Karen Köhler

Polyelectrolyte complexes as a “smart” depot for self-healing anticorrosion coatings

Various types of “intelligent” self-healing anticorrosion coatings using stimuli-responsive behaviour of polyelectrolyte/inhibitor complexes are presented. Flat nanocomposite multilayers as well as colloidally-templated micro- and nanocarriers with incorporated inhibitor are employed as main building blocks for the formation of novel protective materials. The corrosion inhibitor is incorporated as a structural element (organic molecule), as an inorganic precipitate or in a porous inorganic particle. Being induced by local pH changes during corrosion development, polyelectrolyte/inhibitor complexes afford the unique ability of active feedback and sustained release of inhibitor exactly at the corrosion-damaged sites. Elimination of the corrosive attack returns the complex layer back into the sealed state, providing effective storage and consumption of inhibitor. Insertion of complex-based elements into the coating matrix not only allows the combination of passive and active corrosion protection but also imparts the self-healing properties.

Effect of microwave radiation on polymer microcapsules containing inorganic nanoparticles

The effect of microwave radiation on polymer microcapsules containing inorganic nanoparticles has been studied. The samples were exposed to 2.45 and 8.208 GHz microwaves of variable power. The data of scanning electron microscopy show that the character of microwave action upon polymer microcapsules depends on their composition and on the frequency and power of radiation.

Salt-induced fusion of microcapsules of polyelectrolytes

Fusion of microcapsules of the polyelectrolytes poly-diallyldimethylammonium chloride (PDADMAC) and sodium poly-styrenesulfonic acid (PSS) is achieved during the evaporation of NaCl solution in open chambers. The increasingly concentrated salt solution induces a series of faster and accumulating effects in the structure of the membranes and the cores of microcapsules. It creates defects in the membranes, decreases the electrostatic repulsion of polyelectrolytes in the membranes, causes a conformational change of the polyelectrolytes, increases the osmotic pressure gradient across the microcapsule membranes, and decreases the supporting force of the core by sucking water outwards. Due to the surface tension of the microcapsules and the hydrophobic interaction of the polyelectrolytes, microcapsules decrease the surface area and finally fuse. During fusion, their shapes change from peanut to oblate and then finally to round spheres. The neutral polymer molecules in the core diffuse and mix but do not leak out. The polyelectrolytes in the membranes do not mix due to the molecular entanglement. The work on fusion with salt as a critical parameter is important to approach promising artificial micro-containers, whose novel functions arise from the mixing of the inner content.

Effect of microwave irradiation on composite iron oxide nanoparticle/polymer microcapsules

Iron oxide nanoparticle/polymer microcapsules containing different number of layers of iron oxide nanoparticles have been made using the layer-by-layer alternating absorption technique. Nanoparticles as well as composite microcapsules have been characterized by TEM and SEM. The electronic paramagnetic resonance (EPR) spectra of water suspensions of iron oxide nanoparticles and microcapsules with iron oxide nanoparticles inside the capsule shell have been measured. Parameters of the EPR spectra are sensitivity to nanoparticle concentration in solution as well as to thermal and microwave microcapsules treatment. The shell permeability, as explored by confocal fluorescence microscopy, is decreased after temperature treatment of microcapsules but increased after microwave radiation. These results can find practical application in medicine and bioengineering for remote control over the permeability of microcapsule shells.