Improved lithium exchange at LiFePO4 cathode particles by coating with composite polypyrrole–polyethylene glycol layers

The polypyrrole–LiFePO₄ composites were synthesized by simple chemical oxidative polymerization of pyrrole (Py) monomer directly on the surface of LiFePO₄ particles. Properties of resulting polypyrrole–LiFePO₄ (PPy-LiFePO₄) samples (especially conductivity) are strongly affected by the preparation technique, polymer additives, and conditions during synthesis. For increasing of PPy-LiFePO₄ conductivity, we used polyethylene glycol (PEG) as additive during polymerization. The electrochemical behavior of the samples was examined by cyclic voltammetry and electrochemical impedance spectroscopy. It was found that PPy/PEG composite polymer decreased the particle to particle contact resistance. Impedance measurements showed that the coating of PPy/PEG significantly decreases the charge transfer resistance of LiFePO₄ electrodes.     

Phase equilibria in a polyethylene–polystyrene system

The method of optical interferometry is used to study the interaction of PE with PS in situ. On the basis of the obtained data, phase diagrams of the PE–PS system are constructed for a number of molecular masses of the components. For PE and PS oligomers, the UCMT values are determined. Pair parameters for the interaction of homopolymers are calculated, and their dependences on temperature and molecular mass are considered. The quantitative analysis of the behavior of high-molecular-mass fractions of PE and PS at high temperatures is carried out, and the regions of a partial compatibility of the components are predicted.     

Use of polyethylene glycol in the process of sol–gel encapsulation of Burkholderia cepacia lipase

Lipases from Burkholderia cepacia were encapsulated using polyethylene glycol (PEG, M _w 1500) at various concentrations (0.5–3.0 %, w/v) as an additive during the sol–gel immobilisation process. Matrixes immobilized in the presence and absences of additives were characterized by thermal analysis [thermogravimetric (TG) and differential scanning calorimetry (DSC)], scanning electron microscopy (SEM), enzymatic activity, and total activity recovery yield (Ya). The addition of PEG increased the activity values, with Ya just above 1.0 % (w/v) in the presence of PEG. The additional of 1.0 % (w/v) PEG increased enzyme activity from 33.98 to 89.91 U g^?1 and the values of recovery yield were 43.0–91.4 %, compared to values of the samples without PEG. PEG enhanced the thermal stability of the matrix structure in the temperature range 50–200 °C, as confirmed by TG and DSC analyses. This was influenced by the presence of water bound to the matrix. The SEM micrographs clearly showed an increase in the number of deposits on the material surface, producing matrices with greater porosity.     

Dynamic properties of the polyethylene glycol molecules on the oscillating solid–liquid interface

The dynamic properties of polyethylene glycol (PEG) molecules on the solid–liquid interface oscillating at MHz were investigated using the quartz crystal microbalance (QCM). The number-average molecular weights (M_n) of the PEG molecules were systematically varied over 4 orders of magnitude. This study makes it clear that the series-resonant frequency shift, ΔF, of the QCM against the square root of the density–viscosity product of the PEG solution is linear and has the intercept. Moreover, systematical analysis reveals that the ΔF slope rapidly decreases with M_n and that the ΔF intercept becomes constant above 4.0 × 10³ g mol⁻¹. As a result, those reveal that the resonant length of the PEG molecule moving with the oscillating plate of 9 MHz is 54.2 Å. We also find that the behaviors of ΔF due to M_n are mainly caused by the length of the PEG molecule.     

Fat crystallisation at oil–water interfaces

This review focuses on recent advances in the understanding of lipid crystallisation at or in the vicinity of an interface in emulsified systems and the consequences regarding stability, structure and thermal behaviour. Amphiphilic molecules such as emulsifiers are preferably adsorbed at the interface. Such molecules are known for their ability to interact with triglycerides under certain conditions. In the same manner that inorganic crystals grown on an organic matrix see their nucleation, morphology and structure controlled by the underlying matrix, recent studies report a templating effect linked to the presence of emulsifiers at the oil/water interface. Emulsifiers affect fat crystallisation and fat crystal behaviour in numerous ways, acting as impurities seeding nucleation and, in some cases, retarding or enhancing polymorphic transitions towards more stable forms. This understanding is of crucial importance for the design of stable structures within emulsions, regardless of whether the system is oil or water continuous. In this paper, crystallisation mechanisms are briefly described, as well as recent technical advances that allow the study of crystallisation and crystal forms. Indeed, the study of the interface and of its effect on lipid crystallisation in emulsions has been limited for a long time by the lack of in-situ investigative techniques. This review also highlights reported interfacial effects in food and pharmaceutical emulsion systems. These effects are strongly linked to the presence of emulsifiers at the interface and their effects on crystallisation kinetics, and crystal morphology and stability.     

