A new multiplet-cluster model for the morphology of random ionomers

Self-Organization of Polyurethane Ionomers Based on Organophosphorus-Branched Polyols

Based on organophosphorus branched polyols (AEPAs) synthesized using triethanolamine (TEOA), ortho-phosphoric acid (OPA), and polyoxyethylene glycol with MW = 400 (PEG), vapor-permeable polyurethane ionomers (AEPA-PEG-PUs) were obtained. During the synthesis of AEPAs, the reaction of the OPA etherification with polyoxyethylene glycol was studied in a wide temperature range and at different molar ratios of the starting components. It turned out that OPA simultaneously undergoes a catalytically activated etherification reaction with triethanolamine and PEG. After TEOA is fully involved in the etherification reaction, excess OPA does not react with the terminal hydroxyl groups of AEPA-PEG or the remaining amount of PEG. The ortho-phosphoric acid remaining in an unreacted state is involved in associative interactions with the phosphate ions of the AEPA. Increasing the synthesis temperature from 40 °C to 110 °C leads to an increase in OPA conversion. However, for the AEPA-PEG-PU based on AEPA-PEG obtained at 100 °C and 110 °C, ortho-phosphoric acid no longer enters into associative interactions with the phosphate ions of the AEPA. Due to the hydrophilicity of polyoxyethylene glycol, the presence of phosphate ions in the polyurethane structure, and their associative binding with the unreacted ortho-phosphoric acid, the diffusion of water molecules in polyurethanes is enhanced, and high values of vapor permeability and tensile strength were achieved.

Dynamics in polymers with phase separated dynamic bonds: the case of a peculiar temperature dependence

The topic of polymers with dynamic bonds (stickers) appears as an exciting and promising area of materials science, thanks to their attractive self-healable, recyclable, extremely tough, and super extensible properties. Polymers with phase separated dynamic bonds revealed several unique properties, but mechanisms controlling their viscoelastic properties remain poorly understood. In this work, we present a dynamic analysis of a model polymer system with phase separated hydrogen bonding functionalities. The results confirm that terminal relaxation in these systems is independent of polymer segmental dynamics and is instead controlled by structural relaxations in clusters of stickers. Detailed analysis revealed a surprising result: terminal relaxation time of these systems has weaker temperature dependence than that of structural relaxation in clusters, although the former is slower than the latter. Borrowing ideas from the field of block copolymers, we ascribed this unusual result to an LCST-like behavior for the miscibility of the stickers in the polymer matrix. The presented results and ideas deepen the understanding of the viscoelasticity for polymers with dynamic bonds, enabling intelligent design of functional materials with desired macroscopic properties.

Crystallization Behavior of Copolyesters Containing Sulfonates

The polar sulfonate groups in cationic dyeable polyester (CDP) lead to complex crystallization behavior, affecting CDP production's stability. In this study, cationic dyeable polyesters (CDP) with different sulfonate group contents were prepared via one-step feeding of sodium isophthalic acid-5-sulfonate (SIPA), terephthalic acid (PTA), and ethylene glycol (EG). The non-isothermal crystallization behavior of these copolyesters was analyzed by differential scanning calorimetry (DSC). Results show that the crystallization temperature of the sample shifts to lower values with the increase in SIPA content. The relaxation behavior of the molecular chain is enhanced due to the ionic aggregation effect of sulfonate groups in CDP. Therefore, at low cooling rates (2.5 °C/min and 5 °C/min), some molecular chain segments in CDP are still too late to orderly stack into the lattice, forming metastable crystals, and melting double peaks appear on the melting curve after crystallization. When the cooling rate increases (10-20 °C/min), the limited region of sulfonate aggregation in CDP increases, resulting in more random chain segments, and a cold crystallization peak appears on the melting curve after crystallization. The non-isothermal crystallization behavior of all samples was fitted and analyzed by the Jeziorny equation, Ozawa equation, and Mo equation. The results indicate that the nucleation density and nucleation growth rate of CDP decrease with the increase in SIPA content. Meanwhile, analysis of the Kissinger equation reveals that the activation energy of non-isothermal crystallization decreases gradually with the increase in SIPA content, and the addition of SIPA makes CDP crystallization more difficult.

