Self‐healing Ag/epoxy electrically conductive adhesive using encapsulated epoxy‐amine healing chemistry

In this study, a dual‐microcapsule epoxy‐amine self‐healing concept is used for electrically conductive adhesives (ECAs). It provides the ECA samples with the ability to recover mechanical and electrical properties automatically. Epoxy and amine microcapsules were prepared and incorporated into silver/epoxy ECAs. The healing efficiency and bulk resistivity of the undamaged, damaged, and healed specimens were measured, respectively. The optimal loading of the epoxy and amine microcapsules is 6 wt % (weight ratio 1.05), and the bulk resistivity of the healed specimens is 3.4 × 10^?3 Ω cm. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41483.     

High-performance self-healing anticorrosion epoxy coating based on microencapsulated epoxy-amine chemistry

Attributed to the merits of excellent material compatibility, healing performance, and long-term stability, the self-healing system based on microencapsulated epoxy-amine chemistry is a potentially practical self-healing system for both structural and functional materials. Herein, based on the microencapsulated epoxy-amine chemistry, a self-healing anticorrosion coating was successfully developed. This self-healing coating system was modeled theoretically to explore the factors that influence the crack filling and the self-healing anticorrosion function. The established quantitative relationship shows that the filling depth of the crack in the coating is proportional to the microcapsule parameters and coating thickness, but inversely proportional to the crack width. Based on the above theoretical model, the effects of various parameters on the anticorrosion performance were experimentally studied. The actual filling of small in-situ cracks (<100 μm) generated by impact damage was semi-quantitatively characterized using scanning electron microscopy (SEM). The filling behavior is consistent with the theoretical modeling. After being healed at room temperature for 2 days upon impact damage, the formulated self-healing coatings were subjected to accelerated corrosion tests in 10 wt% sodium chloride (NaCl) solution for 2 days to observe their anticorrosion behavior. Compared to the neat epoxy coating, all the formulated self-healing epoxy coatings show evident anticorrosion function. Good self-healing anticorrosion performance was achieved by adding 10.0 wt% microcapsules with a size of 100–150 μm to the coating with a thickness of 300 μm. The results of this investigation laid a theoretical and technical foundation for the further development of both the self-healing chemistry and the self-healing anticorrosion coating.     

Self-healing of a high temperature cured epoxy using poly(dimethylsiloxane) chemistry

A high temperature cured self-healing epoxy is demonstrated by incorporating microcapsules of poly(dimethylsiloxane) (PDMS) resin and separate microcapsules containing an organotin catalyst. Healing is triggered by crack propagation through the embedded microcapsules in the epoxy matrix, which releases the healing agents into the crack plane initiating crosslinking reactions. A series of tapered double-cantilever beam (TDCB) fracture tests were conducted to measure virgin and healed fracture toughness. Healing efficiencies, based on fracture toughness recovery, ranged from 11 to 51% depending on the molecular weight of PDMS resin, quantity of healing agent delivered, and use of adhesion promoters.     

Soybean oil based thermoset networks via photoinduced CuAAC click chemistry

A simple method based on photochemically induced copper(I)‐catalyzed azide ? alkyne cycloaddition click reaction (CuAAC ) is developed for the preparation of thermoset networks from soybean oils as renewable resources. The incorporation of clickable azide and alkyne functionalities into epoxidized soybean oils is done by simultaneous ring‐opening reactions between the epoxide group of soybean oils and sodium azide and propargyl alcohol, respectively. The obtained azide‐ and alkyne‐functionalized soybean oils are easily transformed crosslinked networks via the photoinduced CuAAC reaction in ambient conditions. The introduction of additional multifunctional monomers in the formulation not only increases the crosslinking density but also improves the mechanical properties of the thermoset material obtained. In a comparison of the two formulations, the sample containing additional multifunctional monomers has a higher glass transition temperature, storage modulus and damping properties. © 2017 Society of Chemical Industry     

Chemically decomposable imine-based thermoset using oxidized sugar

Increasing environmental concerns have driven the pursuit of sustainable alternatives to petrochemical-based plastics in polymer chemistry. In this study, we demonstrated a method by which sugar, the most chemically produced biomass, can be used as a thermosetting resin. The sucrose was successfully oxidized, synthesized, and then incorporated into a resin. Sodium periodate (NaIO₄) was used to convert sucrose into chemical raw materials. The resulting polymer, prepared via the imine reaction, exhibited a glass transition temperature T_g of 96°C, as determined by differential scanning calorimetry. Additionally, the thermosetting resin exhibited a tensile strength of 7 MPa, a modulus of 515 MPa, and a T_g of 100°C. We obtained reaction rate constants of 0.7 × 10⁻³ h⁻¹ and 3.2 × 10⁻¹ h⁻¹ using THF and citric acid solutions, respectively. Furthermore, we reused the resin from the decomposed organic matter and confirmed that the resynthesized overall, our findings suggest the potential for green recycling by converting commonly used sugars into nature-derived raw materials, leading to the development of eco-friendly polymer synthesis.     

