Polymeric Precursor Solution Research Articles

Fabrication and properties of ceramic 1D nanostructures from preceramic polymers: a review

This paper reviews different methodologies for the fabrication of various ceramic one-dimensional (1D) nanostructures (nanotubes/fibres/wires/belts, etc.) produced by using preceramic polymers. Diverse processing approaches together with a wide range of precursor types enable the fabrication of 1D nanostructures with varied morphology, composition, purity as well as yield. The strategies used are based on three different methods; starting with the utilisation of decomposition gases which are released upon pyrolysing the preceramic polymer precursors at high temperatures, with the absence or presence of a catalytic metal source. The second is the template modulated synthesis routes (i.e. infiltration of the polymeric precursor melt or solution inside a template porosity, polymer to ceramic conversion followed by the removal of the template), and the last strategy discussed is electrospinning.

Nanoimprint patterning of thin cadmium stannate films using a polymeric precursor route

The synthesis of cadmium stannate (Cd2SnO4 CTO) nanoparticle powders and the deposition and patterning of thin Cd2SnO4 films were achieved via a polymeric precursor approach. Conditions for the phase formation of the cubic spinel phase were evaluated, and for the first time the system was obtained in single phase powder form from a precursor system. Thin Cd2SnO4 films were prepared by spin coating the polymeric precursor solution followed by thermal treatment. Highly transparent and 20 nm thick films with a minimum sheet resistance of 110 Ohm were prepared. A thermal imprint process with PDMS molds was used for patterning of the films in the sub-micrometre range. Nanostructured CTO films are essential to improve structured electrodes in opto-electronic devices such as CdTe-based thin film solar cells.

Ferroelectric Properties of BiFeO3 Thin Films Prepared via a Simple Chemical Solution Deposition

Bi1+xFeO3 (BFO, x = 0,0.05,0.1,0.15) thin films are fabricated on LaNiO3 (LNO) buffered Si substrates by using a polymeric precursor solution under appropriate crystallization condition. All films possess highly (100) preference oriented. SEM analyses show that the average grain size decreases and thin films become dense and smoother with increasing of excess Bi content. The enhancement of polarization and improvement of leakage current are observed for BFO thin films with 10% excess Bi content. It indicates that the optimized excess Bi content plays an important role in the microstructure and ferroelectric property for BFO thin films.

Generation of Porous Poly(Ethylene Glycol) Hydrogels by Salt Leaching

Poly(ethylene glycol) (PEG) hydrogels have been investigated for a number of applications in tissue engineering. The hydrogels can be designed to mimic tissues that have desired chemical and mechanical properties, but their physical structure can hinder cell migration, tissue invasion, and molecular transport. Synthesis of porous PEG hydrogels could improve transport, enhance cell behavior, and increase the surface area available for cell adhesion. Salt leaching methods have been used extensively to generate porous biomaterial scaffolds but have not previously been applied to hydrogels. In this article we describe a modification of traditional salt leaching techniques for application to hydrogels. Salt-saturated polymer precursor solutions are prepared, and salt crystals of a defined size are added before polymerization. The salt crystals are then leached out, resulting in porous hydrogels. Examples are provided for application of this technique to PEG hydrogels. Porous PEG hydrogels were generated with pore sizes ranging from 15 to 86 microm and porosities from 30% to 75%. Porous hydrogels that were incorporated with a cell adhesion peptide supported cell adhesion with morphology varying with pore size. The simple, reproducible technique described here could be used to generate porous hydrogels with controlled pore sizes for applications in tissue engineering.

