Study of cryostructurization of polymer systems VII. Structure formation under freezing of poly(vinyl alcohol) aqueous solutions

Abstract

Rheological properties of the cryogels produced by freezing of concentrated aqueous solutions of poly(vinyl alcohol) have been studied. These properties were shown to depend on the polymer concentration in the initial solution, on PVA molecular weight, cryostructurization duration and temperature. Electron microscopy demonstrates the heterogeneous porous structure of these cryogels and the dependence of the observed pattern on the conditions of formation of the studied objects.

Studies on elastic hydrogel membrane. I. Effect of preparation conditions on the membrane performance

“…PVA aqueous solutions (7,5,10,12,20 w t W ) were prepared. PVA-hydrogel membranes were prepared by casting the PVA aqueous solutions on the petri dishes and repeating freezing-thawing for 7 days.…”

1H NMR Self-diffusion Study of PVA Cryogels Containing Ethylene Glycol and Its Oligomers

“…They are also able to depress the freezing temperatures of aqueous solutions, to reduce a size of the ice polycrystals, and even to result in the glass formation of respective water systems by their fast low-temperature cooling (17). Inasmuch as the PVA cryogels are taken up in biotechnology as carriers for cells (2,9) or enzyme entrapment (8), within these porous gel matrices the cryogenic treatment is subjected to the hazardous freezing stress capable of lowering the biological activity. Therefore, it is desirable to use cryoprotectants, for instance, oligooxyethylene glycols.…”

“…It was established that cryogels have a porous compartmented structure, which originated from a gelation of the continuous PVA-rich solution phase that is segregated around the large ice crystallites (1,2). The morphology of cryogels is fairly complicated.…”

“…The concentrated aqueous PVA solutions form the rubberlike elastic gels by the freezing-thawing cyclic treatment (1)(2)(3)(4). The last leads to the sol-gel transition, producing the thermo-reversible gels (5,6).…”

Study of cryostructurization of polymer systems. IX. Poly(vinyl alcohol) cryogels filled with particles of crosslinked dextran gel

“…Regarding the physico-mechanical properties of cryogels, this conclusion is quite evident because an increase in the concentration of the * The experiments were performed on a Series 700 HPLC instrument (Bio-Rad Lab., USA) with a 7.5 X 300 mm column of TSK Gel Type 4000 PW (Varian, USA) as described elsewhere. 15 reinforcing filler to a certain extent will produce, for instance, a growth in the composite ~trength.~' Moreover, the use of a large-pore disperse additive (of G-100 type), which is permeable for the cryogelforming macromolecules of PVA, may in principle form (in contrast to the small-pore additive) the "network-in-network" type structures within each particle of a weakly crosslinked Sephadex. As a consequence, another factor enhancing the reinforcing effect of fillers is the increase of the "size" of contacts between the discrete phase and the binder,4244 which is also one of the possible reasons for the observed differences in the effects of G-100 and G-25 types of Sephadex on the rheological characteristics of the composite PVA cryogels.…”