Self-healing Conditions Research Articles

Self-healing performance of engineered geopolymer composites subjected to sodium sulphate

Engineered geopolymer composites (EGCs) have self-healing potential due to their multiple fine-cracking features. However, water immersion, as a self-healing condition for fibre-reinforced cement-based composites, may limit the self-healing ability of EGCs due to water would not directly participate in the precipitation reaction. By contrast, sodium sulphate is proved as an effective activator to promote the geopolymerisation process, while the self-healing performance of EGCs exposed to sodium sulphate has not been comprehensively demonstrated in the literature. Therefore, this paper investigates the self-healing performance of the EGCs subjected to sodium sulphate (Na2SO4) under wet-dry cycles. The results show that the EGCs preloaded at 3 days attain a higher increment of C-(A)-S-H gels at the cracks than those preloaded at 28 days, indicating the EGCs cracked at the early age have better self-healing performance under sulphate exposure. Besides, ettringite and calcium carbonate are detected as the self-healing products in the EGCs preloaded at 3 days, while the ettringite cannot be found in the EGCs preloaded at 28 days. The EGCs exposed to 5 % Na2SO4 solution and wet-dry cycles can achieve self-healing by forming more CaCO3. Increasing the Na2SO4 concentration to 10 % can accomplish self-healing by facilitating the C-(A)-S-H and CaCO3 formation, enhancing the tensile stiffness recovery and crack width reduction ratios for the EGCs with tensile strains of 2 % and 4 % at 3 days. Decreasing the preloading level also improves the tensile stiffness recovery and crack width reduction ratios regardless of the Na2SO4 concentration and preloading age, since the self-healing products are easier to fill the small cracks. Through a combination of Na2SO4 solution and wet-dry cycles, this study develops a new strategy for the accomplishment of self-healing of EGCs.

Capacitance Evaluation of Metallized Polypropylene Film Capacitors Considering Cumulative Self-Healing Damage

Self-healing (SH) in metallized polypropylene film capacitors (MPPFCs) can lead to irreversible damage to electrode and dielectric structures, resulting in capacitance loss and significant stability degradation, especially under cumulative SH conditions. To enhance the reliability assessment of MPPFCs post-SH, this study conducted SH experiments on MPPFCs, examined the damage patterns of the electrodes and dielectric films, and proposed a novel capacitance evaluation method for MPPFCs under cumulative SH conditions. The results reveal that with increasing SH voltage, the number of dielectric layers experiencing single SH breakdowns rises, SH energy significantly escalates, and the loss area of the electrode due to high-temperature evaporation expands. Under cumulative SH conditions, the number of SH events is linearly correlated with the total number of SH-breakdown film layers and shows an exponential decay with the average single SH energy. By utilizing a Support Vector Machine (SVM) to classify the SH condition and damage features within the capacitor based on the correlation and distribution patterns of SH feature parameters, this study introduces an advanced method for evaluating the capacitance of MPPFCs under cumulative SH conditions. This method promises to improve the predictive maintenance and reliability of power electronic systems utilizing MPPFCs.

Crack monitoring strategy for concrete structures in various service conditions via multiple CNT-CF/cement composite sensors: Experiment and simulation approaches

A crack monitoring strategy using parallelly-arranged multiple conductive cement composites for reinforced concrete was verified through a series of experiments and simulations. First, the electrical resistances of various locations of the mortar embedding the CNT-CF/composites were measured along with changes in humidity. Then, shear and flexural cracks were generated through a bending test of the reinforced mortar in which the CNT-CF/cement composite bars were embedded. The change in resistance of the composite bars themselves and between adjacent composite bars before and after cracking was measured. Differences in the results with the cracks in dried, wet, and also self-healing conditions were compared. Additionally, a finite element simulation on the electrical resistance under the experimental conditions was conducted to better understand the measurement results. Based on these experimental and simulation results, the strategy for monitoring structural damage under various operating scenarios was discussed. It was possible to monitor cracks of the reinforced mortar by detecting the increases and/or fluctuations in resistances of the composite bars themselves and between adjacent composite bars.