Prediction of thermoset viscosity using a thermomechanical analyzer

A thermomechanical analyzer (TMA) in the parallel-plate configuration was employed to study the viscosity behavior of an unfilled, FR-4 type epoxy resin by monitoring its thickness change with time under a constant compressive force at various temperatures. With a dual-Arrhenius reheology model, we were able to predict viscosities under nonisothermal conditions of high heating rate from more easily obtained isothermal viscosity data. Due to its simplicity and speed, this technique is well suited for investigating resin viscosity behavior during composite lamination in a manufacturing environment.     

Self-healing polymeric materials based on microencapsulated healing agents: From design to preparation

Inspired by naturally occurring species that allow for self-healing of nonfatal harm, self-healing polymeric materials have been prepared and represent a component of the intelligent materials family. These materials possess the inherent ability to rehabilitate damage produced during manufacturing and/or usage. The self-healing methodologies developed to date can be classified as intrinsic or extrinsic according to the method used to deliver the healing components to the target site in the material. Intrinsic self-healing operates through inter- or intra-macromolecular interactions, whereas extrinsic self-healing makes use of a pre-embedded healing agent. Extrinsic self-healing can be more easily realized in commercially available polymers because no structural modification of the matrix molecules is required. In recent years, extrinsic self-healing based on microencapsulated healing agents has attracted growing interest. Extrinsic self-healing in a variety of materials (including thermosets, thermoplastics, rigid, and elastomeric materials) has been demonstrated and offers recovery of both mechanical and non-structural functional properties. Self-healing based on microcapsules can deliver further results if combined with intrinsic self-healing. Using a bottom-up perspective, the current article presents a comprehensive review of recent progress in this field from the viewpoint of material design and preparation. The topics presented include (i) a basic overview of self-healing systems, (ii) microencapsulation techniques (e.g., in situ polymerization, interfacial polymerization, Pickering emulsion templating, miniemulsion polymerization, solvent evaporation/solvent extraction, sol–gel reaction, etc.), (iii) crack response of microcapsules, and (iv) healing chemistries (e.g., ring-opening metathesis polymerization, polycondensation, anionic ring opening polymerization, cationic polymerization, free radical polymerization, addition reaction, etc.). The strengths and weaknesses of each microencapsulation technique and type of healing chemistry are analyzed and compared. Additionally, formulation optimization (including species of healing agent and wall substance of capsules), processing, structure and property relationship, healing mechanisms, and stability are discussed. Trends and challenges are summarized at the end of the review. The scope of this review is to provide the reader with an overview of achievements to date and insight into future development for engineering applications.     

Self-healing performance assessment of epoxy resin and amine hardener encapsulated polymethyl methacrylate microcapsules reinforced epoxy composite

In order to study the effect of healing materials viscosity on the self-healing performance of polymer composite, mostly available epoxy resin of viscosity 10–12 Pa.s and amine hardener of viscosity 0.01–0.02 Pa.s were chosen as two different healing materials and successfully encapsulated. Effect of core to shell(c/s) ratio on the synthesis of epoxy microcapsules was investigated and 1:1 c/s ratio is suggested as an ideal ratio to synthesize epoxy capsules. Chemical structure and thermal decomposition patterns of both microcapsules and capsules reinforced composite were analyzed. Tensile strength, impact strength and fracture toughness of capsules reinforced self-healing epoxy composite were evaluated. It was observed that the toughness of epoxy composite increased with the increase in microcapsules concentration. An optimum healing efficiency of 66% was observed with the addition of 7.5 wt% epoxy and hardener microcapsules at equal weight ratio. Stresses developed in the pure epoxy composite crack front were analyzed using Ansys V18.1.     

