| Abstract
| - The poly(vinyl alcohol)−Congo Red (PVA/CR) complex in aqueous solutions exhibited areentrant sol−gel transition at ambient temperature by increasing the CR concentration, CCR, when thePVA concentration was near the chain overlap concentration (CPVA ≈ 455 mM). The system was in thesol state at CCR ≤ 1.0 mM and 10.0 ≤ CCR ≤ 30.0 mM, while it underwent gelation at two CCR regions: 1.5 ≤ CCR ≤ 9.0 mM and 35 mM ≤ CCR. This reentrant transition has been investigated microscopicallyby means of dynamic light scattering. Speckle patterns appeared exclusively in the gel phase. Thereentrant sol−gel transition was also demonstrated by a shape change of the time−intensity correlationfunction (ICF), which varied from a stretched-exponential function for sol states to a power-law functionfor gel states. The variations of the correlation length ξ and the power-law exponent, n, in ICF have beenextensively discussed.
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