1H NMR Self-Diffusion Study of Morphology and Structure of Polyvinyl Alcohol Cryogels

The multicomponent self-diffusion of the polyvinyl alcohol (PVA) cryogels prepared by a freezing-thawing treatment of aqueous and water-DMSO solutions of PVA has been studied with the NMR FT-PGSE method. The temperature dependencies of the self-diffusion coefficients, Ds, for the PVA chains have a maximum at 45 degrees C due to the syneresis of cryogels. They are quite different from the monotonous increase of Ds for the aqueous solutions of PVA. Evaluated apparent activation energies, Ea, of the self-diffusion for the PVA chains in the PVA solutions and cryogels in D2O are practically the same and equal 22-24 kJ/mol below the crucial point. The proton spin-lattice relaxation times, T1, of the PVA chain also coincide with one another for solutions and cryogels. This means that molecular packing in cryogels depends mainly on the dimensions of the ice and polymer microcrystallites formed by freezing the solution. Above the crucial point polymer compartments become firmer, and the chain mobility somewhat reduces. The strength of cryogels also increases along with growing the DMSO contents and decreases by the BSA addition. For estimation of the cryogel morphology, effects of the restricted diffusion of both the water and PVA in a q-space have been taken into account. By the introduction of DMSO to cryogels the solvent filled pores become smaller, and channels become much shorter. The diameter of the PVA filaments is similar to those for all the cryogels, but the length of filaments with D2O is twice that for cryogels with a mixed solvent. Entrapment of BSA in the cryogel matrix by preparation leads to the increase of an average diameter of the water filled pores and destroys molecular packing the cryogel. Copyright 1999 Academic Press.     

A Study of cryostructuring of polymer systems. 41. Complex and composite poly(vinyl alcohol) cryogels containing soluble and insoluble forms of chitosan,respectively

Complex macroporous poly(vinyl alcohol) (PVA) cryogels have been obtained by cryogenic treatment (freezing at–20°C for 12 h followed by defrosting at a rate of 0.03°C/min) of PVA–chitosan hydrochloride mixed solutions. The subsequent alkaline treatment of the cryogels has resulted in the transformation of the water-soluble salt form of chitosan into its insoluble basic form, which coagulates inside the bulk of the continuous phase of PVA cryogel into small particles with sizes of 2–5 µm. In the resulting composite cryogels, these particles play the role of an “active” filler, which increases the rigidity and heat endurance of the gel material. It has been shown that the sorption capacity of such chitosan particles entrapped into the bulk of composite cryogels with respect of bivalent copper ions is noticeably higher than the sorption capacity of ground chitosan particles incorporated as a discrete filler into the continuous phase PVA cryogels. The study of the properties of PVA–chitosan hydrochloride mixed solutions revealed that these polymers are, to a large extent, compatible with one another in a common solvent at a low ionic strength. Therefore, liquidliquid phase separation of these systems due to the thermodynamic incompatibility of macromolecules of different natures is observed only upon increasing the ionic strength by adding a low-molecular-mass salt (NaCl, 0.15 mol/L) to the solution.     

Study of Cryostructuring of Polymer Systems: 25. The Influence of Surfactants on the Properties and Structure of Gas-Filled (Foamed) Poly(vinyl alcohol) Cryogels

Foamed poly(vinyl alcohol) (PVA) cryogels are studied. Such heterogeneous gel composites are formed as a result of the cryogenic treatment (freezing—storage in a frozen state—thawing) of water— PVA liquid foams in the absence and presence of surfactants. It is shown that the addition of ionic and nonionic surfactants to an aqueous PVA solution and its subsequent foaming result in the formation of liquid foam whose stability is lower than that of the foam prepared from an aqueous PVA solution in the absence of surfactant, i.e., surfactants cause a destabilizing effect on the foams containing PVA. Gas-filled PVA cryogels formed as a result of freezing—thawing of such foams contain large (up to ～180 μm) pores (air bubbles incorporated into the matrix of heterogeneous gel). Mechanical and thermal properties of cryogels depend on the nature and concentration of surfactants, as well as on the regime of cryogenic treatment. The rigidity of foamed PVA cryogels prepared in the presence of sodium dodecyl sulfate and cetyltrimethylammonium bromide ionic surfactants is lower and that in the presence of nonionic decaoxyethylene cetyl ether is higher than for equiconcentrated (by the polymer) foamed PVA cryogel containing no surfactant. Microscopic studies and the analysis of obtained images of cryogel structure demonstrate that the effect of surfactant on the morphology of freezing foam can be different, depending on the type of surfactant added to the initial system. This leads to foam-destabilizing effects such as the collapse, deformation, and coalescence of air bubbles; the failure of gel phase structure near the bubble surface; etc. However, the complete disintegration of the foamed structure is prevented by a very high viscosity of the unfrozen liquid microphase of a macroscopically solid sample and by the cryotropic PVA gelation that fixes the structure of partially destroyed foam.     

