Polymer‐Based Rectifying Diodes on a Glass Substrate Fabricated by Ink‐Jet Printing

Summary: The fabrication of polymer diodes on a glass substrate by an ink‐jet printing technique is reported. Both an n‐type semiconductive polymer, poly[2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐(1‐cyanovinylene)phenylene] (CN‐PPV), and a p‐type semiconductive polymer, polypyrrole (PPy) or poly(3,4‐ethylenedioxythiophene) (PEDOT), were printed through a piezoelectric ink‐jet printer. The printed CN‐PPV/PPy and CN‐PPV/PEDOT diodes showed good rectifying characteristics. These results indicate the potential of the low‐cost ink‐jet printing technique to produce polymer microelectronic devices and circuits.

Schematic diagram of the printed polymer diode     

Ink‐Jet Printing of Luminescent Ruthenium‐ and Iridium‐Containing Polymers for Applications in Light‐Emitting Devices

Summary: Defined films of luminescent ruthenium(II ) polypyridyl‐poly(methyl methacrylate) (PMMA) and iridium(III ) polypyridyl‐polystyrene (PS) copolymers could be prepared by ink‐jet printing. The copolymers were deposited on photoresist‐patterned glass substrates. Films as thin as 120 nm could be printed with a roughness of 1 to 2%. In addition, the film thickness could be varied in a controlled way through the number of droplets deposited per unit area. The topography of the ink‐jet printed films was analyzed utilizing an optical profilometer. The absorbance and emission spectra were measured using fast parallel UV‐vis and fluorescence plate reader.

Photo of the solutions of luminescent ruthenium (left) and iridium (right) containing polymers in a glass microtiter plate (top). The subsequently prepared films using ink‐jet dispensing techniques are shown below.     

A Low Curing Temperature Silver Ink for Use in Ink‐Jet Printing and Subsequent Production of Conductive Tracks

Summary: A drop‐on‐demand ink‐jet printer has been used to print a silver‐organic solution onto glass substrates. Conductive silver tracks were obtained by heat treatment of the ink‐jet printed deposits at temperatures ranging from 125 °C–200 °C in air. Resistivity values were found to have dropped to two to three times the theoretical resisitivity of bulk silver after temperatures of 150 °C and above were used.

Resistivity values of a silver‐based ink.     

One‐Step Preparation of Antimicrobial Polyrhodanine Nanotubes with Silver Nanoparticles

A simple synthetic method has been developed for the fabrication of antimicrobial polyrhodanine nanotubes with silver nanoparticles. Rhodanine monomer first forms one‐dimensional complexes with silver ions due to coordinative interactions and consecutively reduces the silver ions during chemical‐oxidation polymerization. The polymerization procedure is analyzed by transmission electron microscopy and scanning electron microscopy in situ. The synthesized silver nanoparticles/polyrhodanine nanotubes are applied as an antimicrobial agent against Gram‐negative bacteria, E. coli and Gram‐positive bacteria, S. aureus. The antimicrobial tests demonstrate that the silver/polyrhodanine nanotubes have superior antimicrobial properties to silver nanoparticles and rhodanine monomer.

     

Preparation of Antimicrobial Ultrafine Cellulose Acetate Fibers with Silver Nanoparticles

Summary: A feasible method for the preparation of antimicrobial ultrafine fibers with silver nanoparticles was developed by direct electrospinning of a cellulose acetate (CA) solution with small amounts of silver nitrate followed by photoreduction. Silver nanoparticles in ultrafine CA fibers were stabilized by interactions with carbonyl oxygen atoms in CA. Ultrafine CA fibers with silver nanoparticles showed very strong antimicrobial activity.

TEM image of an ultrafine CA fiber electrospun from 10 wt.‐% CA solution with 0.5 wt.‐% AgNO₃.     

Simple Modification of Sheet Resistivity of Conducting Polymeric Anodes via Combinatorial Ink‐Jet Printing Techniques

Summary: Due to its capability of dispensing very small volumes of different liquids in a controlled manner, ink‐jet printing is well suited for combinatorial experiments. The multi‐nozzle ink‐jet delivery system is especially advantageous for parallel chemical synthesis of different materials. We have used ink‐jet printing of an oxidizing agent to pattern a pre‐coated conducting polymer, poly(3,4‐ethylenedioxy)‐thiophene‐poly(styrene sulfonate) (PEDOT‐PSS), yielding electrodes with predefined shapes and a controlled degree of sheet resistivity for use in gray‐scale organic light‐emitting devices (OLEDs). The electrical and optical properties of the PEDOT‐PSS layer are modified via chemical interaction using the oxidizing agent. These experiments were performed using a desktop ink‐jet printer in conjunction with common graphic software which employed color functions such as CMY (cyan, magenta and yellow), HSL (hue, saturation and luminosity) and RGB (red, green and blue).

Photographs of gray‐scale OLEDs patterned on PEDOT‐PSS surfaces by an ink‐jet printer on plastic substrates.     

One‐Pot Fabrication of Supramolecular Polymer Particles via Situ Polymerization Stringed Assembly of a Two‐Monomer Microemulsion

Summary: A novel method, situ polymerization stringed assembly (SPSA), is proposed to prepare stable solid or hollow supramolecular polymer particles, which are assembled by numerous nanoparticles. By this method, the fabrication of primary nanoparticles (poly(methyl methacrylate), PMMA), the linkers (polyvinylpyrrolidone, PVP, chains) between the nanoparticles, and the final assembled solid or hollow particles could be achieved in just one‐pot by methyl methacrylate (MMA)/N‐vinylpyrrolidone (NVP) microemulsion polymerization under UV irradiation. The structures of the supramolecular particles can be changed from solid to hollow by tuning the mass ratio of MMA/NVP in the microemulsion. AFM, TEM, and SEM experiments are performed to identify the results.

AFM image of the PMMA/PVP solid particles obtained from the photopolymerization of the microemulsion containing 20 wt.‐% MMA, 10 wt.‐% NVP, and 5 × 10⁻² wt.‐% BP.     

Reactive Hydrogel Networks for the Fabrication of Metal–Polymer Nanocomposites

In this study, highly stable gold and silver nanoparticles evenly distributed within a crosslinked poly(acrylamide)/poly(N‐(hydroxymethyl)acrylamide) (PAAm‐PHMAAm) network have been fabricated without addition of a reducing agent. Remarkably, the same chemical hydrogel composition has been involved in the successful fabrication of spherical gold and silver nanoparticles within the hydrogel template. The hydrogel network acts simultaneously as an efficient reducing agent and stabilizer. The PAAm–PHMAAm hydrogel network binds metal ions and, following reduction of bound to crosslinked template metal ions, proceeds via oxidation of hydroxymethyl hydrogel fragments. A one‐electron mechanism is proposed for the formation of the silver and gold nanoparticles.

     

Fabrication of Silver Nanoparticles in Hydrogel Networks

Summary: This paper describes a simple and facile approach to fabricate well dispersed silver nanoparticles (AgNPs) in poly[N‐isopropylacrylamide‐co‐(sodium acrylate)] hydrogels. The silver nanoparticles formed are spherical in shape with a narrow size distribution in the hydrogel networks in which the nanoparticles are stabilized by the polymer network. Uniformly dispersed silver nanoparticles were obtained with poly[N‐isopropylacrylamide‐co‐[sodium acrylate)] hydrogels, whereas a poly(N‐isopropylacrylamide)/poly(sodium acrylate) IPN gel showed aggregated nanoparticles. It is demonstrated that the hydrogel network structure determines the size and shape of the nanoparticles. These particles are more stable in the gel networks compared to other reduction methods. The hydrogel/silver nanohybrids were well characterized by XRD, UV‐vis spectrometry, scanning electron microscopy and transmission electron microscopy.

Schematic representation of the preparation of Ag nanoparticles in hydrogel networks.     

Synthesis of Poly(methyl methacrylate) Nanoparticles Initiated by 2,2′‐Azoisobutyronitrile via Differential Microemulsion Polymerization

The synthesis of nanosized poly(methyl methacrylate) initiated by 2,2′‐azoisobutyronitrile via differential microemulsion polymerization has been investigated. Poly(methyl methacrylate) with a molecular weight of around 1 × 10⁶ and a particle size of about 20 nm was achieved under mild reaction conditions. A typical condition was that the surfactant amount required could be as low as 1/130 of the monomer amount in weight, and the surfactant/water ratio could be as low as 1/600, which is much less than the corresponding amounts reported in the literature. “Molecular bricks”, i.e., nanoparticles in which there are only one or two polymer chains, can be achieved using mild conditions by differential microemulsion polymerization, which may have potential applications for making molecular devices.

     

Solid‐State Synthesis of Silver Nanoparticles at Room Temperature: Poly(vinylpyrrolidone) as a Tool

Silver nanoparticles have been used for a long time and recently various methods have been additionally developed for their production. Here we report for the first time a solid‐state high‐speed vibration milling method for the synthesis of silver nanoparticles, in which poly(vinylpyrrolidone) is used for the reduction of the silver salt. The synthesis is performed at room temperature and no surfactant to direct the anisotropic growth of the nanoparticles is required. The formation of the nanoparticles was studied by UV–Visible spectroscopy, transmission electron microscopy, and powder X‐ray diffraction techniques. The nanoparticles synthesized were found to be uniform in size and shape with an average diameter of less than 5 nm. In addition, the antimicrobial activity of these silver nanoparticles was investigated against Escherichia coli and found to be positive.

     

Preparation of Hybrid Microgels Functionalized by Silver Nanoparticles

Summary: Hybrid microgels functionalized with silver nanoparticles (AgNP) have been prepared and their physico‐chemical properties examined. Composite particles have been obtained by formation of AgNP in presence of poly[vinylcaprolactam‐co‐(acetoacetoxyethyl methacrylate)] (VCL/AAEM) microgel particles. It has been demonstrated that hybrid particles with different AgNP amounts can be prepared. Hybrid particles are sensitive to temperature and swelling, and collapse processes are reversible. Incorporation of AgNP leads to shrinkage of microgel template due to the partial immobilization of polymer chains on the microgel surface. As a consequence, gradual loss of temperature sensitivity is observed. Hybrid microgels form highly transparent well‐organized films on solid substrates, providing homogeneous distribution of AgNP in bulk material. Presence of AgNP increases considerably the thermal stability of composite films.

Schematic representation (left) and TEM image (right) of hybrid microgels containing silver nanoparticles (AgNP).     

One‐Pot Synthesis of Colloidal Nanobowls and Hybrid Multipod‐like Nanoparticles by Radiation Miniemulsion Polymerization

A facile approach is proposed to one‐pot synthesis of two kinds of nanoparticles: a new type of PS nanobowls (a hole appearing at the bottom of nanobowl) and PS/silica hybrid multipod‐like nanoparticles. The two type of nanoparticles generated together during polymerization could be separated easily by centrifugation. Furthermore, the structure of nanobowls could be easily controlled by the weight ratio of monomer/silica. In addition, we find that the multipod‐like nanoparticles play important roles in hydrophobic properties. The water contact angle increased from 24.0° to 143.3° after coated with the multipod‐like nanoparticles.

     

Microstructure,Kinetics, and Transport in Oil‐in‐Water Microemulsion Polymerizations

The kinetics of microemulsion polymerization depend on the structure of the initial microemulsion and the transport of species between the aqueous domain, the micelles, and the polymer particles. The water solubility of the monomer and the proximity of the initial microemulsion composition to a phase boundary are key considerations for studying microemulsion polymerization kinetics and producing the desired products. Complications frequently arise in the synthesis of copolymers or the incorporation of controlled polymerization mechanisms because of the compartmentalized nature of microemulsion polymerizations.

     

Nanofibrilar Polyaniline: Direct Route to Carbon Nanotube Water Dispersions of High Concentration

Water dispersible nanofibrilar polyaniline (NF‐PANI) provides a novel and direct route towards carbon nanotube water dispersions of high concentration. Carrying out the chemical synthesis of NF‐PANI in the presence of carbon nanotubes (CNTs) results in an entirely nanostructured nanofibrilar polyaniline/carbon nanotube (NF‐PANI/CNT) composite material that contains well segregated CNTs partially coated by NF‐PANI. This new approach is simple, fast, and inexpensive, and enables the direct preparation of stable and homogeneous dispersions of the composites in water at concentrations up to 10 mg · mL⁻¹, even for the highest CNT loadings of 50 wt.‐% without the participation of surfactants or stabilizers.

     

Gold Nanoparticles Functionalized by a Dextran‐Based pH‐ and Temperature‐Sensitive Polymer

A dextran‐based dual‐sensitive polymer is employed to endow gold nanoparticles with stability and pH‐ and temperature‐sensitivity. The dual‐sensitive polymer is prepared by RAFT polymerization of N‐isopropylacrylamide from trithiocarbonate groups linked to dextran and succinoylation of dextran after polymerization. The functionalized nanoparticles show excellent stability under various conditions and can be stored in powder‐form. UV and DLS measurements confirm that the temperature‐induced optical changes and aggregation behaviors of the particles are strongly dependent on pH.

     

Polysorbate 80 as a Tool: Synthesis of Gold Nanoparticles

The preparation of metal nanoparticles generally requires the use of mostly toxic reducing agents according to state‐of‐the‐art procedures. Here, we report that polysorbate 80, a polymeric nonionic surfactant, when reacted with a gold salt in water at room temperature, yields well‐dispersed gold nanoparticles. Furthermore, we could control the particle size by simply altering concentration or temperature. The synthetic procedure presented here is easy, inexpensive, straightforward, and user‐friendly.

     

Stabilization of Silver Nanoparticles by Polyelectrolytes and Poly(ethylene glycol)

Silver nanoparticles of 23 nm size were formed by chemical reduction of silver nitrate in excess of aqueous sodium borohydride. To examine the aggregation behavior in NaCl solutions, they were coated with poly(diallyldimethylammonium chloride), poly(allylamine hydrochloride) and poly(ethylene glycol) by layer‐by‐layer assembly. Silver nanoparticles coated with PDADMAC of both high and low molecular weight revealed the lowest stability independent of salt concentration. Silver nanoparticles coated with PAH and PEG are stable in 0.1 or 0.01 M NaCl, whereas addition of 0.5 M NaCl destroys the colloidal solution. The destruction of silver agglomerates and the increase of monodispersity in the case of PEG coated silver nanoparticles were observed after heating at 90 °C. In contrast, uncoated silver nanoparticles readily agglomerate and precipitate even after heating at 65 °C.

     

Controlled Dispersion of Silver Nanoparticles into the Bulk of Thermosensitive Polymer Microspheres: Tunable Plasmonic Coupling by Temperature Detected by Surface Enhanced Raman Scattering

By in situ reduction of Ag⁺ ions pre‐dispersed inside thermosensitive microspheres of poly[(N‐isopropylacrylamide)‐co‐(methacrylic acid)] (P(NIPAM‐co‐MAA)), a 3D copolymer‐supported network of silver nanoparticles is created and extensively characterized by surface‐enhanced Raman scattering (SERS). The effective dispersion and the suitable density of the silver nanoparticles in the composite microspheres are demonstrated by the thermal‐induced SERS signal and its high reproducibility during thermocycling. When the temperature of the system increases above 32 °C, spatial separation of the silver nanoparticles decreases and the numbers of Ag nanoparticles and P(NIPAM‐co‐MAA) microspheres under illumination spot increase as a result of the shrinkage of the P(NIPAM‐co‐MAA) chains, leading to the ramp of the SERS effect. By means of the high reversibility of the thermosensitive phase transition of the P(NIPAM‐co‐MAA) microspheres, SERS activity of the silver nanoparticle network embedded in the microsphere can be well controlled by thermal‐induced variation of special separation.