Dmitry G. Shchukin

Halloysite clay nanotubes for controlled release of protective agents.

Halloysite aluminosilicate nanotubes with a 15 nm lumen, 50 nm external diameter, and length of 800 +/- 300 nm have been developed as an entrapment system for loading, storage, and controlled release of anticorrosion agents and biocides. Fundamental research to enable the control of release rates from hours to months is being undertaken. By variation of internal fluidic properties, the formation of nanoshells over the nanotubes and by creation of smart caps at the tube ends it is possible to develop further means of controlling the rate of release. Anticorrosive halloysite coatings are in development and a self-healing approach has been developed for repair mechanisms through response activation to external impacts. In this Perspective, applications of halloysite as nanometer-scale containers are discussed, including the use of halloysite tubes as drug releasing agents, as biomimetic reaction vessels, and as additives in biocide and protective coatings. Halloysite nanotubes are available in thousands of tons, and remain sophisticated and novel natural nanomaterials which can be used for the loading of agents for metal and plastic anticorrosion and biocide protection.

Halloysite Tubes as Nanocontainers for Anticorrosion Coating with Benzotriazole

Halloysite clay nanotubes were investigated as a tubular container for the corrosion inhibitor benzotriazole. Halloysite is a naturally occurring cylindrical clay mineral with an internal diameter in the nanometer range and a length up to several micrometers, yielding a high-aspect-ratio hollow tube structure. Halloysite may be used as an additive in paints to produce a functional composite coating material. A maximum benzotriazole loading of 5% by weight was achieved for clay tubes of 50 nm external diameters and lumen of 15 nm. Variable release rates of the corrosion inhibitor were possible in a range between 5 and 100 h, as was demonstrated by formation of stoppers at tube openings. The anticorrosive performance of the sol-gel coating and paint loaded with 2-5% of halloysite-entrapped benzotriazole was tested on copper and on 2024-aluminum alloy by direct exposure of the metal plates to corrosive media. Kinetics of the corrosion spot formation at the coating defects was analyzed by the scanning vibrating electrode technique, and an essential damping of corrosion development was demonstrated for halloysite-loaded samples.

Self-Healing Anticorrosion Coatings Based on pH-Sensitive Polyelectrolyte/Inhibitor Sandwichlike Nanostructures

An anticorrosion layer of a smart polymer coating is developed. The nature and properties of the coating simultaneously provide three mechanisms of corrosion protection: passivation of the metal degradation by controlled release of an inhibitor, buffering of pH changes at the corrosive area by polyelectrolyte layers, and self-curing of the film defects due to the mobility of the polyelectrolyte constituents in the layer-by-layer assembly.

Carbonate microparticles for hollow polyelectrolyte capsules fabrication

Calcium, cadmium and manganese carbonate crystals were used as core material for fabrication of hollow polyelectrolyte capsules by means of the Layer-by-Layer assembly. The use of inorganic templates is a way of fabrication of clean capsules, which is essential for basic research and is a significant step towards their biocompatibility. The ways of particle and capsule fabrication and characterization are described. Scanning electron microscopy (SEM)-Energy dispersive X-ray spectroscopy (EDX) measurements proved the purity of the hollow capsules from the core material. The capsules obtained were characterized by scanning force microscopy, and confocal fluorescence microscopy.

Mesoporous Silica Nanoparticles for Active Corrosion Protection

This work presents the synthesis of monodisperse, mesoporous silica nanoparticles and their application as nanocontainers loaded with corrosion inhibitor (1H-benzotriazole (BTA)) and embedded in hybrid SiOx/ZrOx sol-gel coating for the corrosion protection of aluminum alloy. The developed porous system of mechanically stable silica nanoparticles exhibits high surface area (∼1000 m2·g(-1)), narrow pore size distribution (d∼3 nm), and large pore volume (∼1 mL·g(-1)). As a result, a sufficiently high uptake and storage of the corrosion inhibitor in the mesoporous nanocontainers was achieved. The successful embedding and homogeneous distribution of the BTA-loaded monodisperse silica nanocontainers in the passive anticorrosive SiOx/ZrOx film improve the wet corrosion resistance of the aluminum alloy AA2024 in 0.1 M sodium chloride solution. The enhanced corrosion protection of this newly developed active system in comparison to the passive sol-gel coating was observed during a simulated corrosion process by the scanning vibrating electrode technique (SVET). These results, as well as the controlled pH-dependent release of BTA from the mesoporous silica nanocontainers without additional polyelectrolyte shell, suggest an inhibitor release triggered by the corrosion process leading to a self-healing effect.