Multiscale Mathematical Analysis of Influencing Factors and Experimental Verification of Microcrack Self-Healing Efficiency of Bitumen Composites Using Microcapsules.

The preparation and application of microcapsules containing healing agents have become a crucial way to enhance the self-healing capability of bitumen. This intelligent material has become a hot topic in the field of pavement material and has greatly stimulated the development and applications of pavement engineering. However, there has been no research focused on the relationship of the multistructures from the viewpoint of molecular-size, microsize, and macrosize, which significantly limits the predictions of the self-healing efficiency and structure design of this self-healing material. The purpose of this study was to make a mathematical analysis of the influencing factors of self-healing efficiency based on the self-healing mechanism of bitumen using microcapsules, fully considering the structural dimensions, preparation conditions, and self-healing conditions. In the mathematical analysis, the cross-linking degree of the shell material molecules of the microcapsules was considered for its damage strength from the perspective of molecular structure. The final tip stress of the microcrack was believed to be equal to the puncture strength of the microcapsules in terms of microsize. From a macroscale point of view, the amount of healing agent released from the microcapsule rupture was considered more significant than or equal to the volume of the microcracks. At the same time, the time-temperature superposition principle was applied to simplify the influence factors. The above derivation based on multiscale structures found that the additive amount of the microcapsules, temperature, and time were the three main influencing factors on the self-healing features of bitumen. Finally, the experimental data was investigated considering the three factors, which thoroughly verified the feasibility of the derivation. All results will help to establish a bridge between the initial structural design of self-healing bitumen and the prediction of the final self-healing effects.

Analyzing the Damage–Healing Performance of Asphalt Mixture from Macroscopic and Mesoscopic Scales

Owing to their self-healing ability, asphalt mixtures have great potential for improving the service life of asphalt pavement, and can play an important role in sustainable infrastructures. In this study, a semicircular bending damage-healing-fracture experiment was conducted to evaluate the healing effect of a 90# asphalt mixture and styrene-butadiene-styrene copolymer modified asphalt mixture. The digital image correlation technique was used to synchronously observe the semicircular specimen to analyze its surface displacement and strain changes during the healing process. The experimental results showed that, on the macroscopic scale, the healing index HIFE based on fracture energy density was recommended to evaluate the healing effect of asphalt mixtures, and the healing effect of the 90# asphalt mixture was better than that of the styrene-butadiene-styrene copolymer modified asphalt mixture. On the mesoscopic scale, the horizontal displacements of the notch of the specimen position gradually recovered under self-healing conditions. The strain concentration at the crack gradually weakened, and the strain degree in the non-cracked area of the specimen also decreased gradually under self-healing conditions. The recovery of the macromechanics of the specimen is related not only to the healing of the crack area but also to the recovery of the non-cracked area.

Machine learning-based damage sensing and self-healing of carbon fiber/nylon composites via addressable conducting networks

In this work, addressable conducting network (ACN) was used for the damage sensing and self-healing of continuous carbon fiber reinforced nylon composite (CFRP). The machine-learning was used for accurate damage sensing by training the resistance change of composites along ACN due to their structural damage. Also, self-healing of the carbon fiber composite material was performed by applying the electrical current to generate local heating through the detected damage location. The self-healing conditions such as the current input pairs of ACN and amount of the electrical current were determined through the artificial neural network (ANN)-based machine-learning technique. As a result, high-accuracy damage sensing based on machine learning with ACN was conducted, and self-healing with a healing efficiency of 98% could be achieved.