Self-healing anticorrosive organic coating based on an encapsulated water reactive silyl ester: Synthesis and proof of concept

In this paper a self-healing anticorrosive organic coating based on an encapsulated water reactive organic agent is presented. A reactive silyl ester is proposed as a new organic reactive healing agent and its synthesis, performance, incorporation into an organic coating and evaluation of self-healing capabilities is described. Such silyl esters are good candidates to be used in self-healing anticorrosive organic coating systems since they present the capability to react with water/humidity and metallic substrates, removing thus the need of presence of a crosslinker or catalyst in the system unlike traditional encapsulated approaches. In order to prove the self-healing ability and reactivity of the presented silyl ester encapsulated system, Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET) were used, showing the high capability of these techniques to be used in the development and evaluation of self-healing anticorrosive organic coatings and the good results in corrosion protection offered by the proposed silyl ester healing agent.     

Self-healing polyurethane based on a substance supplement and dynamic chemistry: Repair mechanisms and applications

This review systematically summarizes the repair mechanisms and applications of self-healing polyurethane (SHPU) materials aiming at energy conservation and safety under different repair methods. As of now, the repair methods that have emerged can be divided into two categories: substance landfill and bond repair. In terms of the repair mechanisms for both, the former involves the release of healing agents from micro-carriers (microcapsules, hollow fibers, and microvascular) to fill the damaged area upon external impact. In contrast, bond repair combines physical and chemical changes triggered by light, heat, and other factors. To achieve efficient self-healing in this mode, both the reorganization of broken chemical bonds and the high mobility of chain segments are crucial. Reversible covalent bonds and supramolecular interactions, as two branches of aforementioned reversible chemical bonds, share the responsibility for maintaining efficient self-healing despite infinite cycling. Additionally, multiple synergistic crosslinked networks, special nanomaterials, and microphase separation are often used to solve the problem of incompatible healing efficiency and mechanical strength in bond repair. When the perspective is focused on the application, this gradually improved SHPU with strong potential and comprehensive performance has provided raw materials for many fields related to human development, such as road, architecture, healthcare, and electronic.     

Surface quality prediction of thermoset composite structures using geometric simulation tools

Abstract

The surface quality of polymer composite laminates was examined via geometric modelling techniques and compared to experimental data. TexGen software provided the platform for the development of a surface roughness simulation tool which accounted for textile architecture and specific cure kinetics of the matrix. The study focused on the influence of thermal and chemical shrinkage during cure and the change in localised volume fraction across the surface of a unit cell. A one-dimensional analysis was used to determine proportional dimensional changes to the matrix region, with the results stitched together to form a three-dimensional topological plot. Three demonstrator geometric models were developed to represent a carbon 2 × 2 twill weave fabric with 3000, 6000 or 12 000 tows. These models were analysed with low and high shrink resin properties. Optical microscopy was used to determine accurate tow forms for compacted tows which aided the development of the geometric model. Simulated profiles, topography and surface roughness measures were compared to experimental data which demonstrated the significance of matrix contraction and fabric architecture on the final surface quality. The simulations were shown to represent experimental data typically within 6%.     

Deeper insights into the thermal properties of epoxy thermoset resins using torsion measurements

The glass transition temperature (T_g) of epoxy thermosets is a critical material property that depends on the component chemistry, the final cross-link density, and processing conditions. This study incorporates dynamic mechanical analysis (DMA) testing with a torsion clamp geometry on a TA Instruments DHR-2 and differential scanning calorimetry (DSC) to characterize five different two-component epoxy-amine systems. Investigation of the T_g dependence on DMA frequency and heating shows that lowering the frequency from 1 to 0.01 Hz results in a T_g very similar to that measured using DSC, while a heating rate of 0.3°C/min using DMA gives a T_g comparable to the DSC measured value at 30°C/min. The DMA technique reveals secondary relaxation transitions and peak broadening in the tan(δ) plots of poorly mixed epoxy blends, quantified using full width at half maximum (FWHM) of tan(δ) peaks, and are indicative of a non-homogeneous cross-linked network and off-ratio blending, respectively. The increase in the FWHM due to poor mixing ranges from 8% to 96%. These parameters are easily measurable and quantifiable in DMA, but are not observed in DSC. The additional DMA insights are valuable for process development and failure analysis, and can improve the understanding of epoxies.     

Study of the degradation of a thermoset system using TGA and modulated TGA

The degradation of the epoxy system diglycidyl ether of bisphenol A (this epoxy is also named DGEBA (n = 0), where n indicates the number of structural units inside the molecule) cured with hardener metaxylilene diamine (m-XDA) was studied on a dynamic basis using TGA and modulated TGA techniques under a nitrogen atmosphere with 5% O₂. We observed that under such atmosphere the degradation process becomes more complex. The experimental results showed that modulated thermogravimetric analysis provides key information on the activation energy values, which are consistent with values found in the literature and others obtained by methods derived from TGA measurements.     

