In situ infrared spectroscopic and scanning Kelvin probe measurements of water and ion transport at polymer/metal interfaces

Scanning ATR-spectroscopy and scanning Kelvin probe studies are introduced as new analysis techniques for the study of water and ion transport at polymer/metal interfaces. The new approach of scanning ATR spectroscopic analysis of water transport at the adhesive/metal interface is combined with scanning measurements in transmission mode of water transport along adhesive joints and non-scanning ATR-measurements of the water transport in a vertical direction through the adhesive. D₂O was chosen in some cases instead of water due to its excellent traceability in the infrared spectra. A scanning Kelvin probe was chosen for the detection of the transport kinetics of hydrated alkali ions along the adhesive/metal interface based on the local measurement of interfacial electrode potentials.The complimentary FT-IR techniques showed that the interfacial diffusion of water, in the case of epoxy adhesives on iron, is about two orders of magnitude faster that the transport through the adhesive itself. Similar transport kinetics at the interface is also shown by hydrated ions. Moreover, the here presented FT-IR-ATR and SKP results reveal more information on how adhesion promoting organosilane layers and organosilanes as additives act at polymer/metal interfaces in the presence of water incorporated in the interphase zone.     

Heterogeneous hydrogen evolution on corroding Fe-3 at.% Si surface observed by scanning electrochemical microscopy

Corrosion behavior of Fe-3 at.% Si alloy in 0.01 mol dm⁻³ HCl solution was investigated by using scanning electrochemical microscopy (SECM) as well as general electrochemistry. The rate of corrosion coupled with hydrogen evolution was initially 0.44 A m⁻² but decreased significantly with time. Localized hydrogen evolution on the specimen surface was probed by an SECM system in which a force sensor was mounted to determine the probe height from the specimen surface. SECM images revealed that hydrogen evolution took place heterogeneously on the specimen surface depending on crystallographic orientation of substrate single grains in the initial stage and then became relatively homogeneous. Finally, a heterogeneous hydrogen distribution corresponding to the appearance of localized corrosion sites was observed.     

反应型荧光探针在检测金属离子中的研究进展

金属离子广泛存在于自然界中,与环境科学、生命科学、医学等领域有着密切的联系。一些金属离子如Hg²⁺、Fe³⁺、Cu²⁺、Zn²⁺、Al³⁺等,在生物体的生理和病理中扮演着重要角色,摄入过量或不足都会导致生理功能的紊乱,引发各种疾病。近几年来,反应型荧光探针因其高选择性和高灵敏性的特点得到了快速的发展。本文主要综述了近五年来反应型荧光探针在检测金属离子中的研究进展,主要介绍了各类探针分子的设计合成、传感机理、检测结果以及其在生物检测中的应用。指出反应型荧光探针的研究发展还处在初级阶段,该领域将会朝着灵敏度更高、反应时间更少、应用范围更广的方向发展,此外,反应型荧光探针在生物检测以及实际应用方面也有望得到进一步的应用发展。     

Dispersive forces of particle–surface interactions: direct AFM measurements and modelling

Fundamentals of particle–particle interaction are of great interest in agglomeration processes. Particle adhesion depends on dispersive forces (van der Waals force), local chemical bindings, Coulomb force and capillary attractions. Additionally, surface properties like roughness, adsorption layers and surface chemistry strongly affect adhesion forces. van der Waals interactions are poorly understood because popular ab initio force calculations for molecules like density functional theory (DFT) often do not lead to proper results. van der Waals forces are difficult to measure directly. We present direct measurements of particle–particle and particle–surface interactions in the gas phase carried out with an atomic force microscope (AFM). Special emphasis is given to a proper statistical treatment of the data. For modelling of particle adhesion, we use computer-assisted empirical potential methods. Parameters like adsorbed water and surface roughness are considered. We extract parameters for weak interactions from the Lifshitz theory and gas adsorption data. Adsorbing molecules can be used as probes to measure dispersive forces. Studying surface and particle properties combined with computer-assisted modelling is a basic requisite to reach the aim of predicting particle–particle interactions in industrial processes.     

