COMPLEXATION OF POLY(VINYL ALCOHOL) CONGO RED AQUEOUS-SOLUTIONS .2. SANS AND SAXS STUDIES ON SOL-GEL TRANSITION

Poly(vinyl alcohol)-congo red (PVA-CR) complexes in aqueous solutions undergo a reentrant sol-gel transition with respect to C-CR [Shibayama; et al. Macromolecules 1994, 27, 1738]. This transition was investigated from the structural viewpoints in terms of small angle neutron and X-ray scattering techniques. The static scattered intensity, I(q), was observed as functions of PVA and CR concentrations, C-PVA and C-CR, and temperature, where q is the magnitude of the scattering vector. The contribution of the CR cluster scattering was successfully subtracted from I(q), and the corrected scattered intensity function, I-corr(q) was analyzed in terms of a so-called Kratky plot, i.e. q(2)I(q) vs a. A scattering maximum due to cluster formation and/or gelation was observed in the Kratky plot. I-corr(q) was decomposed to Lorentz-type and Gauss-type scattering functions, where the Lorentz function represents the liquidlike fluctuations and the Gauss function indicates the presence of the static inhomogeneity created by complexation and/or gelation, The mechanism of the reentrant type sol-gel transition was discussed in terms of the structural parameters obtained by a curve fitting with this function.