Finite element analysis of proof test for self-healing ceramics

Ceramic materials are superior to metallic materials in variable respects such as lightness, strength, corrosive and thermal resistance and so on. Therefore, they are expected to be used as structural materials. However, internal and surface defects of them generated during manufactural processes could cause rapid crack growth and fracture. Thus, there is significant scatter of fracture strength even if manufactured in the same condition. This is the most serious obstacle for the practical use of ceramics. To resolve such a matter, the method in which “self-healing” and “proof test” are combined is suggested. It is known that Al2O3/SiC composite ceramics shows self-healing behavior using oxidation reaction under high temperature environment. It will be possible to remove the surface defects with this performance. After heat-treating surface defects, components which satisfy the required strength could be picked up with the proof test. In this study, we conducted the finite element analysis of treating surface defects and three-point bending proof test by using the damage-healing constitutive model based on the oxidation kinetics. In addition, we evaluated the scatter of bending strength with the Weibull distribution. In the analysis, we used specimens which have pre-cracks and internal defects to represent the competition between these defects. Finally, we demonstrated that how proof test condition depends on the self-healing conditions and microstructure.

The Serum Immunoglobulin E Level: Is There a Relationship With the Clinical Course of the Gianotti-Crosti Syndrome?

Background: Gianotti Crosti syndrome (GCS) is a self-healing condition with a spontaneous resolution in 2–6 weeks but, even if rarely, recurrent episodes have been reported.Objective: The aim of this observational study is to investigate serum Immunoglobulin E (IgE) level in children with GCS, evaluating if there is a relationship between IgE level and clinical course of the disease.Methods: Children with GCS diagnosed at a tertiary care children's university hospital between June 2018 and November 2019 were prospectively enrolled. Demographic, clinical and hematochemical data of children investigated were collected. In particular, IgE level were investigated at symptoms onset and, if available, at the following blood tests. Patients were divided in 2 groups on the bases of the clinical course: children with a chronic relapsing course and children who did not present any relapse.Results: Among 29 patients enrolled in this study, 14 (48.3%) children had a chronic relapsing course and 15 (51.7%) did not present any relapse. A statistically significant difference was present considering the length of the disease: 210 days (IQR: 161.25–255) for patients with a chronic relapsing course compared to 40 days (IQR: 30–75) for the other group (p < 0.0001). About the median IgE level in the 2 groups, a value about 10 time higher was found in children with chronic course compared to the other group (1,144 vs. 116 U/mL) with a statistically significant difference (p < 0.0001).Conclusion: Despite the study limitations, a significant correlation between higher IgE levels and chronic-relapsing course of the GCS can be assumed.

The Nocturnal Kissing of an Annoying Mosquito; Unusual Insect Bite Reaction, a Case Report and a Literature Review

Insects represent more than half of all known living organisms in the world. Both human beings and insects share a common biodiversity and the influence of insects on human life is enormous. They share an intimate relationship in which human beings are both benefitted and harmed. Insects inflict harm by stinging, biting or transmitting diseases. Rarely, humans are harmed by inadvertently coming in contact with the toxin of an insect. Insect dermatitis is characterized by tingling and burning within 10 minutes of contact, and sometimes the incurred dermatitis is a self-healing condition. Such cases usually happen while asleep when there is a lag time between the crush of the insect and waking up in the morning. A case while sleeping, heard the insect fly around her bare chest, in summer time, and on waving it away instinctively while sleeping, and the insect had been crushed on her bare upper chest skin, incurring a subsequent skin reaction without the typical red bite mark followed by an evolving burning ulcerative skin lesion, that took a while to subside and heal completely. Key words: insect bite, crash, skin reaction.

Preparation of a high strength, rapid self-healing composite gel and its application in electrochemical capacitor

It is imperative to develop ideal self-healing material with intrinsic mechanical strength and mild self-healing conditions. Here, a rapid self-healing poly(vinyl alcohol) (PVA)/chitosan (CS) composite gel with multiple hydrogen bonds is designed. PVA/CS gel shows a particularly high strength of 0.266 MPa and can heal rapidly after completely broken. The self-healing performance can be ascribed to multiple hydrogen bonds provided by the PO/P–O⋯H groups of phytic acid. In particular, PVA/CS gel can be served as solid electrolyte. A flexible all-solid-state capacitor can be assembled based on the flexible polyaniline electrode and PVA/CS gel used as solid electrolyte. The capacitor exhibits a high specific capacitance of 390.6 mF/cm2 and high capacitance retention ratio after hundreds of bends. Additionally, the PVA/CS gel can reconnect the broken capacitor with partial capacitance retention. This work can contribute to the design and fabrication of rapid self-healing gel and flexible all-solid-state capacitor.