From Molecular Constraints to Macroscopic Dynamics in Associative Networks Formed by Ionizable Polymers: A Neutron Spin Echo and Molecular Dynamics Simulations Study

The association of ionizable polymers strongly affects their motion in solutions, where the constraints arising from clustering of the ionizable groups alter the macroscopic dynamics. The interrelation between the motion on multiple length and time scales is fundamental to a broad range of complex fluids including physical networks, gels, and polymer-nanoparticle complexes where long-lived associations control their structure and dynamics. Using neutron spin echo and fully atomistic, multimillion atom molecular dynamics (MD) simulations carried out to times comparable to that of chain segmental motion, the current study resolves the dynamics of networks formed by suflonated polystryene solutions for sulfonation fractions 0 ≤ f ≤ 0.09 across time and length scales. The experimental dynamic structure factors were measured and compared with computational ones, calculated from MD simulations, and analyzed in terms of a sum of two exponential functions, providing two distinctive time scales. These time constants capture confined motion of the network and fast dynamics of the highly solvated segments. A unique relationship between the polymer dynamics and the size and distribution of the ionic clusters was established and correlated with the number of polymer chains that participate in each cluster. The correlation of dynamics in associative complex fluids across time and length scales, enabled by combining the understanding attained from reciprocal space through neutron spin echo and real space, through large scale MD studies, addresses a fundamental long-standing challenge that underline the behavior of soft materials and affect their potential uses.

Unlocking the potential of self-healing and recyclable ionic elastomers for soft robotics applications

In the field of soft robotics, current materials face challenges related to their load capacity, durability, and sustainability. Innovative solutions are required to address these problems beyond conventional strategies, which often lack long-term ecological viability. This study aims to overcome these limitations using mechanically robust, self-healing, and recyclable ionic elastomers based on carboxylated nitrile rubber (XNBR). The designed materials exhibited excellent mechanical properties, including tensile strengths (TS) exceeding 19 MPa and remarkable deformability, with maximum elongations (EB) over 650%. Moreover, these materials showed high self-healing capabilities, with 100% recovery efficiency of TS and EB at 110 °C after 3 to 5 h, and full recyclability, preserving their mechanical performance even after three recycling cycles. Furthermore, they were also moldable and readily scalable. Tendon-driven soft robotic grippers were successfully developed out of ionic elastomers, illustrating the potential of self-healing and recyclability in the field of soft robotics to reduce maintenance costs, increase material durability, and improve sustainability.

Role of hierarchy structure on the mechanical adaptation of self-healing hydrogels under cyclic stretching

Soft materials with mechanical adaptability have substantial potential for various applications in tissue engineering. Gaining a deep understanding of the structural evolution and adaptation dynamics of soft materials subjected to cyclic stretching gives insight into developing mechanically adaptive materials. Here, we investigate the effect of hierarchy structure on the mechanical adaptation of self-healing hydrogels under cyclic stretching training. A polyampholyte hydrogel, composed of hierarchical structures including ionic bonds, transient and permanent polymer networks, and bicontinuous hard/soft-phase networks, is adopted as a model. Conditions for effective training, mild overtraining, and fatal overtraining are demonstrated in soft materials. We further reveal that mesoscale hard/soft-phase networks dominate the long-term memory effect of training and play a crucial role in the asymmetric dynamics of compliance changes and the symmetric dynamics of hydrogel shape evolution. Our findings provide insights into the design of hierarchical structures for adaptive soft materials.

Bead-Spring Simulation of Ionomer Melts-Studying the Effects of Chain-Length and Associating Group Fraction on Equilibrium Structure and Extensional Flow Behavior

Ionomers are associative polymers with diverse applications ranging from selective membranes and high-performance adhesives to abrasion- and chemical-resistant coatings, insulation layers, vacuum packaging, and foamed sheets. Within equilibrium melt, the ionic or associating groups are known to form thermally reversible, associative clusters whose presence can significantly affect the system's mechanical, viscoelastic, and transport properties. It is, thus, of great interest to understand how to control such clusters' size distribution, shape, and stability through the designed choice of polymer architecture and the ionic groups' fraction, arrangement, and interaction strength. In this work, we represent linear associating polymers using a Kremer-Grest type bead-spring model and perform large-scale MD simulations to explore the effect of polymer chain-length (l) and fraction (fs) of randomly placed associating groups on the size distribution and stability of formed clusters. We consider different chain-lengths (below and above entanglement), varying fractions of associating groups (represented by 'sticky' beads) between 5 and 20%, and a fixed sticky-sticky nonbond interaction strength of four times that between regular non-associating beads. For all melts containing associating groups the equilibrium structure factor S(q) displays a signature ionomer peak at low wave vector q whose intensity increases with increasing fs and l. The average cluster size Nc increases with fs. However, the effect of chain-length on Nc appears to be pronounced only at higher values of fs. Under extensional flows, the computed stress (and viscosity) is higher at higher fs and l regardless of strain rate. Beyond a critical strain rate, we observe fragmentation of the associative clusters, which has interesting effects on the stress/viscous response.