Molecular electronics at electrode–electrolyte interfaces

Four contemporary examples, all published in recent years, of studies of molecular electronics at electrode–electrolyte interfaces are reviewed in this opinion article. The first illustrative example involves the switching of the redox active molecular wire between redox states, with concomitant changes in molecular conductance. This example illustrates how molecular electronics at electrode–electrolyte interfaces can be used to analyse mechanisms of electron transfer, to distinguish electrolyte effects and to provide details not readily available from ensemble measurements. The second example shows that the fluctuations of molecular conductance of a redox active molecular wire can be followed as a function of electrode potential. This shows how the stochastic kinetics of individual reaction events at electrode–electrolyte interfaces can be followed. The third example demonstrates how electrochemistry can be used to control quantum interference in single molecular wires. The fourth example shows a single-molecule electrochemical transistor concept for well-defined metal cluster containing molecular wires.     

Functional gigaporous polystyrene microspheres facilitating separation of poly(ethylene glycol)–protein conjugate

A novel sulfopropyl gigaporous polystyrene (SP-GP) microsphere enhancing the separation of poly(ethylene glycol)–protein (PEGylated protein) was first presented. The SP-GP microspheres were successfully prepared by introducing sulfopropyl groups into agarose-coated gigaporous polystyrene microspheres and used as chromatography media. Compared with a commercial medium, SP-GP microspheres exhibited improved column efficiency and reduced backpressure with increasing flow velocity, which could ensure its use in high-speed chromatography. Furthermore, a higher protein recovery and purity of the PEGylated protein could be obtained, even when SP-GP was applied at a flow velocity of 1224 cm h⁻¹. Additionally, the dynamic binding capacity (DBC) of SP-GP was significantly improved, which was higher than 10 mg mL⁻¹ medium even at a flow velocity of 306 cm h⁻¹. Further investigation using a laser scanning confocal microscope (LSCM) demonstrated that the static adsorption equilibrium of the PEGylated protein on SP-GP could be completed in 5 min, whereas a much longer period (ca. 60 min) was required for the commercial medium, indicating that the mass transfer of SP-GP was much faster with the gigaporous structure. All of these results strongly support that our developed SP-GP could serve as a promising cation exchange chromatography resin for high-speed separation, especially for biomolecules of high molecular weight.     

Rheological characterization of polyvinyl caprolactam–polyvinyl acetate–polyethylene glycol graft copolymer (Soluplus®) water dispersions

Soluplus® is a graft copolymer, with PEG and vinylcaprolactam/vinyl acetate side chains, recently available as excipient used to promote fast drug release in pharmaceutical dosage forms and as solubility enhancer. Despite this copolymer is reported to be able to act as a thickening additive and even as gelling agent as a function of temperature, there is a lack of information about the physical–chemical properties of its water dispersions. Thus, the aim of this paper is to investigate the influence of Soluplus® concentration and experimental temperature on the modification of the rheological properties of Soluplus® water dispersions. The results clearly indicated the influence of both the studied parameters and of their interactions on the Soluplus® thickening ability. Although some systems appear gel by human perception at 37 °C, the mechanical spectra demonstrated the lack of the formation of a tridimensional network structure. Overall, in all the analyzed temperatures and concentrations, the systems always behave as a “rheological” dilute or semidilute polymer solution.     

Measuring the optical chirality of molecular aggregates at liquid–liquid interfaces

Some new experimental methods for measuring the optical chirality of molecular aggregates formed at liquid–liquid interfaces have been reviewed. Chirality measurements of interfacial aggregates are highly important not only in analytical spectroscopy but also in biochemistry and surface nanochemistry. Among these methods, a centrifugal liquid membrane method was shown to be a highly versatile method for measuring the optical chirality of the liquid–liquid interface when used in combination with a commercially available circular dichroism (CD) spectropolarimeter, provided that the interfacial aggregate exhibited a large molar absorptivity. Therefore, porphyrin and phthalocyanine were used as chromophoric probes of the chirality of itself or guest molecules at the interface. A microscopic CD method was also demonstrated for the measurement of a small region of a film or a sheet sample. In addition, second-harmonic generation and Raman scattering methods were reviewed as promising methods for detecting interfacial optical molecules and measuring bond distortions of chiral molecules, respectively.     

