Self-healing dynamic bond-based rubbers: understanding the mechanisms in ionomeric elastomer model systems

Abstract

While it is traditionally accepted that the chain interactions responsible for the elastic response in an elastomeric network are ideally permanent and instantaneously active, the ongoing investigation of self-healing materials reveals that the introduction of self-healing properties into elastomers requires high mechanical integrity under dynamic load conditions, while on long timescales (or at extended temperatures), the chain and bond dynamics must allow for an intrinsic repair of micro cracks occurring during operation and aging. Based on an acrylate-based amorphous ionomer model system with pendant carboxylate groups allowing the systematic variation of the composition and the nature of the counter ion, we demonstrate the interrelation between the morphological, thermal, and mechanical properties, and identify the prerequisites and tools for property adjustment and optimization of self-healing efficiency. While the ion fraction is directly related to the effective network density and elastic performance, the crossover frequency between viscous and elastic behavior is influenced by the nature of the counter ion. In order to achieve reliable elastic response and optimal damage repair, the ion fraction in these systems should be in the range of 5 mol% and the chain dynamics should be appropriate to allow for excellent self-healing behavior at moderate healing temperatures.

Remote-controlled activation of self-healing behavior in magneto-responsive ionomeric composites

“…The present study on the magnetically activated self-healing behavior of elastomeric nanocomposites based on dynamic bonds is exemplarily accomplished on a zinc-neutralized ionomer material serving as the matrix [15]. While n-butyl acrylate as the main component of the ionomer leads to a flexible backbone with low T g and no tendency to crystallize, tert.-butyl acrylate comonomer units are selectively hydrolyzed to carboxylic acid groups located statistically along the main chain, and neutralized using zinc acetate as the neutralizing agent.…”

“…Cobalt(II) acetylacetonate (Co(acac) 2 , Aldrich, 97%), iron(III) acetylacetonate (Fe(acac) 3 , ABCR, 99%), oleyl alcohol (ABCR, 85%), oleylamine (Acros Organics, 80e90%) and oleic acid (Fisher Scientific, 70%) are used as received. The ionomer PZn-5.2% (M w~6 0.000 g mol À1 , PDI~1.3) used in this study is prepared according to our previously published procedure [15]. In a salt bath, the mixture is heated to 200 C under stirring.…”

“…This study demonstrates that the energy dissipation from magnetic nanoparticles observed in AC electromagnetic fields offers the possibility to locally accelerate the self-healing behavior in acrylate-based elastic ionomer [15,16] nanocomposites with suitable magnetic fillers. The local development of heat induces a thermally activated rearrangement of the ionic multiplets in the particles' environment within the irradiated region only (see Scheme 1).…”

Self-Healing, High-Permittivity Silicone Dielectric Elastomer

“…Only a few approaches to self-healing dielectric elastomers have been presented to date, [6][7][8] and although multiple approaches to self-healing polymers and elastomers based on for example metal complexes 9 , ionomers 10,11 , hydrogen-bonding 12,13 , π-π stacking 14 and supramolecular assemblies 15,16 have been developed, there has been no focus on dielectric properties. 17 Recently, we presented a novel class of interpenetrating silicone and ionic networks exhibiting increased dielectric permittivity.…”

Dynamic ionic crosslinks enable high strength and ultrastretchability in a single elastomer

“…Recently, supramolecular elastomers comprising low glass transition temperature (T g ) polymer chains and weak dynamic bonds, such as hydrogen bonds 7 , metal-ligand coordination [8][9][10] , and ionic bonds [11][12][13][14][15] , have been designed for autonomic self-healing at room temperature. In contrast to most self-healing materials, these supramolecular elastomers do not require the input of any external energy (such as heat or light) [16][17][18][19][20] , healing agents (such as monomers and catalysts) 21,22 , plasticizers 23 , or solvents [24][25][26][27] .…”