Viscoelasticity of Reversible Gelation for Ionomers

Abstract

Linear viscoelasticity (LVE) of low-ion-content and lowmolecular-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 crosslinking. 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 for gelation with effective breakup has been modified to include critical percolation close to the gel point and predicts well the observed LVE of lightly sulfonated polystyrene oligomers.

Viscoelastic properties of poly(methyl methacrylate) with high glass transition temperature by lithium salt addition

“…Similar viscoelastic properties were reported for ionomers . The research group of Weiss studied the rheological properties of ionomers whose molecular weight is lower than the entanglement molecular weight . According to them, the residence time of a free ion‐pair, that is, the lifetime of ion‐pair hopping from one cluster to another, decides the longest relaxation mechanism.…”

Activation Energy for Dissociation of Hydrogen‐Bonding Crosslinkers in Phase‐Change Salogels: Dynamic Light Scattering versus Rheological Studies

“…Determining the activation energy of dissociation of physical bonds can be a challenging task, however, because of the multiple hierarchical length and time scales involved in the polymer chain relaxation as well as diverse contributions of crosslinkers of varying functionality and binding strength to network dynamics …”

“…While there is a sizable body of literature on the rheology‐based studies of the flow activation energy, only a few studies assessed the activation energy of dissociation of physical networks from the temperature dependence of the DLS slow mode . This study aims to explore the role of the hydrogen‐bonding crosslinkers of varied functionality on gelation of a new family of physical gels—phase change salogels, recently developed in our group .…”

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of varying functionality and binding strength to network dynamics. [9][10][11][12][13][14] Rheology has been proven to be a powerful technique that is uniquely suited for studying viscoelasticity and dynamic bonding in physical gels. Specifically, in rheological studies, temperature dependences of the time-temperature shift factor, [8,15,16] zero-shear viscosity, [17,18] and macroscopic relaxation time of the transient network [19][20][21][22][23][24][25][26] have been all used to calculate a flow activation energy (E a ).

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Linear viscoelastic studies on a transient network formed by host–guest interaction

“…This method roughly can be categorized into two classes. One is the polymeric system with associations induced by hydrogen bonds, metal coordination, ion complexation, and so on. The other is the thermoplastic elastomer, which consists of hard associating segments and soft rubbery segments.…”