Cryogenic Designing of Biocompatible Blends of Polyvinyl alcohol and Starch with Macroporous Architecture

The present paper discusses synthesis, characterization, and blood compatibility studies of macroporous cryogels of PVA and starch. Biocompatible spongy porous hydrogels of polyvinyl alcohol–starch have been synthesized by repeated freezing–thawing methods and characterized by Infra red (FTIR) and environmental scanning electron microscopy (ESEM) techniques, respectively, to gain insights for structural and morphological features. The FTIR analysis of prepared cryogels indicated that starch was introduced into the network of cryogel possibly via formation of hydrogen bonds between the PVA and starch clusters. The “cryogels” were evaluated for their water uptake potentials and influence of various factors such as chemical architecture of the spongy hydrogels, pH and temperature of the swelling bath were investigated on the degree of water sorption by the cryogels. The hydrogels were also swollen in salt solutions and various simulated biological fluids. The biocompatibility of the prepared cryogels was judged by in vitro methods of blood–clot formation viz. percent haemolysis and protein (BSA) adsorption. The cryogels were also studied for their pores morphology and percent porosity and the effect of chemical composition on the extent of porosity was also investigated.     

Study of cryostructuring of polymer systems: 28. Physicochemical properties and morphology of poly(vinyl alcohol) cryogels formed by multiple freezing-thawing

Macroporous viscoelastic poly(vinyl alcohol) (PVA) cryogels are prepared from aqueous concentrated (80–120 g/l) PVA solutions subjected to 1–5 cycles of cryogenic treatment (freezing at ?20°C for 19 h and subsequent thawing at a rate of 0.3°C/min). Shear moduli and fusion temperatures of corresponding samples are determined and the structure of thin sections is studied by optical microscopy with subsequent processing and analysis of images obtained. The previously described effect of a substantial increase in the rigidity and thermal stability of PVA cryogels resulted from the repeated freezing-thawing cycles is confirmed. The largest (jumpwise) changes in the physicochemical characteristics of such gels and their macroporous morphology take place after the second cycle of cryogenic treatment. Moreover, depending on the PVA concentration in the initial solution, the mean cross section of micropores increases by a factor of 2–3 and the total porosity of cryogel rises by a factor of 1.5–2; i.e., the imperfection of material increases. Nevertheless, this negative (from view-point of the integral properties of cryogel) effect is completely overpowered by processes of additional structuring, which result in the strengthening of polymer phase proceeding during the repeated freezing-thawing cycles.     

DNA adsorption via Co(II) immobilized cryogels

The separation and purification of important biomolecule deoxyribonucleic acid (DNA) molecules are extremely important. The adsorption technique among these methods is highly preferred as the adsorbent cryogels are pretty much used due to large pores and the associated flow channels. In this study, the adsorption of DNA via Co(II) immobilized poly(2-hydroxyethyl methacrylate-glycidyl methacrylate) [poly(HEMA-GMA)] cryogels was performed under varying conditions of pH, interaction time, initial DNA concentration, temperature, and ionic strength. For the characterization of cryogels; swelling test, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), surface area (BET), elemental and ICP-OES analysis were performed. L-lysine amino acid was chosen as Co(II)-chelating agent and the adsorption capacity of cryogels was determined as 33.81 mg DNA/g cryogel. Adsorption of pea DNA was studied under the optimum adsorption conditions and DNA adsorption capacity of cryogels was found as 10.14 mg DNA/g cryogel. The adsorption process was examined via Langmuir and Freundlich isotherm models and the Langmuir adsorption model was determined to be more appropriate for the DNA adsorption onto cryogels.     

