Protective organic coatings with anticorrosive and other feedback-active features: micro- and nanocontainers-based approach

Development of materials possessing the ability to recover their main function(s) in response to destructive impacts is today one of most rapidly growing fields in the material science. In particular, protective organic coatings with the features to heal or restore their protective function autonomously are of great interest in fighting surface deterioration processes like corrosion, biofouling and other affecting metallic structures. Embedding of micro- and nanocontainers in protective coatings is nowadays frequently used technique to provide them one or several feedback active functionalities. Depending on containers morphology and active agent(s) filled, coatings with specifically aimed self-recovering functionalities (anticorrosive, water-repelling, antifouling etc.) or multifunctional coatings can be created. In the present paper, different types of containers for self-recovering functional coatings synthesized by use of mesoporous nano- and microparticles or on the emulsion basis are presented. L-b-L polyelectrolyte deposition, interfacial polymerization, surface precipitation, Pickering emulsions and in-situ emulsion polymerization were utilized for the preparation of nano- or microscaled containers. Morphology of containers, efficiency of encapsulation and kinetics of active agents release were investigated using modern techniques such as T-SEM, Cryo-SEM etc. Incorporation of containers in the coating matrix was followed by the experimental modeling of external impacts leading to the simultaneous containers damage. Subsequent release of the active agent at the affected site caused the active feedback of the coating and self-recovery of its specific protective function. The advantages of novel container based protective coatings as compared to conventional ones are illustrated by corrosion tests results according to ASTM Standard B 117

Self-assembly of a metallosupramolecular coordination polyelectrolyte in the pores of SBA-15 and MCM-41 silica

It is shown that intrinsically stiff chain aggregates of a metallosupramolecular coordination polyelectrolyte (MEPE) can form in the cylindrical nanopores of MCM-41 and SBA-15 silica by self-assembly of its constituents (metal ions and organic ligand). The UV/vis spectra of the resulting MEPE-silica composites exhibit the characteristic metal-to-ligand charge transfer band of the MEPE complex in solution. For the MEPE-silica composite in SBA-15 an iron content of 1.2 wt % was found, corresponding to ca. 10 MEPE chains disposed side by side in the 8 nm wide pores of the SBA-15 matrix. In the case of MCM-41 (pore width < 3 nm), where only one MEPE chain per pore can be accommodated, an iron content of 0.3 wt % was obtained, corresponding to half-filling of the pores. It was also found that MEPE chains spontaneously enter the pores of SBA-15, when a solution of MEPE is exposed to the silica matrix

NMR provides checklist of generic properties for atomic-scale models of periodic mesoporous silicas

MCM-41 and SBA-15 silicas were studied by Si-29 solid-state NMR and (15) N NMR in the presence of (15) Npyridine with the aim to formulate generic structural parameters that may be used as a checklist for atomicscale structural models of this class of ordered mesoporous materials. High-quality MCM-41 silica constitutes quasi-ideal arrays of uniform-size pores with thin pore walls, while SBA-15 silica has thicker pore walls with framework and surface defects. The numbers of silanol Q(3)) and silicate (Q(4)) groups were found to be in the ratio of about 1:3 for MCM-41 and about 1:4 for our SBA-15 materials. Combined with the earlier finding that the density of surface silanol groups is about three per nm(2) in MCM-41 (Shenderovich, et al. J. Phys. Chem. B 2003, 107, 11924) this allows us to discriminate between different atomic-scale models of these materials. Neither tridymite nor edingtonite meet both of these requirements. On the basis of the hexagonal pore shape model, the experimental Q(3):Q(4) ratio yields a wall thickness of about 0.95 nm for MCM-41 silica, corresponding to the width of ca. four silica tetrahedra. The arrangement of Q3 groups at the silica surfaces was analyzed using postsynthesis surface functionalization. It was found that the number of covalent bonds to the surface formed by the functional reagents is affected by the surface morphology. It is concluded that for high-quality MCM-41 silicas the distance between neighboring surface silanol groups is greater than 0.5 nm. As a result, di- and tripodical reagents like (CH3)(2)Si(OH)(2) and CH3Si(OH)(3) can form only one covalent bond to the surface. The residual hydroxyl groups of surface-bonded functional reagents either remain free or interact with other reagent molecules. Accordingly, the number of surface silanol groups at a given MCM41 or SBA-15 silica may not decrease but increase after treatment with CH3Si(OH)(3) reagent. On the other hand, nearly all surface silanol groups could be functionalized when HN(Si(CH3)(3))(2) was used

NMR study of proton transfer to strong bases on inner surfaces of MCM-41

Variable temperature (1)H and (15)N NMR techniques have been used to study the interaction of (15)N enriched 4-dimethylaminopyridine (AP) and 4-diethyl-2,6-di-tert-butylaminopyridine (TBAP) with the surface of MCM-41 silica Both bases become protonated on the surface. AP-H(+) and TBAP-H(+) remain immobilized on the surface at room temperature, but are free to rotate around the molecular C(2) axis The concentration of the protonated species is not affected by the presence of water and water is not involved in or coordinated around the protonated species We propose that strong electrostatic interactions can affect the local structure of the inner surfaces of MCM-41 that result in mutual interactions of neighboring silanol groups which enables proton transfer to the guests There are good reasons to suggest that three surface silanol groups are involved in each cluster with one protonated base The N H distance in the AP-H(+) cation is lengthened by a hydrogen bond to the deprotonated silanol group The N H distance in the TBAP-H(+) cation is shorter and the interaction to the anion is purely electrostatic. In the presence of water and an excess of AP, 2.1 AP, water complexes are formed, with one water bonded between two bases and the N H distances of about 1 7 angstrom. The reorientation of these complexes and the molecular exchange among different species are slow at room temperature. TBAP does not interact with water on the silica surface (C) 2010 Elsevier Inc. All rights reserve

Phase Separation of a Binary Liquid System in Controlled-Pore Glass

Schemmel S, Akcakayiran D, Rother G, et al. Phase Separation of a Binary Liquid System in Controlled-Pore Glass. MRS Online Proceedings Library Archive. 2004;790: P7.2

Carboxylic Acid-Doped SBA-15 Silica as a Host for Metallo-supramolecular Coordination Polymers†

The adsorption of a metallo-supramolecular coordination polymer (Fe−MEPE) in the cylindrical pores of SBA-15 silica with pure and carboxylic acid (CA) carrying pore walls has been studied. Fe−MEPE is an intrinsically stiff polycation formed by complexation of Fe(II)−acetate with an uncharged ditopic bis-terpyridine ligand. The adsorption affinity and kinetics of the Fe−MEPE chains is strongly enhanced when the pore walls are doped with CA, and when the pH of the aqueous medium or temperature is increased. The initial fast uptake is connected with a decrease of pH of the aqueous solution, indicating an ion-exchange mechanism. It is followed by a slower (presumably diffusion-controlled) further uptake. The maximum adsorbed amount of Fe−MEPE in the CA-doped material corresponds to a monolayer of Fe−MEPE chains disposed side-by-side along the pore walls. The stoichiometry of Fe−MEPE in the pores (determined by XPS) was found to be independent of the loading and similar to that of the starting material. The mean chain length of Fe−MEPE before and after embedding in the CA-doped matrix was studied by solid-state 15N NMR using partially 15N-labeled Fe−MEPE. It is shown that the average chain length of Fe−MEPE is reduced when the complex is incorporated in the pores