Intrinsic Self-healing Polymers Research Articles

Preparation of Epoxy Resin with Disulfide-Containing Curing Agent and Its Application in Self-Healing Coating.

Intrinsic self-healing polymers via dynamic covalent bonds have been attracting extensive attention because of their repeatable self-healing property. Herein, a novel self-healing epoxy resin was synthesized with disulfide-containing curing agent via the condensation of dimethyl 3,3'-dithiodipropionate (DTPA) and polyether amine (PEA). Therefore, in the structure of cured resin, flexible molecular chains and disulfide bonds were imported into the cross-linked polymer networks for triggering self-healing performance. The self-healing reaction of cracked samples was realized under a mild condition (60 °C for 6 h). The distribution of flexible polymer segments, disulfide bonds and hydrogen bonds in cross-linked networks plays a great role in the self-healing process of prepared resins. The molar ratio of PEA and DTPA strongly affects the mechanical performance and self-healing property. Especially when that molar ratio of PEA to DTPA is 2, the cured self-healing resin sample showed great ultimate elongation (795%) and excellent healing efficiency (98%). The products can be used as an organic coating, in which the crack could self-repair during a limited time. The corrosion resistance of a typical cure coating sample has been testified by an immersion experiment and electrochemistry impedance spectrum (EIS). This work provided a simple and low-cost route to prepare a self-healing coating for prolonging the service life of conventional epoxy coatings.

High-Performance Self-Healing Polymers

ConspectusSelf-healing ability is one of the most attractive features of biological tissues, as it helps living creatures to recover physiological functions and prolongs their lifespans after unexpected injuries. Inspired by this feature, self-healing artificial polymers have been developed based on extrinsic and intrinsic designs since the 1950s. In particular, the intrinsic self-healing polymers have received enormous attention since 2001 because of their unlimited self-healing times and easy preparation. Therefore, many excellent works are reported, and our understanding of the self-healing polymer goes deeper and deeper. Self-healing is the process of the rejoining of the dynamic bonds/interactions. Therefore, the healing process involves two critical factors. One is the dynamic nature of dynamic bonds/interactions. The other is the high mobility of the polymer chains. However, the dynamic bonds/interactions are vulnerable to external forces and environmental stimuli because their bond energy is lower than that of the covalent bonds, which leads to several innate drawbacks of intrinsic self-healing polymers, such as poor mechanical properties (low fracture strength, low fracture strain, low modulus, and low fracture toughness) and poor resistance against the external environment (vulnerable to acid, alkali, or moisture). Also, since high chain mobility is also a prerequisite for intrinsic self-healing, most polymers cannot be healed in the glassy state where the polymer chains are frozen. Therefore, it is challenging to develop high-performance self-healing polymers, which not only possess high mechanical strength, toughness, and stability under ambient conditions or severe environments but also manifest high self-healing efficiency in the rubbery state or even in the glassy state. Therefore, how to overcome this challenge has become a hot topic in the field of self-healing polymers.To address the above problem, many high-performance self-healing polymers with high mechanical properties, high self-healing ability, or high environmental stability are published by using different strategies. These strategies are effective at enhancing the mechanical properties or increasing its environmental stability and are worth learning about. Our group has carried out some work in this field. In this Account, we highlight our works toward fabricating high-performance self-healing polymers. We summarize the high-performance self-healing polymers from three aspects: self-healing polymers with high mechanical properties (such as high toughness, tensile strength, stretchability, and modulus), glassy polymers capable of self-healing in the glassy state, and environmentally stable self-healing polymers. In particular, strategies based on tailoring molecular-level structure, condensed structure, and filler reinforcement are discussed in detail to construct self-healing polymers with high mechanical properties. Finally, the future development of intrinsic self-healing polymers is examined from the perspective of practical application and fundamental research.

