Polyelectrolyte Chain Flexibility and Entanglements─A Rheo NMR Study

Long-chain polymers can form entanglements in melts or solutions that have a significant impact on mechanical properties. In order to establish entanglements, the polymers in a solution have to be at a sufficiently high concentration, chain length, and flexibility. Entanglements and possible chains to slip along those entanglements result in the viscoelastic behavior of polymers that in turn has a significant impact on the processability of such materials. The flexibility of the polyelectrolyte poly(styrenesulfonate) solutions has been modulated by variation of the ionic strength. The fractal dimension determined from the hydrodynamic radius has been used to illustrate the increased flexibility with ionic strength. The transverse NMR relaxation time T2 was measured to investigate the polymer chain mobility. Below the entanglement length and at low ionic strength, no signature of entanglement has been observed. Only for the sample larger than the entanglement length at sufficiently high ionic strength, entanglements are observed; these become reduced by external shear.