volume of the gel samples is shown as a function of the deswelling time. Synthesis conditions initial monomer concentration 5.66 wt% molar ratio of vinyl to divinyl monomers 200 1 gelation temperature +20 °C (curve 1) and — 10 C (curve 2). (From [172] with permission from Springer)...

Numerous studies on various aspects of cryotropic gelation phenomena have demonstrated that cryogels can be prepared, similarly to the traditional gels formed at positive temperatures, from precursor systems that fall into the following categories (see review articles [1, 18-29]) ... 

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)...

Using (8), one may estimate the polymer concentration i/ in the unfrozen gel phase at a given temperature Tprep (Tprep < Tf ). To apply (8) to the cryogelation systems, we assume that the monomers completely accumulate in the unfrozen reaction phase before the onset of gelation. We also assume that, after cryogelation, the conversion of mraiomer to crosslinked polymer is complete. Thus, the monomer concentration C in the unfrozen zones (in % w/v) can be estimated from i/ as ... 

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