We have studied the dynamics of poly(vinyl alcohol) (PVA) in aqueous borax solution by dynamic light scattering (DLS) and dynamic viscoelastic (DVE) measurements. DLS measurement showed the presence of two dominant modes with decaying rates of Γf and Γs (Γf > Γs). Different dynamical behaviors were observed above and below a critical concentration, CN. The slow mode was manifested to be the diffusive mode for PVA concentration C < CN and the relaxation mode for C > CN. Dynamical correlation length, ξH, estimated from Γf exhibited a jump at CN with increasing C. Detailed analysis revealed the applicability of the dynamic scaling theory to Γs for C < CN and the presence of the dynamic coupling between concentration fluctuation and elastic stress of the transient network for C > CN. From these results, we drew the picture on a growing process of associating PVA chains to a temporally cross-linked network with increasing C and proposed that CN corresponded to the gel point of the chemically cross-linked gel in the short-time domain. The concept is found to be useful for interpretation of the concentration dependence of the plateau modulus.
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