Hydrophobic cryogels for DNA adsorption: Effect of embedding of monosize microbeads into cryogel network on their adsorptive performances

As alternative hydrophobic adsorbent for DNA adsorption, supermacroporous cryogel disks were synthesized via free radical polymerization. In this study, we have prepared two kinds of cryogel disks: (i) poly(2‐hydroxyethyl methacrylate‐N‐methacryloyl‐l ‐tryptophan) [p(HEMA‐MATrp)] cryogel containing specific hydrophobic ligand MATrp; and (ii) monosize p(HEMA‐MATrp) particles synthesized via suspension polymerization embedded into p(HEMA) cryogel structure to obtain p(HEMA‐MATrp)/p(HEMA) composite cryogel disks. These cryogel disks containing hydrophobic functional group were characterized via swelling studies, Fourier transform infrared spectroscopy, elemental analysis, surface area measurements and scanning electron microscopy. DNA adsorption onto both p(HEMA‐MATrp) cryogel and p(HEMA‐MATrp)/p(HEMA) composite cryogels was investigated. Maximum adsorption of DNA on p(HEMA‐MATrp) cryogel was found to be 15 mg/g polymer. Otherwise, p(HEMA‐MATrp)/p(HEMA) composite cryogels significantly increased the DNA adsorption capacity to 38 mg/g polymer. Composite cryogels could be used repeatedly without significant loss on adsorption capacity after 10 repetitive adsorption–desorption cycles. Copyright © 2013 John Wiley & Sons, Ltd.     

Study of cryostructuring of polymer systems: 31. Effect of additives of alkali metal chlorides on physicochemical properties and morphology of poly(vinyl alcohol) cryogels

Macroporous viscoelastic poly(vinyl alcohol) (PVA) cryogels were prepared from aqueous PVA solutions containing additives (0–1.2 mol/l) of alkali metal chlorides (LiCl, NaCl, KCl, CsCl) by cryogenic treatment (freezing at −20°C for 12 h and subsequent thawing at a rate of 0.03°C/min). Shear moduli and fusion temperatures of corresponding samples were determined and the structure of thin sections was studied by optical microscopy with subsequent processing and analysis of images obtained. It was shown that the rigidity, heat endurance, and mean pore sizes of formed cryogels monotonically decrease with increasing content of chaotropic lithium chloride. In the case of other three salts, the dependences of rheological characteristics of cryogels on the concentration of low-molecular-weight electrolyte were extreme due to the competition between factors that promote and prevent PVA cryotropic gelation. At the same time, fusion temperatures of gel samples increased steadily with increasing content of these salts. Microscopic studies revealed substantial (by factor of two to three) decrease in macropore sizes even at low content of salt compared to mean cross sections of pores in cryogel containing no additive; morphometric analysis of obtained images makes it possible to reveal the linear correlations between the rheological characteristics of cryogels formed in the presence of LiCl and the sizes of their macropores.     

A study of the microstructural and diffusion properties of poly(vinyl alcohol) cryogels containing surfactant supramolecular aggregates

Surfactant-containing poly(vinyl alcohol) (PVA) cryogels have been prepared by drying and reswelling hydrogel patches, previously obtained by the freeze/thaw procedure, in decyltrimethylammonium bromide (C10TAB) aqueous solutions. The microstructural and diffusive properties of the resulting material have been characterized by a combined experimental strategy. Gravimetric measurements show that the cryogel maximum swelling is not affected by the surfactant. The surfactant concentration within the cryogel, measured by ion chromatography, is the same as that in the rehydrating surfactant solution. Electron paramagnetic resonance (EPR) spin-probe and small-angle neutron scattering (SANS) measurements show that surfactant self-aggregation in the gel is similar to that in water, occurring at the same critical concentration and resulting in the formation of micellar aggregates whose structure is not affected by the cryogel polymeric scaffold. However, both the micelle intradiffusion coefficients, measured by PGSE-NMR, and the spin-probe correlation times, measured by EPR, indicate that dynamic processes in the hydrogel are much slower than in bulk water. A quantitative analysis of these results suggests that the cryogel polymer-poor domains, in which surfactant molecules are solubilized, have an average dimension of approximately 0.1 microm. Interestingly the experimental data also show that the polymer-poor phase contains more polymer than expected, suggesting that the spinodal decomposition, which occurs during the freezing step of cryogel preparation, is not complete or prevented by ice formation.     

