cryogels in water, plotted against the pH of the initial feed solution. The homophase
chemically crosslinked PVA gels swell strongly in water (Fig. 9d), and their
swelling degree increases considerably (from tens of grams to more than 100 g
water per gram of dry polymer) as the pH of the feed rises from 1 to 3 due to the
decreasing crosslinking efficiency. However, the heterophase sponge-like cryogels
are not only formed under apparently less acidic initial conditions, but also their gel
phase swells significantly less than the corresponding homophase gels (from several
to 20–30 g water per gram of dry polymer). This indicates a higher crosslinking
extent of the 3D networks in the cryogel samples as compared to the conventional
gels synthesized under identical crosslinking agent content and pH. The reason for
the different swelling behavior of PVA gels and cryogels is because the cryoconcentration processes in UFLMP give rise to an increase in the concentrations
of both the gel precursors and H
+ ions. This facilitates the formation of a more
concentrated, highly crosslinked gel matrix forming the pore walls in such cryogels.
In this connection, we should note that for such wide-pore gel matrices, the
swelling capacity of the gel phase is an essential indicator of the polymer content in
this phase and of the crosslinking extent. By contrast, the total volume occupied by
such swollen gel materials is a less informative indicator for the properties of the
polymeric network. This is due to the fact that the volume occupied by free solvent
inside the capillary-sized pores accounts for the greater part of the liquid absorbed
by these wide-pore sponges. In turn, the fraction of tightly bound solvate liquid
…-(CH 2 -CH-CH 2 -CH) m -(CH 2 -CH) n -…
|
|
|
Poly(VA-co-VAc)
OH
OH
OCOCH 3
OHC-(CH 2 ) 3 -CHO
[H
+ ]
Glutaraldehyde
…-(CH 2 -CH-CH 2 -CH) m’ -(CH 2 -CH) n -…
|
|
|
O
O
OCOCH 3
\
/
CH
|
(CH 2 ) 3
Cross-linked
|
polymer
CH
/
\
O
O
|
|
…-(CH 2 -CH-CH 2 -CH) m’ -(CH 2 -CH) n -…
|
OCOCH 3
a
Fig. 9 (continued)
Basic Principles of Cryotropic Gelation
69
chemically crosslinked PVA gels swell strongly in water (Fig. 9d), and their
swelling degree increases considerably (from tens of grams to more than 100 g
water per gram of dry polymer) as the pH of the feed rises from 1 to 3 due to the
decreasing crosslinking efficiency. However, the heterophase sponge-like cryogels
are not only formed under apparently less acidic initial conditions, but also their gel
phase swells significantly less than the corresponding homophase gels (from several
to 20–30 g water per gram of dry polymer). This indicates a higher crosslinking
extent of the 3D networks in the cryogel samples as compared to the conventional
gels synthesized under identical crosslinking agent content and pH. The reason for
the different swelling behavior of PVA gels and cryogels is because the cryoconcentration processes in UFLMP give rise to an increase in the concentrations
of both the gel precursors and H
+ ions. This facilitates the formation of a more
concentrated, highly crosslinked gel matrix forming the pore walls in such cryogels.
In this connection, we should note that for such wide-pore gel matrices, the
swelling capacity of the gel phase is an essential indicator of the polymer content in
this phase and of the crosslinking extent. By contrast, the total volume occupied by
such swollen gel materials is a less informative indicator for the properties of the
polymeric network. This is due to the fact that the volume occupied by free solvent
inside the capillary-sized pores accounts for the greater part of the liquid absorbed
by these wide-pore sponges. In turn, the fraction of tightly bound solvate liquid
…-(CH 2 -CH-CH 2 -CH) m -(CH 2 -CH) n -…
|
|
|
Poly(VA-co-VAc)
OH
OH
OCOCH 3
OHC-(CH 2 ) 3 -CHO
[H
+ ]
Glutaraldehyde
…-(CH 2 -CH-CH 2 -CH) m’ -(CH 2 -CH) n -…
|
|
|
O
O
OCOCH 3
\
/
CH
|
(CH 2 ) 3
Cross-linked
|
polymer
CH
/
\
O
O
|
|
…-(CH 2 -CH-CH 2 -CH) m’ -(CH 2 -CH) n -…
|
OCOCH 3
a
Fig. 9 (continued)
Basic Principles of Cryotropic Gelation
69