Study of cryostructuring of polymer systems. 33. Effect of rate of chilling aqueous poly(vinyl alcohol) solutions during their freezing on physicochemical properties and porous structure of resulting cryogels

Abstract

Poly(vinyl alcohol) cryogels are obtained and investigated. The cryogels are prepared by freezing an initial polymer solution (100 g/L) at chilling rates of 1.85, 0.3, 0.03, or 0.003°C/min followed by defrosting the frozen (-20°C/12 h) preparations at heating rates of 0.3, 0.03, or 0.003°C/min. It is shown that a notice able influence of the chilling rate on the rigidity and heat endurance of the gel matrix is observed at very slow regimes of chilling (on the order of thousandths of degree centigrade per minute). One of the reasons for a reduction in the rigidity of resulting cryogels and the fusion enthalpy of the nodes in their supramolecular net works is the formation of a homo phase hydrogel during the long term exposure of the concentrated polymer solution to low temperatures prior to the onset of ice crystallization. The effect of the regime of chilling the polymer solution being frozen on the porous structure of cryogels resulting from the thawing of the prepara tions is ambiguous due to the multifactor character of this effect; therefore, in many cases, well defined struc ture-property correlations are not observed.

Poly(Vinyl Alcohol) Cryogels for Biomedical Applications

“…In addition, the effects of these two parameters on the PVA-C mechanical properties are quite different. Decreasing the thawing rate leads to significant increases in the mechanical properties, whereas changing the freezing rate had little or no effect [7,63,64]. Although the close parallel between the effects of processing parameters on diffusion and the mechanical properties of PVA-C can be clearly seen, the structural characteristics leading to these observations are quite different.…”

A Brief History of Polymeric Cryogels

“…Features of the microstructure of PVA cryogels were ascertained using various microscopy techniques [330,331,333,[338][339][340][341][342][343][344][345][346] and other physicochemical analysis methods [237,326,[347][348][349][350][351]. In these studies, the following five principal facts were established:…”

Cryostructuring of Polymeric Systems †: Application of Deep Neural Networks for the Classification of Structural Features Peculiar to Macroporous Poly(vinyl alcohol) Cryogels Prepared without and with the Additives of Chaotropes or Kosmotropes

“…Thus, in or series of previous studies that dealt with the exploration of the structure/properties relations of different PVA cryogels, the evaluation of their macroporous morphology was accomplished via statistical methods and cluster analysis of the optical microscopy images recorded for thin sections of the respective PVACGs in an intact water-swollen state [ 43 , 44 , 45 , 46 , 47 ]. Such cryogels were prepared from aqueous or DMSO solutions of various PVA concentrations and molecular weights.…”