Electrochemical Properties and Structure of Membranes from Perfluorinated Copolymers Modified with Nanodiamonds

In this study, we aimed to design and research proton-conducting membranes based on Aquivion®-type material that had been modified with detonation nanodiamonds (particle size 4-5 nm, 0.25-5.0 wt. %). These nanodiamonds carried different functional groups (H, OH, COOH, F) that provided the hydrophilicity of the diamond surface with positive or negative potential, or that strengthened the hydrophobicity of the diamonds. These variations in diamond properties allowed us to find ways to improve the composite structure so as to achieve better ion conductivity. For this purpose, we prepared three series of membrane films by first casting solutions of perfluorinated Aquivion®-type copolymers with short side chains mixed with diamonds dispersed on solid substrates. Then, we removed the solvent and the membranes were structurally stabilized during thermal treatment and transformed into their final form with -SO3H ionic groups. We found that the diamonds with a hydrogen-saturated surface, with a positive charge in aqueous media, contributed to the increase in proton conductivity of membranes to a greater rate. Meanwhile, a more developed conducting diamond-copolymer interface was formed due to electrostatic attraction to the sulfonic acid groups of the copolymer than in the case of diamonds grafted with negatively charged carboxyls, similar to sulfonic groups of the copolymer. The modification of membranes with fluorinated diamonds led to a 5-fold decrease in the conductivity of the composite, even when only a fraction of diamonds of 1 wt. % were used, which was explained by the disruption in the connectivity of ion channels during the interaction of such diamonds mainly with fluorocarbon chains of the copolymer. We discussed the specifics of the mechanism of conductivity in composites with various diamonds in connection with structural data obtained in neutron scattering experiments on dry membranes, as well as ideas about the formation of cylindrical micelles with central ion channels and shells composed of hydrophobic copolymer chains. Finally, the characteristics of the network of ion channels in the composites were found depending on the type and amount of introduced diamonds, and correlations between the structure and conductivity of the membranes were established.

Modular Synthesis and Patterning of High-Stiffness Networks by Postpolymerization Functionalization with Iron–Catechol Complexes

Bioinspired iron-catechol cross-links have shown remarkable success in increasing the mechanical properties of polymer networks, in part due to clustering of Fe³⁺-catechol domains which act as secondary network reinforcing sites. We report a versatile synthetic procedure to prepare modular PEG-acrylate networks with independently tunable covalent bis(acrylate) and supramolecular Fe³⁺-catechol cross-linking. Initial control of network structure is achieved through radical polymerization and cross-linking, followed by postpolymerization incorporation of catechol units via quantitative active ester chemistry and subsequent complexation with iron salts. By tuning the ratio of each building block, dual cross-linked networks reinforced by clustered iron-catechol domains are prepared and exhibit a wide range of properties (Young's moduli up to ∼245 MPa), well beyond the values achieved through purely covalent cross-linking. This stepwise approach to mixed covalent and metal-ligand cross-linked networks also permits local patterning of PEG-based films through masking techniques forming distinct hard, soft, and gradient regions.

Supramolecular Elastomers with Excellent Dielectric Properties and High Recyclability Based on the Coordinative Bond

The enhancement in dielectric properties and self-healing ability for dielectric materials has been a challenging subject these years. Herein, a series of self-healed dielectric elastomers by combining the ferric ions and carboxyl-containing poly(sulfone siloxane)s is reported. Experimental results indicate the excellent dielectric properties of obtained elastomers, as the dielectric constant up to 12.8. SEM micrographs exhibit that carboxyl groups and ferric ions can aggregate together to generate clusters, which further result in interfacial polarization. Besides, high polarity dipole units including sulfonyl units and carboxyl groups contribute to dipole polarization. The overlay of the two mentioned polarization eventually results in the high dielectric property. The dielectric constant obviously increases with the contents of carboxyl groups and ferric ions. Moreover, the samples are feasible for recycling and reprocessing with high self-healing efficiency, owing to the reversibility of the coordination bond. A self-healing efficiency of 92.1% in tensile strength of the obtained samples can be reached after 2 h treatment at 60 °C. And the elastomers can also conveniently recover most mechanical properties after solution treatment. This work may offer a promising method for preparing dielectric elastomers with high dielectric properties and self-healing ability.

Structure-Bioactivity Relationship of the Functionalized Polysulfone with Triethylphosphonium Pendant Groups: Perspective for Biomedical Applications

Development of new biomaterials based on polysulfones tailored to act in various biomedical fields represents a promising strategy which provides an opportunity for enhancing the diagnosis, prevention, and treatment of specific illnesses. To meet these requirements, structural modification of the polysulfones is essential. In this context, for design of new materials with long-term stability, enhanced workability, compatibility with biological materials and good antimicrobial activity, the functionalization of chloromethylated polysulfones with triethylphosphonium pendant groups (PSFEtP+) was adopted. The surface chemistry analysis (Fourier transform infrared spectroscopy (FTIR), Energy-dispersive X-ray spectroscopy (EDX)), rheological properties, morphological aspects (Scanning electron microscopy (SEM), polarized light microscopy (POM)), and antimicrobial activity of the synthetized polysulfone were investigated to establish the relationship between its structure and properties, as an important indicator for targeted applications. Based on the obtained features, evaluated by the relationship between the rheological properties and microstructural aspects, and also the response at the biomaterial-bacteria interface, these qualities have been confirmed in their performance, in terms of thermal stability, antimicrobial activity, and also an increase in lifetime. Consequently, derived results constitute the preliminary basis for future tests concerning their functionality as gel matrices in biomedical devices.