A type of self-healable, dissoluble and stretchable organosilicon elastomer for flexible electronic devices

Polymer materials with good mechanical properties, solubility and flexible self-healing conditions were of great value to the development of modern high-tech fields. Herein, α,ω-aminopropyl terminated polydimethylsiloxane (PDMS, Mn = 2000), terephthalaldehyd (TA) and 3-aminophenylboronic acid (APB) were used to construct a three-dimensional network via simple and effective reactions, such as the Schiff base reaction and the dehydration reaction. The obtained PDMS elastomer prepared by low molecular weight main chain could achieve very good mechanical performance of tensile strength 2.54 MPa and the average elongation at break of 275.3%. Through the dynamic imine bonds formed by Schiff base reaction and the coordination of boron oxygen bonds and hydrogen bonds, we have constructed a high efficiency self-healing network. The network could achieve self-healing at room temperature with a self-healing efficiency of 91.6%, at high temperature with a self-healing efficiency of 95.1% and in water at a self-healing efficiency of 85.5%. In addition, multi-walled carbon nanotubes (MWCNTs) was compounded with a polymer system to prepare self-healing flexible electronic devices. Due to the electric resistance of PDMS/MWCNTs sensitively modified with the change of tensile and bending angles, this might be of great significance for the application of sensors.

18F-FDG PET/CT in Lymphomatoid Papulosis Mimicking Primary Cutaneous Anaplastic Large Cell Lymphoma

Lymphomatoid papulosis is a benign self-healing condition, presenting as papulonodular skin eruptions and mimicking malignant cutaneous lymphomas histopathologically. F-FDG PET/CT findings in this benign condition have not been described in detail in the literature. We present a case of lymphomatoid papulosis mimicking primary cutaneous anaplastic large cell lymphoma histopathologically and demonstrating intensely FDG-avid cutaneous lesions on F-FDG PET/CT, which disappear spontaneously in the follow-up scan.

Damage detection and self-healing of carbon fiber polypropylene (CFPP)/carbon nanotube (CNT) nano-composite via addressable conducting network

In this work, damage sensing and self-healing of carbon fiber polypropylene (CFPP)/carbon nanotube (CNT) nano-composite were performed based on addressable conducting network (ACN). To increase damage sensing resolution of CFPP/CNT nano-composite, through-thickness electrical conductivity was improved by adjusting press condition and spraying carbon nanotubes (CNT) between prepregs. From the results, electrical resistivity in thickness direction was reduced to 19.44 Ω·mm under 1.0 MPa and 1.0 wt% of CNT condition. Also, self-healing efficiency was examined with respect to the temperature and time via resistive heating of CFPP/CNT nano-composite. As a result, the optimized fabrication and self-healing condition exhibited high resolution of damage sensing with outstanding self-healing efficiency (96.83%) under fourth cycle of repeated three-point bending test.

Recent Achievements of Self-Healing Graphene/Polymer Composites.

Self-healing materials have attracted much attention because that they possess the ability to increase the lifetime of materials and reduce the total cost of systems during the process of long-term use; incorporation of functional material enlarges their applications. Graphene, as a promising additive, has received great attention due to its large specific surface area, ultrahigh conductivity, strong antioxidant characteristics, thermal stability, high thermal conductivity, and good mechanical properties. In this brief review, graphene-containing polymer composites with self-healing properties are summarized including their preparations, self-healing conditions, properties, and applications. In addition, future perspectives of graphene/polymer composites are briefly discussed.

Self-Healing Polymer Dielectric for a High Capacitance Gate Insulator.