pH responsive alginate polymeric rafts for controlled drug release by using box behnken response surface design

Aim of the present work was to develop alginate raft forming tablets for controlled release pantoprazole sodium sesquihydrate (PSS). Box behnken design was used to optimize 15 formulations with three independent and three dependent variables. Physical tests of all formulations were within pharmacopoeial limits. Raft was characterized by their strength, thickness, resilience, acid neutralizing capacity, floating lag time and total floating time. Raft strength, thickness and resilience of optimized formulation AR9 were 7.43 ± 0.019 g, 5.8 ± 0.245 cm and greater than 480 min, respectively. Buffering and neutralizing capacity were 11.2 ± 1.01 and 6.5 ± 0.56 meq, respectively. Dissolution studies were performed by using simulated gastric fluid pH 1.2 and cumulative percentage release of optimized formulation AR9 was found 98%. First order release kinetics were followed and non-fickian diffusion was observed as value of n was greater than 0.45 in korsmeyer-peppas model. PSS, polymers, tablets and rafts were further characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and differential scanning calorimetry (DSC). FTIR spectra of PSS, polymers and raft of optimized formulation AR9 showed peaks at 3223.09, 1688.17, 1586.67, 1302.64 and 1027.74 cm^?1 due to –OH stretching, ester carbonyl group (C=O) stretching, existence of water and carboxylic group in raft, C–N stretching and –OH bending vibration showed no interaction between them. XRD showed diffraction lines indicates crystalline nature of PSS. DSC thermogram showed endothermic peaks at 250 °C for PSS. The developed raft was suitable for controlled release delivery of PSS.     

Electrochemical oxidation of organic pollutants in water at metal oxide electrodes: A simple theoretical model including direct and indirect oxidation processes at the anodic surface

The electrochemical oxidation of organics in water at metal oxide electrodes was investigated with the aim to discuss the correlations between the instantaneous current efficiency ICE and operative conditions by considering both the hypothesis of a direct oxidation process and of an indirect process mediated by adsorbed hydroxyl radicals or chemisorbed “oxygen”, in order to explicit the main differences expected between these cases. Thus, a simple theoretical model was discussed, as an extension of previous studies of Comnnellis and co-workers which were focused on indirect oxidation paths [C. Comninellis, Electrochim. Acta 39 (1994) 1857; O. Simond, V. Schaller, Ch. Comninellis, Electrochim. Acta, 42 (1997) 2009], concerning both the cases of mass transfer control and oxidation reaction control and mixed kinetic regimes. A very good agreement, between theoretical predictions and experimental data pertaining to the electrochemical oxidation of oxalic and formic acid at IrO₂–Ta₂O₅, was observed.     

Infrared spectrometric studies of the surface basicity of metal oxides and zeolites using adsorbed probe molecules

Infrared spectra analysis of species formed by acid probe adsorption on divided metal oxides and alkaline zeolites can lead to information on their surface basicity, particularly on the nature and strength of basic sites. Results obtained from carbon monoxide, carbon dioxide, sulfur dioxide, pyrrole, chloroform, acetonitrile, alcohols, thiols, boric acid trimethyl ether, ammonia and pyridine are critically reviewed. It is concluded that no probe can be universally used. Pyrrole in the case of alkaline zeolites, CO₂ for weakly basic metal oxides and for basic OH groups and CO for the characterization of highly basic structural defects on metal oxides activated at high temperature appear quite suitable probes. When other methods are used (TPD, microcalorimetry, volumetry, etc.) IR spectroscopy is a complementary method necessary for the knowledge of the type of sites involved; in particular, data obtained from CO₂ and SO₂ adsorption have to be carefully used since both probes can lead on highly basic metal oxides to polydentate (bulk) species which do not result from their adsorption but from their reaction with the given oxide. Ammonia and pyridine, generally used as probes for the measure of the acidity of catalysts, also adsorb on basic oxides through a dissociative chemisorption.     