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.

LIonomers-New Generation of Ionomer: Understanding of Their Interaction and Structuration as a Function of the Tunability of Cation and Anion

In this work, by combining maleic anhydride-grafted polypropylene (PPgMA) and three different ionic liquids (ILs), i.e., tributyl (ethyl) phosphonium diethyl phosphate (denoted P⁺DEP), 1-ethyl-3-methylimidazolium diethyl phosphate (denoted EMIM DEP), and 1-ethyl-3-methylimidazolium acetate (denoted EMIM Ac), new ionic PP/IL polymer materials are generated and denoted as LIonomers. The structuration of ILs in LIonomers occurs from a nano/microphase separation process proved by TEM. NMR analyses reveal the existence of ionic-ionic and ionic-dipolar interactions between PPgMA and ILs within LIonomers. The rheological behavior of such IL/polymer combinations interpret the existence of interactions between maleic anhydride group and cation or anion composing the ionic liquid. These interactions can be tuned by the nature of cation (P⁺DEP vs. EMIM DEP) and anion (EMIM DEP vs. EMIM Ac) but also depend on the IL content. Thermal analyses demonstrate that IL could affect the crystallization process according to different pathways. Thanks to the maleic anhydride/IL interactions, an excellent compromise between stiffness and stretchability is obtained paving the way for processing new polyolefin-based materials.

Advanced Flame-Retardant Methods for Polymeric Materials

Most organic polymeric materials have high flammability, for which the large amounts of smoke, toxic gases, heat, and melt drips produced during their burning cause immeasurable damages to human life and property every year. Despite some desirable results having been achieved by conventional flame-retardant methods, their application is encountering more and more difficulties with the ever-increasing high flame-retardant requirements such as high flame-retardant efficiency, great persistence, low release of heat, smoke, and toxic gases, and more importantly not deteriorating or even enhancing the overall properties of polymers. Under such condition, some advanced flame-retardant methods have been developed in the past years based on "all-in-one" intumescence, nanotechnology, in situ reinforcement, intrinsic char formation, plasma treatment, biomimetic coatings, etc., which have provided potential solutions to the dilemma of conventional flame-retardant methods. This review briefly outlines the development, application, and problems of conventional flame-retardant methods, including bulk-additive, bulk-copolymerization, and surface treatment, and focuses on the raise, development, and potential application of advanced flame-retardant methods. The future development of flame-retardant methods is further discussed.

Self-Healability of Poly(Ethylene-co-Methacrylic Acid): Effect of Ionic Content and Neutralization

Self-healing polymers such as poly(ethylene-co-methacrylic acid) ionomers (PEMAA) can heal themselves immediately after a projectile puncture which in turn lowers environmental pollution from replacement. In this study, the thermal-mechanical properties and self-healing response of a library of 15 PEMAA copolymers were studied to understand the effects of the ionic content (Li, Na, Zn, Mg) and neutralization percentage (13 to 78%) on the results. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and tensile testing were used to study the thermo-mechanical properties of PEMAA copolymers while the self-healing response was studied using the projectile test. Puncture sites were observed using scanning electron microscopy (SEM) and the healing efficiency was quantitatively measured using the water leakage test. Five different self-healing responses were observed and correlated to ionic content and neutralization. At high neutralization, divalent neutralizing ions (Zn and Mg) that have stronger ionic interactions exhibited brittle responses during projectile testing. PEMAA samples neutralized with Mg and Li at low concentrations had a higher healing efficiency than PEMAA samples neutralized with Zn and Na at low neutralization. The PEMAA copolymers with higher tensile stress and two distinct peaks in the graph of loss factor versus temperature that indicate the presence of sufficient ionic aggregate clusters had improved healing efficiency. By increasing the neutralization percentage from 20% to 70%, the tensile strength and modulus of the samples increased and their self-healability generally increased. Among the investigated samples, the copolymer with ~50% neutralization by Li salt showed the highest healing efficiency (100%). Overall, the strength and elastic response required for successful self-healing responses in PEMAA copolymers are shown to be governed by the choice of ion and the amount of neutralization.

