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

Chiral Metallacrown Supramolecular Compartments that Template Nanochannels: Self-Assembly and Guest Absorption

No AbstractPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64519/1/asia_200900612_sm_miscellaneous_information.pd

Native und säurefunktionalisierte geordnete mesoporöse Silikas: Wirtmaterialien für die supramolekulare Metall-Koordinations-polymere

Native und funktionalisierte Silika Materialien, die periodisch und mesoporös sind, wurden synthetisiert und mittels N2-adsorption, SAXD, SEM, TEM, CHNS-Analyse, NMR, TGA/DTA, XPS, FT-IR und potentiometrischer Titration charakterisiert. Die Funktionalisierung wurde nach den Grafting und Co-Kondensation Methoden durchgeführt. Die funktionalisierten Silikas wurden (i) für die Untersuchung der Oberflächeneigenschaften von MCM-41 und SBA-15, (ii) für Aziditätsmessungen in beschränkten Geometrien in wasserfreier Umgebung und (iii) als Wirtsysteme für MEPE verwendet. Die Verteilung der Silanol Gruppen an den Porenwänden wurde durch Grafting von di- und tripodalen funktionellen Reagenzien F ((CH3)2Si(OCH3)2, (CH3)Si(OCH)3) an die Oberfläche untersucht. Die Anzahl der kovalenten Bindungen zwischen der Silikaoberfläche und F wurde durch 29Si CPMAS NMR Spektroskopie bestimmt. Für hoch geordnete MCM-41 können di- und tripodale F nur eine kovalente Bindung zur Oberfläche bilden. Im Fall von SBA-15 ist auch die Bildung von zwei kovalenten Bindungen zur Oberfläche möglich, was auf einen kleineren Abstand zwischen den Silanolgruppen hinweist. Die Co-Kondensation Methode wurde verwendet, um SBA-15 mit Carboxlysäure (CA), Phosphonsäure (PA) und Sulfonsäuregruppen (SA) zu funktionalisieren. Die Reaktionsbedingungen für die Maximierung des Funktionalisierungsgrades von SBA-15 unter Beibehaltung seiner strukturellen Ordnung werden wesentlich durch die Kinetik der Self-assembly bestimmt. Für ein tieferes Verständnis des Effektes der Hydrolyse und Kondensation der Silikaprecursors (TEOS oder F) sowie deren Wechselwirkung mit Templatmolekülen wurden verschiedene Parameter wie der Anteil des funktionellen Silans , der prehydrolysierte Silikaprecursor (TEOS oder F) und die Zeit der Prehydrolyse variiert. Die Erhöhung von senkt den Anteil des Templats in der funktionalisierten Silika und bewirkt dabei eine bessere Entfernung des Polymers durch die H2SO4 Behandlung. Die höchsten Oberflächenbedeckungen von SBA-15 mit CA, PA und SA sind jeweils 50%, 40% und 30% mit einer ähnlichen Abnahme der Ausbeute der Funktionalisierungsreaktionen. Aziditätsmessungen der funktionalisierten Materialien wurden mit der 15N NMR Methode durchgeführt. Die erhaltenen chemischen Verschiebungen der Pyridin Molekülen zeigen, dass SA, PA and CA Gruppen durch Pyridin Moleküle deprotoniert werden können, was auf ein hohes Protondonorvermögen von diesen festen Säuren hinweist. FT-IR Messungen von CA funktionalisierten SBA-15 beweisen, dass die CA Gruppen im wässrigen Medium bei pH 8 deprotoniert werden. Der Effekt der Säurefunktionalisierung auf die Adsorptionseigenschafen von SBA-15 wurde für Fe-MEPE untersucht, welches ein metallo-supramolekulares Koordinationspolymer ist und durch die Komplexierung von Fe(II)-Acetat mit einem neutralen ditopen Bis-Terpyridin Liganden entsteht. Die Adsorptionsaffinität und Kinetik der MEPE-Ketten wird stark erhöht, wenn (i) die Poren mit CA Gruppen funktionalisiert sind oder (ii) der pH Wert der Lösung oder die Temperatur steigt. Das Adsorptionsgleichgewicht von MEPE lässt sich gut durch die Langmuir Isotherme beschreiben. Die große Adsorptionskonstante weist dabei auf eine starke Wechselwirkung zwischen Fe-MEPE und CA dekorierten Porenwänden hin. Die MEPE Aufnahme in die Poren kann als eine Überlagerung eines langsamen und eines schnellen Prozesses erster Ordnung dargestellt werden. Der schnelle Prozess ist mit einer Erniedrigung des pH Werts verbunden, die durch einen Ionenaustauschprozess verursacht wird. Der langsame Prozess dauert über mehrere hundert Stunden. MEPE-Aufnahme ist ein diffusionskontrollierter Prozess, und die Aufnahme ist ihrerseits kontrolliert durch