Structural and ionic conductivity studies of solid polymer electrolytes based on poly (vinylchloride) and poly (methylmethacrylate) blends

Thin film of poly (vinylchloride) and poly (methylmethacrylate) blend polymer electrolytes plasticized with a combination of DBP and Li₂SO₄ salts have been prepared by solution casting technique. The prepared films were subjected to a.c. impedance measurements as a function of temperature ranging from 304–373 K. The maximum conductivity at 304 K was found to be 1.24 × 10⁻⁸ S·cm⁻¹ for PVC-PMMA-Li₂SO₄-DBP (7.5-17.5-5-70 mole-%). Temperature dependence studies on the ionic conductivity in the PVC-PMMA-Li₂SO₄-DBP system suggest that the ion conduction follows the Williams-Landel-Ferry (WLF) mechanism, which is further confirmed by Vogel-Tamman-Fulcher (VTF) plots. XRD, FTIR, SEM and thermal studies revealed complex formation in.     

Live cell refractometry using microfluidic devices

Using Hilbert phase microscopy for extracting quantitative phase images, we measured the average refractive index associated with live cells in culture. To decouple the contributions to the phase signal from the cell refractive index and thickness, we confined the cells in microchannels. The results are confirmed by comparison with measurements of spherical cells in suspension.     

High-brightness white light-emitting organic electroluminescent devices using poly(N-vinylcarbazole) as a hole-transporter

A white light-emitting organic electroluminescent (EL) device with multilayer thin-film structure, which shows high-brightness and high-efficiency, is demonstrated. The device structure of glass substrate/indium–tin oxide/poly(N-vinylcarbazole) (PVK)/1,1,4,4-tetraphenyl-1,3-butadiene/8-(quinolinolate)-aluminum (Alq) doped with 5,6,11,12-tetraphenylnaphthacene/Alq/Mg/Al was employed. The turn-on voltage is as low as 2.5 V. The white light emission covers a wide range of the visible region, and the Commission Internationale de 1' Eclairage coordinates of the emitted light are (0.319, 0.332) at 10 V. Bright white light, over 20 000 cd/m², was successfully obtained at about 18 V, and the maximum efficiency reaches to 1.24 lm/W at 9 V. The reasons of obtaining high level EL properties of our device have been discussed.     

Monte Carlo calculation of penetration of electrons into poly(methylmethacrylate)

Monte-Carlo method is applied to the problem of penetration of 20 keV and 30 keV electrons to polymethylmethacrylate. In this paper the ranges and backscattering yields are calculated and a comparison with the results obtained by different methods is made. Depth-dose functions are depicted as well.The authors wish to thank Mr. J. Kae of the Research Institute of Mathematical Machines for a valuable help in programming.     

Thermoelectric transport in conductive poly(3,4-ethylenedioxythiophene)

Poly(3,4-ethylenedioxythiophene)(PEDOT)has proved its quite competitive thermoelectric properties in flexible electronics with its excellent electrical and mechanical properties.Since the early discovery of PEDOT,considerable experimental progress has been achieved in optimizing and improving the thermoelectric properties as a promising organic thermoelectric material(OTE).Among them,theoretical research has made significant contributions to its development.Here the basic physics of conductive PEDOT are reviewed based on the combination of theory and experiment.The purpose is to provide a new insight into the development of PEDOT,so as to effectively design and preparation of advanced thermoelectric PEDOT material in the future.     

Probing single cells using flow in microfluidic devices

Enabling fluids to be manipulated on the micron-scale, microfluidic technologies have facilitated major advances in how we study cells. In this review, we highlight key developments in how flow in microfluidic devices is exploited to investigate the behavior of individual cells, from trapping and positioning single cells to probing cell deformability. Exploiting the properties of fluids and flow patterns in microchannels makes it possible to study large populations of single cells at micron-length scales with increased throughput and efficiency.     

Femtosecond laser-fabricated microstructures in bulk poly(methylmethacrylate) and poly(dimethylsiloxane) at 800 nm towards lab-on-a-chip applications

Laser direct writing technique is employed to fabricate microstructures, including gratings (buried and surface) and two-dimensional photonic crystal-like structures, in bulk poly(methylmethacrylate) (PMMA) and poly(dimethylsiloxane) (PDMS) using ∼100 femtosecond (fs) pulses. The variation of structure size with different writing conditions (focussing, speed and energy) was investigated in detail. Diffraction efficiencies of the gratings were calculated and the changes in diffraction efficiency (DE) as a function of period, energy and scanning speed were evaluated. Highest diffraction efficiencies of 34% and 10%, for the first order, were obtained in PMMA and PDMS respectively. Heat treatment of these gratings demonstrated small improvement in the diffraction efficiency. Several applications resulting from these structures are discussed. Fs modification in PMMA and PDMS demonstrated emission when excited at a wavelength of 514 nm. We attempted to prepare buried waveguides in PMMA with higher refractive index at the core. We have successfully fabricated branched and curved structures in PMMA and PDMS finding impending applications in microfluidics.     

Thickness dependence of the dynamics in thin films of isotactic poly (methylmethacrylate)

The film thickness dependence of both the glass transition temperature (T(g)) and the 1 kHz alpha relaxation were studied for thin films of isotactic Poly (methylmethacrylate) (i-PMMA) supported on aluminium substrates. Films in the thickness range 7-200 nm were studied. The ellipsometrically determined T(g) was found to show reductions for films thinner than 60 nm, with the largest observed reduction being 12 K for a 7 nm thick film. Measurements of the T(g) were also performed on i-PMMA films supported on silicon substrates. Dielectric studies of the temperature dependent 1 kHz alpha relaxation peak, showed that the position (T(alpha)) and shape of the peak have no film thickness dependence. This was shown to hold for films with one free surface and films with a 30 nm thermally evaporated capping layer. Capping the films was shown to have no effect on the thickness dependence of either T(g) or T(alpha). The implications of these results are discussed further and the different film thickness dependencies of T(g) and T(alpha) are discussed. This is done within the framework of the Vogel-Fulcher-Tamann (VFT) theory of glass forming materials and also in the context of the existence of a dynamic correlation length xi.     

Thickness dependence of the dynamics in thin films of isotactic poly (methylmethacrylate)

The European Physical Journal E - The film thickness dependence of both the glass transition temperature (T g ) and the 1 kHz alpha relaxation were studied for thin films of isotactic Poly...     

Surface modification of poly(dimethylsiloxane) for microfluidic assay applications

The surface of a poly(dimethylsiloxane) (PDMS) film was imparted with patterned functionalities at the micron-scale level. Arrays of circles with diameters of 180 and 230 μm were functionalized using plasma oxidation coupled with aluminum deposition, followed by silanization with solutions of 3-aminopropyltrimethoxy silane (3-APTMS) and 3-mercaptopropyltrimethoxy silane (3-MPTMS), to obtain patterned amine and thiol functionalities, respectively. The modification of the samples was confirmed using X-ray photoelectron spectroscopy (XPS), gold nanoparticle adhesion coupled with optical microscopy, as well as by derivatization with fluorescent dyes. To further exploit the novel surface chemistry of the modified PDMS, samples with surface amine functionalities were used to develop a protein assay as well as an array capable of cellular capture and patterning. The modified substrate was shown to successfully selectively immobilize fluorescently labeled immunoglobulin G (IgG) by tethering Protein A to the surface, and, for the cellular arrays, C2C12 rat endothelial cells were captured. Finally, this novel method of patterning chemical functionalities onto PDMS has been incorporated into microfluidic channels. Finally, we demonstrate the in situ chemical modification of the protected PDMS oxidized surface within a microfluidic device. This emphasizes the potential of our method for applications involving micron-scale assays since the aluminum protective layer permits to functionalize the oxidized PDMS surface several weeks after plasma treatment simply after etching away the metallic thin film.     

Solvent and temperature-dependent conductive behavior of poly(3-hexylthiophene)

Impedance characterization at different temperatures has been used to investigate the conductive behavior of Poly(3-hexylthiophene) (P3HT), prepared in different solvents, as the semiconductor layer in organic multilayer capacitor. It has been found that the P3HT films using chloroform and toluene solvents exhibit an enhancement in conductivity by heating following an Arrhenius law with an activation energy transition from 0.004 to 0.026 eV and from 0.002 to 0.015 eV at ~313 K, respectively, which originates from band tail hopping that occurs around the Fermi edge. The boiling point of the used solvents can affect P3HT crystallization process, which causes the difference in conduction and activation energy.     

Saturable absorption in poly(indenofluorene): a picket-fence polymer

Poly(indenofluorene) shows a strong degenerate four-wave mixing (DFWM) response when it is excited with 100-fs pulses at 800 nm. The DFWM signal scales with the 1.5 power of the input intensity, which we interpret as being due to absorption saturation phenomena. The saturation was studied by open-aperture Z scan in dilute solutions of poly(indenofluorene) in chloroform. The changes in the absorption coefficient alpha are described by the formula alpha = alpha(0)/[1 + (I/I(sat))(1/2)], where I(sat) is the saturation intensity, which is found to be of the order of 100>MW/cm(2).     

Ionic conductivity and electrochemical stability of poly(methylmethacrylate)-poly(ethylene oxide) blend-ceramic fillers composites

The role of inorganic ceramic fillers namely nanosized Al₂O₃ (15-25 nm) and TiO₂ (10-14 nm) and ferroelectric filler SrBi₄Ti₄O₁₅ (SBT CIT) (0.5 μm) synthesized by citrate gel technique (CIT) on the ionic conductivity and electrochemical properties of polymer blend 15 wt% PMMA+PEO₈:LiClO₄+2 wt% EC/PC electrolytes were investigated. Enhancement in conductivity was obtained with a maximum of 0.72×10⁻⁵ S cm⁻¹ at 21 °C for 2 wt% of SrBi₄Ti₄O₁₅ (SBT CIT) composite polymer electrolyte. The lithium-ion transport number and the electrochemical stability of the composite polymer electrolytes at ambient temperature were analyzed. An enhancement in electrochemical stability was observed for polymer composites containing 2 wt% of SrBi₄Ti₄O₁₅ (SBT CIT) as fillers.     

Dielectric study of polyaniline/poly (methylmethacrylate) composite films below the percolation threshold

We report results of dielectric relaxation studies of polyaniline/poly(methylmethacrylate) composites with polyaniline amount less than the percolation threshold in the frequency range of 0.1 Hz to 1 MHz and temperature range of 10 °C–170 °C. We find a significant dependence of the glass transition temperature Tg on the polyaniline amount in the composite. α and β relaxation processes relative to the PMMA matrix are also affected by the presence of polyaniline inclusion. We identify a relaxation process due to ionic conductivity and another process attributed to residual solvent. The characteristic relaxation frequency of each process and the activation energy depend on the polyaniline amount in the composite. The ac conductivity in the high frequency range is fitted to the universal power law of Jonscher characteristic of disordered materials.     

Crystallizaion and surface morphology of poly(vinylidene fluoride)/poly(methylmethacrylate) films by solution casting on different substrates

The dependence of surface structure of the poly(vinylidene fluoride) (PVDF)/poly(methylmethacrylate) (PMMA) films by solution casting on properties of seven substrates was investigated by wide angle X-ray diffraction (WAXD), Fourier transform infrared (FTIR), scanning electron microscope (SEM) and differential scanning calorimetry (DSC). It was revealed that the polyblend films obtained by casting onto each substrate contained exclusively β phase PVDF. Higher crystallinity of the film was obtained by casting onto ceramic, polytetrafluoroethylene (PTFE), copper (Cu), stainless steel and glass substrates than that by casting onto aluminium (Al) and polypropylene (PP) substrates, depending on the degree of close lattice matching. The surface crystalline structure of PVDF was strongly affected by the wettability of substrate. The largest size of PVDF spherulitic crystal structure with about 6 μm presented in the casting film grown at the air/solution interface on glass substrate, while the smallest spherulite size with about 3 μm was generated by casting onto PTFE, stainless steel and PP substrates. It implied that the higher surface tension the substrate had, the larger PVDF spherulite grew at the air/solution interface.     

Characterisation of PMMA microfluidic channels and devices fabricated by hot embossing and sealed by direct bonding

In this study we fabricated a silicon-based stamp with various microchannel arrays, and demonstrated successful replication of the stamp micro-structure on poly methyl methacrylate (PMMA) substrates. We used maskless UV lithography for the production of the micro-structured stamp. Thermal imprint lithography was used to fabricate microfeatured fluidic platforms on PMMA substrates, as well as to bond PMMA lids on the fluidic platforms. The microfeature in the silicon-based (silicon wafer coated with SU-8) stamp includes microchannel arrays of approximately 30 μm in depth and 5 mm in width. We produced various channels without pillars, as well as with SU-8 pillars in the range of 50–100 μm wide and 6 μm in height. PMMA discs of 1 mm thickness were utilized as the molding substrate. We found 10 kN applied force and 100 °C embossing temperature were optimum for transferring the micro-structure to the PMMA substrate.     

Ultra-fine pitch chip-on-glass (COG) bonding with metal bumps having insulating layer in the side walls using anisotropic conductive film (ACF)

We developed a new ultra-fine pitch chip-on-glass (COG) bonding technique using insulated metal bumps and anisotropic conductive film (ACF). An insulating layer was formed by spin coating a photosensitive insulating polymer and subsequently exposing it without any mask. The shape of the insulating layer coverage on the side walls of the metal bumps can be controlled by changing the exposure time and the viscosity of the photosensitive insulating polymer. In our experiment, we successfully fabricated COG joints with a 25 μm pitch using Au bumps with an insulating layer on their side walls and a conventional single-layer ACF. When the bumps were covered with the photosensitive insulating polymer, a few conductive particles were trapped between neighboring bumps and many conductive particles were embedded between bumps and pads. The electrical resistance between neighboring bumps was measured by the two-point probe method. The resistances were measured only in uncoated specimens. The measured resistance indicates that electrical shorting between neighboring bumps occurred in uncoated specimens. Therefore, electrical shorting was successfully prevented by the insulating layer on the side walls of the bumps.