Catalytic Etherification of ortho-Phosphoric Acid for the Synthesis of Polyurethane Ionomer Films

The etherification reaction of ortho-phosphoric acid (OPA) with polyoxypropylene glycol in the presence of tertiary amines was studied. The reaction conditions promoting the catalytic activity of triethanolamine (TEOA) and triethylamine (TEA) in the low-temperature etherification of OPA were established. The catalytic activity of TEOA and TEA in the etherification reaction of phosphoric acid is explained by the hydrophobic-hydrophilic interactions of TEA with PPG, leading, as a result of collective interactions, to a specific orientation of polyoxypropylene chains around the tertiary amine. When using triethylamine, complete etherification of OPA occurs, accompanied by the formation of branched OPA ethers terminated by hydroxyl groups and even the formation of polyphosphate structures. When triethanolamine is used as a catalyst, incomplete etherification of OPA with polyoxypropylene glycol occurs and as a result, part of the phosphate anions remain unreacted in the composition of the resulting aminoethers of ortho-phosphoric acid (AEPA). In this case, the hydroxyl groups of triethanolamine are completely involved in the OPA etherification reaction, but the catalytic activity of the tertiary amine weakens due to a decrease in its availability in the branched structure of AEPA. The kinetics of the etherification reaction of OPA by polyoxypropylene glycol catalyzed by TEOA and TEA were studied. It was shown that triethanolamine occupies a central position in the AEPA structure. The physico-mechanical and thermomechanical properties of polyurethane ionomer films obtained on the basis of AEPA synthesized in a wide temperature range were studied.

Gummy Nanoparticles with Glassy Shells in Electrostatic Nanocomposites

Nanocomposites with unusual and superior properties often contain well-dispersed nanoparticles. Polydimethylsiloxane, PDMS, offers a fluidlike or rubbery (when cross-linked) response, which complements the high-modulus nature of inorganic nanofillers. Systems using PDMS as the nanoparticulate, rather than the continuous, phase are rare because it is difficult to make PDMS nanoparticles. Aqueous dispersions of hydrophobic polymer nanoparticles must survive the considerable contrast in hydrophobicity between water and the polymer component. This challenge is often met with a shell of hydrophilic polymer or by adding surfactant. In the present work, two critical advances for making and using aqueous colloidal dispersions of PDMS are reported. First, PDMS nanoparticles with charged amino end groups were prepared by flash nanoprecipitation in aqueous solutions. Adding a negative polyelectrolyte, poly(styrene sulfonate), PSS, endowed the nanoparticles with a glassy shell, stabilizing them against aggregation. Second, when compressed into a nanocomposite, the small amount of PSS leads to a large increase in bulk modulus. X-ray scattering studies revealed the hierarchical nanostructuring within the composite, with a 4 nm PDMS micelle as the smallest unit. This class of nanoparticle and nanocomposite presents a new paradigm for stabilizing liquidlike building blocks for nanomaterials.

Scalable Manufacturing of Solid Polymer Electrolytes with Superior Room-Temperature Ionic Conductivity

A scalable manufacturing protocol is developed to prepare polymer-based solvent-free all-solid flexible energy storage devices based on a two-roll mill and adapted rubber mixing technology. The as-prepared solid polymer electrolytes (SPEs) consisting of commercial poly(methyl methacrylate)-grafted natural rubber (MG30) and lithium bis(trifluoromethanesulfonyl)imide achieve a superior ionic conductivity of 2.7 × 10-3 S cm-1 at 30 °C. The superior ionic conductivity is attributed to the formation of an ionic cluster network in the composite as proved by small-angle X-ray scattering and infrared spectroscopy measurements. Moreover, the as-prepared SPEs show good mechanical stability over a broad temperature range, that is , a storage modulus above 1 × 104 Pa from 30 to 120 °C as indicated by the rheology data. Furthermore, the SPEs were assembled with the carbon black-filled MG30 (i.e., MG30C) electrode into a flexible supercapacitor cell, which had a wide voltage window of 3.5 V, good energy density of 28.4 μW h·cm-2 at 160 °C, and good temperature tolerance up to 160 °C. This scaling-up manufacture strategy shows tremendous potential to the advancing of SPEs in applications of flexible energy storage device.

Flexible Composite Films Made of EMAA-Na+ Ionomer: Evaluation of the Influence of Piezoelectric Particles on the Thermal and Mechanical Properties

