Hierarchical Sticker and Sticky Chain Dynamics in Self-Healing Butyl Rubber Ionomers

Abstract

We present a detailed comparison of the microscopic dynamics and the macroscopic mechanical behavior of novel butyl rubber ionomers with tunable dynamics of sparse sticky imidazole-based sidegroups that form clusters of about 20 units separated by essentially unperturbed chains. This material platform shows promise for application as self-healing elastomers. Size and thermal stability of the ionic clusters were probed by small-angle X-ray scattering, and the chain and sticker dynamics were studied by a combination of broadband dielectric spectroscopy (BDS) and advanced NMR methods. The results are correlated with the rheological behavior characterized by dynamic− mechanical analysis (DMA). While the NMR-detected chain relaxation and DMA results agree quantitatively and confirm relevant aspects of the sticky-reptation picture on a microscopic level, we stress and explain that apparent master curves are of limited use for such a comparison. The cluster-related relaxation time detected by BDS is much shorter than the elastic chain relaxation time, although the weak conductivity does follow the latter. The systematic trends across the sample series suggest that all relaxations are dominated by a cluster-related activation barrier, but also that the BDS-based cluster relaxation does not seem to be directly associated with the effective sticker lifetime. Nonlinear stress−strain experiments demonstrate a reduction of sticker lifetime on stretching and that the stored stress and the elastic recovery depend on the deformation rate.

Functionalized Elastomeric Ionomers Used as Effective Toughening Agents for Poly(lactic acid): Enhancement in Interfacial Adhesion and Mechanical Performance

“…This unique thermal transition of the ionomers is usually denoted as an ionic transition . Because of the ionic interactions between the ionic pairs, ionic multiples are initially formed in the ionomers, which is followed by the formation of a phase-separated structure (ionic clusters) due to the aggregation of the ionic multiples. − In elastomeric ionomers, both the chemical structure of the cations and the type of anions greatly influence the cluster behavior. ,,− For the ionomers studied in the present work, the main differences are the chemical structure of the imidazolium cations in the ionomers, including the type of functional group, pendant alkyl chain length, etc. Figure a clearly shows that the relaxation ionic transition peak of i -BIIR-2-OH shifts toward a higher temperature compared to that of the other i -BIIRs.…”

Design Principles of Interfacial Dynamic Bonds in Self‐Healing Materials: What are the Parameters?

“…In reversible dynamic networks, the cross-linking density decreased with rise in temperature, leading to a decrease in D res . [242][243][244][245] Stein and co-workers showed a decreasing trend in D res values as a function of temperature (100-140°C), indicating increasing chain mobility that ultimately resulted in self-sealing of the composite.…”

Chain dynamics in partially cross‐linked polyethylene by combined rheology and NMR‐based molecular rheology

“…D res can be measured most quantitatively via time‐domain double‐quantum (DQ) NMR, and even its distribution has been assessed for studying of the network structure in the rubbers 25 . More general investigations have been performed via extracting the segmental dynamics in terms of the orientation auto‐correlation function (OACF) of the second Legendre polynomial C(t) = 5 < P 2 (cos θ [ t + τ ]) P 2 (cos θ ( t ))>, where θ is the instantaneous segmental orientation with respect to the magnetic field, for the cases of monodisperse polymer melts 26–29 and transient networks 30,31 . In the former case, a good adherence to predictions of the tube‐reptation model could be confirmed, including the expected corrections due to constraint release (CR) and contour length fluctuations (CLF).…”