Abstract
Linear viscoelasticity (LVE) of low-ion-content and low-molecular-weight (nonentangled) randomly sulfonated polystyrene shows a sol–gel transition when the average number of ionic groups per chain approaches unity. This transition can be well understood by regarding the number of ionizable sites over a chain as the relevant functionality for cross-linking. For ionomers below but very close to the gel point, the LVE shows power law relaxation similar to gelation of chemical cross-linking. Nevertheless, ionomers near and beyond the gel point also show terminal relaxation not seen in chemically cross-linking systems, which is controlled by ionic dissociation. Careful analysis of the power law region of the frequency dependence of complex modulus close to the gel point shows a change in exponent from ∼1 at high frequency to ∼0.67 at low frequency, which strongly suggests a transition from mean-field to critical percolation known as the Ginzburg point. A mean-field percolation theory by Rubinstein and Semenov ...
Published Version
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