Microcapsule-Type Organogel-Based Self-Healing System Having Secondary Damage Preventing Capability

Repeatable Self-Healing of a Protective Coating Based on Vegetable-Oil-Loaded Microcapsules

Generally, microcapsule-based self-healing materials have the limitation of single local self-healing. A few studies have reported repeatable self-healing in these microcapsular materials, but there is a challenge to develop multi-cycle self-healing materials that have the advantages of easier preparation and a more efficient operation. In this work, a mixture of two vegetable oils, soybean and olive oil, was used as a healing agent. The atmospheric oxygen-induced reaction behavior (in the presence of a catalyst) was investigated for various compositions of the vegetable oil mixtures; infrared spectroscopy, recovery testing, and viscoelasticity measurement were performed to find an optimum composition of the healing agent. Microcapsules loaded with soybean oil and catalyst-containing olive oil were separately prepared and used to prepare a dual-capsule self-healing coating. It was demonstrated through optical and scanning electron microscopy that, upon scribing the self-healing coating, the vegetable oils flowed out from microcapsules to self-heal the damaged area. When the healed area of the self-healing coating was re-scribed, self-healing was repeated, which was confirmed by scanning electron microscopy (SEM) and anticorrosion and electrochemical testing. Our new repeatable self-healing coating provides the merits of easy preparation, no need for external intervention such as light irradiation, and an environmentally-friendly nature.

Microcapsule-Type Self-Healing Protective Coating That Can Maintain Its Healed State upon Crack Expansion

The purpose of this study was to develop a microcapsule-type self-healing coating system that could self-heal cracks and then maintain the healed state even upon crack expansion. Mixtures consisting of a photoinitiator and two methacrylate components, bismethacryloxypropyl-terminated polydimethylsiloxane (BMT-PDMS) and monomethacryloxypropyl-terminated PDMS (MMT-PDMS), were transformed into viscoelastic semi-solids through photoreaction. The viscoelasticity of the reacted mixtures could be controlled by varying the mass ratio of the two methacrylates. Through a stretchability test, the optimal composition mixture was chosen as a healing agent. Microcapsules loaded with the healing agent were prepared and dispersed in a commercial undercoating to obtain a self-healing coating formulation. The formulation was applied onto mortar specimens, and then cracks were generated in the coating by using a universal testing machine (UTM). Cracks with around a 150-μm mean width were generated and were allowed to self-heal under UV light. Then, the cracks were expanded up to 650 μm in width. By conducting a water sorptivity test at each expanded crack width, the self-healing efficiency and capability of maintaining the healed state were evaluated. The B-M-1.5-1-based coating showed a healing efficiency of 90% at a 150-μm crack width and maintained its healing efficiency (about 80%) up to a 350-μm crack width. This self-healing coating system is promising for the protection of structural materials that can undergo crack formation and expansion.

Effect of Microcapsules with Waterborne Coating as Core Material on Properties of Coating for Tilia Europaea and Comparison with Other Microcapsules

Urea formaldehyde was used as wall material and waterborne coatings as a core material to prepare microcapsules. So as to explore the influence of mass ratio of core to shell, reaction temperature and standing time on the performance of microcapsules, the orthogonal test of three factors and two levels was put into effect. The orthogonal experimental results showed the mass ratio of core to shell was the most important factor. With the increase of the mass ratio of core to shell, the output and clad ratio of microcapsules increased first and then decreased. The microcapsule with the mass ratio of core to shell of 0.67:1 had better appearance, output, and encapsulation performance. The optical properties of waterborne wood coating with the microcapsules of waterborne coating as core materials did not decrease significantly, while the hardness, impact resistance, and toughness were improved. At the same time, the microcapsules have a certain self-repairing effect on coating micro-cracks. Compared with the properties of waterborne coatings with other microcapsules, the coating with waterborne coating as core material has better comprehensive performance. The results provide a new research idea for the performance enhancement and self-healing of wood waterborne coating.

