Effect of co-solvent complex on preferential adsorption phenomenon in polyvinyl alcohol ternary solutions

In this work, the effect of co-solvent complex on preferential adsorption p henomenon in polyvinyl alcohol (PVA)/N-methyl-2-pyrrolidone (NMP)/water ter nary solutions was studied. It should be noticed that in this system one NM P molecule could bind with two water molecules to form NMP(water)(2) ter-so lvency complex. The formation of the NMP(water)(2) complex is found to sign ificantly affect the preferential adsorption phenomenon. At the NMP volume fraction of phi(1) < 0.73 in co-solvent mixture, the PVA chains preferentia lly adsorb the water molecule. Owing to the poorer affinity of water compar ed with that of NMP to PVA, contracted PVA coils are formed at this conditi on. At phi(1) > 0.73, the PVA chains preferentially adsorb the NMP molecule , which is a better solvent for PVA, inducing an A(2) value that rapidly in creases. The PVA coil exhibits a much-extended conformation. Moreover, the theoretical values of preferential adsorption coefficient, alpha(a), obtain ed from two Read formalisms are in poor agreement with the experimental res ults. This is due, considerably, to the effect of the NMP(water)(2) complex formation in this co-solvent system. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.