Interfacial activity of particles at PI/PDMS and PI/PIB interfaces: analysis based on Girifalco–Good theory

Particles that are partially wetted by oil and water are known to adsorb at oil/water interfaces. By the same mechanism, particles that are partially wetted by two immiscible polymers should adsorb at the interface between those two polymers. However, since chemical differences between immiscible polymers are relatively modest, particle adsorption at polymer/polymer interfaces may be expected to be relatively uncommon. We have conducted experiments with several particle types added to two pairs of model polymers, polyisoprene/polydimethylsiloxane and polyisoprene/polyisobutylene. Contrary to our expectation, in every case, particles readily adsorbed at the polymer/polymer interfaces. We evaluated the Girifalco–Good theory as a means to predict the interfacial activity of the particles. The solid surface energy required by the Girifalco–Good theory was assumed to be equal to the critical surface tension, which was then found by float/sink tests. Our results suggest that this approach is not able to predict the observed interfacial activity of particles at polymer/polymer interfaces.     

In situ formation of polyethylene glycol–titanium complexes as solvent-free electrolytes for electrochromic device application

Transparent and ionic conductive polymeric electrolytes have been prepared through sol–gel method by adding titanium isopropoxide into an acidic polyethylene glycol (PEG) solution. After hydrolysis and condensation processes, new associations between titanium cations and ether oxygen atoms of PEG have been formed according to Fourier-transform infrared spectroscopy. Thermogravimetric analysis results of these hybrid materials indicate a better thermal stability with a less polydispersion of the molecular mass distribution in comparison with PEG. For the purpose of electrochromic or photoelectrochromic device applications, LiI was added into the hybrid materials to form solvent-free polymeric electrolytes. Optical transmittance spectra of these electrolytes show a red shift of the cutoff wavelength as a function of titanium isopropoxide percentage in the original sol–gel solutions. It is also observed that the amount of hydroxyl groups in the hybrid materials was reduced in comparison with the PEG one. This makes electrical conductivity of the hybrid electrolytes with LiI salt insensitive to humidity and solvents, which was about 2 × 10^-4 Ω⁻¹ cm⁻¹ at room temperature. A solid WO₃-based electrochromic device with the hybrid electrolyte keeps the same optical transmittance value after 1,000 cycles of switching polarization potentials between −1 and +1 V.     

Controlled preparation of core–shell polystyrene/polypyrrole nanocomposite particles by a swelling–diffusion–interfacial polymerization method

Polystyrene/polypyrrole (PS/PPy) core–shell nanocomposite particles with uniform and tailored morphology have been successfully synthesized using the “naked” PS particulate substrate with the aid of a proposed strategy, the so-called swelling–diffusion–interfacial polymerization method. After initially forming pyrrole-swollen PS particles, diffusion of the monomer toward the aqueous phase was controlled through the addition of hydrochloric acid, eventually leading to its polymerization on the substrate particle surface. This process allows the nanocomposite particles to possess uniform and intact PPy overlayer and affords much more effective control over the structure and morphology of the resultant nanocomposites by simply changing the PS/pyrrole weight ratio or the addition amount of the doping acid. In particular, the nanocomposite particles with a thin, uniform, and intact PPy overlayer and their corresponding PPy hollow particles were obtained at a low addition amount of pyrrole. The resultant nanocomposite particles have been extensively characterized using scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetry.     

