Thin films of cross-linked metallo-supramolecular coordination polyelectrolytes

We report on the synthesis of a new tristerpyridine ligand, tris(2,2':6',2' '-terpyridinyl-4'-oxymethyl)ethane (tritpy), as well as its introduction into metal ion induced self-assembly of cross-linked metallo-supramolecular coordination polyelectrolytes (MEPE). For cross-linking degrees of 9.5% and below, soluble homogeneous networks are obtained. The molar mass of the networks is large and depends on the cross-linking degree. Due to the charges in the MEPE, the soluble networks are suitable for film formation on the basis of layer-by-layer self-assembly and to study the details of film growth. UV-vis spectroscopy, X-ray reflectivity, AFM, and ellipsometry show that the film growth is linear and continuous. The multilayers exhibit no inner structure and have a very low surface roughness. The thickness of the adsorbed layer of MEPE networks is in the range of 3 nm. The important point is that an influence of cross-linking is not seen in multilayers, which is the opposite of what is observed for the MEPE in solution. Our experiments did not reveal an influence of the preparation procedure on the adsorption process, e.g., increasing the layer thickness.

Polyelectrolyte/magnetite nanoparticle multilayers: preparation and structure characterization

Polyelectrolyte composite planar films containing a different number of iron oxide (Fe3O4) nanoparticle layers have been prepared using the layer-by-layer adsorption technique. The nanocomposite assemblies were characterized by ellipsometry, UV-vis spectroscopy, and AFM. Linear growth of the multilayer thickness with the increase of the layer number, N, up to 12 reflects an extensive character of this parameter in this range. A more complicated behavior of the refractive index is caused by changes in the multilayer structure, especially for the thicker nanocomposites. A quantitative analysis of the nanocomposite structure is provided comparing a classical and a modified effective medium approach taking into account the influence of light absorption by the Fe3O4 nanoparticles on the complex refractive index of the nanocomposite and contributions of all components to film thickness. Dominant influence of co-adsorbed water on their properties was found to be another interesting peculiarity of the nanocomposite film. This effect, as well as possible film property modulation by light, is discussed.

A lithography-free method for directed colloidal crystal assembly based on wrinkling

A simple, novel, and completely lithography-free assembly strategy is reported for directed colloidal crystal assembly on optically transparent substrates. The templates are stable, well-controlled relaxation-wrinkles of ultrathin multilayer films in a non-stretched state, which are fabricated by layer-by-layer self-assembly of polymeric films on soft elastomeric substrates followed by uniaxial plastic deformations. The results show that the wrinkles can be used efficiently to topographically direct colloidal crystal assembly in dip coating. Remarkably highly regular 1- and 2-dimensional patterned colloidal crystals with controlled structures have been obtained. Furthermore, the concept is rather universal and applicable to various particle types provided surface interactions between particles and template are suitable.

Fabrication of multiplex quasi-three-dimensional grids of one-dimensional nanostructures via stepwise colloidal lithography

By using O2-plasma etched monolayers of hexagonally close-packed latex spheres as masks for metal vapor deposition, we successfully demonstrate a stepwise colloidal lithography to stepwise grow highly ordered multiplex quasi-three-dimensional grids of metallic one-dimensional nanostructures, e.g., nanowires and nanorods. The success of the present approach is centered at manipulation of the incidence angle of metal vapor beams with respect to the normal direction of colloidal masks and particularly the azimuth angle phi of the projection of the vapor beam incidence on the masks with respect to the vector from one sphere to the nearest neighbors. Stepwise deposition of different metals by regularly varying phi allows consecutively stacking of 1D nanostructures into multiplex quasi-3D grids. This stepwise angle-resolved colloidal lithography should provide a significant nanochemical complement of conventional lithographic techniques, enabling us to easily fabricate sophisticated 3D nanostructures with defined vertical and lateral heterogeneity.

Thermometric MIP sensor for fructosyl valine

Interactions of molecularly imprinted polymers containing phenyl boronic acid residues with fructosyl valine, fructose and pinacol, respectively are analysed in aqueous solution (pH 11.4) by using a flow calorimeter. The reversible formation of (two) cyclic boronic acid diesters per fructosyl molecule generates a 40-fold higher exothermic signal as compared to the control polymer. Whereas binding of pinacol to either the MIP or the control polymer generates a very small endothermic signal reflecting a negligible contribution of the esterification to the overall process. An "apparent imprinting factor" of 41 is found which exceeds the respective value of batch binding procedures by a factor of 30. Furthermore, the MIP sensor was used to characterise the crossreactivity. The influence of shape selective molecular recognition is discussed.

Solvent-filled matrix polyelectrolyte capsules: preparation, structure and dynamics

Stable surfactant-free, water-dispersed, micron-sized organic solvent colloids have been a challenging subject of major interest both experimentally and theoretically in recent years. In this article, novel matrix capsules are introduced to carry an organic solvent ( toluene) into water and form a stable solvent dispersion in the aqueous phase without the addition of a surfactant. The structure and dynamics of the dispersion are investigated by confocal Raman microscopy, surface force microscopy, and pulsed field gradient nuclear magnetic resonance (PFG-NMR). The matrix capsules are fabricated according to a literature method using alternating layer-by-layer adsorption of oppositely charged polyelectrolytes onto porous calcium carbonate (CaCO) particles, followed by core removal. The highly rough surface and the inner cavities of CaCO particles result in a heavy matrix capsule, which can achieve a high solvent encapsulation efficiency and form a micron-sized carrier for the solvent in water that is stable for long times ( at least one week.) Two distinct diffusion coefficients are evidenced by PFG-NMR, which may indicate two distinct diffusion environments in the sample. This suggests that the toluene undergoes a partial exchange between environments within the 100 ms time frame of the NMR experiment.

Novel type of self-assembled polyamide and polyimide nanoengineered shells--fabrication of microcontainers with shielding properties

Two types of microcontainers were prepared by using the adsorption of polyamide on the surface of micrometer-sized inorganic porous calcium carbonate microparticles followed by thermal conversion of the polyamide layers into polyimide coatings. The effect of the preparation conditions on the structure and morphology of the microcontainers was studied by transmission electron microscopy and scanning electron microscopy. The smoothest and defect-free coatings were prepared using polyethylenimine as the supporting polymer. The thickness of the polyamide/polyimide shells was estimated by atomic force microscopy and scanning electron microscopy between 50 and 150 nm depending on the quantity of the layers. The water-soluble antibiotic, doxorubicin hydrochloride, was used as a model compound to demonstrate the efficiency of the microcontainers for encapsulation. The resistance of the novel microcontainers to solvent treatment was visualized by the confocal scanning fluorescence microscopy. It was demonstrated that the combination of the high thermal and chemical resistance of polyamide/polyimide shell and the sorption capacity of the CaCO3 is very useful for development of highly protective microcontainers and thermal detectors for smart fabrics.

Soft X-ray Microscopy To Characterize Polyelectrolyte Assemblies†

Transmission microscopy with soft X-rays (TXM) is applied to image in-situ polyelectrolyte assemblies in aqueous environment. The method is element specific and at this stage exhibits a lateral resolution of 20 nm. With the specific examples of hollow capsules and full spheres made of PAH/PSS polyelectrolyte multilayers, it is shown quantitatively that heat treatment irreversibly reduces the water content in the membrane. These experiments complement those reported recently on the polyion system PDADMAC/PSS, which shows a different glass-transition behavior. Finally, the potential and present limitations of TXM are discussed.

Supramolecular assembly of water-soluble poly(ferrocenylsilanes): multilayer structures on flat interfaces and permeability of microcapsules

We report on the layer-by-layer (LBL) supramolecular assembly of redox responsive, organometallic polyion films on planar and curved (spherical) substrates. Organometallic poly(ferrocenylsilane) (PFS) polyanions and polycations were first used to assemble multilayers on planar quartz, silicon and quartz-crystal microbalance (QCM) electrodes. UV/Vis spectroscopy, spectroscopic ellipsometry and quartz-crystal microgravimetry showed a linear increase of UV absorbance, film thickness and frequency shift with increasing the number of deposited bilayers. Additional ellipsometric studies showed a square-root dependence of the film thickness on solution salt (NaCl) concentration. For the preparation of multilayer films on colloidal particles (manganese carbonate, MnCO), relatively high salt concentrations (0.5 M) were employed. PFS microcapsules were subsequently obtained by colloidal template removal using ethylenediaminetetraacetic acid (EDTA). Following the removal of the spherical template, hollow microcapsules were obtained, whose wall structure-permeability characteristics received particular attention. Atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM) were used to study the wall thickness, integrity and permeability of the capsules. Capsule-wall thickness obtained from AFM indicated the existence of a linear film growth regime when the number of adsorbed bilayers was larger than four. Capsules made of PFS polyanions and rhodamine-labelled PFS polycations were directly visualized by CLSM. Using tetramethylrhodamine isothiocyanate (TRITC)-labelled dextran (∼ 4 400 g mol) as probe, CLSM showed that capsules containing more than four PFS polycation-polyanion bilayers displayed good stability and integrity. These stable capsules are excellent candidates for the investigation of polyelectrolyte microcapsule permeability control triggered by redox stimuli.

Development of fructosyl valine binding polymers by covalent imprinting

Molecularly imprinted polymers (MIPs) against fructosyl valine (Fru-Val), the N-terminal constituent of hemoglobin A1c beta-chains, were prepared by cross-linking of beta-D-Fru-Val-O-bis(4-vinylphenylboronate) with an excess of ethylene glycol dimethacrylate (EDMA) or trimethylolpropane trimethacrylate (TRIM). Control MIPs were prepared in analogy by cross-linking the corresponding vinylphenylboronate esters of fructose and pinacol. After template extraction batch rebinding studies were performed using different pH values and buffer compositions. The Fru-Val imprinted TRIM cross-linked polymer binds about 1.4 times more Fru-Val than the fructose imprinted polymer and 2.7 times more Fru-Val than pinacol imprinted polymer. The highest imprinting effect was obtained in 100 mM sodium carbonate/10% methanol (pH 11.4). The TRIM cross-linked Fru-Val imprinted polymer showed a better specificity than the EDMA cross-linked polymer. The binding of valine was very low. Thermo gravimetric analysis indicated that the generated Fru-Val imprinted polymer has high thermo stability. No change in binding was observed after incubation of the polymers in buffer at 80 degrees C for 36 h. Since the functional group of the polymers (phenyl boronic acid) targets the sugar part of Fru-Val the imprint technique used should also be applicable for the development of MIPs against other glycated amino acids and peptides.

Self-repairing coatings containing active nanoreservoirs

Nanocontainers with the ability to release encapsulated active materials in a controlled way can be employed to develop a new family of self-repairing multifunctional coatings, which possess not only passive functionality but also rapid feedback activity in response to changes in local environment. Several approaches to fabricate self-repairing coatings on plastic and metal substrates were surveyed. The release of the active materials occurs only when triggered, which prevents leakage of the active component out of the coating and increases coating durability. This Review also covers some principles and recent developments in the fabrication of nanocontainers with good compatibility with the coating components, the possibility to encapsulate and upkeep active material, and permeability properties of the shell controlled by external stimuli. Depending on the nature of the sensitive components introduced into the container shell, reversible and irreversible changes of the shell permeability can be induced by various stimuli. Different responses can be then observed varying from fine effects like tunable permeability to more drastic ones like total rupture of the container shell.

Adsorption of the fusogenic peptide B18 onto solid surfaces: insights into the mechanism of peptide assembly

The adsorption and assembly of B18 peptide on various solid surfaces were studied by reflectometry techniques and atomic force microscopy. B18 is the minimal membrane binding and fusogenic motif of the sea urchin protein bindin, which mediates the fertilization process. Silicon substrates were modified to obtain hydrophilic charged surfaces (oxide layer and polyelectrolyte multilayers) and hydrophobic surfaces (octadecyltrichlorosilane). B18 does not adsorb on hydrophilic positively charged surfaces, which was attributed to electrostatic repulsion since the peptide is positively charged. In contrast, the peptide irreversibly adsorbs on negatively charged hydrophilic as well as on hydrophobic surfaces. B18 showed higher affinity for hydrophobic surfaces than for hydrophilic negatively charged surfaces, which must be due to the presence of hydrophobic side chains at both ends of the molecule. Atomic force microscopy provided the indication that lateral diffusion on the surface affects the adsorption process of B18 on hydrophobic surfaces. The adsorption of the peptide on negatively charged surfaces was characterized by the formation of globular clusters.