In-situ graft-polymerization preparation of cation-exchange supermacroporous cryogel with sulfo groups in glass columns

Graft polymerization of monomer chains with expected functional groups onto the matrix pore surfaces by initiator is an effective approach for introducing ion-exchange groups to cryogel matrix to get anion- or cation-exchange supermacroporous cryogels. In this work, a novel cation-exchange cryogel with sulfo binding groups was prepared by grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) onto polyacrylamide-based cryogels in glass columns. The grafting polymerization was achieved in an in-situ manner which was performed by pumping the initiator and the reactive solution of graft monomer with sulfo binding groups directly through a cryogel bed pre-produced in a glass column under frozen condition. The axial liquid dispersion characteristics within the monolithic cryogel beds before and after the in-situ polymerization were compared by measuring residence time distributions (RTDs) at various liquid flow rates using tracer pulse-response method. Microstructure morphology of pores within cryogels was analyzed by scanning electron microscopy (SEM). Chromatography of lysozyme was carried out to reveal the protein breakthrough and elution characteristics in the obtained cryogel beds.     

Detection and quantitative determination of the crystalline phase in poly(vinyl alcohol) cryogels by ATR FTIR spectroscopy

The molecular structure of poly(vinyl alcohol) in its cryogels obtained via a single freeze-thaw cycle of aqueous solutions of the polymer is investigated by ATR FTIR spectroscopy. By means of Fourier deconvolution and spectral subtraction, methods, it is found that the spectra of cryogels contain a hidden crystallinity band at 1144 cm^?1 due to poly(vinyl alcohol). For poly(vinyl alcohol) films crystallized at different temperatures, a quantitative relationship is established between the relative intensity of absorption at a frequency of 1144 cm^?1 in the spectra of the polymer and its degree of crystallinity estimated via wide-angle X-ray diffraction. In terms of this relationship, the degree of crystallinity of poly(vinyl alcohol) in the cryogels is determined from their ATR FTIR spectra. This parameter is found to be 6, 10, and 14% for the cryogels with PVA concentrations of 9, 17, and 29%, respectively. The obtained data suggest that the formation of the cryogels is accompanied not only by the appearance of polymer crystallites but also by a change in the system of hydrogen bonds between the polymer and water.     

Study of cryostructuring of polymer systems: 27. Physicochemical properties of poly(vinyl alcohol) cryogels and specific features of their macroporous morphology

Based on aqueous poly(vinyl alcohol) (PVA) solutions with different content of polymer having different molecular masses and chain tacticity, macroporous viscoelastic gels (PVA cryogels) are prepared in various regimes of freezing-storage in a frozen state-thawing. Shear modulus and fusion temperature of corresponding samples are measured; the structure of thin sections is studied by optical microscopy and the images are processed and analyzed. It is shown that the rigidity and heat endurance of cryogels rise with an increase in the concentration of initial PVA solution and a decrease in the rate of thawing. The influence of the temperature of cryogenic treatment and the PVA molecular mass has an extreme character. At the same time, the effect of the main parameters of cryotropic gelation on the macroporous morphology of PVA cryogels is manifested in the form of more complex dependences because of its multiple-factor character. Therefore, distinct structure-property correlations are not observed in many cases. Cluster analysis of the morphometric characteristics of cryogels in comparison with data on their rigidity makes it possible to classify these systems.     

An improved capillary model for describing the microstructure characteristics, fluid hydrodynamics and breakthrough performance of proteins in cryogel beds

