Johannes Fickert

Encapsulation of Self-Healing Agents in Polymer Nanocapsules

Considerable attention has been devoted to self-healing (SH) materials in recent years. [ 1 ] Among them, extrinsic SH materials play an important role, for which the healing process is achieved by embedding containers fi lled with a healant in a matrix. When damage occurs, the healant is released from the containers into the cracks and heals the materials by polymerization, [ 1a , 2 ] or solventor plasticizer-assisted welding. [ 3 ] Compared with monolithic particles, polymer capsules can encapsulate a larger quantity of guest substances within their cores and release the substances on demand at a later stage. [ 4 ] This characteristic allows polymer capsules to fi nd application as containers for healants, examples including capsules with poly(urea-formaldehyde) (PUF), [ 5 ]

Design and characterization of functionalized silica nanocontainers for self-healing materials

Silica nanocapsules functionalized with thiol or amine groups with sizes between 100 and 400 nm could be successfully synthesized using the interface of direct miniemulsion droplets for the hydrolysis and condensation of silicon alkoxides. We show that healing agents such as monomers and catalysts can be successfully encapsulated in the silica shell. The catalyst was encapsulated as a solution to allow a better mobility when released for a self-healing reaction. The functional groups were quantified by 29Si MAS-NMR, XPS, and chemical titration. Therefore a precise picture for the gradient of concentration of functional groups inside the shell could be given. The encapsulated reagents were found to be still active and the self-healing reaction could be successfully monitored by solid-state NMR spectroscopy and thermogravimetry.

Regenerative Nano‐Hybrid Coating Tailored for Autonomous Corrosion Protection

A novel bilayer coating system for autonomous corrosion-triggered self-healing is demonstrated. The storage of the encapsulated monomer and the catalyst is separated in two different layers. The encapsulated catalyst is stored inside a metallic coating, which ensures its activity even for an extended exposure time. The release from the capsules is triggered by corrosion and the correlated pH increase.

Silica nanocapsules for redox-responsive delivery

Redox-responsive silica nanocapsules with a hydrophobic liquid core were synthesized by reactive templating of miniemulsion droplets with functional alkoxysilanes. Tetrasulfide bridges were successfully introduced into the inorganic shell and were found to be accessible for chemical reactions as shown by 31P-NMR spectroscopy. Indeed, the tetrasulfide groups could be reduced to yield thiol groups. A subsequent increase of permeability of the silica shell was observed upon reduction of the tetrasulfide groups.

Self-Healing for Anticorrosion Based on Encapsulated Healing Agents

Although the protection of metals from corrosion appears to be a Sisyphean work, promising developments have recently been proposed in the literature. We present here some new strategies, in which traditional methodologies employed for corrosion protection are married with the concept of self-healing. Efficient anticorrosion properties can be achieved by the encapsulation of corrosion inhibitors and/or monomers and catalysts for self-healing reactions. Nanocontainers for anticorrosion comprise a shell that is responsive to stimuli induced by corrosion and a core containing the healing substance. We present here the requirements for their design, synthesis, and application in coatings for metal substrates. The important factors to be taken into account and future directions are also discussed.

pH-Responsive nanocapsules from silylated copolymers

We introduce here a concept allowing the synthesis of smart nanocapsules without a surfactant. Copolymers with masked carboxylic acid groups are desilylated during the nanocapsule preparation and this leads to pH-responsive and self-stabilized nanocontainers encapsulating a large amount of hydrophobic substances. The nanocapsules can be either disrupted for release applications or reversibly aggregated by lowering the pH of the dispersion. The concentration of the nanocapsules in water can be increased by more than 6 times by isolating the nanocontainers at low pH and re-dispersing them at high pH values.