Studies that aim to produce flexible films of composite materials based on ionomers-PZT, and volume fractions lower than 10% PZT, in order to monitor damage in aeronautical structures are seldom investigated. The growing emphasis on the use of polymers capable of self-healing after damage or activation by heating has motivated the application of self-healing ionomers as polymeric matrices in composites with piezoelectric particles aiming to monitor damage. Flexible composite films were developed based on the self-healing polymer matrix Surlyn^® 8940 ionomer (DuPont^TM—Wilmington, DE, USA) and PZT particles (connectivity 2–3) in volume fractions of 1, 3, 5 and 7%, with thickness around 50–100 µm. The choice of PZT volume fractions followed the preliminary requirement that establishes a final density, which is lower or at least close to the density of the materials used in aeronautical structures. Since the application of composites based on epoxy resin/carbon fibers has been increasing in the aeronautical segment, this material (with density lower than 1500 kg/m³) was chosen as a reference for the present work. Thus, due to self-healing (a characteristic of the matrix Surlyn^® 8940) combined with recyclability, high flexibility and low thickness, the flexible composite films showed advantages to be applied on aeronautical structures, which present complex geometries and low-density materials. The manufactured films were characterized by SEM, XRD, DMA and mechanical tensile tests. The results were discussed mainly in terms of the volume fraction of PZT. X-ray diffraction patterns showed coexistent rhombohedral and tetragonal phases in the PZT particles-dispersed composite, which can potentialize the alignment of ferroelectric domains during polarization under strong electrical field, enhancing dielectric and piezoelectric properties toward sensing applications. DMA and tensile testing results demonstrated that the addition of PZT particles did not impair either dynamic or quasi-static mechanical performance of the flexible composite films. It was concluded that the PZT volume fraction should be lower than 3% because, for higher values, the molecular mobility of the polymer would suffer significant reductions. These findings, combined with the high flexibility and low density of the ceramic particle-filled thermoplastic polymer, render the developed flexible composite film a very promising candidate for strain and damage sensing in aeronautical structures.

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. This article is protected by copyright. All rights reserved.

Assessing the suitability of self-healing rubber glove for safe handling of pesticides

Rubber gloves used for protection against chemicals or hazards are generally prone to tearing or leaking after repeated use, exposing the worker to potentially hazardous agents. Self-healing technology promises increased product durability and shelf life appears to be a feasible solution to address these issues. Herein, we aimed to fabricate a novel epoxidized natural rubber-based self-healable glove (SH glove) and investigate its suitability for handling pesticides safely. In this study, breakthrough time analysis and surface morphological observation were performed to determine the SH glove's ability to withstand dangerous chemicals. The chemical resistance performance of the fabricated SH glove was compared against four different types of commercial gloves at different temperatures. Using malathion as a model pesticide, the results showed that the SH glove presented chemical resistance ability comparable to those gloves made with nitrile and NR latex at room temperature and 37 °C. The self-healing test revealed that the SH glove could be self-healed and retained its chemical resistance ability close to its pre-cut value. Our findings suggested that the developed SH glove with proven chemical resistance capability could be a new suitable safety glove for effectively handling pesticides and reducing glove waste generation.

Exploiting Sodium Coordination in Alternating Monomer Sequences to Toughen Degradable Block Polyester Thermoplastic Elastomers

Thermoplastic elastomers (TPEs) that are closed-loop recyclable are needed in a circular material economy, but many current materials degrade during recycling, and almost all are pervasive hydrocarbons. Here, well-controlled block polyester TPEs featuring regularly placed sodium/lithium carboxylate side chains are described. They show significantly higher tensile strengths than unfunctionalized analogues, with high elasticity and elastic recovery. The materials are prepared using controlled polymerizations, exploiting a single catalyst that switches between different polymerization cycles. ABA block polyesters of high molar mass (60–100 kg mol^–1; 21 wt % A-block) are constructed using the ring-opening polymerization of ε-decalactone (derived from castor oil; B-block), followed by the alternating ring-opening copolymerization of phthalic anhydride with 4-vinyl-cyclohexene oxide (A-blocks). The polyesters undergo efficient functionalization to install regularly placed carboxylic acids onto the A blocks. Reacting the polymers with sodium or lithium hydroxide controls the extent of ionization (0–100%); ionized polymers show a higher tensile strength (20 MPa), elasticity (>2000%), and elastic recovery (>80%). In one case, sodium functionalization results in 35× higher stress at break than the carboxylic acid polymer; in all cases, changing the quantity of sodium tunes the properties. A leading sample, 2-COONa75 (M_n 100 kg mol^–1, 75% sodium), shows a wide operating temperature range (−52 to 129 °C) and is recycled (×3) by hot-pressing at 200 °C, without the loss of mechanical properties. Both the efficient synthesis of ABA block polymers and precision ionization in perfectly alternating monomer sequences are concepts that can be generalized to many other monomers, functional groups, and metals. These materials are partly bioderived and have degradable ester backbone chemistries, deliver useful properties, and allow for thermal reprocessing; these features are attractive as future sustainable TPEs.

