Abstract
Interactions between water and two polymers used in membrane technology which are cellulose acetate (39.8% acetyl content: CA) and poly-trans-2, 5-dimethyl piperazinthiofurazanamide (DMP-TFZ) are presented. Experimental adsorption isotherms are discussed on the basis of BET, Zimn, Flory-Huggins theories. DMP-TFZ shows a lower water cluster formation tendency than CA at low and mean activities. The state of water was studied also by IR: in both the polymers the adsorbed water stretching OH frequencies are shifted to higher values showing weaker H bonds than in water. This can be related to the existence of water in the state of monomer and small size aggregates and favours high mobility. The structure of CA dense films is amorphous to X rays, but a certain amount of crystallinity is revealed by DTA. DMP-TFZ is amorphous to X rays, has a high T and shows high stiffness to mechanical dynamical tests. The suggestion is made that stiff chain polymers which contain hydrophilic groups and which cannot easily crystallize, but can get a close packing, do not allow the formation of big free volume packets across which large size water clusters, able to solvate ions, can move.
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