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.