Study of cryostructuration of polymer systems. XIV. Poly(vinyl alcohol) cryogels: Apparent yield of the freeze-thaw-induced gelation of concentrated aqueous solutions of the polymer
Vi. Lozinsky et al., Study of cryostructuration of polymer systems. XIV. Poly(vinyl alcohol) cryogels: Apparent yield of the freeze-thaw-induced gelation of concentrated aqueous solutions of the polymer, J APPL POLY, 77(8), 2000, pp. 1822-1831
Poly(vinyl alcohol) (PVA) cryogels, which are formed as a result of freeze-
thaw treatment of concentrated solutions of the polymer, were studied in re
spect to the amount of gel and sol fractions in these heterogeneous macropo
rous gel materials depending on the conditions of the thawing step of simil
ar cryotropic gelation. It was shown that the yield of gel fraction (the ef
ficiency of the gelation process) was not quantitative; this was controlled
by the initial PVA concentration in the solution to be frozen, and to a hi
gher extent, by the thawing rate, when the yield increased with slowing of
the defrostation process. The sol fraction could be extracted from the PVA
cryogels by their rinsing with water at room temperature; the extraction of
the sol was accompanied with the variations of the swelling parameters of
the gels (initial slight upswelling and subsequent gradual deswelling), as
well as with analogous, in their character, variations of the gel strength.
It was also demonstrated that at the evaluation of the fusion enthalpies o
f PVA cryogels with the aid of the Eldridge-Ferry equation a consideration
of the values of gel-fraction yield gave rise to the significantly higher D
elta H values than in traditional cases commonly used for the thermoreversi
ble gels, where such an yield was not taken into account. (C) 2000 John Wil
ey & Sons, Inc.