Intrinsically Self-Healing Polymers: From Mechanistic Insight to Current Challenges

Self-healing materials open new prospects for more sustainable technologies with improved material performance and devices' longevity. We present an overview of the recent developments in the field of intrinsically self-healing polymers, the broad class of materials based mostly on polymers with dynamic covalent and noncovalent bonds. We describe the current models of self-healing mechanisms and discuss several examples of systems with different types of dynamic bonds, from various hydrogen bonds to dynamic covalent bonds. The recent advances indicate that the most intriguing results are obtained on the systems that have combined different types of dynamic bonds. These materials demonstrate high toughness along with a relatively fast self-healing rate. There is a clear trade-off relationship between the rate of self-healing and mechanical modulus of the materials, and we propose design principles of polymers toward surpassing this trade-off. We also discuss various applications of intrinsically self-healing polymers in different technologies and summarize the current challenges in the field. This review intends to provide guidance for the design of intrinsic self-healing polymers with required properties.

Dynamic Modeling of Intrinsic Self-Healing Polymers Using Deep Learning.

The properties of self-healing polymers are traditionally identified through destructive testing. This means that the mechanics are explored in hindsight with either theoretical derivations and/or simulations. Here, a self-healing property evolution using energy functional dynamical (SPEED) model is proposed to predict and understand the mechanics of self-healing of polymers using images of cuts dynamically healing over time. Using machine learning, an energy functional minimization (EFM) model extracted an effective underlying dynamical system from a time series of two-dimensional cut images on a self-healing polymer of constant thickness. This model can be used to capture the physics behind the self-healing dynamics in terms of potential and interface energies. When combined with a static property prediction model, the SPEED model can predict the macroscopic evolution of material properties after training only on a small set of experimental measurements. Such temporal evolutions are usually inaccessible from pure experiments or computational modeling due to the need for destructive testing. As an example, we validate this approach on toughness measurements of an intrinsic self-healing conductive polymer by capturing over 100 000 image frames of cuts to build the machine learning (ML) model. The results show that the SPEED model can be applied to predict the temporal evolution of macroscopic properties using few measurements as training data.

Bio-inspired self-healing MXene/polyurethane coating with superior active/passive anticorrosion performance for Mg alloy

The presence of micropores/cracks and the poor self-healing performance cause the organic coating to degrade its protective ability during long-term corrosion. In this work, a bio-inspired anticorrosion coating has been successfully fabricated on Mg alloy, which exhibits superior active/passive corrosion protection and self-healing performance. The polyurethane (PU) with synergistic effect derived from disulfide bond and hydrogen bond can self-repair at ambient temperature. The methionine functionalized Ti3C2 MXene (f-MXene) can form hydrogen bonds with self-healing PU matrix and remarkably improve the active/passive anticorrosion properties, which can be ascribed to the corrosion inhibition and labyrinth effect. Based on the electrochemical tests, the f-MXene doped PU (f-MXene@PU) coating displays excellent anticorrosion performance with an ultra-low current density value of 5.107 × 10-11 A cm−2. Besides, the f-MXene@PU coating possesses a remarkable anticorrosion self-healing efficiency of 140 %, as compared to the as-reported traditional intrinsic self-healing polymers with a maximum repair efficiency of 100 %. Combining with the triple effects of active (inhibiting effect) and passive (barrier performance) anticorrosion and self-healing functions, it can provide a green and facile synthesis strategy for constructing self-healing coating with the excellent anticorrosion properties.

An Overview of Self-Healable Polymers and Recent Advances in the Field.

The search for materials with better performance, longer service life, lower environmental impact, and lower overall cost is at the forefront of polymer science and material engineering. This has led to the development of self-healing polymers with a range of healing mechanisms including capsular-based, vascular, and intrinsic self-healing polymers. The development of self-healable systems has been inspired by the healing of biological systems such as skin wound healing and broken bone reconstruction. The goal of using self-healing polymers in various applications is to extend the service life of polymers without the need for replacement or human intervention especially in restricted access areas such as underwater/underground piping where inspection, intervention, and maintenance are very difficult. Through an industrial and scholarly lens, this paper provides: a) an overview of self-healing polymers; b) classification of different self-healing polymers and polymer-based composites; c) mechanical, thermal, and electrical analysis characterization; d) applications in coating, composites, and electronics; e) modeling and simulation; and f) recent development in the past 20 years. This review highlights the importance of healable polymers for an economically and environmentally sustainable future, the most recent advances in the field, and current limitations in fabrication, manufacturing, and performance.