Characteristics of graphene-layer encapsulated nanoparticles fabricated using laser ablation method

Graphene layer-encapsulated Ni nanoparticles with diameters between 3 and 10 nm were fabricated by laser ablation techniques and deposited directly on the Si substrate at room temperature. It was found from the field-emission type scanning electron microscopy (FE–SEM) and transmission electron microscopy(TEM) analyses that any carbon nanotubes were not fabricated in the deposited nano-materials. High-resolution TEM observation showed the core-shell structure of Ni–C particles with crystalline nickel core surrounded by graphite-like layers. The X-ray diffraction(XRD) pattern also revealed that nanoparticles embedded in graphene capsules are crystalline nickel. With these Ni–C nanoparticles, we demonstrated the growth of vertically aligned carbon nanotubes with low spatial density on a silicon substrate by thermal CVD.     

Understanding nucleic acids using synthetic chemistry

This Account describes work done in these laboratories that has used synthetic, physical organic, and biological chemistry to understand the roles played by the nucleobases, sugars, and phosphates of DNA in the molecular recognition processes central to genetics. The number of nucleobases has been increased from 4 to 12, generating an artificially expanded genetic information system. This system is used today in the clinic to monitor the levels of HIV and hepatitis C viruses in patients, helping to manage patient care. Work with uncharged phosphate replacements suggests that a repeating charge is a universal feature of genetic molecules operating in water and will be found in extraterrestrial life (if it is ever encountered). The use of ribose may reflect prebiotic processes in the presence of borate-containing minerals, which stabilize ribose formed from simple organic precursors. A new field, synthetic biology, is emerging on the basis of these experiments, where chemistry mimics biological processes as complicated as Darwinian evolution.     

Unsaturated polyester resins for thermoset applications using renewable isosorbide as a component for property improvement

Unsaturated polyester (UPE) resins are used in a variety of thermosetting applications due to the reduced cost when compared to epoxy resins; however, UPE resins also have reduced thermomechanical performance. Investigating avenues to improve the performance of UPEs has led to the use of bio‐based starting materials as structural components of the synthesized prepolymers as a result of their advantageous structural features. Isosorbide, a compound derived from renewable feedstocks, has been utilized to provide additional stiffness from the diol component for novel unsaturated polyesters resins. These resins have been shown to possess T_g's (32?72°C) and storage moduli (540?2200 MPa) that are in the desired range for composite materials with viscosities (1.2?25 Pa s) amenable to a variety of liquid molding techniques. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42315.     

The removal of encapsulated catalyst particles from carbon nanotubes using molten salts

A novel method, using molten salts, is described for the removal of encapsulated nickel catalyst particles from multi-walled carbon nanotubes. The multi-walled carbon nanotubes, synthesised by the decomposition of methane and hydrogen over a NiO/SiO₂ aerogel catalyst, were treated in a LiCl-KCl eutectic molten salt and subsequently by hydrochloric acid to remove the nickel catalyst particles. The influence of the molten salt treatment on the microstructure of the carbon nanotubes was investigated by XRD, SEM and TEM analyses. The molten salt treatment promoted uncapping of the carbon capsules and the formation of strip-shaped carbon fragments. It was found that the hydrochloric acid treatment could then remove the nickel particles from the broken carbon capsules which was not possible prior to the molten salt treatment. The stability of carbon nanotubes in the molten salt is closely related to their ordered structure.     

Study of uranium adsorption using amidoximated polyacrylonitrile‐encapsulated macroporous beads

Polyacrylonitrile beads, containing the amidoximated polyacrylonitrile, were prepared for adsorption of uranium. The synthesized amidoximated polyacrylonitrile chelating beads were evaluated, for their ability to adsorb uranium from aqueous solution, at different temperatures and pH values. The kinetic measurement showed that about 120 min of equilibration time was enough, to remove saturation amount of uranium from the solution. The pseudo first‐order and pseudo second‐order equations were used to analyze the kinetic data, and the rate constants were determined. The equilibrium adsorption data were examined by the Langmuir, Freundlich, and Temkin isotherms. The data showed a better fit to the Langmuir isotherm. The loaded uranium could also be leached out from the beads, by treating with dilute acids. The uranium uptake capacity of the polymeric beads was found to be 3.5 mg/g of the swollen beads. Reusability of the beads was also established by multiple adsorption–desorption experiments. The pore volume and the surface area of the dried beads, measured by BET method, were found to be 1.93 cc/g and 320 m²/g, respectively. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013