Poly(styrene-b-ethylene oxide) copolymers as stabilizers for the synthesis of silica–polystyrene core–shell particles

Following previous works [1, 2], silica–polystyrene core–shell particles have been synthesized by dispersion polymerization of styrene in an ethanol/water mixture in the presence of a poly(styrene-b-ethylene oxide) block copolymer as stabilizer. Besides the formation of composite core–shell particles, a large number of free latex particles that do not contain silica were also formed. This number decreases as the size of the silica beads decreases from 300 to 29 nm in diameter, and becomes very low compared to the number of composite particles for the smallest silica beads used. In every case, the composite particles could be easily separated from the free latex particles by centrifugation, providing a material made of regular core–shell composite particles. On the basis of the mechanisms involved in dispersion polymerization, hypotheses were formulated to account for the formation of the silica–polystyrene composite particles. Received: 6 May 1999 Accepted in revised form: 29 June 1999     

Electrosynthesis of polyphenylpyrrole coated silver particles at a liquid–liquid interface

This communication reports the production of polyphenylpyrrole coated silver nanoparticles at the liquid/liquid interface by an EC-type mechanism. In the electrochemical step of the reaction N-phenylpyrrole facilitates the transfer of the silver ion from an aqueous to an organic phase. This step is followed by a slow homogeneous electron transfer reaction from the N-phenylpyrrole to the silver ion followed by polymerization and metal cluster growth.     

Enhanced CO2 electrolysis at metal–oxide interfaces

Journal of Solid State Electrochemistry - The catalytic reduction of CO2 to CO using solid oxide electrolytic cells (SOECs) is considered as a sustainable solution to simultaneously remove...     

Synthesis of ZnO–SnO2 nanocomposites: impact of polyethylene glycol on morphological,luminescence and photocatalytic properties

Research on Chemical Intermediates - Zinc oxide-doped tin dioxide (ZnO–SnO2) nanomaterials were prepared by a sol–gel method with and without different amounts (0.5, 1.0 and...     

Fabrication of rod-shaped β-FeOOH: the roles of polyethylene glycol and chlorine anion

β-FeOOH nanorods of 40 nm wide and 450 nm long were fabricated through precisely regulating the hydrolysis kinetics of Fe~(3+) in polyethylene glycol and the concentration of Cl~- as the structure-directing agent. Detailed structural and chemical analyses of the intermediates during the synthesis identified that the strong interaction between PEG and Fe~(3+) modulated the hydrolysis kinetics of Fe~(3+) and prevented the aggregation of β-FeOOH nanorods; while Cl~- provided sufficient nucleation sites, stabilized the hollow channel of β-FeOOH, and more importantly induced the growth of the nanorods along [001] direction.     

Extraction–thermal lens quantification of cobalt with Nitroso-R-Salt in two-phase aqueous systems with water-soluble polymer polyethylene glycol

A novel method is proposed for the extraction-thermal lens quantification of cobalt with Nitroso-R-Salt based on the distribution of the colored complex in a two-phase aqueous system on the basis of poly-ethylene glycol (PEG) and an ammonium sulfate solution followed by its thermal lens detection in the extract. The limit of detection is 0.3 μM (20 ng/mL); the lower limit of the analytical range is 0.7 μM (40 ng/mL); the relative standard deviation for the concentrations 1–50 μM makes 1–3% (n = 6, P = 0.95). In the determination of cobalt by spectrophotometry under the same conditions, the detection limit is 10 μM (0.6 μg/mL) and the lower limit of the analytical range is 40 μM (2.5 μg/mL). The precision of thermal lens measurements in PEG solutions is higher in comparison to that in aqueous ones because of the weaker interference of convection in aqueous solutions of PEG.     

Transition behaviors and hybrid nanofibers of poly(vinyl alcohol) and polyethylene glycol–POSS telechelic blends

We report solution properties of the blend solutions of poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG)–POSS telechelic and its corresponding hybrid nanofibers prepared by electrospinning. The morphologies, microstructures, and wettability of the resulting PVA/PEG3.4k–POSS hybrid nanofibers are studied. The morphologies of the resultant PVA/PEG3.4k–POSS nanofibers are regular with the fiber diameter ranging from 610 ± 110 to 810 ± 280 nm. When the content of PEG3.4k–POSS telechelic increases above 20 wt.%, the beaded fiber morphologies are observed due to severe aggregations of the PEG3.4k–POSS telechelics as well as increased viscosity at higher concentration. In addition, the solution properties of pure PEG3.4k–POSS telechelic solution (ca. 3–5 wt.%) and PVA/PEG3.4k–POSS solutions blended with PVA are explored, and found to show the reversible turbid-to-transparent transition behavior with respect to the solution temperature. Water contact angle measurement of the PVA/PEG3.4k–POSS nanofiber membranes demonstrates an enhanced hydrophobic nature due to the incorporated POSS moieties.