Plate coating: influence of concentrated surfactants on the film thickness

We present a large range of experimental data concerning the influence of surfactants on the well-known Landau-Levich-Derjaguin experiment where a liquid film is generated by pulling a plate out of a bath. The thickness h of the film was measured as a function of the pulling velocity V for different kinds of surfactants (C(12)E(6), which is a nonionic surfactant, and DeTAB and DTAB, which are ionic) and at various concentrations near and above the critical micellar concentration (cmc). We report the thickening factor α = h/h(LLD), where h(LLD) is the film thickness obtained without a surfactant effect, i.e., as for a pure fluid but with the same viscosity and surface tension as the surfactant solution, over a wide range of capillary numbers (Ca = ηV/γ, with η being the surfactant solution viscosity and γ its surface tension) and identify three regimes: (i) at small Ca α is large due to confinement and surface elasticity (or Marangoni) effects, (ii) for increasing Ca there is an intermediate regime where α decreases as Ca increases, and (iii) at larger (but still small) Ca α is slightly higher than unity due to surface viscosity effects. In the case of nonionic surfactants, the second regime begins at a fixed Ca, independent of the surfactant concentration, while for ionic surfactants the transition depends on the concentration, which we suggest is probably due to the existence of an electrostatic barrier to surface adsorption. Control of the physical chemistry at the interface allowed us to elucidate the nature of the three regimes in terms of surface rheological properties.     

Activation energy of ignition for catalytic oxidation of ethanol in oscillatory regime

Activation energies of ignition for the thermokinetic oscillations obtained during the heterogeneous catalytic oxidation of ethanol on Pd/Al₂O₃ in a dynamic calorimeter were obtained using the minimum values of the temperature oscillations. These activation energies of ignition are greater than the activation energies of the corresponding oscillations. The obtained results are discussed by assuming a PdO_x redox cycle.     

Moisture absorption and absorption kinetics in polyelectrolyte films: influence of film thickness

Specular X-ray reflectivity (XR) and quartz crystal microbalance (QCM) measurements were used to determine the absorption of water into thin poly(4-ammonium styrenesulfonic acid) films from saturated vapor at 25 degrees C. The effect of film thickness on the absorption kinetics and overall absorption was investigated in the range of thickness from (3 to 200) nm. The equilibrium swelling of all the films irrespective of film thickness was (0.57+/-0.03) volume fraction. Although the equilibrium absorption is independent ofthickness, the absorption rate substantially decreases for film thickness < 100 nm. For the thinnest film (3 nm), there is a 5 orders of magnitude decrease in the diffusion coefficient for water.     

Electrochemical oxidation and determination of methylparaben at overoxidized polypyrrole film modified a boron-doped diamond electrode

Electrochemical oxidation of methylparaben (MP) is studied on an overoxidized polypyrrole (OPPy)-modified boron-doped diamond electrode using the cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques. The OPPy-modified BDD electrode displays the catalytic activity of electrooxidation of methylparaben. The modification of BDD electrode surface results in higher values of recorded oxidation currents of the methylparaben than on a bare BDD electrode. The diffusion character of recorded current is determined on the basis of the relation between the current and the scan rate. The linear relationship between methylparaben oxidation peak current is obtained in the range 1.57?×?10^??6–2.06?×?10^??5 mol L^??1. A new voltammetric procedure is proposed to quantify methylparaben in cosmetic products using an overoxidized polypyrrole (OPPy)-modified BDD electrode. The results are compared to the HPLC technique described in the literature as the reference method.     