The fabrication of highly ordered block copolymer micellar arrays: control of the separationdistances of silicon oxide dots

We demonstrate the fabrication of highly ordered silicon oxide dotted arrays prepared frompolydimethylsiloxane (PDMS) filled nanoporous block copolymer (BCP) films and the preparationof nanoporous, flexible Teflon or polyimide films. Polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) films were annealed in toluene vapor to enhance the lateral order of micellar arraysand were subsequently immersed in alcohol to produce nano-sized pores, which can beused as templates for filling a thin layer of PDMS. When a thin layer of PDMSwas spin-coated onto nanoporous BCP films and thermally annealed at a certaintemperature, the PDMS was drawn into the pores by capillary action. PDMSfilled BCP templates were exposed to oxygen plasma environments in order tofabricate silicon oxide dotted arrays. By addition of PS homopolymer to PS-b-P2VP copolymer, the separation distances of micellar arrays were tuned. As-prepared siliconoxide dotted arrays were used as a hard master for fabricating nanoporous Teflon or polyimidefilms by spin-coating polymer precursor solutions onto silicon patterns and peeling off. Thissimple process enables us to fabricate highly ordered nanoporous BCP templates, siliconoxide dots, and flexible nanoporous polymer patterns with feature size of sub-20 nm over5 cm × 5 cm.

Thin Films of Conductive ZnO Patterned by Micromolding Resulting in Nearly Isolated Features

Patterned and continuous thin films of conductive Al-doped zinc oxide (ZnO:Al) were prepared on different substrates from a polymeric precursor solution. Their electric conductivity and light transmittance (for visible and UV light) was measured at room temperature. By means of a simple device, conductive ZnO:Al films with high fidelity patterns with features of 2-20 microm width could be obtained by simply micromolding the liquid precursor film prior to heat treatment. The individual features were interconnected by a very thin residual ZnO layer.

YAG:Ce 3+ nanostructured particles obtained via spray pyrolysis of polymeric precursor solution

Cerium-doped yttrium aluminum garnet (YAG:Ce 3+) powder phosphor is synthesized via spray pyrolysis of polymeric precursor solution obtained by dissolving the corresponding nitrates in ethylenediaminetetraacetic acid (EDTA). Ultrasonically generated aerosol droplets are decomposed at 600 °C in argon atmosphere. Following the initial attempt in providing pure YAG:Ce 3+ phase generation the particles were additionally thermally treated for 3 h in air at 1000 and 1100 °C. The powder morphology is followed with scanning electron microscopy (SEM), while inner particle structure is analysed by analytical and high-resolution transmission electron microscopy (TEM). Phase identification is performed by X-ray powder diffraction (XRPD) based on which a structural refinement through Rietveld method was done. The spherical submicronic particles have grained sub-structure comprising clustered garnet monocrystals sized below 100 nm. The YAG:Ce 3+ emission shows wide peak in the range 470–600 nm with the maximum near 520 nm.

Fine-sized LiNi 0.8Co 0.15Mn 0.05O 2 cathode particles prepared by spray pyrolysis from the polymeric precursor solutions

Fine-sized LiNi 0.8Co 0.15Mn 0.05O 2 cathode particles with high discharge capacities and good cycle properties were prepared by spray pyrolysis from the polymeric precursor solutions. The cathode particles obtained from the spray solution without polymeric precursors had irregular morphology and hardly aggregated morphology. On the other hand, the cathode particles obtained from the spray solution with citric acid and ethylene glycol had fine size and regular morphologies. The cathode particles obtained from the spray solution containing adequate amounts of citric acid and ethylene glycol had several hundreds nanometer and narrow size distribution. The maximum discharge capacity of the cathode particles was 218 mAh/g when the excess of lithium component added to the spray solution was 6 mol% of the stoichiometric amount to obtain the LiNi 0.8Co 0.15Mn 0.05O 2 particles. The discharge capacities of the fine-sized LiNi 0.8Co 0.15Mn 0.05O 2 particles dropped from 218 to 213 mAh/g by the 50th cycle at a current density of 0.1 C.

Multilayer film preparation of poly(4-vinylphenol) from aqueous media

The use of weak polyelectrolytes in multilayer polymer systems provides a means of altering the physico-chemical properties of these thin films. This paper examines the limits of the polyanions by incorporating the extremely weak polyelectrolyte, poly(4-vinylphenol) (PVPh), into a multilayer system with poly(allylamine hydrochloride) (PAH) from a dilute aqueous media. Film growth was monitored using absorption spectroscopy and revealed a clear linear trend in film thickness. The surface morphology, thickness, and swelling of the multilayer films systems were examined using atomic force microscopy (AFM). Film thickness greatly depended upon the pH of the polymer precursor solutions; 50-layer systems created at pH 12.5 and 11.0 were 8.2 and 246.6 nm thick, respectively, a difference of over 2900%. This is the first report on the incorporation of PVPh into a multilayer system from an aqueous media.

Formed-in-place Polyelectrolyte Complex Membranes for Atrazine Recovery from Aqueous Media

A permeable system composed of a polyelectrolyte complex (PEC) membrane formed by alternated deposition of chitosan (CHI) and carboxymethylcellulose (CMC) onto a porous solid substrate was investigated. The films, with thicknesses not superior to 20 nm, were obtained by a self-assembly technique, i.e., by direct dipping of chemically cleaned porous glass membranes, into concentrated polymeric precursor solutions. The resulting depositions have irregular structures and reduce the initial membrane permeability, especially for higher flux velocities. Concerning filtration tests for herbicide removal in aqueous medium, the chitosan deposition attained better results. A tentative model of binding involving hydrogen bonding and/or charge-transfer to nonspecific sites available dynamically as a function of the conformational estate of the deposited polymers is proposed for polysaccharide-herbicide interactions.

YBCO nanofibers synthesized by electrospinning a solution of poly(acrylic acid) and metal nitrates

A versatile approach to the synthesis of YBCO (high temperature superconductor ceramics) nanofibers via electrospinning a polymer precursor solution is reported. The aqueous polymer precursor solution consists of poly(acrylic acid) (PAAc) and a mixture of yttrium nitrate, barium nitrate, and copper nitrate, henceforth termed (Y,Ba,Cu)–N. The conductivity of the polymer precursor solution at 27.1 °C was 14.70 mS/cm, its zero shear viscosity was 52.00 cP, and its pH was 1.88. Typical YBCO nanofibers were 50–100 nm in diameter and around of 10 μm length. The nanofibers also contain relatively small amounts of yttrium oxide and copper yttrium oxide.

Photopolymerized diffusion-defined polyacrylamide gradient gels for on-chip protein sizing

We report on a facile diffusion-based photopatterning technique for generating linear and non-linear decreasing pore-size gradients in cross-linked polyacrylamide gels. Diffusion of low viscosity polymer precursor solutions and a two-step photopatterning process were used to define the decreasing pore-size gradient gels in a microfluidic format, thus eliminating the need for controlled mixing and delivery of polymer precursor solutions. We present an analytical model of the non-steady state diffusion process and numerically evaluate that model for direct comparison with empirical characterizations of the gradient gels. We show that the analytical model provides an effective means to predict the steepness and linearity of a desired gradient gel prior to fabrication. To assess electrophoretic assay performance in the microfluidic gradient gels, on-chip sizing of protein samples (20-116 kDa) was investigated. Baseline resolution of six proteins was demonstrated in 4 s using 3.5% to 10% polyacrylamide gradient gels. The demonstrated ability to conduct efficient protein sizing in ultra-short separation lengths (0.3 cm) means low applied electric potentials are needed to achieve the electric field strengths required for protein separations. The low required electric potentials relax operating constraints on electrical components, as is especially important for translation of the assay into pre-clinical and clinical settings. The gradient gel fabrication method reported is amenable to adaptation to non-sizing protein assays, as well as integration with upstream sample preparation steps and subsequent orthogonal downstream assays.

Porous Polymer Films with Size-Tunable Surface Pores

A novel method was developed to produce a porous polymer film with size-tunable pores on its surface. The porous film was produced using polystyrene microspheres as a template and the surface pore size can be tuned without changing the size of the template microsphere. Polystyrene microspheres were self-assembled on a substrate precoated with a thin layer of polystyrene and heated at an appropriate temperature, prior to infusion of a polymer precursor solution into cavities of the template microspheres, solidification of the polymer, and removal of the microspheres. The surface pore sizes can be tuned by changing the temperature and time for the heat treatment. With use of this method, porous films with nanosized surface pores can be produced using microsized spheres as the template, which can find applications in many areas.

Ferroelectric characteristics of BiFeO3 thin films prepared via a simple chemical solution deposition

BiFeO 3 (BFO) thin films were fabricated on Pt(111)∕Ti∕SiO2∕Si substrates by using a polymeric precursor solution under appropriate crystallization conditions. The capacitance dependence on voltage is strongly nonlinear, confirming the ferroelectric properties of the films resulting from the domain switching. The leakage current density increases with annealing temperature. The polarization electric field curves could be obtained in BFO films annealed at 500 °C, free of secondary phases. X-ray photoelectron spectroscopy spectra of films annealed at 500 °C indicated that the oxidation state of Fe was purely 3+, demonstrating that our films possess stable chemical configurations.

The effects of cell–matrix interactions on encapsulated β-cell function within hydrogels functionalized with matrix-derived adhesive peptides

The influence of matrix-derived adhesive peptide sequences on encapsulated β-cell survival and glucose-stimulated insulin release was explored by covalently incorporating synthetic peptide sequences within a model encapsulation environment. Photopolymerized poly(ethylene glycol) (PEG) hydrogels were functionalized via the addition of acrylate-PEG-peptide conjugates to the polymer precursor solution prior to β-cell photoencapsulation. Individual MIN6 β-cells were encapsulated in the presence of the laminin-derived recognition sequences, IKLLI, IKVAV, LRE, PDSGR, RGD, and YIGSR, and the collagen type I sequence, DGEA. In the absence of cell–cell and cell–matrix contacts, encapsulated MIN6 β-cell survival diminishes within one week; however, in PEG hydrogel derivatives including the laminin sequences IKLLI and IKVAV, encapsulated β-cells exhibit preserved viability, reduced apoptosis, and increased insulin secretion. Interactions with the laminin sequences LRE, PDSGR, RGD, and YIGSR contribute to improved viability, but insulin release from these samples was not statistically greater than that from controls. MIN6 β-cells were also encapsulated with various concentrations of IKLLI and IKVAV (0.05–5.0 m m), individually, and the peptide combinations IKLLI–IKVAV, IKVAV–YIGSR, and PDSGR–YIGSR to explore synergistic effects. The presented results give evidence that synthetic peptide epitopes may be useful in the design of an islet encapsulation environment that promotes cell survival and function via targeted cell–matrix interactions.

Synthesis and properties of oxynitrides (La,Sr)Ti(O,N)3 thin films

Abstract We report on the synthesis, optical and electrical properties of thin films of LaxSr(1−x)Ti(O,N)3, x = 0, 0.25, 0.50, 0.75 and 1. The films were grown by a soft chemistry process from polymeric precursor solutions, which were deposited by spin coating on 〈100〉-oriented SrTiO3 substrates. After drying, the organic matrix was burned at 400 °C. These steps were repeated six times to obtain a reasonable thickness of the films. Afterwards, the samples were heated in a tube furnace at 950 °C in flowing ammonia. The oxynitride films showed different colours from red-orange for LaTiO2N to greenish-blue for SrTiO3:N. The films were characterised by X-ray diffraction, scanning electron microscopy, atomic force microscopy, UV–vis spectroscopy, secondary ion mass spectrometry and electrical measurements. The results show that the films are polycrystalline and have the perovskite structure. Their thickness is about 440 nm and the average roughness value is 7.5 nm. UV–vis transmittance measurements showed a strong decrease in the band gap values for the oxynitrides compared to the respective oxides. The values change from approximately 3.2 eV for the oxides to an average value of 2.4 eV for the oxynitrides. The electrical measurements indicate a change in the electrical behaviour from insulator for LaTiO2N to semiconductor for SrTiO3:N.

Lanthanum-doped Bi 4Ti 3O 12 prepared by the soft chemical method: Rietveld analysis and piezoelectric properties

Bi 4− x La x Ti 3O 12 (BLT) thin films and powders with x ranging from 0 to 0.75 were prepared by the polymeric precursor solution. The effect of lanthanum on the structure of BIT powders was investigated by Rietveld Method. The increase of lanthanum content does not lead to any secondary phases. Orthorhombicity of the bismuth titanate (BIT) crystal lattice decreased with the increase of lanthanum content due the reduction of a/b ratio. The BLT films show piezoelectric coefficients of 45, 19, 16 and 10 pm/V for x = 0, 0.25, 0.50 and 0.75, respectively. The piezoelectric response is strongly reduced by the amount of lanthanum added to the system.

Electrical properties of lanthanum doped Bi 4Ti 3O 12 thin films annealed in different atmospheres

Pure and lanthanum doped Bi 4Ti 3O 12 thin films were deposited on Pt/Ti/SiO 2/Si substrate using a polymeric precursor solution. Annealing in static air and oxygen atmosphere was performed at 700 °C for 2 h. The obtained films were characterized by X-ray diffraction and atomic force microscopy. The dielectric constant and dissipation factor were measured in the frequency region from 1 kHz to 1 MHz. Electrical characterization of the films pointed to ferroelectricity via hysteresis loop. Films annealed in static air possess a dielectric constant higher than films annealed in oxygen atmosphere due to differences in the grain size, crystallinity and structural defects. A regularly shaped hystereses loop is observed after annealing in static air. The obtained results suggest that the annealing in oxygen atmosphere can increase the trapped charge and the relaxation phenomenon.

The characteristics of Li(Ni 1/3Co 1/3Mn 1/3)O 2 particles prepared from precursor particles with spherical shape obtained by spray pyrolysis

Spherical and fine-sized Li(Ni 1/3Co 1/3Mn 1/3)O 2 particles were prepared using spray pyrolysis. Precursor particles with mixed Mn 2O 3, Co 3O 4 and NiO compositions were prepared using spray pyrolysis from aqueous and polymeric precursor solutions. The precursor particles prepared from the aqueous solution had hollow and porous morphologies. The precursor particles prepared from the polymeric precursor solution with citric acid and ethylene glycol were spherical in shape and had filled morphologies. The spherical precursor particles with filled morphologies formed spherical, fine-sized Li(Ni 1/3Co 1/3Mn 1/3)O 2 particles with filled morphologies after post-treatment with LiOH. The mean crystallite sizes of the Li(Ni 1/3Co 1/3Mn 1/3)O 2 particles prepared from spray solutions with and without lithium at the post-treatment temperature of 800 °C were 56 and 31 nm, respectively. The initial discharge capacities of the Li(Ni 1/3Co 1/3Mn 1/3)O 2 particles prepared using spray pyrolysis from spray solutions with and without lithium were 178 and 181 mAh g −1, respectively, after a post-treatment temperature of 800 °C.

Fine-sized LiCoO 2 particles prepared by spray pyrolysis from polymeric precursor solution

Fine-sized LiCoO 2 particles with high discharge capacities and good cycle properties were prepared by spray pyrolysis from a spray solution with citric acid and ethylene glycol. The precursor particles obtained from the spray solution with citric acid and ethylene glycol transformed into fine-sized LiCoO 2 particles with regular morphology after post-treatment at temperatures between 700 and 900 °C. The mean size and aggregation degree of the primary particles were affected by the concentrations of polymeric precursors added into spray solutions. The LiCoO 2 particles obtained from the spray solution without polymeric precursors had irregular and aggregated morphology. The discharge capacities of the LiCoO 2 particles changed from 132 to 151 mAh/g when the concentrations of the citric acid and ethylene glycol changed from 0 to 1 M. The particles prepared from the spray solution containing 0.3 M each of citric acid and ethylene glycol had the maximum discharge intensity.