Swap-Driven Self-Adhesion and Healing of Vitrimers

Simone Ciarella,Wouter Ellenbroek

doi:10.3390/coatings9020114

Simone Ciarella, Wouter Ellenbroek

Open Access

https://doi.org/10.3390/coatings9020114

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Journal: Coatings	Publication Date: Feb 12, 2019
Citations: 13	License type: CC BY 4.0

Affiliation: Eindhoven University of Technology

Abstract

Vitrimers are covalent network materials, comparable in structure to classical thermosets. Unlike normal thermosets, they possess a chemical bond swap mechanism that makes their structure dynamic and suitable for activated welding and even autonomous self-healing. The central question in designing such materials is the trade-off between autonomy and material stability: the swap mechanism facilitates the healing, but it also facilitates creep, which makes the perfectly stable self-healing solid a hard goal to reach. Here, we address this question for the case of self-healing vitrimers made from star polymers. Using coarse-grained molecular dynamics simulations, we studied the adhesion of two vitrimer samples and found that they bond together on timescales that are much shorter than the stress relaxation time. We showed that the swap mechanism allows the star polymers to diffuse through the material through coordinated swap events, but the healing process is much faster and does not depend on this mobility.

Highlights

Equipping materials with a mechanism to repair themselves after damage is a cornerstone of the sustainable use of natural resources [1]
We considered the situation in which two surfaces of this material are brought together after a long time, which for most healing strategies based on reversible crosslinking should be considered a worst-case scenario, and showed that two such surfaces develop a bulk-like mechanical connection on time scales that are much shorter than the diffusion time of the star polymers or the stress relaxation time of the material
In our previous work, we demonstrated that stress relaxation in star polymer vitrimers takes many swap events, and can be controlled via the topology of the network [19]

Summary

Introduction

Equipping materials with a mechanism to repair themselves after damage is a cornerstone of the sustainable use of natural resources [1]. Strategies have been developed towards this goal for material classes as diverse as linear polymers [2], supramolecular networks [3,4], dendrimer-clay systems [5], metal ion–polymer systems [6,7], and multicomponent systems [8,9,10,11,12]. Crosslinked polymeric materials have been at the heart of many developments [14]. Along those lines: polymers form a huge part of the materials industry, and physical crosslinks that can reform after being broken are a natural choice for self-healing. For strong and stable materials, polymer networks that are covalently crosslinked yet adaptable are preferred [15]. In particular, have emerged as a new paradigm for combining malleability and recyclability with strength and solvent-resistance, based on the chemical swapping of bonds [16]

Results

Discussion

Conclusion