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

Abstract

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.