Heterogeneity, Segmental and Hydrogen Bond Dynamics, and Aging of Supramolecular Self-Healing Rubber

Abstract

In recent years, self-healing materials have attracted increasing attention due to their potentially spontaneous self-repairing ability after mechanical damage. Here, we focus on a supramolecular self-healing rubber based on fatty acids following the work of Leibler and co-workers. We study the heterogeneous network structure and hydrogen bond dynamics as well as its significant aging properties using several experimental techniques. NMR experiments reveal that the rubber is basically a two-component system, with a ∼85% fraction of material rich in hydrogen-bonded structures and associated aliphatic moieties, undergoing a glass transition just below ambient temperature, and the other one being comprised of more mobile aliphatic chains. Changes in the IR bands corresponding to the NH bending and CO stretching vibrations show that water in the rubber not only takes the role of a plasticizer, reducing the glass transition temperature of the main component, but also is involved in changes of the hydrogen-bonding network. On the basis of shear rheology experiments and proton low-field NMR, we deduce that the rubber undergoes irreversible chemical cross-linking reactions at temperatures above 110 °C, going along with a weakening of its self-healing ability.

Linear rheology of bis-urea functionalized supramolecular poly(butylacrylate)s: Part I – weak stickers

“…The rheological properties of the latter systems (i.e. type 2) have been thoroughly studied, in particular in the melt but with a strong emphasis on polymer chains that bear at least two stickers per chain, in order to allow for an efficient elastic behavior 12,13,14,15,16 . Many experimental and theoretical studies showed that in both cases the presence of these stickers strongly affects the rheological properties.…”

Critical Effect of Segmental Dynamics in Polybutadiene/Clay Nanocomposites Characterized by Solid State 1H NMR Spectroscopy

“…36−44 In principle, molecular mobility can be deduced from simple FID signals where a fast or slow decay indicates the presence of rigid or mobile components, respectively. 45 In comparison, proton multiple quantum NMR (MQ NMR) mostly probes molecular motions that involve a large number of segments up to the level of the whole chain, which dominates the mechanical properties of soft polymeric systems. 39 Graf et al used 1 H MQ NMR under fast magic angle spinning (MAS) to elucidate the nature of the polymer segmental dynamics in polybutadiene 46 and cross-linked poly(styrene-co-butadiene) 47 melt far above the glass transition with site resolution.…”

“…39 Saalwachter et al introduced a reference signal by changing the phase cycling and were able to quantitatively analyze the segmental dynamics and structural constraints in polymeric soft materials utilizing Baum-Pines sequences 51 with a benchtop low-field NMR spectrometer. 39 45 Also, Litvinov et al utilized DQ NMR and T 2 relaxometry to study the rubber−filler interaction in carbon black and silica filled rubbers, and quantitative information about immobilization of rubber chains on the surface of fillers was obtained. 60−62 The segmental dynamics near clay surfaces had been hypothesized to play an important role in a new class of telechelic polybutadiene/clay nanocomposite physical gels.…”

Healable supramolecular polymer solids

“…Further investigations of Leibler's self-healing polymer by Sun, Saalwächter and coworkers showed that this material can be regarded as a nanophase segregated system [71]. The fatty acid chains form a minor mobile phase that accounts for 15% of the total sample.…”