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 phenomenon in polyvinyl alcohol (PVA)/N-methyl-2-pyrrolidone (NMP)/water ternary solutions was studied. It should be noticed that in this system one NMP molecule could bind with two water molecules to form NMP(water)(2) ter-solvency complex. The formation of the NMP(water)(2) complex is found to significantly affect the preferential adsorption phenomenon. At the NMP volume fraction of phi(1) < 0.73 in co-solvent mixture, the PVA chains preferentially adsorb the water molecule. Owing to the poorer affinity of water compared with that of NMP to PVA, contracted PVA coils are formed at this condition. 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 increases. The PVA coil exhibits a much-extended conformation. Moreover, the theoretical values of preferential adsorption coefficient, alpha(a), obtained from two Read formalisms are in poor agreement with the experimental results. 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 rights reserved.