A capillary-based model modified for characterization of monolithic cryogels is presented with key parameters like the pore size distribution, the tortuosity and the skeleton thickness employed for describing the porous structure characteristics of a cryogel matrix. Laminar flow, liquid dispersion and mass transfer in each capillary are considered and the model is solved numerically by the finite difference method. As examples, two poly(hydroxyethyl methacrylate) (pHEMA) based cryogel beds have been prepared by radical cryo-copolymerization of monomers and used to test the model. The axial dispersion behaviors, the pressure drop vs. flow rate performance as well as the non-adsorption breakthrough curves of different proteins, i.e., lysozyme, bovine serum albumin (BSA) and concanavalin A (Con A), at various flow velocities in the cryogel beds are measured experimentally. The lumped parameters in the model are determined by matching the model prediction with the experimental data. The results showed that for a given cryogel column, by using the model based on the physical properties of the cryogel (i.e., diameter, length, porosity, and permeability) together with the protein breakthrough curves one can obtain a reasonable estimate and detailed characterization of the porous structure properties of cryogel matrix, particularly regarding the number of capillaries, the capillary tortuousness, the pore size distribution and the skeleton thickness. The model is also effective with regards to predicting the flow performance and the non-adsorption breakthrough profiles of proteins at different flow velocities. It is thus expected to be applicable for characterizing the properties of cryogels and predicting the chromatographic performance under a given set of operating conditions.     

A study of cryostructuring of polymer systems. 34. Poly(vinyl alcohol) composite cryogels filled with microparticles of polymer dispersion

Macroporous filled and unfilled poly(vinyl alcohol) (PVA) cryogels are produced by cryogenic treatment (freezing at ?20°C for 12 h followed by thawing at a rate of 0.03°C/min) of mixtures of an aqueous PVA solution and a full-component poly(vinyl acetate) (PVAc) dispersion or its individual components. The values of the elasticity modulus and fusion temperature are determined for obtained samples; their microstructure is studied by light microscopy of thin sections. It is shown that the effects that are induced by the incorporation of PVAc dispersion into the macroporous matrix of the PVA cryogel are due to the presence of both a discrete phase, i.e., solid PVAc microparticles, and ingredients of the liquid phase of the PVAc dispersion, mainly, urea. Therewith, the dispersed particles themselves serve as a reinforcing filler, i.e., increase the rigidity and (to a lesser extent) heat endurance of the cryogel, while urea, which possesses chaotropic properties and hinders the intermolecular hydrogen bonding of PVA chains, reduces the rigidity and heat endurance of the composites. As a result, the total effect is determined by the competition of differently directed influences of these components of PVAc dispersion and depends on its concentration in the resulting filled cryogel. It is also shown that PVAc microparticles are mainly entrapped in the gel phase of the macroporous matrix and form necklacelike aggregates, the cross-sectional areas and lengths of which depend on the degree of composite filling.     

Histidine-epoxy-activated sepharose beads embedded poly (2-hydroxyethyl methacrylate) cryogels for pseudobiospecific adsorption of human immunoglobulin G

The use of highly purified immunoglobulin became among the most powerful adopted strategies in therapeutic trials nowadays. Their role as immunomodulatory and anti-inflammatory agents has widened their scope of use. A novel continuous supermacroporous monolithic cryogels embedded with histidine-epoxy-activated-sepharose beads were synthetized as a new monolithic adsorbents for the separation of immunoglobulin G from human serum. The histidine-epoxy-activated-sepharose beads were embedded into the 2-hydroxyethyl methacrylate (HEMA) cryogels present in frozen aqueous solution inside a plastic syringe. The microstructure morphology of the cryogels was characterized by swelling measurement and scanning electron microscopy. The adsorption of human IgG on the histidine-epoxy-activated-sepharose beads pHEMA cryogels appeared to follow the Langmuir–Freundlich adsorption isotherm model. The maximum IgG adsorption was observed at 4°C and pH 7.4 and was found to be 26.95 mg/g of cryogel which is close to that obtained experimentally (24.49 mg/g). The cryogels were used for several adsorption-desorption cycles without any negligible decrease in their adsorption capacity.     

Impact of double cryogelation process on a macroporous dye-affinity hydrogel

Cryogels with interconnected channels allow high flow-through properties and mass transfer when dealing with complex mixtures such as non-clarified crude extracts. However, their mechanical strength can be challenged due to a large void volume inside the polymeric network. We have addressed this problem by forming a double-layer cryogel applied as a dye-affinity chromatography gel. In this study, poly(acrylamide-co-allyl glycidyl ether) cryogel was prepared at sub-zero temperature. The second layer was then prepared inside the primary cryogel under the same conditions to form a double-layer network. Cibacron Blue F3GA, a dye molecule, was immobilized on the surface of the cryogels. Bovine serum albumin was used as a model molecule to study the adsorption/elution procedure in batch and continuous modes. The maximum batch binding capacity and the dynamic binding capacity for the single-layer cryogel were 18 and 0.11, and for the double-layer cryogel were 7.5 and 0.9 mg/g of gel, respectively. However, the mechanical stability of the double-layer cryogel increased 7-fold (144 kPa). It was found that the kinetic and adsorption isotherms follow pseudo-second-order and Freundlich models, respectively. The regeneration of the columns after adsorption/elution cycles was evaluated, and no significant loss of capacity was observed after 10 cycles.     