Self-healing materials are required for development of various flexible electronic devices to repair cracks and ruptures caused by repetitive bending or folding. Specifically, a self-healing dielectric layer has huge potential to achieve healing electronics without mechanical breakdown in flexible operations. Here, we developed a high performance self-healing dielectric layer with an ionic liquid and catechol-functionalized polymer which exhibited a self-healing ability for both bulk and film states under mild self-healing conditions at 55 °C for 30 min. Due to the sufficient ion mobility of the ionic liquid in the polymer matrix, it had a high capacitance value above 1 μF/cm(2) at 20 Hz. Moreover, zinc oxide (ZnO) thin-film transistors (TFTs) with a self-healing dielectric layer exhibited a high field-effect mobility of 16.1 ± 3.07 cm(2) V(-1) s(-1) at a gate bias of 3 V. Even after repetitive self-healing of the dielectric layer from mechanical breaking, the electrical performance of the TFTs was well-maintained.

Effective Crack Control of Concrete by Self-Healing of Cementitious Composites Using Synthetic Fiber.

Although concrete is one of the most widely used construction materials, it is characterized by substantially low tensile strength in comparison to its compression strength, and the occurrence of cracks is unavoidable. In addition, cracks progress due to environmental conditions including damage by freezing, neutralization, and salt, etc. Moreover, detrimental damage can occur in concrete structures due to the permeation of deteriorating elements such as Cl− and CO2. Meanwhile, under an environment in which moisture is being supplied and if the width of the crack is small, a phenomenon of self-healing, in which a portion of the crack is filled in due to the rehydration of the cement particles and precipitation of CaCO3, is been confirmed. In this study, cracks in cementitious composite materials are effectively dispersed using synthetic fibers, and for cracks with a width of more than 0.1 mm, a review of the optimal self-healing conditions is conducted along with the review of a diverse range of self-healing performance factors. As a result, it was confirmed that the effective restoration of watertightness through the production of the majority of self-healing products was achieved by CaCO3 and the use of synthetic fibers with polarity, along with the effect of inducing a multiple number of hairline cracks. In addition, it was confirmed that the self-healing conditions of saturated Ca(OH)2 solution, which supplied CO2 micro-bubbles, displayed the most effective self-healing performance in the surface and internal sections of the cracks.

High temperature healing of Ti 2AlC: On the origin of inhomogeneous oxide scale

The microstructure of oxide scales formed on Ti2AlC surface after oxidation at 1200 °C is investigated. The results reveal an inhomogeneous morphology of the oxide scales, i.e. islands of coarse rutile grains pile up on fine-grained Al2O3 layer. Local cross-sectional observations show that the rutile islands grow on top of cavities in the parent material. A model is proposed to describe the resulting microstructure after oxidation. These results are relevant in optimizing the self-healing conditions of Ti2AlC at high temperature.

DISCITIS FOLLOWING LUMBAR PUNCTURE IN NON-HODGKIN LYMPHOMA

Discitis in children is a rare disorder of intervertebral disc and vertebral end plate. Infection or trauma, like lumbar puncture, may be the possible causes. Low-back pain and gait disturbance are the main symptoms. The most appropriate diagnostic procedure is MRI. Treatment is mainly empirical. Here a case with non-Hodgkin lymphoma is discussed. Treatment consisted of strict bed rest and antibiotics. Safe and sterile technique is important in patients with invasive procedures like intrathecal chemotherapy. Although discitis is a self-healing condition, it might cause vertebral osteomyelitis. In this regard, physicians should be aware of this probable complication after lumbar puncture and manage it earlier in children with cancer.

Lymphomatoid papulosis in children: a study of 10 children registered by the Dutch Cutaneous Lymphoma Working Group.

Lymphomatoid papulosis (LyP) is a chronic recurrent self-healing condition, with histological features suggestive of a malignant lymphoma. Only a few cases have been described in children. We report 10 children with this skin disease and compare them with the adult type of LyP and childhood cases described in the literature. Although LyP has the same clinical picture and histology in both age groups, in contrast with the adult type no transformation into malignancy has been described in childhood.