Brittle-to-Ductile Transition of Sulfonated Polystyrene Ionomers

Abstract

This study examines the brittle-to-ductile transition of sulfonated polystyrene ionomers (SPS) with different counterions. The polystyrene precursor was unentangled and had two ionic groups per chain on average. Thus, its terminal relaxation time was comparable to the lifetime of the associating ionic groups. Three types of ionomer samples were used to tune the association lifetime: (1) fully neutralized SPS with different alkali-metal counterions, (2) fully neutralized SPS with mixed sodium and cesium counterions, and (3) partially neutralized SPS with sodium or cesium counterions. For all three systems, the brittle-to-ductile transition could be represented by a diagram of two Weissenberg numbers, Wi and Wi R, defined with respect to the terminal and Rouse relaxation times, respectively. A flowable region existed at sufficiently low Wi, independent of Wi R. At higher Wi, a brittle-to-ductile transition of the ionomer melt occurred above a critical value of Wi R. To achieve ductility during the application of rapid elongational flow, the Rouse-type motions should be sufficiently slow relative to the rate of ion-dissociation, so that the strain-induced breakup of the ionic cross-links would not cause very strong chain retraction that may further lead to the macroscopic fracture.

Nonlinear Rheology of Telechelic Ionomers Based on Sodium Sulfonate and Carboxylate

“…Similar results were found for the ionomers with different M n (= 5K and 16K), as shown in Section S6 in the Supporting Information. Besides, we note that the drop of the transient stress after the overshoot is stronger for M n -SO 3 Na than for M n -COONa, which may be attributable to the stronger chain retraction after the strain-induced breakup of the former ionomer …”

“…Besides, we note that the drop of the transient stress after the overshoot is stronger for M n -SO 3 Na than for M n -COONa, which may be attributable to the stronger chain retraction after the strain-induced breakup of the former ionomer. 31 As shown in Figure 12, the η E + data under fast extension at Wi > 1 are converted into the tensile stress σ E (= η E + εḢ) and plotted against the Hencky strain ε H (= εḢt). If the ionomers hardly relax under fast extension to behave as a rubber network but exhibit no FENE effect, we expect that σ E of the ionomers is described by the neo-Hookean model, σ E,neo-H = G pl (λ 2 − 1/ λ) + 3η R εḢ where λ and G pl denote the stretch ratio and the equilibrium plateau modulus, respectively, and η R is the LVE viscosity resulting from fast relaxation of the ionomers, as shown in Figures 4 and 5.…”

“…For Wi ≪ 1, the association/dissociation is much faster than the flow so that the sample as a whole can relax and flow. In contrast, for Wi ≫ 1, the sample behaves as an elastic rubber at short times ( t ), whereas the flow forces the stickers to dissociate at long t ; namely, the flow largely deforms the chains, and thus, the elastic energy stored in the deformed chain overwhelms the association energy, and the dissociation occurs. , Thus, the macroscopic flow behavior of the associative polymers should strongly depend on whether the energy can be dissipated and the associated structure can be reconstructed during the flow. ,,− …”

Molecular Understanding of Viscoelasticity in Transient Polymer Networks Based on Multiple Methods

“…In particular, controlling the viscoelastic relaxation time of transient networks has been reported to significantly affect large deformation behavior, such as rupture and ductile/brittle fracture [55][56][57] . In addition, natural silk materials, including cocoon silk and spider silk [58][59][60] also utilize dynamic crosslinks between proteins to form high-order structures and their novel physical characteristics such as toughness and heat-resistance.…”

How to Choose a Secondary Interaction to Improve Stretchability of Associative Polymers?

“…Then, a natural question is: whether higher or lower chain mobility is more preferred for improving the stretchability? Recently, we designed a model system that enabled us to answer this question . We used sulfonated polystyrene with two ionic groups per chain, on average, as the model system.…”