Correction for wall effect in point probe measurements of bubble size

During the measurement of bubble size by a probe inserted into a fluidized bed, parts of some of the bubbles located near the bed boundary are not accessible to the probe. This effect is analyzed theoretically using considerations of geometry and probability and results are given which may be used to correct experimental probe measurements of bubble size for the boundary effect. The procedure is demonstrated using electroresistivity probe measurements taken on a 2 ft-dia. bed of fluidized coke particles.     

Application of polyethyleneimine-quinone modified electrodes for voltammetric measurements of pH

A modified polymer, ie benzylated polyethyleneimine (PEI), coated on a glassy carbon electrode in which negatively charged quinones have been incorporated, has been used for voltammetric measurement of pH. A linear dependence of the average of the peak potentials as a function of pH was observed. The system has been successfully applied also to ultramicroelectrodes.     

A fluorescence resonance energy transfer probe for sensing pH in aqueous solution

A fluorescence resonance energy transfer (FRET) sensor, which has a FRET donor and an acceptor attached to each chain end of pH-sensitive polysulfonamide, is synthesized and its pH sensitivity is examined in terms of the FRET efficiency. This polymeric sensor exhibits an instantaneous conformation change from coil to globule at a specific pH, which results in the drastic on-and-off FRET efficiency. To detect a specific pH region, sulfadimethoxine and sulfamethizole are selected among various sulfonamides since their pK_a values are in the physiological pH. For tuning the emission color arising from FRET, 7-hydroxy-4-bromomethyl coumarin and coumarin 343 are used as a FRET donor and an acceptor, respectively, for a blue-to-green FRET sensor, and fluorescence amine isomer I and rhodamine B are used for a green-to-red FRET sensor. Each sensor shows a distinct color change from the emission wavelength of FRET donor to the emission wavelength of FRET acceptor, which well explains their feasibility as a useful optical sensor.     

Influence of heavy metal contaminants at variable pH regimes on rheological behaviour of bentonite

Long-term competent performances of clays as barrier and liner systems for waste landfills are dependent on both the physico-mechanical properties and attenuation characteristics of the clay soils. The presence of heavy metal ions in the pore water will alter the physico-chemical characteristics of the clay–water system, resulting in changes in the short- and long-term mechanical and chemical behaviour of the clay soil barrier materials. This study investigates bentonite–contaminant interaction at different pH levels and heavy metal ion concentrations, and their resultant effect on the mechanical behaviour of bentonite soil. A set of physico-chemical experiments including Atterberg limits, precipitation testing, pH measurement and consolidation were performed to investigate the fundamental mechanism of soil–contaminant interaction from a rheological point of view. Consolidation tests were performed to study volume change behaviour with respect to the control exercised by mechanical and osmotic stresses. The impact of multiple aspects of heavy metal ion interaction on the osmotic compressibility and consolidation of bentonite is investigated. It is shown that while the selectivity phenomenon governs the adsorption characteristics of contaminated bentonite, the microstructural change due to the lower pH level and the high concentration of HMs, the different onset of precipitation for Zn and Pb, and the osmotic phenomenon control the rheological performance of compacted bentonite. The theoretical aspect of the experimental investigation is addressed and the restrictions of classical double layer theory for heavy metal/clay soils interaction are illustrated.     