Novel Smart Insulating Materials Achieving Targeting Self-Healing of Electrical Trees: High Performance, Low Cost, and Eco-Friendliness

It remains challenging to promptly inhibit and autonomically heal electrical trees inside insulating dielectrics, which are caused by sustained strong electrical fields and substantially shorten electronic device lifetimes and even cause premature failure of electrical equipment. Therefore, we demonstrate a magnetically targeted ultraviolet (UV)-induced polymerization functional microcapsule (MTUF-MC) to endow insulating materials with physical and electrical dual-damage self-healing capabilities. Specifically, Fe₃O₄@SiO₂ and TiO₂ nanoparticles, which serve as magnetic targets and UV shields (thereby preventing the healing agent from prematurely triggering), constitute a functional microcapsule shell, ensuring a low dopant concentration and excellent self-healing ability of the epoxy composites without affecting the intrinsic performance of the matrix. By exploiting in situ electroluminescence originating from electrical trees, UV-induced polymerization of healing agent is handily triggered without any applying external stimuli to intelligently, contactlessly, and autonomously self-healing electrical trees inside insulating dielectrics.

Self-Healing Structural Materials

Self-healing materials have been developed since the 1990s and are currently used in various applications. Their performance in extreme environments and their mechanical properties have become a topic of research interest. Herein, we discuss cutting-edge self-healing technologies for hard materials and their expected healing processes. The progress that has been made, including advances in and applications of novel self-healing fiber-reinforced plastic composites, concrete, and metal materials is summarized. This perspective focuses on research at the frontier of self-healing structural materials.

Fabrication of self-healing hydrogels with surface functionalized microcapsules from stellate mesoporous silica

This report describes a dual-healing method for self-healing hydrogels, in which stellate mesoporous silica (STMS) was used to prepare surface-functionalized microcapsules.

Effect of a Surfactant in Microcapsule Synthesis on Self-Healing Behavior of Capsule Embedded Polymeric Films

Recently, there has been increased interest in self-healing membranes containing functional microcapsules in relation to challenges involving water treatment membranes. In this study, a self-healing membrane has been prepared by incorporating microcapsules with a polyurethane (PU) shell and a diisocyanate core in a poly(ether sulfone) (PES) membrane. Depending on the characteristics of the microcapsule, to precisely quantify the self-healing behavior and performance of the produced microcapsule embedded membranes, it is important to understand the effect of a used surfactant on microcapsule synthesis. It is noteworthy that mixed surfactants have been employed to control and tailor the size and morphology of microcapsules during the synthetic process, and the surfactant system employed was one of the most dominant parameters for affecting the healing capability of microcapsule embedded membranes. Various techniques including microscopy (optical and electron), thermal analyses (DSC and TGA), and water flux measurements have been employed. This article provides essential and important information for future research into the subtle relation between microcapsule properties with varied synthetic parameters and the self-healing behavior of membrane.

Water-adaptive and repeatable self-healing polymers bearing bulky urea bonds

A crosslinked copolymer having a reversible covalent bond between a bulky amine and an isocyanate presents reshapable, repeatable, and water-adaptive self-healing properties.