Recent Advances of Self-Healing Polymer Materials via Supramolecular Forces for Biomedical Applications

Noncovalent interactions can maintain the three-dimensional structures of biomacromolecules (e.g., polysaccharides and proteins) and control specific recognition in biological systems. Supramolecular chemistry was gradually developed as a result, and this led to design and application of self-healing materials. Self-healing materials have attracted attention in many fields, such as coatings, bionic materials, elastomers, and flexible electronic devices. Nevertheless, self-healing materials for biomedical applications have not been comprehensively summarized, even though many reports have been focused on specific areas. In this Review, we first introduce the different categories of supramolecular forces used in preparing self-healing materials and then describe biological applications developed in the last 5 years, including antibiofouling, smart drug/protein delivery, wound healing, electronic skin, cartilage lubrication protection, and tissue engineering scaffolds. Finally, the limitations of current biomedical applications are indicated, key design points are offered for new biological self-healing materials, and potential directions for biological applications are highlighted.

Fluorescent Ionic Probe for Determination of Mechanical Properties of Healed Poly(ethylene-co-methacrylic acid) Ionomer Films

In recent years, advanced materials with properties resembling biological systems, particularly artificial muscles, have received intense scrutiny. This is because the interesting conformational shape characteristics of such materials have benefited a variety of technologies, including textiles, 3D printing, and medical devices. Although a multitude of shape memory properties have been studied and developed in recent years, self-healing of these polymers after puncture or rupture has also become a major area of study. Most techniques for detection of such processes are mechanically based and require considerable hands-on monitoring. Thus, a rapid visual detection method for self-healing is highly desirable. Herein, we describe fluorescence studies for rapid detection of self-healing properties of a partially neutralized sodium ionomer poly(ethylene-co-methacrylic acid) (PEMA). In this study, two different fluorophores, parent non-ionic 4,6-dipyrenylpyrimidine and ionic 4,6-dipyrenylpyrimidinium iodide fluorophores, were evaluated as possible sensors of self-healing. Incorporation of these probes via solution blending and compatibility into a PEMA of these fluorophores were evaluated. Thermal characterizations using differential scanning calorimetry were also performed to elucidate physical characteristics of healed sites. Ratiometric fluorescence emission variations were explored within puncture-healed ionomer films and related to Young's modulus properties with good linearity, indicating potential utility of this approach for monitoring elastic modulus properties after healing has occurred. Further statistical analyses of mechanical processes using quadratic discriminant analysis resulted in development of several highly accurate predictive models for determining time since damage healing.

Highly Impact-Resistant Block Polymer-Based Thermoplastic Elastomers with an Ionically Functionalized Rubber Phase

There has been a great deal of interest in incorporating noncovalent bonding groups into elastomers to achieve high strength. However, the impact resistance of such elastomers has not been evaluated, even though it is a crucial mechanical property in practical usage, partly because a large-scale synthetic scheme has not been established. By ionizing the rubber component in polystyrene-b-polyisoprene-b-polystyrene (SIS), we prepared several tens of grams of SIS-based elastomers with an ionically functionalized rubber phase and a sodium cation (i-SIS(Na)) or a bulky barium cation (i-SIS(Ba)). The i-SIS(Na) and i-SIS(Ba) exhibited very high tensile toughness of 520 and 280 MJ m-3, respectively. They also exhibited excellent compressive resistance. Moreover, i-SIS(Ba) was demonstrated to have a higher impact resistance, that is, more protective of a material being covered compared to covering by typical high-strength glass fiber-reinforced plastic. As such elastomers can be produced at an industrial scale, they have great market potential as next-generation elastomeric materials.

Charged Block Copolymers: From Fundamentals to Electromechanical Applications

Charged block copolymers are promising materials for next-generation battery technologies and soft electronics. Although once it was only possible to prepare randomly organized structures, nowadays, well-ordered charged block copolymers can be prepared. In addition, theoretical and experimental analyses of the thermodynamic properties of charged polymers have provided insights into how to control nanostructures via electrostatic interactions and improve the ionic conductivity without compromising mechanical strength, which is crucial for practical applications. In this Account, we discuss methods to control the self-assembly and ion diffusion behavior of charged block copolymers by varying the type of tethered ionic moieties, local concentration of embedded ions with controlled electrostatic interactions, and nanoscale morphology. We discuss with particular emphasis on the structure-transport relationship of charged block copolymers using various ionic additives to control the phase behavior electrostatically as well as the ion transport properties. Through this, we establish the role of interconnected ionic channels in promoting ion-conduction and the importance of developing three-dimensional interconnected morphologies such as gyroid, orthorhombic Fddd (O⁷⁰) networks, body-centered cubic (bcc), face-centered cubic (fcc), and A15 structures with well-defined interfaces in creating less tortuous ion-conduction pathways. Our prolonged surge and synthetic advances are pushing the frontiers of charged block copolymers to have virtually homogeneous ionic domains with suppressed ion agglomeration via the nanoconfinement of closely bound ionic moieties, resulting in efficient ion conduction and high mechanical strength.Subsequently, we discuss how, by using zwitterions, we have radically improved the ionic conductivity of single-ion conducting polymers, which have potential for use in next-generation electrochemical devices owing to the constrained anion depletion. Key to the improvement stems from hierarchically ordered ionic crystals in nanodomains of the single-ion block copolymers through the self-organization of the dipolar/ionic moieties under confinement. By precisely tuning the distances between ionic sites and the dipolar orientation in the ionic domains with varied zwitterion contents, unprecedented dielectric constants close to those of aqueous electrolytes have been achieved, leading to the development of high-conductivity solid-state single-ion conducting polymers with leak-free characteristics. Further, using these materials, low-voltage-driven artificial muscles have been prepared that show a large bending strain and millisecond-scale mechanical deformations at 1 V in air without fatigue, exceeding the performance of previously reported polymer actuators. Finally, smart multiresponsive actuators based on tailor-made charged polymers capable of programmable deformation with high force and self-locking without power consumption are suggested as candidates for use in soft robotics.

