Structure of poly(vinyl pyrrolidone) - C70 complexes in aqueous solutions

Aqueous solutions of poly(vinyl pyrrolidone)-fullerene complexes, PVP/C₇₀, have been studied using static and dynamic light scattering. Two diffusive processes were observed. The slow diffusion describes the motion of large PVP/C₇₀ clusters, whereas the fast diffusion is associated with the presence of single PVP molecules or small individual PVP/C₇₀ complexes of the order of a single PVP chain. The molar mass and the size of the PVP/C₇₀ clusters increase upon increasing the fullerene content. However, when the fullerene content is kept constant, an increase in the molar mass of the matrix PVP does not influence the mass and the size of the clusters. Dilution of the PVP/C₇₀ solutions has no effect on the clusters either. In PVP/C₇₀ there is a specific molar ratio of C₇₀ per repeating units of PVP that is same for all the samples studied.     

Static and dynamic light scattering study of strong intermolecular interactions in aqueous solutions of PVP/C60 complexes

The investigations of the dilute aqueous solutions of polyvinylpyrrolidone/fullerene (PVP/C₆₀) complexes by static (SLS) and dynamic (DLS) light scattering showed that strong intermolecular interactions, effective on the distances of about 45-50 nm, take place in the solutions. Two concentration ranges are well distinguished in these solutions. Above a critical concentration (c_cr) the fluctuations in the solutions are hindered and only one, diffusive, mode is observed in DLS experiments. Upon dilution (c<c_cr) this unified structure divides into large fragments (domains) and the slow mode attributed to long-range concentration fluctuations, gradually appears. The angular and concentration dependencies of the diffusion coefficient of the slow mode indicate the existence of strong intermolecular interactions.     

Dielectric dispersion study of coexisting phases of aqueous polymeric solution: Poly(vinyl alcohol) + poly(vinyl pyrrolidone) two-phase systems

The complex dielectric constant ?^∗(ω)=?^′−j?^″, electric modulus M^∗(ω)=M^′+jM^″, impedance Z^∗(ω)=Z^′−jZ^″ and ac conductivity dispersion behaviour of 5, 10 and 15 wt% concentration aqueous solutions of poly(vinyl alcohol) (PVA) (14?000 and 77?000 g mol⁻¹) and poly(vinyl pyrrolidone) (PVP) (24?000, 40?000 and 360?000 g mol⁻¹) and their binary mixtures were investigated in the frequency range 20 Hz to 1 MHz at 25 °C. Analysis of dielectric constant values confirms that hydrophilic effect of PVA in aqueous solution increases the real part of dielectric constant ?′, whereas for aqueous PVP solutions the hydrophobic effect masks the hydrophilic effect, which reduces ?′ values below 10 kHz. Low-frequency dielectric constant of these aqueous polymeric systems is sensitive to ionic conduction and electrode polarization. The monotonous change in various electrical properties with change in volume percentage of mixture constituents indicates that individual aqueous polymer system retains their own electrical properties in the aqueous two-phase polymeric system.     

TEM investigation of MnO2 cathode containing TiS2 and its influence in aqueous lithium secondary battery

The discharge characteristics of manganese dioxide (MnO₂) cathode in the presence of small amounts (1, 3 and 5 wt.%) of TiS₂ additive has been investigated in an alkaline cell using aqueous lithium hydroxide as the electrolyte. The incorporation of small amounts of TiS₂ additives into MnO₂ was found to improve the battery discharge capacity from 150 to 270 mAh/g. However, increasing the additive from 3 to 5 wt.% causes a decrease in the discharge capacity. Hence, the objective is to gain insight into the role of TiS₂ on the discharge characteristics of MnO₂ and its mechanism. For this purpose, we have used transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) techniques.     