Preparation of supermacroporous cryogels with improved mechanical strength for efficient purification of lysozyme from chicken egg white

A novel, facile, and robust strategy was proposed to increase the pore size and mechanical strength of cryogels. By mixing the monomers of acrylamide and 2‐hydroxyethyl methacrylate as the precursor, a monolithic copolymer cryogel with large interconnected pores and thick pore walls was prepared. Hydrogen bonding between the two monomers contributed to the entanglement and aggregation of the copolymers, thickening the pore walls and resulting in larger pore sizes. Analysis via mercury porosimetry demonstrated that the interconnected pore diameter of the copolymer cryogel ranged from 10‐350 µm, which was far larger than that of the cryogels from one monomer (10‐50 µm). Additionally, the thicker pore walls of the copolymer cryogel improved its mechanical strength. Affinity cryogels were prepared through covalent immobilization using Tris(hydroxymethyl)aminomethane as a coupling agent, and the affinity binding of lysozymes on Tris‐cryogel was evaluated by the Langmuir isothermal adsorption with the maximum adsorption capacity of 360 mg/g. Compared with that of the Tris‐cryogels produced from one monomer, the copolymer Tris‐cryogel exhibited higher adsorption capacity and lysozyme purity, when the chicken egg white solution flowed solely driven by gravity. This work provides a new avenue for designing and developing supermacroporous cryogels for bioseparation.     

Molecularly imprinted cryogel as a pH-responsive delivery system for doxorubicin

In this study, implantable and degradable molecularly imprinted cryogel was prepared for pH-responsive delivery of doxorubicin. Cryogel discs were synthesized using amino acid-based functional monomer with HEMA and gelatin. The molecularly imprinted discs were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, degradation and swelling tests. In vitro delivery experiments were carried out in order to examine the effects of medium pH and drug content. The degree of degradation of composite cryogels was found to be 83.45±1.86% after 56 days. The release profiles of DOX from molecularly imprinted cryogel discs exhibit a biphasic delivery. It was observed that an initial burst release step from 0 to 12 h was followed by a slower and sustained release. Release rate of DOX from cryogel discs increased in more acidic conditions. Kinetic studies showed that a combination of diffusion and erosion control is mainly responsible from the general release behaviors of molecularly imprinted cryogel discs.     

Effect of Halide Salts of Alkali Metals on Crystallinity of Poly(vinyl Alcohol) Cryogels

The degree of crystallinity of poly(vinyl alcohol) in cryogels obtained by single freezing at–20°С followed by thawing of 13% aqueous solutions of the polymer bearing dissolved NaCl, KCl, CsCl, KBr, and KI in the concentration of 0.7 mol/kg is determined by attenuated total reflectance Fourier transform IR spectroscopy. It is established that the addition of NaCl, KCl, and CsCl to the poly(vinyl alcohol) solution leads to a substantial increase (by 1.5–1.7 times) in the degree of crystallinity in the cryogel prepared from this solution. The effect of KCl, KBr, and KI on the degree of crystallinity strongly depends on the salt anion. The replacement of the Cl^– anion by the larger Br^– anion reduces dramatically the crystallizing effect of the salt, while the even larger I^– anion, in contrast, reduces rather than increases the degree of crystallinity relative to that of the cryogel without a salt. The effect of the salts on the crystallinity of poly(vinyl alcohol) cryogels is explained by the simultaneous action of two processes. One of them facilitates crystallization and consists in the strengthening of dehydration of poly(vinyl alcohol) owing to competition between the polymer molecules and the salt ions for the liquid water molecules during its freezing. The other process hampers crystallization and is connected with a reduction in the water freezing point under action of the salt ions.     

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

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.