Capacitive characteristics of nanocomposites of conducting polypyrrole and functionalized carbon nanotubes: effects of in situ dopant and film thickness

The nanocomposites of functionalized single-walled carbon nanotubes (FSWNTs) and conducting polypyrrole (PPy) doped by FSWNTs, Cl⁻, toluenesulfonate (TOS⁻), and dodecylbenzenesulfonate (DBS⁻), respectively, were electrochemically co-deposited to evaluate their applicability in supercapacitors. The effects of the dopants, with focus on their mass, size and surfactivity, and film thickness on the capacitive characteristics were investigated in 3 M KCl aqueous solution. Although the nanostructure of composites can admittedly improve the capacitive properties, dopant anion was demonstrated to be a more essential factor. The specific capacitance of PPy-TOS/FSWNT nanocomposites was greater than that of pristine PPy/FSWNT nanocomposites and PPy-DBS/FSWNT nanocomposites by ten and 100 times, respectively. Furthermore, PPy-TOS/FSWNT nanocomposites exhibited the lowest dependence of capacitance on the charging–discharging rate and composite thickness due to its high electronic and ionic conductivity resulting from the appropriate doping level and size of TOS^- as well as the synergic effect of PPy-TOS and FSWNTs. In addition, PPy-TOS/FSWNT nanocomposites presented a remarkably stable cycling performance.     

Activation energy for the ignition of the catalytic oxidation of methanol in oscillatory regime

The overall activation energy for the ignition of thermokinetic oscillations observed (in a dynamic calorimeter) during the heterogeneous catalytic oxidation of methanol on Pd/LiAl₅O₈ were obtained and discussed by a PdO_x redox cycle.     

Labeled magnetic nanoparticles assembly on polypyrrole film for biosensor applications

In recent years, conducting polymers combined with metallic nanoparticles have been paid more attention due to their potential applications in microelectronics, microsystems, optical sensors and photoelectronic chemistry. The work presented in this paper describes the preparation and characterization of a nanocomposite composed by a thin polypyrrole (PPy) film covered with an assembly of magnetic nanoparticles (NPs). The magnetic particles were immobilized on PPy films under appropriate magnetic field in order to control their organization on the PPy film and finally to improve the sensitivity of the system in potential sensing applications. The electrical properties and morphology of the resulting PPy film and the PPy film/NPs composite were characterized with cyclic voltammetry, impedance spectroscopy (IS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and infra-red spectroscopy (IR). By using streptavidin labeled magnetic particles it was possible to functionalize the NPs assembly with biotin-Fab fragment K47 antibody. The designed biosensor had been successfully applied in rapid, simple, and accurate measurements of atrazine concentrations, with a significantly low detection limit of 5 ng/ml.     

The theory of gas-liquid chromatography : The influence of the thickness of the stationary liquid film

The thermodynamic theory of gas-liquid chromatography has been developed, taking into account specific properties of thin films of the liquid phase expressed in terms of the “disjoining pressure”. Equations were derived to describe the dependence of the retention volume on the thickness of the stationary phase over the whole range of thickness. The results are in good agreement with experimental values.A chromatographic method for determining the constants of disjoining pressure is suggested.     

Open tubular columns: The influence of changing the liquid phase film thickness on column efficiency

Summary The factors characterizing the influence of the variation of the liquid phase film thickness on the mass transfer terms in the Golay equations describing the performance of open tubular columns are investigated and numerical values are given.Paper dedicated to Professor S. R. Lipsky on his sixtieth birthday.     

Novel chemical synthesis of polypyrrole thin film electrodes for supercapacitor application

Present investigation describes the cost-effective, novel and simple chemical synthesis of polypyrrole (PPy) thin films for supercapacitor application. These PPy films are characterized by different techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The XRD pattern reveals the amorphous nature of PPy thin film, which is highly feasible for supercapacitors. Further, FTIR study confirms the formation of PPy. The surface morphological study exhibit the coverage of uniform and smooth morphology on thin film. The electrochemical supercapacitive properties of PPy thin films are evaluated using cyclic voltammetry (CV) in 0.5 M H₂SO₄ electrolyte, which exhibits the maximum specific capacitance of 329 Fg⁻¹ at the scan rate of 5 mV s⁻¹. Additionally, an equivalent series resistance (ESR) of PPy thin films is found to be 1.08 Ω using electrochemical impedance measurement.     