A probabilistic model for correcting the directional sensitivity of optical probe measurements

A probabilistic model is introduced for correcting the directional sensitivity of the optical probe technique routinely used to determine gas holdup and bubble dynamics in gas‐liquid systems. Measurements from optical probes oriented at various angles were collected from the tapered end of optical probes in regions where approximately unidirectional and bubbly flow conditions were observed. Based on logical assumptions, constitutive equations for a probabilistic model were formulated, and contributions to the overall local gas phase holdup from bubbles traveling in two opposite directions were quantified. The results demonstrate a novel and useful way to interpret optical probe measurements. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3516–3527, 2015     

Development of an activity-based probe for autotaxin

Autotaxin (ATX), or ecto-nucleotide pyrophosphatase/phosphodiesterase 2 (ENPP2), is a secreted lysophospholipase D that hydrolyses lysophosphatidylcholine into the lipid mediator lysophosphatidic acid (LPA), a mitogen and chemoattractant for many cell types. ATX has been implicated in tumour progression and inflammation, and might serve as a biomarker. Here we describe the development of a fluorescent activity-based probe that covalently binds to the active site of ATX. The probe consists of a lysophospholipid-based backbone linked to a trapping moiety that becomes reactive after phosphate ester hydrolysis, and a Cy5 fluorescent dye to allow visualisation of active ATX. The probe reacts specifically with the three known isoforms of ATX, it competes with small-molecule inhibitors for binding to ATX and allows ATX activity in plasma to be determined. Our activity-based reporter will be useful for monitoring ATX activity in biological fluids and for inhibitor screening.     

Melting behavior of solid polymers on a metal surface at processing conditions

The melting or plasticating behavior of seven commercial polymers (high density polyethylene, low density polyethylene, polypropylene, polyoxymethylene copolymer, polystyrene, poly(methyl methacrylate), and polycarbonate (PC) was investigated using an experimental apparatus specifically designed to measure the melting rate and the viscous shear stress of a solid polymer on a steel surface under precisely controlled conditions of temperature, velocity, pressure and sample width comparable to actual processing. The melting rate (per unit polymer solid/metal contact area) was found to increase with increasing temperature for all polymers except PC, to decrease with increasing sample width and to increase less than proportionally to velocity. Pressure increased the melting rate somewhat for most of the polymers. The viscous shear stress decreased with increasing temperature for all polymers except PC, decreased with increasing sample width and increased with increasing velocity. Pressure generally increased the viscous shear stress. PC showed an unusual behavior with a maximum in the melting rate near 4200°F(215.5°C) and also a maximum in the viscous shear stress near 445°F (229.4°C). The present melting model could be examined unequivocally for the first time using our experimental results. Comparison of our experimental results with the predictions of the present melting model clearly indicates the inadequacy of the present melting model, Our experimental results will provide a basis for rational development of a reliable melting model.     

Frictional behavior of solid polymers on a metal surface at processing conditions

The frictional coefficients of three glassy polymers (polystyrene, polycarbonate, and polymethylmethacrylate) and three crystalline polymers (high density polyethylene, low density polyethylene and polypropylene) on a highly polished steel surface were measured at high temperatures, high pressures, and high speeds, all comparable to actual processing conditions. The frictional behavior of these polymers was found to depend on temperature, pressure-and speed in a very complicated manner. There appears to exist inter-relationships among the temperature, pressure and speed dependences of the frictional coefficients. The frictional coefficients of ductile, crystalline polymers as a function of temperature appear to undergo two distinct transitions: one associated with yielding and the other associated with melting. The frictional coefficients of glassy polymers go through only one transition, associated with the glass transition. The friction-generated heat at high pressures and high speeds can increase the sliding interface temperature of a polymer to values much greater than the metal surface temperature, and thus the polymer can start to melt (or plasticate) at metal surface temperatures appreciably below its thermodynamic melting (or glass transition) temperature.     

A direct method for calculating ternary vapor compositions from total-pressure measurements

Ternary vapor compositions have been successfully calculated from total-pressure measurements for four systems by means of a modified direct method, which involves the previously proposed concept of hypothetical binary mixtures, and permits the numerical integration using a simple P-x relationship. The results of the systems tested further indicate that the ternary y values predicted from only binary P-x data are not significantly different from the y values obtained when binary together with ternary P-x values were used in the calculation, provided that the initial fit of binary P-x data is successful.