Aggregation Behavior in Semidilute Rigid and Semirigid Polysaccharide Solutions

Dynamic and static light scattering experiments were performed on 0.1 M NaCl aqueous solutions of semirigid hyaluronan and rigid xanthan in the dilute and semidilute regime. In the dilute regime, typical good solvent behavior is found, and the intrinsic persistence length of hyaluronan (≈100 Å) and xanthan (≈1000 Å) is determined. However, in the semidilute regime the time autocorrelation function of the scattered electric field is found to be bimodal for hyaluronan and xanthan solutions. The short time relaxation has a typical q -2 dependence and is attributed to the relaxation of concentration fluctuations characterized by a cooperative diffusion mechanism. The long time relaxation has a q -3 dependence, characteristic of intraparticle dynamics. This behavior is not consistent with predicted semidilute, good solvent system behavior but instead indicates the presence of associations or microgels. The corresponding slow relaxation times appear to be related to the macroscopic viscosity of the surrounding polymer solution. The effect of the molecular weight and polymer concentration was investigated.