Polymer-based Device Research Articles

Multilayer Polymer Stacking by In Situ Electrochemical Polymerization for Color‐Stable White Electroluminescence

We report a novel multilayer electrochemical polymerization method and the first color-stable polymer-based multilayer white-emissive device, which exhibited CIE coordinates of (0.35, 0.35), a CRI of 93 and extremely stable white-light emission over a wide range of driving voltages of 8 to 20 V. The multilayer electrochemical polymerization method affords more opportunities to develop multilayer polymer heterostructures in organic solid-state devices.

A Polymer-Based Microfluidic Platform Featuring On-Chip Actuated Hydrogel Valves for Disposable Applications

present a highly functional polymer-based microfluidic device for disposable applications. This device is plastic injection molded and exhibits three levels of functionality: 1) fluidic interconnects are monolithically integrated with the device, enabling robust manufacturing and high-pressure operation (> 3.5 MPa); 2) a metal layer is lithographically patterned in the form of microheaters; and 3) a thermally sensitive hydrogel valve is integrated into the channel. The valve is normally closed at room temperature. Upon heating to above the lower critical solution temperature of 32°C, the polymer valve becomes hydrophobic, shrinks while forming large pores, and permits flow. The device has been actuated reliably over 100 times with no apparent degradation. The valve closing response using the integrated on-chip heaters is 5 s, as opposed to 20 s when using off-chip heat sources. On average, a completed device can be fabricated in less than 2 h and only requires an external pressure source and electrical controller for operation.

The influence of nanostructure on polymer-based optoelectronic device functioning: A computer simulation study

During the last years it has been clear that it is important to understand and control the nanostructure of the active polymer layer used in optoelectronic devices, like polymer diodes, solar cells or field effect transistors. Several experimental studies have shown that the nanostructure of polymer thin films used in these optoelectronic devices depends on the conditions used to deposit the polymer layer between the electrodes. As a result, in solid state conjugated polymer chains tend to be stacked and aligned relative to the electrodes creating domains with different sizes that influence the performance of these devices. To understand how the spatial arrangement of polymer chains affects the functioning of optoelectronic devices, we performed computer simulations using our mesoscopic model based on a generalized dynamic Monte Carlo method. We focus our study on the influence of the nanomorphology on the electric properties of polymer light emitting diodes. Our results show that for a pristine polymer layer and in the presence of ohmic contacts between the electrodes and the polymer layer, the electric properties of the device, namely current density, charge density, internal electric field and the number of charges that undergo recombination strongly depend on the polymer morphology at nanoscale.

Construction and characteristics of tandem organic solar cells featuring small molecule-based films on polymer-based subcells

In this study, we stacked a small molecule-based cell onto another polymer-based device to fabricate a tandem organic solar cell that extended the absorption range of the entire cell over a wider spectral range. Between the two subcells, we positioned a connecting structure comprising layers of Cs2CO3, Ag and MoO3. Current matching phenomena played an important role in determining the device efficiency. The judicious selection of subcells exhibiting superior current matching improved the performance of the tandem cell. Indeed, in the optimally performing tandem cells we obtained both a high open-circuit voltage (1.21 V) and an improved power conversion efficiency (1.81%). From analyses of the surface morphology and transmission spectra of the middle Ag layers, we deduced that the main function of this film was to provide more sites for efficient recombination of holes and electrons. The thickness of this layer was limited by its transmittance. A thinner Ag layer allowed more light to be harvested by the top cell, increasing the overall performance of the tandem cell.

Polymer-based electrospray device with multiple nozzles to minimize end effect phenomenon

In this paper, “end effect”, which represents the deflection of meniscus of boundary nozzles in an array due to asymmetric electric field and repulsive forces between adjacent nozzles, is experimentally investigated and a polymer-based electrospray device is fabricated and tested to minimize the end effect. For the electrically conductive nozzles of electrospray, the end effect could be reduced by dummy nozzles, through which no liquid is supplied, mounted at the boundary of the array. However, the polymer-based electrospray device can eliminate the end effect without using the dummy dry nozzles due to dielectric characteristic. A novel multiple nozzles of Polymethyl Methacrylate (PMMA)-based electrospray device was successfully fabricated and evaluated for reducing the end effect, showing no deflection of menisci through the boundary nozzles. And ten nozzles device was fabricated and observed to eject liquid jet simultaneously. The electrical current of the spray issued from the nozzles of the polymer-based electrospray device is measured with respect to flow rate and shows a good agreement with the scaling law.

Black to Transmissive Switching in a Pseudo Three-Electrode Electrochromic Device

We introduce the first π-conjugated polymer-based, black-to-transmissive and multicolored switching electrochromic device (ECD) constructed in a Pseudo 3-Electrode Electrochromic Device (P3-ECD) architecture. In this ECD, the non-electrochromic, yet electroactive, polymer poly(3,4-propylenedioxypyrrole-N-propionitrile) (PProDOP-N-EtCN) serves as a counter electrode material. This transmissive polymer helps eliminate the contrast limitations seen in dual polymer ECDs that use combinations of anodically and cathodically coloring polymers. The P3-ECD adds colors by transmitting light through two independently controlled working electrodes (coated with two different electrochromic polymer films) and two counter electrodes (coated with PProDOP-N-EtCN) stacked together with a gel electrolyte. The two cathodically coloring EC polymers that were used in this work are, a diester-substituted poly(3,4-propylenedioxythiophene) (PProDOT-(CH2CO2C12H25)2) for the first one, namely PProDOT-ester, and a donor−acceptor ana...

Variable phase retarder made of a dielectric elastomer actuator

We present a polymeric optical phase retarder that is electrically tunable by a dielectric elastomer actuator. The soft material device affords a large tuning range (14pi at lambda=488 nm) combined with high accuracy in optical path length and low drift rate (8.3 nm/min). Furthermore, the phase retarder is not sensitive to polarization, introduces a wavefront distortion<lambda/30, and tolerates high power densities (>141 kW/cm2). We show the dynamics for periodic phase modulation and demonstrate a simple drive technique for fast phase stepping. The polymer-based device is inexpensive, easy to fabricate, and its design can be adapted to specific applications.

Electrospray on superhydrophobic nozzles treated with argon and oxygen plasma

We report on a simple process to fabricate electrohydrodynamic spraying devices with superhydrophobic nozzles. These devices are useful, among other things, in mass spectrometry and printing technology. The superhydrophobic nozzle is created by roughening the surface of the polyfluorotetraethylene (PTFE) by argon and oxygen plasma treatment. We have developed a polymer-based electrospray device with a flat, superhydrophobic nozzle capable of maintaining a high contact angle and stable jetting.

A study on fabrication of silicon mold for polymer hot-embossing using focused ion beam milling

Abstract The need for a flexible and high-throughput process for the fabrication of a polymer-based micro-fluidic device is becoming increasingly important as bio-device industry is expanding very fast. The present work investigated the fabrication of a polymer-based micro-fluidic device by using the combination of the focused ion beam (FIB) milling and the hot-emboss process. The milled depth-ion dose curve for Si was investigated, and some silicon molds were prepared by a repetitive-pass milling with FIB. A Si mold was then used for the hot-emboss of poly-methyl-methacrylate (PMMA) to replicate micro-fluidic parts. Prior to hot-embossing, a FIB milled silicon mold was heat-treated at 500 °C for 10 min in vacuum (0.07 Pa). The FIB milled fields in the Si mold could be replicated on the PMMA with the dimensional deviation less than 1% under the temperature of 150 °C, the force of 50 kgf, the loading force velocity of 50 μm/min and the press hold time of 300 s.

Battery-Inspired, Nonvolatile, and Rewritable Memory Architecture: a Radical Polymer-Based Organic Device

A nonvolatile, bistable, and rewritable organic memory device based on radical polymers was prepared and tested. The excellent performance of a battery-inspired memory architecture with a configuration of p- and n-type charge-transporting radical polymers sandwiching a dielectric layer was characterized. The ON−OFF ratio was more than 4 orders of magnitude, and retention and endurance cycles of more than 104 and 103, respectively, were accomplished.

Polymeric, electrically tunable diffraction grating based on artificial muscles

We demonstrate a low-cost, electrically tunable diffraction grating that is driven by a dielectric elastomer actuator. The angular tuning range of the polymer-based device is up to 118 mrad for the first diffracted order. The achievable grating period change of 32% is an improvement by more than a factor of 150 compared with existing analog tunable diffraction gratings based on hard materials. We show that in combination with a white light source, the presented diffraction grating can be used as a wavelength-adjustable luminous source. Such an illuminant has a potential application in inexpensive color displays that could reproduce all perceivable colors.

A cell counting/sorting system incorporated with a microfabricated flow cytometer chip

Flow cytometry is a popular technique for counting and sorting individual cells. This study presents and demonstrates a new cell counting/sorting system integrated with several essential components including a micromachined flow cytometer chip device, an optical detection system and a data analysis and control system to achieve the functions of cell sample injection, optical signal detection and cell collection. By using MEMS technology, we have integrated several microfluidic components such as micro pneumatic pumps/valves onto a polymer-based chip device. Three pneumatic micropumps are used to provide the hydrodynamic driving force for both sample and sheath flows such that hydrodynamic flow focusing can be achieved, and a micro flow switch device comprising three pneumatic microvalves located downstream of the micro sample flow channel is used for cell collection. Cell samples of human lung cancer cells labelled with commercially available fluorescent dyes have been detected and collected successfully utilizing the developed device. The real-time image of dye-labelled cell samples being excited and detected can be monitored and observed through the LCD panel by a custom designed CCD/APD holder and moving stage. Finally, micro flow switch devices were used to successfully sort the cells into the desired outlet channel, and the counting results of the specific cell samples were monitored through the counting panel. The current study focuses on the setup of the overall system. The proposed flow cytometer system has several advantages such as portability, low cost and easy operation process. The size of the system is 37 cm × 16 cm × 18 cm and the weight is 3.5 kg. The error rate of counting and sorting was 1.5% and 2%, respectively. The sorting frequency of the microvalve device is calculated to be 120 cells min−1. The developed microfluidic chip device could be a promising tool for cell-based application fields such as profiling, counting and sorting.

Polymer-based device for efficient mixing of viscoelastic fluids

We demonstrated rapid mixing of viscoelastic fluids in microchannels constructed based on polymethyl methacrylate. Viscoelastic mixing without diffusion was achieved with an effective mixing length of less than 5mm and a relatively fast flow rate. With an abrupt contraction microgeometry (8:1 contraction ratio), we mixed two different viscoelastic fluids experimentally at very low Reynolds numbers, but enormous Peclet and elasticity numbers. This special geometrical configuration triggers flow instability, leading to turbulent and efficient mixing. This flow regime has negligible inertia effects but significant elastic effects.

Electro-optical microscopy: mapping nonlinear polymer films with micrometric resolution

The first demonstration, to the best of our knowledge, of electro-optical microscopy is presented and applied to a polymer-based optical device. A confocal transmission microscope with interferometric homodyne detection is implemented to measure Pockels phase shifts with micrometric spatial resolution and an accuracy level down to 4 x 10(-7) rad. This technique is applied to poled polymer films in which noncentrosymmetric molecular orientation is preliminarily achieved in the sample plane between transverse planar electrodes. The electro-optic mapping of this structure exhibits nonuniform and asymmetric patterns of the nonlinear response that are characteristic of the poling spatial inhomogeneity as confirmed by second-harmonic generation microscopy.

High efficient polymer light-emitting diode based on a new iridium(III) complex with pyrazolone ligand

A new iridium complex containing two 2-(thiophen-2-yl)quinoline ligands and one single monoanionic ligand 1,3-diphenyl-4-phenylacetyl-5-pyrazolone was designed and synthesized. Its photophysical, electrochemical and electrophosphorescence properties were investigated. The iridium complex in solution showed characteristic phosphorescence with a high quantum efficiency of 19% and lifetime of 0.67 μs. Importantly, a saturated red polymer-based electrophosphorescent device with high external quantum efficiency of 8.5% and CIE coordinate of (0.64, 0.33) was fabricated by using this complex as dopant.

A metal-coated polymer micromirror for strain-driven high-speed multiaxis optical scanning

We have developed a new polymer-based micromirror device capable of high-speed multiaxis out-of-plane scanning motion. The whole device structure integrates a metal-coated three-dimensional polydimethylsiloxane micromirror structure with an optically smooth surface and a single layer of silicon-on-insulator electrostatic comb-drive actuators. The high-strain mechanical elasticity of the polymer material allows for translating the in-plane comb-drive motions into three-degree-of-freedom scanning motion with a single actuator layer. The simple structure design and rapid response characteristics of the demonstrated device may lead to high-yield high-performance scanning micromirror technology.

Characterization of Proton Exchange Membrane Fuel Cells with Catalyst Layers Obtained by Electrospraying

Electrostatic polymer processing ~electro-spraying, electrospinning, and combinations of the two! represents a new and highly versatile approach for the fabrication of polymer-based electrochemical device components. 1,2 Electrospraying and electrospinning can afford particles and fibers with diameters of 100 nm or less, suggesting that nanostructured electrolytes and electrodes may be obtained by judicious choice of materials and electrostatic processing parameters. Moreover, these electrostatic processing approaches may have applicability to a wide variety of polymer-based electrochemical devices, including fuel cells, batteries, capacitors, and electrochromic and electroluminescent displays. We believe that electrostatic processing could be used for the construction of an entire proton-exchange membrane fuel cell ~PEMFC!, including the membrane, electro-catalyst layers, and gas diffusion layers. Particularly appealing is the potential ability to control composition, porosity, and wettability of these fuel cell components. As a first step in the development of this technology, Nafion was electrosprayed from solution to afford thin films and subsequently characterized as having physical properties ~water uptake, dimensional changes, electrical conductivity! similar to those of Nafion 117 films. 1 Following that, electrochemical properties of half-cells with commercial Nafion 117 and catalyst layers obtained by electrostatic processing were characterized. 2 The present research is focused on evaluation of PEM single cells with catalyst layers obtained by the electrospraying technique on commercial Nafion 112 films.

Improved Detectability with a Polymer-based Trapping Device in Rapid HPLC Analysis for Ultra-low Levels of Bisphenol A (BPA) in Environmental Samples

A new high-performance liquid chromatography (HPLC) method has been developed to detect ultra-low concentrations of bisphenol-A (BPA) (below 1 ng/L (ppt)) using column switching electrochemical detection (ECD). The results were superior to those obtained from manual pretreatment procedure with membrane stationary phase. BPA is inherently ubiquitous in the environment, including tools and solvents used for its analysis; to obtain meaningful results, therefore, the concentration of the overall BPA contamination must be below the detection limit for BPA using the analytical system. Therefore, purified water for preparing the standard BPA solution must be filtered with a hydrophobic membrane to suppress BPA background levels of contamination. In addition, we investigated methods for effectively preserving environmental water containing BPA. The addition of a small amount of ethylenediaminetetraacetic acid (EDTA) provided good recovery even after overnight storage. By employing these precautionary measures and procedures to reduce BPA contamination from the analytical procedure, we could accurately determine l(-10) ppt of BPA in environmental water samples using a column switching HPLC system.

A polymer-based microfluidic device for immunosensing biochips.

This paper describes the design, fabrication, and test of a PDMS/PMMA-laminated microfluidic device for an immunosensing biochip. A poly(dimethyl siloxane)(PDMS) top substrate molded by polymer casting and a poly(methyl methacrylate)(PMMA) bottom substrate fabricated by hot embossing are bonded with pressure and hermetically sealed. Two inlet ports and an air vent are opened through the PDMS top substrate, while gold electrodes for electrochemical biosensing are patterned onto the PMMA bottom substrate. The analyte sample is loaded from the sample inlet port to the detection chamber by capillary force, without any external intervening forces. For this and to control the time duration of sample fluid in each compartment of the device, including the inlet port, diffusion barrier, reaction chamber, flow-delay neck, and detection chamber, the fluid conduit has been designed with various geometries of channel width, depth, and shape. Especially, the fluid path has been designed so that the sample flow naturally stops after filling the detection chamber to allow sufficient time for biochemical reaction and subsequent washing steps. As model immunosensing tests for the microfluidic device, functionalizations of ferritin and biotin to the sensing surfaces on gold electrodes and their biospecific interactions with antiferritin antiserum and streptavidin have been investigated. An electrochemical detection method for immunosensing by biocatalyzed precipitation has been developed and applied for signal registration. With the biochip, the whole immunosensing processes could be completed within 30 min.

Contact conductivity detection of polymerase chain reaction products analyzed by reverse-phase ion pair microcapillary electrochromatography.

We describe the development of an integrated microelectrophoretic system consisting of a contact conductivity detector mounted on-chip for monitoring the separation of double-stranded (ds) DNA fragments produced via the polymerase chain reaction (PCR) using microcapillary electrochromatography as the separation mode. The separation was carried out in a polymer-based microfluidic device, hot-embossed into poly(methylmethacrylate) (PMMA), whose walls were functionalized to produce a C(18)-terminated surface to act as the stationary phase (open channel format). The carrier electrolyte contained the ion-pairing agent, triethylammonium acetate (TEAA) to allow the separation to be carried out using reverse-phase ion-pair capillary electrochromatography (RP-IPCEC). The microelectrophoretic separations were investigated utilizing various solvent strengths (acetonitrile/water) with 25 mM TEAA to observe the effects on the separation efficiency as well as the chromatographic development time and detector performance. The field strength significantly affected the quality of the separation, with no separation observed at 333 V/cm for a low mass dsDNA sizing ladder, but baseline separation achieved using a field strength of 67 V/cm. It was observed that the solvent strength affected the retention behavior of the polyanionic molecules as well as the electroosmotic mobility. Higher acetonitrile compositions in the run buffer resulted in reduced plate numbers, which produced lower chromatographic resolution. The use of conductivity detection allowed mass detection sensitivities in the range of 10(-21) mol with a separation efficiency of 10(4) plates and the performance of the detector independent of the acetonitrile content used in the carrier electrolyte.