Optimization of intrinsic self-healing silicone coatings by benzotriazole loaded mesoporous silica

Multifunctional intrinsic self-healing polymers (ISP) are gaining increasing attention these days, and many studies have been devoted to solving the conflict between achieving high mechanical polymer strength and active polymer chain diffusion. In this research, we developed an optimized self-healing composite coating by adding Benzotriazole (BTA) loaded nano silica (SiO2@BTA) to a dynamic cross-linked Polydimethylsiloxane (PDMS) network，which allows substantial and fast healing of the material integrity upon damage due to the hydrogen interaction between urea and BTA. BTA leaching tests demonstrated a longer release profile during the coating service life and corrosion tests in a 3.5 wt% NaCl aqueous solution indicated that the SiO2@BTA modified PDMS coating shows enhanced corrosion protection of carbon steel upon coating damage. Moreover, after addition of SiO2@BTA, the material failure strength increased from ~1.5 MPa to ~5.5 MPa, and the healing efficiency increased from ~59% to ~90% for 24 h healing at room temperature. Above all, this research provides an intrinsic self-healing coating design method to improve the mechanical strength and the self-healing ability of the ISP as well as enhancing the coating's corrosion protection ability.

Intrinsic Self-Healing Epoxies in Polymer Matrix Composites (PMCs) for Aerospace Applications.

This article reviews some of the intrinsic self-healing epoxy materials that have been investigated throughout the course of the last twenty years. Emphasis is placed on those formulations suitable for the design of high-performance composites to be employed in the aerospace field. A brief introduction is given on the advantages of intrinsic self-healing polymers over extrinsic counterparts and of epoxies over other thermosetting systems. After a general description of the testing procedures adopted for the evaluation of the healing efficiency and the required features for a smooth implementation of such materials in the industry, different self-healing mechanisms, arising from either physical or chemical interactions, are detailed. The presented formulations are critically reviewed, comparing major strengths and weaknesses of their healing mechanisms, underlining the inherent structural polymer properties that may affect the healing phenomena. As many self-healing chemistries already provide the fundamental aspects for recyclability and reprocessability of thermosets, which have been historically thought as a critical issue, perspective trends of a circular economy for self-healing polymers are discussed along with their possible advances and challenges. This may open up the opportunity for a totally reconfigured landscape in composite manufacturing, with the net benefits of overall cost reduction and less waste. Some general drawbacks are also laid out along with some potential countermeasures to overcome or limit their impact. Finally, present and future applications in the aviation and space fields are portrayed.

Basic Approaches to the Design of Intrinsic Self-Healing Polymers for Triboelectric Nanogenerators.

Triboelectric nanogenerators (TENGs) as a revolutionary system for harvesting mechanical energy have demonstrated high vitality and great advantage, which open up great prospects for their application in various areas of the society of the future. The past few years have seen exponential growth in many new classes of self-healing polymers (SHPs) for TENGs. This review presents and evaluates the SHP range for TENGs, and also attempts to assess the impact of modern polymer chemistry on the development of advanced materials for TENGs. Among the most widely used SHPs for TENGs, the analysis of non-covalent (hydrogen bond, metal–ligand bond), covalent (imine bond, disulfide bond, borate bond) and multiple bond-based SHPs in TENGs has been performed. Particular attention is paid to the use of SHPs with shape memory as components of TENGs. Finally, the problems and prospects for the development of SHPs for TENGs are outlined.