Fabrication of membranes of polyethersulfone and poly(N‐vinyl pyrrolidone): influence of glycerol on processing and transport properties

In this study, we focus on membranes of polyethersulfone and poly(N‐vinyl pyrrolidone) and elucidate the influence of composition on the rheological, diffusion and precipitation properties of solutions which are used for membrane preparation via a non‐solvent‐induced phase separation process. The low‐molar‐mass component of the solution is a mixture of the solvent N‐methyl‐2‐pyrrolidone and the non‐solvent glycerol. Cloud point, viscosity and diffusion measurements as well as precipitation experiments were performed in order to achieve a comprehensive understanding of the time dependence of the precipitation process. The addition of glycerol yields an increase of viscosity and a stronger tendency for demixing. The enhanced tendency for demixing causes a more rapid precipitation process. The average relaxation time of the solution as a function of glycerol concentration follows a similar trend to its viscosity. The increase of viscosity is associated with the increase of the monomeric friction coefficient. Two diffusive processes with clearly separated time scales appear in dynamic light scattering experiments in the presence of glycerol. This phenomenon is discussed taking into account the phase behaviour of the solution and the quality of the solvent. The addition of glycerol yields a lower pure water permeance whereas the molecular weight cut‐off is not altered in the ultrafiltration range. © 2020 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Theoretical investigation of catalytic HCO3 hydrogenation in aqueous solutions

Density functional theory along with a dielectric continuum solvation model has been applied to identify possible reaction intermediates for the catalytic hydrogenation of HCO₃⁻ anion into HCO₂⁻ that occurs in aqueous solutions in the presence of water-soluble ruthenium complexes. Bicarbonate ion is shown to coordinate to a Ru-dihydride species, which then undergoes a protonation process that yields a CO₂ complex. The CH bond formation is found to take place via CO₂ insertion into a RuH bond and the direct elimination of the formate product is shown to be an energetically favored step, which is assisted by the water medium. We find that water is directly involved in the reaction as a protonating/deprotonating agent and also acts as a coordinating ligand.     

Template-free fabrication of fullerene (C60, C70) nanometer-sized hollow spheres under solvothermal conditions

Fullerene (C₆₀, C₇₀) hollow spheres were fabricated by controlled oxidation of fullerene monoanions under solvothermal conditions. Scanning electron microscope and transmission electron microscope showed the uniform size and the hollow nature of the spheres. Matrix-assisted laser desorption ionization time-of-flight mass spectrum and Raman spectroscopy proved that the hollow spheres are mainly composed of pristine fullerene. An Ostwald ripening mechanism is proposed.     

Molecular diffusion in ternary poly(vinyl alcohol) solutions

The diffusion kinetics of a molecular probe—rhodamine B—in ternary aqueous solutions containing poly(vinyl alcohol), glycerol, and surfactants was investigated using fluorescence correlation spectroscopy and dynamic light scattering. We show that the diffusion characteristics of rhodamine B in such complex systems is determined by a synergistic effect of molecular crowding and intermolecular interactions between chemical species. The presence of glycerol has no noticeable impact on rhodamine B diffusion at low concentration, but significantly slows down the diffusion of rhodamine B above 3.9% (w/v) due to a dominating steric inhibition effect. Furthermore, introducing surfactants (cationic/nonionic/anionic) to the system results in a decreased diffusion coefficient of the molecular probe. In solutions containing nonionic surfactant, this can be explained by an increased crowding effect. For ternary poly(vinyl alcohol) solutions containing cationic or anionic surfactant, surfactant–polymer and surfactant–rhodamine B interactions alongside the crowding effect of the molecules slow down the overall diffusivity of rhodamine B. The results advance our insight of molecular migration in a broad range of industrial complex formulations that incorporate multiple compounds, and highlight the importance of selecting the appropriate additives and surfactants in formulated products.     

