STUDY OF CRYOSTRUCTURATION OF POLYMER SYSTEMS .12. POLY(VINYL ALCOHOL) CRYOGELS - INFLUENCE OF LOW-MOLECULAR ELECTROLYTES

The influence of the presence of low-molecular electrolytes in initial solutions of poly(vinyl alcohol) (PVA) on the results of cryotropic g elation of the polymer (gelation caused by the freezing-thawing) and o n the swelling characteristics of PVA cryogels prepared in a salt-free medium were studied. The reinforcing ability of the electrolytes with respect to the gel strength for both alkaline element cations and sim ple low-molecular anions has been shown to be in agreement with the po sitions of these ions in corresponding lyotropic (Hofmeister) series. Namely, the ions (chaotropic ones), which are capable to interfere the H-bonding, disturbed somewhat the cryotropic gel-formation of PVA and facilitated the marked additional swelling of cryogels preliminary pr epared in pure water medium, whereas the ions (antichaotropic ones), w hich are capable to promote the H-bonding, caused the formation of rei nforced cryogels and resulted in the shrinking of cryogels prepared wi thout salt additives. More pronounced effects were observed for anions as compared with cations. Some anomalous swelling behavior of PVA cry ogel in Cs+-containing solutions was supposed to be associated with th e formation of weak chelates. In addition to antichaotropic inorganic salts like NaF, rather high salting-out effects in respect to PVA were exhibited by well-soluble amino acid salts: glycine zwitter-ions, lys ine monochlorohydrate, and monosodium aspartate. (C) 1996 John Wiley & Sons, Inc.