Intrinsic self-healing polymers for advanced lithium-based batteries: Advances and strategies

Advanced rechargeable lithium-based batteries have a profound effect on our global society and polymer materials are one of the key components of these batteries. The key roles of polymers applied in battery technology are presented in terms of binders, package coatings, separators, and electrolytes. However, the loathsomely structural changes during repeated charge/discharge processes result in the mechanical fracture problems of polymers inside batteries, which significantly reduce the cycling lifetimes. The use of intrinsic self-healing polymers as substitutes is one of the most favored strategies for reviving lithium-based batteries since self-healing polymers spontaneously eliminate the mechanical cracks or damages and result in greatly enhanced electrochemical performances. In this review, we first introduce the advances and working mechanism of intrinsic self-healing polymers. Then, we discuss the opportunities and challenges in the development of advanced lithium-based batteries with Si, Li-metal, S electrodes, and polymer electrolytes, respectively, and summarize the up-to-date key progress in intrinsic self-healing polymers for solving the above-mentioned challenges. Finally, we propose some designing principles of desired intrinsic self-healing polymers from the perspectives of basic structures, ionic conductivities, mechanical properties, chemical interactions, and the self-healing capabilities.

A deconvolution protocol of the mechanical relaxation spectrum to identify and quantify individual polymer feature contributions to self-healing

Starting from experimental macro-rheological data, we develop a fitting protocol that succeeded in the separation of the overlapping relaxation phenomena in the dissipative regime for a set of intrinsic healing polymers healing most effectively near their glass transition temperature Tg. To allow for a proper deconvolution, the rheological master curves are converted to a relaxation spectrum (H(τ)) and this is fitted using an optimized mechanical model, e.g. the Maxwell-Weichert model. The deconvolution of overlapping segmental mobility and reversible interactions is successfully demonstrated for a set of polyimide and polyamide polymers containing none, one and two reversible dynamic features near-Tg. Through the fitting parameters, the relaxation timescale of each feature and their apparent process enthalpies are obtained. The quantitative data obtained using the fitting protocol are then compared to macroscopic healing results. As a result, a clear correspondence between the energy stored by the system to accomplish reversible (e.g. H-bonds, π-π) and chain interdiffusion relaxation transitions and the healing efficiency of such polymers are obtained. The implementation of this protocol allows for a clearer identification of the relevant mechanisms in self-healing polymers and paves the way for the development of more efficiently healable polymeric systems.

Intrinsic self-healing polymers with a high E-modulus based on dynamic reversible urea bonds

The straightforward synthesis of a urea polymer network is presented. Commercially available monomers are polymerized using light-induced polymerization, resulting in networks crosslinked by hindered urea molecules. These moieties are reversible and, thus, can be converted into the starting compounds (that is, isocyanate and amine) by a simple thermal treatment. This process is monitored using differential scanning calorimetry as well as Raman and infrared spectroscopy. Furthermore, the self-healing ability of these polymer networks is investigated using scratch-healing tests as well as bulk-healing investigations using tensile testing. The resultant materials have a high E-modulus, are able to heal scratches at temperatures above 70 °C multiple times and their mechanical properties can be partially regenerated. The underlying healing mechanism is based on the reversible opening of the urea bonds and exchange reactions between two functional groups, which were confirmed from a spectroscopic analysis. In summary, these new materials are a new type of intrinsically healable polymers and provide a first step toward hard and healable polymers.

A tough polyurethane elastomer with self-healing ability

Due to sufficient polymer chain mobility and molecular diffusion, most of the present intrinsic self-healing polymers that heal damage by utilizing reversible bonds are soft or gel. However, a tough self-healing polymer is needed as they can be used as strong and light weight material for engineering applications. Based on the high versitility of polyurethanes, herein we report the development of a disulfide-containing poly(urea-urethane) (PUU) network, where aromatic disulfide diamine is used to establish linkages for tri-functional homopolymer of hexamethylene diisocyanates (tri-HDI) as well as aliphatic prepolymer chains, resulting in the readily conversion between a well cross-linked network and an un-crosslinked structure. With this linkage, the network is able to balance the two seemly contradictory forces, exhibiting simultaneously superior mechanical performances and high self-healing efficiencies in the absence of any catalyst or external intervention. In addition, these materials are capable of repairing themselves repeatedly thus possessing a high potential for industrial applications with further investigation.