Charge trapping in bilayers of conducting polymers under open circuit conditions: a protection of conducting polymer films from spontaneous charging/discharging

Spontaneous charging/discharging processes of polymers: polypyrrole and poly(N-methylpyrrole), doped with perchlorate (anion exchanging PPy and PMPy, respectively) and poly(4-styrenesulphonate) ions (cation exchanging PPy(PSS) and PMPy(PSS)) occurring in aqueous electrolyte solutions were studied using different electrochemical techniques. These reactions (oxidation of the polymer by dissolved oxygen and discharge of the polymer redox capacitance) are usually undesired processes leading to alteration of the charge accumulated in the polymer films. This paper points out that these processes can be significantly limited in polymer bilayers due to effect of charge trapping.     

A new amperometric biosensor for hydrogen peroxide determination based on HRP-nanogold-PTH-nanogold-modified carbon paste electrodes

A new strategy for immobilization of horseradish peroxidase (HRP) has been developed by self-assembling gold nanoparticles to multiporous polythionine (PTH) film modified carbon paste interface. A thionine film was initially electropolymerized onto carbon paste interface in a mildly acidic thionine solution at a bias voltage of −1.0 to 1.5 V. This process is accompanied by the hydrogen evolution reaction, and the released hydrogen gas made the PTH film with multiporous structure. The multiporous PTH film provided a biocompatible microenvironment for gold nanoparticles and enzyme molecules, and greatly amplified the coverage of HRP molecules on the electrode surface. Voltammetric and time-based amperometric techniques were employed to characterize the properties of the derived biosensor. The performance and factors influencing the performance of the biosensor were also proposed. The immobilized HRP displayed a catalytic property to the reduction of H₂O₂. The H₂O₂ biosensor achieved 95% of the steady-state current within 2 s, and exhibited a linear range of 9.6×10⁻⁶ to 1.2×10⁻³ M H₂O₂ with a detection limit of 7.5×10⁻⁷ M (S/N = 3). Furthermore, the biosensor remained at about 90% of its original sensitivity after 2 weeks’ storage.     

Ab initio electronic properties of dual phosphorus monolayers in silicon

In the midst of the epitaxial circuitry revolution in silicon technology, we look ahead to the next paradigm shift: effective use of the third dimension - in particular, its combination with epitaxial technology. We perform ab initio calculations of atomically thin epitaxial bilayers in silicon, investigating the fundamental electronic properties of monolayer pairs. Quantitative band splittings and the electronic density are presented, along with effects of the layers’ relative alignment and comments on disordered systems, and for the first time, the effective electronic widths of such device components are calculated.     

Potential dependence of the capacitance of ionizable bilayers

The effect of the applied potential across a biomimetic model membrane, Δφ, on the extent of dissociation of surface bound ionizable groups has been examined theoretically using a formalism that shares common features with that recently introduced by White and coworkers (Langmuir 9 (1993) 1) to account for the occurrence of peaks in the cyclic voltammetry of self-assembled monolayers rigidly attached to an electrode surface, bearing the same type of ionizable groups facing the electrolyte. Numerical solutions of the governing coupled, highly non-linear system of equations yielded for reasonable membrane parameters, and under conditions of physiological relevance, linear changes in the extent of ionization as a function of Δφ, about Δφ=0, of ca. 0.07 units/V. Also considered in this work was a more general situation in which the contributions to the total interfacial capacity, C_T, due to the diffuse double layers, C_S^j, and to the fixed charges C^j(f_j) on each of the sides of the membrane-like assembly denoted by ‘j’, were comparable in magnitude to the potential independent capacity of the intervening hydrophobic layer, i.e. low-electrolyte concentration. In such case, plots of C_T versus Δφ displayed a global minimum at Δφ=0 and two local maxima at values of Δφ slightly negative and positive to the maxima observed in the corresponding C^j(f_j) versus Δφ plots. Implications of the results obtained to excitable bilayer membranes are briefly discussed.     

Liposome and lipid bilayer arrays towards biosensing applications

Sensitive and selective biosensors for high-throughput screening are having an increasing impact in modern medical care. The establishment of robust protein biosensing platforms however remains challenging, especially when membrane proteins are involved. Although this type of proteins is of enormous relevance since they are considered in >60% of the pharmaceutical drug targets, their fragile nature (i.e., the requirement to preserve their natural lipid environment to avoid denaturation and loss of function) puts strong additional prerequisites onto a successful biochip. In this review, the leading approaches to create lipid membrane-based arrays towards the creation of membrane protein biosensing platforms are described. Liposomes assembled in micro- and nanoarrays and the successful set-ups containing functional membrane proteins, as well as the use of liposomes in networks, are discussed in the first part. Then, the complementary approaches to create cell-mimicking supported membrane patches on a substrate in an array format will be addressed. Finally, the progress in assembling free-standing (functional) lipid bilayers over nanopore arrays for ion channel sensing will be reported. This review illustrates the rapid pace by which advances are being made towards the creation of a heterogeneous biochip for the high-throughput screening of membrane proteins for diagnostics, drug screening, or drug discovery purposes.     

