Synthesis of calcium carbonate microcapsules as self-healing containers

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.

Improved Corrosion Protection of Acrylic Waterborne Coating by Doping with Microencapsulated Corrosion Inhibitors

Herein, a waterborne acrylic coating doped with pH sensitive colophony microcapsules containing corrosion inhibitors was studied on carbon steel plates. The changes in the physical properties of the coatings were studied. The microcapsule coating specimens maintained more noble Ecorr values compared to the control in deionized water and simulated concrete pore solutions with −513 and −531 mVSCE, respectively. Additionally, the microcapsule polarization results for both pH 12.6 and 6.2 electrolyte solutions showed lower icorr values of 1.20 × 10−6 and 3.24 × 10−6 A·cm−2, respectively, compared to the control sample (1.15 × 10−5 and 4.21 × 10−5 A·cm−2). Therefore, the microcapsule coating provided more protection from chloride attack on the substrate as well as the deleterious effects of low pH on carbon steel. The electrochemical impedance spectroscopy analysis corroborated the DC polarization results, showing increased corrosion resistance for the microcapsule coated specimens compared to the control. Moreover, the Rpore and Rct are much higher than the control, indicating the protection of the inhibitors. The Ceff,dl also shows lower values for the microcapsule coating than the control, showing a more protective and less doped double layer.

pH-Triggered Release of NaNO2 Corrosion Inhibitors from Novel Colophony Microcapsules in Simulated Concrete Pore Solution

Herein, pH-sensitive microcapsules containing NaNO₂ corrosion inhibitors for protection of steel reinforced concrete were synthesized via water-in-oil-in-water (W/O/W) double emulsion using colophony as the wall material. The average microcapsule size was 79.07 μm in diameter and exhibited a high encapsulation efficiency of 83.2%. Study of the release of corrosion inhibitors from microcapsules in deionized water (DI water, pH 6.8), carbonate/bicarbonate buffer solution (CBS, pH 9.1), and simulated concrete pore solution (SCPS, pH 12.6) demonstrates that the microcapsules are sensitive to pH and display higher release in alkaline media. This is the first study of colophony as an encapsulating agent for corrosion inhibitors. Furthermore, the alkaline pH-triggered release shows the suitability of its use in reinforced concrete systems. A wide thermal stability range was also found for the colophony microcapsules up to 100 °C. These high pH environments (CBS and SCPS) present pH values above the pK_a of colophony (7.2), thus triggering enhanced inhibitor release by the ionization and deprotonation of colophony shell. The higher release in CBS and SCPS is demonstrated by the increases of the corrosion inhibitor diffusion coefficient by an order of magnitude from 3.30 × 10^-17 m²/s in DI water up to 1.66 × 10^-16 m²/s for SCPS. The release performance indicates that the proposed approach can be used to encapsulate a variety of inhibitors for the protection of steel reinforcements. After immersion in different pH solutions, the corrosion potentials of a carbon steel substrate with microcapsules containing nitrite were more noble than when immersed without microcapsules and the corrosion current densities showed comparable values to free corrosion inhibitors. The formation of a passive ferric oxide layer was confirmed by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy.