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Layer-by-layer Deposition (layer-by-layer + deposition)
Selected AbstractsAutomated Layer-by-Layer Deposition of Polyelectrolytes in Flow ModeMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6-7 2009Svetlozar Ivanov Abstract Multilayer structures of conducting polymers were fabricated by a simply automated approach in flow mode. Polyaniline and poly(styrene sulfonate) were used as a model system, allowing a fast electrochemical and spectroscopic determination of the amount of deposited material. The technology was applied for layer-by-layer deposition of up to 100 bilayers. The results demonstrate a well reproducible and almost constant amount of the adsorbed polymer at each deposition cycle. The method can be applied for deposition of other conducting or non-conducting polymers, biological macromolecules and composites of polyelectrolytes and nanoparticles. [source] Layer-by-Layer Deposition of Rhenium-Containing Hyperbranched Polymers and Fabrication of Photovoltaic CellsCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2007Chui Wan Tse Abstract Multilayer thin films were prepared by the layer-by-layer (LBL) deposition method using a rhenium-containing hyperbranched polymer and poly[2-(3-thienyl)ethoxy-4-butylsulfonate] (PTEBS). The radii of gyration of the hyperbranched polymer in solutions with different salt concentrations were measured by laser light scattering. A significant decrease in molecular size was observed when sodium trifluoromethanesulfonate was used as the electrolyte. The conditions of preparing the multilayer thin films by LBL deposition were studied. The growth of the multilayer films was monitored by absorption spectroscopy and spectroscopic ellipsometry, and the surface morphologies of the resulting films were studied by atomic force microscopy. When the pH of a PTEBS solution was kept at 6 and in the presence of salt, polymer films with maximum thickness were obtained. The multilayer films were also fabricated into photovoltaic cells and their photocurrent responses were measured upon irradiation with simulated air mass (AM) 1.5 solar light. The open-circuit voltage, short-circuit current, fill factor, and power conversion efficiency of the devices were 1.2 V, 27.1 ,,A,cm,2, 0.19, and 6.1×10,3,%, respectively. The high open-circuit voltage was attributed to the difference in the HOMO level of the PTEBS donor and the LUMO level of the hyperbranched polymer acceptor. A plot of incident photon-to-electron conversion efficiency versus wavelength also suggests that the PTEBS/hyperbranched polymer junction is involved in the photosensitization process, in which a maximum was observed at approximately 420 nm. The relatively high capacitance, determined from the measured photocurrent rise and decay profiles, can be attributed to the presence of large counter anions in the polymer film. [source] Gold Nanoparticles in Nonenzymatic Electrochemical Detection of SugarsELECTROANALYSIS, Issue 19-20 2006Fredy Kurniawan Abstract A nonenzymatic electrochemical sensor for detection of sugars was prepared by layer-by-layer deposition of gold nanoparticles on thin gold electrodes. The deposition was optimized by using of surface plasmon resonance. Voltammetric investigation and impedance spectroscopy of the sensor was performed. Electrical currents caused by glucose on bare gold electrodes and on gold electrodes coated by immobilized gold nanoparticles were compared. The electrodes with nanoparticles display much higher current of glucose oxidation. The oxidation becomes blocked when the swept electrode potential exceeded +0.25,V, during the back scan an oxidation peak is observed again but at less positive potential. The magnitudes of these current peaks are linearly dependent on the glucose concentration; this dependence can be used as calibration for analytical applications. The limit of detection for glucose is below 0.5,mM, the sensitivity (normalized to the macroscopic electrode surface) is about 160,,A,cm,2,mM,1. The sensor response is linear till at least 8,mM of glucose concentration. [source] Layer-by-Layer Interference Lithography of Three-dimensional Microstructures in SU-8,ADVANCED ENGINEERING MATERIALS, Issue 5 2009Andrés F. Lasagni We report on rapid fabrication of two-, two and a half-, and 3D planar periodic structures using layer-by-layer deposition and interference patterning of SU-8 photoresist. Complex structures with non-periodic vertical symmetry were fabricated controlling the cure depth by addition of a UV absorber. The fabrication method reported here can be applied for the high-volume manufacturing of solid structures for microelectromechanical systems and microfluidic devices. [source] Capillary Force Lithography: A Versatile Tool for Structured Biomaterials Interface Towards Cell and Tissue Engineering,ADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Kahp-Yang Suh Abstract This Feature Article aims to provide an in-depth overview of the recently developed molding technologies termed capillary force lithography (CFL) that can be used to control the cellular microenvironment towards cell and tissue engineering. Patterned polymer films provide a fertile ground for controlling various aspects of the cellular microenvironment such as cell,substrate and cell,cell interactions at the micro- and nanoscale. Patterning thin polymer films by molding typically involves several physical forces such as capillary, hydrostatic, and dispersion forces. If these forces are precisely controlled, the polymer films can be molded into the features of a polymeric mold with high pattern fidelity and physical integrity. The patterns can be made either with the substrate surface clearly exposed or unexposed depending on the pattern size and material properties used in the patterning. The former (exposed substrate) can be used to adhere proteins or cells on pre-defined locations of a substrate or within a microfluidic channel using an adhesion-repelling polymer such as poly(ethylene glycol) (PEG)-based polymer and hyaluronic acid (HA). Also, the patterns can be used to co-culture different cells types with molding-assisted layer-by-layer deposition. In comparison, the latter (unexposed substrate) can be used to control the biophysical surrounding of a cell with tailored mechanical properties of the material. The surface micropatterns can be used to engineer cellular and multi-cellular architecture, resulting in changes of the cell shape and the cytoskeletal structures. Also, the nanoscale patterns can be used to affect various aspects of the cellular behavior, such as adhesion, proliferation, migration, and differentiation. [source] Design of Multilayered Nanostructures and Donor,Acceptor Interfaces in Solution-Processed Thin-Film Organic Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 10 2008Hiroaki Benten Abstract Multilayered polymer thin-film solar cells have been fabricated by wet processes such as spin-coating and layer-by-layer deposition. Hole- and electron-transporting layers were prepared by spin-coating with poly(3,4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate) (PEDOT:PSS) and fullerene (C60), respectively. The light-harvesting layer of poly-(p -phenylenevinylene) (PPV) was fabricated by layer-by-layer deposition of the PPV precursor cation and poly(sodium 4-styrenesulfonate) (PSS). The layer-by-layer technique enables us to control the layer thickness with nanometer precision and select the interfacial material at the donor,acceptor heterojunction. Optimizing the layered nanostructures, we obtained the best-performance device with a triple-layered structure of PEDOT:PSS|PPV|C60, where the thickness of the PPV layer was 11,nm, comparable to the diffusion length of the PPV singlet exciton. The external quantum efficiency spectrum was maximum (ca. 20%) around the absorption peak of PPV and the internal quantum efficiency was estimated to be as high as ca. 50% from a saturated photocurrent at a reverse bias of ,3,V. The power conversion efficiency of the triple-layer solar cell was 0.26% under AM1.5G simulated solar illumination with 100,mW,cm,2 in air. [source] Self-Rupturing and Hollow Microcapsules Prepared from Bio-polyelectrolyte - Coated Microgels,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2007G. De, Geest Abstract This paper reports on microcapsules obtained by layer-by-layer deposition of bio-polyelectrolyte multilayers at the surface of biodegradable dextran microgels. The behavior of the layer-by-layer coating upon degradation of the microgel core strongly depends on the bio-polyelectrolytes used. Two types of microcapsules, "self-rupturing" microcapsules and "hollow" microcapsules, are presented. Self-rupturing microcapsules are obtained when the swelling pressure of the degrading microgel core is strong enough to rupture the surrounding bio-polyelectrolyte membrane. Self-rupturing microcapsules could be of interest as a pulsed drug delivery system. Hollow microcapsules are obtained after applying multiple layers of bio-polyelectrolyte that can withstand the swelling pressure of the degrading microgel core. Biomacromolecules (such as albumin and dextran) spontaneously accumulate in the hollow microcapsules prepared from dex-HEMA microgels, which could be of interest for drug-encapsulation purposes. [source] Peeling Back the Layers: Controlled Erosion and Triggered Disassembly of Multilayered Polyelectrolyte Thin Films,ADVANCED MATERIALS, Issue 23 2007M. Lynn Abstract Methods for the layer-by-layer deposition of oppositely charged polymers on surfaces can be used to assemble thin multilayered films using a broad range of natural, synthetic, and biologically relevant materials. These methods also permit precise, nanometer-scale control over the compositions and internal structures of multicomponent assemblies. Provided that the individual components of these materials are selected or designed appropriately, these methods provide tantalizing new opportunities to design thin films and coatings that provide spatial, temporal, or active control over the release of one or several different agents from surfaces. The last two years have seen a significant increase in reports describing the development of new chemical, physical, and biomolecular approaches to the controlled erosion, triggered disassembly, or general deconstruction of multilayered polymer films. In this Progress Report, we highlight recent work from our laboratory and several other groups toward the design of ultrathin multilayered assemblies that i),permit broad, tunable, and sophisticated control over film erosion, and ii),provide new opportunities for the localized release of macromolecular therapeutics, such as DNA and proteins, from surfaces. [source] Patterned Co-Culture of Primary Hepatocytes and Fibroblasts Using Polyelectrolyte Multilayer TemplatesMACROMOLECULAR BIOSCIENCE, Issue 3 2007Srivatsan Kidambi Abstract This paper describes the formation of patterned cell co-cultures using the layer-by-layer deposition of synthetic ionic polymers and without the aid of adhesive proteins/ligands such as collagen or fibronectin. In this study, we used synthetic polymers, namely poly(diallyldimethylammonium chloride) (PDAC) and sulfonated polystyrene (SPS) as the polycation and polyanion, respectively, to build the multilayer films. We formed SPS patterns on polyelectrolyte multilayer (PEM) surfaces either by microcontact printing PDAC onto SPS surfaces or vice-versa. To create patterned co-cultures on PEMs, we capitalize on the preferential attachment and spreading of primary hepatocytes on SPS as opposed to PDAC surfaces. In contrast, fibroblasts readily attached to both PDAC and SPS surfaces, and as a result, we were able to obtain patterned co-cultures of fibroblast and primary hepatocytes on synthetic PEM surfaces. We characterized the morphology and hepatic-specific functions of the patterned cell co-cultures with microscopy and biochemical assays. Our results suggest an alternative approach to fabricating controlled co-cultures with specified cell,cell and cell,surface interactions; this approach provides flexibility in designing cell-specific surfaces for tissue engineering applications. [source] Automated Layer-by-Layer Deposition of Polyelectrolytes in Flow ModeMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6-7 2009Svetlozar Ivanov Abstract Multilayer structures of conducting polymers were fabricated by a simply automated approach in flow mode. Polyaniline and poly(styrene sulfonate) were used as a model system, allowing a fast electrochemical and spectroscopic determination of the amount of deposited material. The technology was applied for layer-by-layer deposition of up to 100 bilayers. The results demonstrate a well reproducible and almost constant amount of the adsorbed polymer at each deposition cycle. The method can be applied for deposition of other conducting or non-conducting polymers, biological macromolecules and composites of polyelectrolytes and nanoparticles. [source] Modeling of rotational molding process: Multi-layer slip-flow model, phase-change, and warpagePOLYMER ENGINEERING & SCIENCE, Issue 7 2006K.K. Lim A new multilayer slip-flow model has been developed to simplify and to overcome current numerical difficulties of two-dimensional model in predicting the internal air temperature inside a mold during a rotational molding process. The proposed methodology considers a macroscopic "layer-by-layer" deposition of a heating polymer bed onto the inner mold surface. A semi-implicit approach is introduced and applied to compute the complex thermal interactions between the internal air and its surroundings. In the model, the lumped-parameter system and the coincident node technique are incorporated with the Galerkin finite element model to address the internal air and the deposition of molten polymer beds, respectively. The simple phase-change algorithm has been proposed to improve the computational cost, numerical nonlinearity, and predicted results. The thermal aspects of the inherent warpage are explored to study its correlation to the weak apparent crystallization-induced plateau in the temperature profile of the internal air, as in practice. The overall predicted results are in favor with the available experimental data for rotomolded parts of cross-sectional thicknesses up to 12 mm. POLYM. ENG. SCI. 46:960,969, 2006. © 2006 Society of Plastics Engineers [source] | |||||||||||||||||||||||||