Reaction, transformation and delamination of samarium zirconate thermal barrier coatings

The rare earth zirconates have attracted interest for thermal barrier coatings (TBCs) because they have very low intrinsic thermal conductivities, are stable above 1200 °C and are more resistant to sintering than yttria-stabilized zirconia (YSZ). Samarium zirconate (SZO) has the lowest thermal conductivity of the rare earth zirconates and its pyrochore structure is stable to 2200 °C but little is known about its response to thermal cycling. Here, columnar morphology SZO coatings have been deposited on bond coated superalloy substrates using a directed vapor deposition method that facilitated the incorporation of pore volume fractions of 25 to 45%. The as-deposited coatings had a fluorite structure which transformed to the pyrochlore phase upon thermal cycling between 100 and 1100 °C. This cycling eventually led to delamination of the coatings, with failure occurring at the interface between the TGO and a “mixed zone” that formed between the thermally grown alumina oxide (TGO) and the SZO. While the delamination lifetime increased with coating porosity (reduction in coating modulus), it was significantly less than that of similar YSZ coatings applied to the same substrates. The reduced life resulted from a reaction between the rare earth zirconate and the alumina-rich bond coat TGO, leading to the formation of a mixed zone consisting of SZO and SmAlO₃. Thermal strain energy calculations show that the delamination driving force increases with TGO and mixed layer thicknesses and with coating modulus. The placement of a 10 μm thick YSZ layer between the TGO and SZO layers eliminated the mixed zone and restored the thermal cyclic life to that of YSZ structures.     

Mo/Au Bilayers Deposited by Sputtering at Room Temperature for Transition Edge Sensors Fabrication

We report on the fabrication and characterisation of Mo/Au bilayers which are intended to be used as high resolution cryogenic imaging spectrometers for next generation of X-ray Astrophysical observatories in space. Mo/Au bilayers have been deposited by sputtering at room temperature on Si₃N₄ bulk and membranes. The composition of the bilayers as well as their interfaces have been characterised by Rutherford Backscattering Spectroscopy (RBS). Results indicate absence of interdiffusion. Further structural characterization has been performed by X-ray diffraction and Atomic Force Microscopy. The transition temperature T _c of the Mo/Au bilayers has been tuned by changing the Au layer thickness. Very sharp superconducting transitions have been observed with transition widths as small as 0.3 mK. These films look therefore extremely promising for the intended detectors, as well as for other applications in materials science and nanotechnology.      

Effect of the polymer layers and bilayers on the corrosion behaviour of mild steel: Comparison with polymers containing Zn microparticles

Electrodeposition methods have been used to obtain polypyrrole and polyaniline polymer layers, bilayers and blends of these polymers on carbon steel by passivation of the steel surface in the electrodeposition solution (oxalic acid and monomer) between −0.5 and 0.3 V versus Ag/AgCl and subsequent electrodeposition using different techniques (potentiodynamic, galvanostatic and potentiostatic). The results obtained indicate that prepassivation gives rise to adherent polymer layers with excellent corrosion resistance. Of all the bilayers obtained, the best results are yielded with those in which polyaniline is deposited as the base for the deposition of polypyrrole.

The electrodeposition of Zn microparticles on the previously deposited polymer layers promotes a great improvement in the corrosion current in highly aggressive solutions such as NaCl due to the effect of Zn as an anodic corrosion inhibitor. The drop in the corrosion rate depends on the amount of Zn deposited on the polymer layer, up to a certain point after which the protective effect ceases to be observed.     

Potentiometric properties of polypyrrole bilayers

The spatially separated polypyrrole (PPy) bilayers composed of easily (PPy/Cl) and heavily permeable (PPy/dodecylsulfate) for anions component layers have been prepared by consecutive electrodeposition. The set-up of quasi-equilibrium potential E_r during conditioning in the solution of electrolyte and the potentiometric response of bilayers to ions and redox system in the test solution were studied. The short-term potentiometric response of the bilayer system is mainly determined by the outer layer. The participation of the inner layer is related with permeability of the outer layer and with sensitivity of the inner layer to the ions of the test solution, and leads to the dependence of the electrode potential on the duration of the bilayer system’s exposure to the test solution.