Solvent effects on aggregation behavior of polyvinyl alcohol solutions

The present study elucidates the effects of solvent quality and polymer con centration on the aggregation behavior of polyvinyl alcohol (PVA) solutions from the dilute solution to semi-dilute solution regions. Combination of t he results in static and dynamic light scattering indicates that in dilute solution the thermodynamic driving forces primarily dominate the dynamic be havior of PVA/N-methylpyrrolidone (PVA/NMP) solution. In contrast with PVA/ water solution, the hydrodynamic interaction would dominate the dynamic beh avior of the solution. The concentration dependence on the dynamic behavior of semi-dilute solution has also been studied through DLS measurement. For PVA/water solutions, the hydrodynamic correlation length of fast mode has a concentration dependence given by xi (D), = [eta ]C-0.42, and the value o f exponent is close to the predicted value from scaling theory in the margi nal solvent. On the other hand, for PVA/NMP solutions the value of exponent is close to the predicted value from the scaling theory in good solvent li mit: -0.75. However, contrary to the expectation, the gelation behavior cou ld not occur in PVA/water solutions at the same condition of gelation in PV A/NMP solution even though the affinity of water to PVA is much lower than that of NMP. In this work, we considered that the PVA/NMP solution might po ssess a character that could form a homogeneous network structure. The inte rmolecular associations must play a dominant role as soon as the chains sta rt to overlap in PVA/NMP solution. On the other hand, combining the DLS res ult with our previous work, the gelation of PVA/NMP solutions is considered due to complex formation in the transient network junctions, i.e. the form ation of molecular complex is crucial to the physical gelation in a good so lvent system. (C) 2001 Elsevier Science Ltd. All rights reserved.