Frederico Maia

Polyelectrolyte-modified layered double hydroxide nanocontainers as vehicles for combined inhibitors

In this work, nanocontainers based on layered double hydroxide (LDH) loaded with two different corrosion inhibitors, namely 2-mercaptobenzothiazole (MBT) and cerium(III) nitrate, were prepared. MBT was intercalated into LDH galleries in anionic form by anion-exchange, while Ce3+ was fixed between polyelectrolyte layers on the surface of LDH-MBT nanoplatelets by the Layer-by-Layer (LbL) method. Both inhibitors were found in the modified LDHs (LDH-Mod) by X-ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy. The release studies performed by UV-vis spectrophotometry indicated that the main triggering conditions for release of MBT from LDHs changed when LDH nanoplatelets were covered with polyelectrolytes. Furthermore, electrochemical impedance spectroscopy and DC polarization were used to investigate the effect in combining MBT− and Ce3+ within the same nanocontainer, for the corrosion protection of 2024-T3 aluminium alloy directly in solution as well as in a hybrid sol–gel coating. The obtained results open prospects for application of these systems as additives in multifunctional smart coatings.

Nanocontainer-based corrosion sensing coating

The present paper reports on the development of new sensing active coating on the basis of nanocontainers containing pH-indicating agent. The coating is able to detect active corrosion processes on different metallic substrates. The corrosion detection functionality based on the local colour change in active cathodic zones results from the interaction of hydroxide ions with phenolphthalein encapsulated in mesoporous nanocontainers which function as sensing nanoreactors. The mesoporous silica nanocontainers are synthesized and loaded with pH indicator phenolphthalein in a one-stage process. The resulting system is mesoporous, which together with bulkiness of the indicator molecules limits their leaching. At the same time, penetration of water molecules and ions inside the container is still possible, allowing encapsulated phenolphthalein to be sensitive to the pH in the surrounding environment and outperforming systems when an indicator is directly dispersed in the coating layer.The performed tests demonstrate the pH sensitivity of the developed nanocontainers being dispersed in aqueous solutions. The corrosion sensing functionality of the protective coatings with nanocontainers are proven for aluminium- and magnesium-based metallic substrates. As a result, the developed nanocontainers show high potential to be used in a new generation of active protective coatings with corrosion-sensing coatings.

Control of crystallite and particle size in the synthesis of layered double hydroxides: Macromolecular insights and a complementary modeling tool

Zinc-aluminum layered double hydroxides with nitrate intercalated (Zn(n)Al-NO3, n=Zn/Al) is an intermediate material for the intercalation of different functional molecules used in a wide range of industrial applications. The synthesis of Zn(2)Al-NO3 was investigated considering the time and temperature of hydrothermal treatment. By examining the crystallite size in two different directions, hydrodynamic particle size, morphology, crystal structure and chemical species in solution, it was possible to understand the crystallization and dissolution processes involved in the mechanisms of crystallite and particle growth. In addition, hydrogeochemical modeling rendered insights on the speciation of different metal cations in solution. Therefore, this tool can be a promising solution to model and optimize the synthesis of layered double hydroxide-based materials for industrial applications.

Active sensing coating for early detection of corrosion processes

A corrosion sensing coating based on specially developed polymeric microcapsules with a pH-indicator is reported. The synthesis of the microcapsules is designed in a way to ensure their optimal compatibility with the polyurethane protective coatings and to allow release of the indicator at higher pH values. The obtained polyurea microcapsules have a regular and microsized morphology and a loading content of 12 wt%. The developed sensing coating applied on aluminium and magnesium alloys is able to indicate initiation of corrosion processes through a pink coating coloration, as a result of local pH increase in the cathodic areas.

A novel approach for immobilization of polyhexamethylene biguanide within silica capsules

Antibacterial agents have been in the spotlight over the past few years either due to their extensive applications or for the increasing concern with the spreading of biocide resistance. The encapsulation of large spectrum antibacterial agents, that are human safe, has been proposed as an alternative to overcome some of these problems but also to impart a controlled release of the encapsulated material. Polyhexamethylene biguanide (PHMB) is a bactericide polymer widely used in various applications, from industrial to household and everyday applications, with little to no documented bacterial resistance. In this work, the encapsulation/immobilization of antibacterial agent PHMB into silica capsules produced in a one-step emulsification process is reported for the first time. The synthesized capsules were characterized by Fourier transform infrared spectroscopy (FTIR), UV-Visible spectrophotometry, electron microscopies (SEM, STEM) and thermogravimetric analysis (TGA), confirming the presence of PHMB in the silica capsules. Furthermore, the incorporation of PHMB into the silica capsules led to significant changes in the textural properties, as revealed by nitrogen adsorption–desorption experiments. The biological performance of PHMB-loaded silica capsules was evaluated against a recombinant bioluminescent strain of Escherichia coli. Although after 60 min encapsulated PHMB has afforded the same bactericidal activity as an equivalent amount of free PHMB, the former demonstrated a delayed action consistent with a limited release of active compound from capsules, which may be advantageous in applications where a controlled release is required.

Brittle Coating Layers for Impact Detection in CFRP

The detection of possible impacts in carbon-fiber-reinforced plastic (CFRP) structures is important for the evaluation of structural integrity of CFRP. Sol–gel-based sensitive coatings for impact detection on CFRP substrates have been developed and investigated by University of Aveiro (UAVR). The coatings are based on hybrid sol–gel formulations with tunable mechanical properties, i.e., brittleness adjusted for a defined range of impact energy. This sensitive layer allows the identification and location of mechanical impacts under visible light and without supplementary tools or conditions for its detection. A systematic study was performed to enhance the coating response for the defined impact threshold. A set of different parameters such as composition, fillers, curing conditions, surface roughness, and chemistry of the surface were tested and optimized.