Low-Temperature Self-Healing of a Microcapsule-Type Protective Coating

Low-temperature self-healing capabilities are essential for self-healing materials exposed to cold environments. Although low-temperature self-healing concepts have been proposed, there has been no report of a microcapsule-type low-temperature self-healing system wherein the healing ability was demonstrated at low temperature. In this work, low-temperature self-healing of a microcapsule-type protective coating was demonstrated. This system employed silanol-terminated polydimethylsiloxane (STP) as a healing agent and dibutyltin dilaurate (DD) as a catalyst. STP underwent a condensation reaction at −20 °C in the presence of DD to give a viscoelastic product. The reaction behavior of STP and the viscoelasticity of the reaction product were investigated. STP and DD were separately microencapsulated by in situ polymerization and interfacial polymerization methods, respectively. The STP- and DD-loaded microcapsules were mixed into a commercial enamel paint, and the resulting formulation was applied to glass slides, steel panels, and mortars to prepare self-healing coatings. When the self-healing coatings were damaged at a low temperature (−20 °C), STP and DD were released from broken microcapsules and filled the damaged area. This process was effectively visualized using a fluorescent dye. The self-healing coatings were scratched and subjected to corrosion tests, electrochemical tests, and saline solution permeability tests. The temperature of the self-healing coatings was maintained at −20 °C before and after scratching and during the tests. We successfully demonstrated that the STP/DD-based coating system has good low-temperature self-healing capability.

Soft, Peelable Organogels from Partially Hydrolyzed Poly(vinyl acetate) and Benzene-1,4-diboronic Acid: Applications to Clean Works of Art

We have developed soft, peelable organogels from 40% hydrolyzed poly(vinyl acetate) (40PVAc) and benzene-1,4-diboronic acid (BDBA). The organic liquids gelated include dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, 2-ethoxyethanol, and methanol. The rheology of these soft materials can be tuned by altering the concentration of the polymer and/or crosslinker. Insights into the mechanisms leading to gelation were obtained from ¹H NMR experiments, fluorescence measurements, and studies comparing properties of materials made from BDBA and phenylboronic acid, a molecule incapable of forming covalent crosslinks between the polymer chains. These organogels can be easily peeled off a surface, leaving no residue detectable by UV-vis spectroscopy. They are demonstrated to be effective at softening and removing deteriorated coatings from water-sensitive works of art and delicate surfaces. They have the needed characteristics to clean topographically complex surfaces: good contact with the surface, easy removal, and little to no residue after removal. A 2-ethoxyethanol organogel was used to remove oxidized varnish from a 16th century reliquary decorated with painted gold leaf, and an ethanol gel was used to remove solvent-resistant coatings from 16th and 18th century oil paintings.

Research Advances of Microencapsulation and Its Prospects in the Petroleum Industry

Additives in the petroleum industry have helped form an efficient system in the past few decades. Nowadays, the development of oil and gas has been facing more adverse conditions, and smart response microcapsules with the abilities of self-healing, and delayed and targeted release are introduced to eliminate obstacles for further exploration in the petroleum industry. However, limited information is available, only that of field measurement data, and not mechanism theory and structural innovation data. Thus we propose that the basic type, preparation, as well as mechanism of microcapsules partly depend on other mature fields. In this review, we explore the latest advancements in evaluating microcapsules, such as X-ray computed tomography (XCT), simulation, and modeling. Finally, some novel microencapsulated additives with unparalleled advantages, such as flexibility, efficiency, and energy-conservation are described.

Microcapsule-Type Self-Healing Protective Coating for Cementitious Composites with Secondary Crack Preventing Ability

A microcapsule-type self-healing protective coating with secondary crack preventing capability has been developed using a silanol-terminated polydimethylsiloxane (STP)/dibutyltin dilaurate (DD) healing agent. STP undergoes condensation reaction in the presence of DD to give a viscoelastic substance. STP- and DD-containing microcapsules were prepared by in-situ polymerization and interfacial polymerization methods, respectively. The microcapsules were characterized by Fourier-transform infrared (FT-IR) spectroscopy, optical microscopy, and scanning electron microscopy (SEM). The microcapsules were integrated into commercial enamel paint or epoxy coating formulations, which were applied on silicon wafers, steel panels, and mortar specimens to make dual-capsule self-healing protective coatings. When the STP/DD-based coating was scratched, self-healing of the damaged region occurred, which was demonstrated by SEM, electrochemical test, and water permeability test. It was also confirmed that secondary crack did not occur in the healed region upon application of vigorous vibration to the self-healing coating.