Sonochemical Synthesis of Highly Luminescent Zinc Oxide Nanoparticles Doped with Magnesium(II)

A bright idea: Mg/ZnO nanoparticles that exhibit bright, stable photoluminescence both in colloidal dispersions and in the solid state are formed by doping Mg(II) ions into ZnO nanoparticles by sonochemical synthesis. The changes in their band gaps and luminescence properties rely on the defect concentrations inside the ZnO nanoparticles; these concentrations are determined by the Mg/Zn molar ratios (see picture).

Ultrasonic Cavitation at Solid Surfaces

In spite of the great potential of applying high-intensity ultrasound, which enables high-temperature and high-pressure chemistry with a reactor near room temperature and ambient pressure, sonochemistry at solid surfaces is at a weak stage of understanding with regards to the development of new materials and composite nanostructures. The science towards a quantitative understanding is only now emerging. On the other hand, in many applications an ultrasonic bath is used without thinking of the mechanism. Often surfaces are exposed to ultrasound for cleaning. Since ultrasonic treatment is not an exotic process and applicable even on large scale in industrial manufacturing, controlling the process may lead to new applications making use of the specially designed surface. This review is intended to summarize recent progress in this field and to point out most promising directions of ultrasound application for the development of new materials with functional surfaces.

New Method for Fabrication of Loaded Micro-and Nanocontainers: Emulsion Encapsulation by Polyelectrolyte Layer-by-Layer Deposition on the Liquid Core

A novel approach to the emulsion encapsulation was developed by combining the advantages of direct encapsulation of a liquid colloidal core with the accuracy and multifunctionality of layer-by-layer polyelectrolyte deposition. Experimental data obtained for the model oil-in-water emulsion confirm unambiguously the alternating PE assembly in the capsule shell as well as the maintenance of the liquid colloidal core. Two different mechanisms of capsule destruction upon interaction with the solid substrate were observed and qualitatively explained. The proposed method can be easily generalized to the preparation of oil-filled capsules in various oil/water/polyelectrolyte systems important in the field of pharmacy, medicine, and food industry.

Silica/Polymer Double-Walled Hybrid Nanotubes: Synthesis and Application as Stimuli-Responsive Nanocontainers in Self-Healing Coatings

We report the development of silica/polymer double-walled hybrid nanotubes, which consist of a hollow cavity, a porous silica inner wall, and a stimuli-responsive (pH, temperature, and redox) polymeric outer wall, as a novel nanocontainer system. The length, diameter, wall thickness, and aspect ratio of the hybrid nanotubes are precisely controlled in the range of 48-506 nm, 41-68 nm, 3-24 nm, and 1.2-7.6, respectively. The hybrid nanotubes loaded with active molecules exhibit morphology-dependent release and pH-, temperature-, redox-responsive release, which enable a wide range of applications from energy storage to drug delivery and self-healing coatings for metal corrosion protection.

Micron-scale hollow polyelectrolyte capsules with nanosized magnetic Fe3O4 inside

Two novel methods for imparting magnetic properties to the hollow polyelectrolyte capsules were proposed. The first one includes the impregnation of the capsules with pre-formed Fe3O4 magnetite nanoparticles; the second approach is based on selective synthesis of magnetic Fe3O4 inside the polyelectrolyte capsules filled with polycations. Synthesized Fe3O4 core/polyelectrolyte shell composites were characterized by transmission electron microscopy (TEM) and WAXS techniques. Perspectives of the usage of hollow polyelectrolyte capsules as microreactors for spatially restricted inorganic synthesis were demonstrated.