Force detection with Donnan equilibrium in polypyrrole film

Mechanical stimuli to polypyrrole (PPy) composite film could be detected as a spike-wise current by applying or releasing a stepwise tensioning-load in electrochemical cell. The current polarity observed here varies with the film preparation. A negative current was observed in the PPy film electrodeposited in dodecylbenzene sulfonic acid (PPyDBS), besides a positive current was observed in the film electrodeposited in bis(trifluoromethane sulfonyl)imide (PPyTFSI) with applying a load. Reversal currents were observed with releasing a load from the films. Switching of the polarity of the induced current well corresponded to the film actuation polarity, indicating that the current induction is the phenomenological counterpart of the electrochemical actuation. Perturbation of Donnan equilibrium by external pressure possibly generates an ion flux across the film/electrolyte interface, resulting in (dis)charge of the PPy similar to the redox process.     

Pulse polymerized polypyrrole electrodes for high energy density electrochemical supercapacitor

A novel method of pulsed polymerization for pyrrole exhibiting highest capacitance and very high energy density polypyrrole supercapacitor is reported. Stable polypyrrole films with good electrochemical reversibility and high doping degree were obtained by applying ultra short on time current pulse for polymerization. Pulse on time plays an important role in controlling chain size and chain defects whereas pulse off time contributes in polymer conjugation and orientation. A regime of pulse on time is identified to yield highly capacitive and stable films for supercapacitor application. Very high specific capacitance of 400 F/g and an unexpectedly high energy density of 250 Wh/kg were obtained form pulsed polymerized ordered polypyrrole structures in acidic electrolyte. Stability tests performed on pulsed polymerized pPy electrode yield long cycling life up to 10,000 cycles at charge/discharge current density of 5 mA/cm².     

Trimethylenemethane: Activation energy for ring-closure of the diradical

The energy of activation for ring-closure of ground state triplet trimethylenemethane (I) to methylenecyclopropane has been measured by following the rate of dissappearance of the electron spin resonance spectrum over the temperature range –155° to –140°, in a series of frozen solid matrices. The experiments described make use of 3-methylenecyclobutanone and methylenecyclopropane as precursors to trimethylene-methane.Kinetic results obtained starting from methylenecyclopropane were most satisfactory and lead to an energy of activation for ring-closure of 7 kcal/mole. This value is significantly smaller than the aprpox. 20 kcal/mole barrier estimated on the basis of theoretical models. Truncation of the barrier by a tunnelling mechanism is made unlikely by the finding that trimethylenemethane-d₆(I-d₆) undergoes ring-closure with the same 7 kcal/mole energy of activation as the parent I.     

聚吡咯的电子能带结构

本文用EHMO方法计算了类苯型,类等键长型及类醌型等聚吡咯的电子能带.分析了原子电荷分布及价带,导带与能隙的宽度,并由此探讨了聚吡咯可能的电导机理.     

导电聚吡咯膜电极的现场电化学-ESR研究

本文报导聚吡咯(PP)膜电极在水溶液中的电化学─ESR行为, 定性地探讨了电位,电量对PP膜中极化学形成与转化过程的影响, 并在PP膜/溶液界面存在电化学反应的情形下, 考察了PP膜中可能的电荷传输机理。     

Raman spectroscopic investigation of film thickness

The determination of film thickness is of prime importance in the quality assurance of coated pharmaceutical preparations. The rapid measurement of this parameter is problematic for multi-particulate pellet systems. The aim of this study was to apply the Raman spectroscopic method for the determination of the thickness of polymer coating on pellets. The change of Raman intensity was compared with measured film thickness, which was calculated from the change of the geometric parameters of the pellets, measured with an image-analyzing system. The results revealed that despite some difficulties Raman spectroscopy is a suitable method for the fast and accurate determination of film thickness on multi-particulate systems.     

Activation of DMSO for Swern-type oxidation by 1,1-dichlorocycloheptatriene

A new dimethylsulfoxide activation method employing 1,1-dichlorocycloheptatriene has been developed for a mild Swern-type oxidation of a variety of alcohols. The carbonyl products can be obtained in good to excellent yields from this operationally simple and efficient method. This work is the first report of dimethylsulfoxide activation by a simple chlorinated hydrocarbon reagent, which has the unique ability of equilibrating to its reactive aromatic cationic form.