4D bioprintable self-healing hydrogel with shape memory and cryopreserving properties

Four-dimensional (4D) bioprinting is an emerging biofabrication technology that integrates time as a fourth dimension with three-dimensional (3D) bioprinting for fabricating customizable tissue-engineered implants. 4D bioprinted implants are expected to possess self-healing and shape memory properties for new application opportunities, for instance, fabrication of devices with good shape integrity for minimally invasive surgery. Herein, we developed a self-healing hydrogel composed of biodegradable polyurethane (PU) nanoparticles and photo-/thermo-responsive gelatin-based biomaterials. The self-healing property of hydrogel may be associated with the formation of reversible ionomeric interaction between the COO^-group of PU nanoparticles and NH₃⁺group on the gelatin chains. The self-healing hydrogel demonstrated excellent 3D printability and filament resolution. The UV-crosslinked printed hydrogel showed good stackability (>80 layers), structural stability, elasticity, and tunable modulus (1-60 kPa). The shape-memorizable 4D printed constructs revealed good shape fixity (∼95%) and shape recovery (∼98%) through the elasticity as well as forming and collapsing of water lattice in the hydrogel. The hydrogel and the printing process supported the continuous proliferation of neural stem cells (NSCs) (∼3.7-fold after 14 days). Moreover, the individually bioprinted NSCs and mesenchymal stem cells in the adjacent, self-healed filaments showed mutual migration and such interaction promoted the cell differentiation behavior. The cryopreserved (-20 °C or -80 °C) 4D bioprinted hydrogel after awakening and shape recovery at 37 °C demonstrated cell proliferation similar to that of the non-cryopreserved control. This 4D bioprintable, self-healable hydrogel with shape memory and cryopreserving properties may be employed for customized biofabrication.

Understanding the Molecular Dynamics of Dual Crosslinked Networks by Dielectric Spectroscopy

The combination of vulcanizing agents is an adequate strategy to develop multiple networks that consolidate the best of different systems. In this research, sulfur (S), and zinc oxide ( ZnO) were combined as vulcanizing agents in a matrix of carboxylated nitrile rubber (XNBR). The resulting dual network improved the abrasion resistance of up to ~15% compared to a pure ionically crosslinked network, and up to ~115% compared to a pure sulfur-based covalent network. Additionally, the already good chemical resistance of XNBR in non-polar fluids, such as toluene and gasoline, was further improved with a reduction of up to ~26% of the solvent uptake. A comprehensive study of the molecular dynamics was performed by means of broadband dielectric spectroscopy (BDS) to complete the existing knowledge on dual networks in XNBR. Such analysis showed that the synergistic behavior that prevails over purely ionic vulcanization networks is related to the restricted motions of rubber chain segments, as well as of the trapped chains within the ionic clusters that converts the vulcanizate into a stiffer and less solvent-penetrable material, improving abrasion resistance and chemical resistance, respectively. This combined network strategy will enable the production of elastomeric materials with improved performance and properties on demand.

Enhancement of EPDM Crosslinked Elastic Properties by Association of Both Covalent and Ionic Networks

The objective of this study was to replace elastomer crosslinking based on chemical covalent bonds by reversible systems under processing. One way is based on ionic bonds creation, which allows a physical crosslinking while keeping the process reversibility. However, due to the weak elasticity recovery of such a physical network after a long period of compression, the combination of both physical and chemical networks was studied. In that frame, an ethylene-propylene-diene terpolymer grafted with maleic anhydride (EPDM-g-MA) was crosslinked with metal salts and/or dicumyl peroxide (DCP). Thus, the influence of these two types of crosslinking networks and their combination were studied in detail in terms of compression set. The second part of this work was focused on the influence of different metallic salts (KOH, ZnAc₂) and the sensitivity to the water of the physical crosslinking network. Finally, the combination of ionic and covalent network allowed combining the processability and better mechanical properties in terms of recovery elasticity. KAc proved to be the best ionic candidate to avoid water degradation of the ionic network and then to preserve the elasticity recovery properties under aging.