Oberflächenschicht-Resistenz. Die Stöchiometrie von MEPE in den Poren (bestimmt mit XPS) ist unabhängig von der Beladung und ähnlich zu der des Bulkmaterials. Die Länge der 15N markierten MEPE-Ketten wurde vor und nach der Einlagerung in die CA-SBA-15 durch die 15N CPMAS NMR Methode untersucht. Demnach bewirkt die Einlagerung eine Abnahme der Durchschnittskettenlänge, wenn der Komplex in die Poren eingelagert wird.Pure and functionalized periodic mesoporous silicas were synthesized and characterized by N2 adsorption, SAXD, SEM, TEM, CHNS analysis, NMR, TGA/DTA, FT-IR and potentiometric titration. Functionalization was performed by grafting and by the co-condensation route. The functionalized silicas were used (i) for examination of the surface properties of MCM-41 and SBA-15 silicas, (ii) for acidity measurements in waterless confined geometry, and (iii) as hosts for MEPE. The arrangement of the silanol groups at the pore walls was studied by grafting di- and tripodical functional reagents F ((CH3)2Si(OCH3)2, CH3Si(OCH)3) to the surface. The number of covalent bonds to the surface formed by F was studied by pyridine adsorption using 15N CPMAS NMR spectroscopy. For high-quality MCM-41, di- and tripodical F can form only one covalent bond to the surface. In case of SBA-15 the formation of two covalent bonds to the surface is possible as well, indicating a closer mean distance between the silanol groups at the surface. The co-condensation route was used to functionalize of SBA-15 with carboxylic acid (CA), phosphonic acid (PA) and sulfonic acid (SA) groups. Reaction conditions for maximizing the degree of functionalization of SBA-15 without losing structural order are strongly affected by the kinetics of self-assembly. To better understand the influence of the hydrolysis and condensation steps of the silica sources and their interaction with template, the percentage of the functional silane the prehydrolyzed silica source (TEOS or F), and the prehydrolysis time were varied. Increasing decreases the amount of template in the functionalized SBA-15 and results in a better polymer removal by H2SO4 treatment. The highest surface coverages of SBA-15 by CA, PA, and SA groups are 50%, 40% and 30%, respectively, with a similar decrease in the yields of the corresponding functionalization reactions. Acidity measurements of the functionalized SBA-15 materials performed via 15N NMR. Chemical shifts measurements of pyridine indicate that SA, PA as well as CA groups are deprotonated by pyridine, suggesting a high proton donor ability of all three solid acids. FT-IR measurements of CA functionalized SBA-15 show that the carboxylic acid groups are deprotonated in aqueous media at pH 8. The effect of surface functionalization on the adsorption properties of SBA-15 was investigated for Fe-MEPE, a metallo-supramolecular coordination polyelectrolyte formed by complexation of Fe(II)-acetate with an uncharged ditopic bis-terpyridine ligand. The adsorption affinity and kinetics of the 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 adsorption equilibrium of MEPE in the pores conforms to the Langmuir isotherm with a high adsorption constant, indicating a strong interaction between Fe-MEPE and the CA-decorated pore walls. The uptake of MEPE into the pores can be represented by a superposition of a slow and a fast first-order process. The fast process is connected with a decrease of pH of the aqueous solution, indicating an ion-exchange mechanism. The slow process extends over hundreds of hours. MEPE uptake is a diffusion controlled process, and uptake is controlled by the surface layer resistance. The stoichiometry of MEPE in the pores (determined by XPS) is independent of the loading and similar to that of the starting material. The mean chain length of MEPE before and after embedding in the CA-SBA-15 was studied by solid-state 15N NMR using 15N-labeled MEPE. The average chain-length is reduced when the complex is incorporated in the pores

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

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

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