Thermodynamic parameters of poly(lactic acid) solutions in dialkyl phthalate

Some of thermodynamic parameters for poly(lactic acid) (PLA)/dialkyl phthalate systems have been investigated. Both poly(dl-lactic acid) (PDLLA) and poly(l-lactic acid) (PLLA), which are stereoisomers of PLA, were used and a series of 1,2-dialkyl phthalates with different alkyl chain, from methyl to hexyl, was adopted as a solvent. Theta temperatures of PLA/dialkyl phthalate system were determined and subsequently the second virial coefficient and the interaction parameter were evaluated. Theta temperature was determined by the extrapolation of the highest liquid-liquid phase separation temperatures and Zimm plots were constructed by static light scattering to obtain second virial coefficient and z-average radius of gyration. Second virial coefficient and z-average radius of gyration was examined quantitatively as a function of temperature and solvent. Thermodynamic parameters that could not be obtained experimentally were calculated based on the Flory-Huggins theory.     

Polymeric fullerene oxide (fullerene ozopolymers) produced by prolonged ozonation of C60 and C70 fullerenes

The prolonged ozonation of C₆₀ and C₇₀ fullerene produces light brown to brown amorphous solids which are insoluble in chlorinated and hydrocarbon solvents but which are readily soluble in water, acetone and ethanol where they give dark-brown solutions. The polymeric and polyelectrolytic nature of these solids has been shown by viscosimetric and cryoscopic measurements. Due to the polymeric nature the solids have been called ‘ozopolymers’. The reactivity and the ozone uptake have been measured quantitatively during the ozonation of C₆₀ and C₇₀ fullerene in CCl₄. Three different C₆₀ ozopolymer samples have been produced at different degrees of ozonation: at O₃/C₆₀ molar ratio of 8, 14 and 26. The C₇₀ ozopolymer has been produced at an O₃/C₇₀ molar ratio of 30. All the samples have been studied by FT-IR spectroscopy and the C₆₀ ozopolymers have been easily reduced by the action of Zn dust and acetic acid or by the action of H₂S and studied by FT-IR. The action of oxidizing agents has been studied as well. C₆₀ ozopolymer is a polyelectrolyte rich in carboxyl groups and for this reason it possesses a high metal binding capacity similar to that of humic acids. The thermal stability of C₆₀ ozopolymer and its reduced derivatives as well as the thermal stability of C₇₀ ozopolymer has been checked by thermogravimetric analysis in nitrogen and air flow. Finally, the electrical conductivity of C₆₀ ozopolymer was found to be σ=2.8×10⁻⁸ S/cm which is three orders of magnitude lower than that of pure C₆₀.     

Effect of Poly(vinyl pyrrolidone) on Antifouling Properties of Asymmetric Poly(ethylene‐co‐vinyl alcohol) Membranes

Poly(ethylene‐co‐vinyl alcohol)/poly(vinyl pyrrolidone) (EVAL/PVP) blend membranes with antifouling properties were prepared by nonsolvent induced phase separation. Residual PVP in the sample was calculated by infrared spectroscopic data and confirmed by thermogravimetric analysis. The effect of residual PVP on hydrophilicity and permeation characteristics of the membranes was evaluated. Porosity and equilibrium water content of the membranes were influenced by the addition of PVP. The effect of protein fouling on flux using bovine serum albumin as a model system was studied in detail. The residual PVP content could enhance the antifouling property of the membrane. All membranes proved to have sufficient mechanical strength to withstand pressure‐driven filtrations.     

A novel LiTi2(PO4)3/MnO2 hybrid supercapacitor in lithium sulfate aqueous electrolyte

In this work, carbon-coated lithium-ion intercalated compound LiTi₂(PO₄)₃ and MnO₂ have been synthesized and they deliver a capacity of 90 and 60 mAh/g in 1 M Li₂SO₄ neutral aqueous electrolyte within safe potentials without O₂ and H₂ evolution, respectively. The novel hybrid supercapacitor in which MnO₂ was used as a positive electrode and carbon-coated LiTi₂(PO₄)₃ as a negative electrode was assembled and the LiTi₂(PO₄)₃/MnO₂ hybrid supercapacitor showed a sloping voltage profile from 0.7 to 1.9 V, at an average voltage near 1.3 V, and delivers a capacity of 36 mAh/g and an energy density of 47 Wh/kg based on the total weight of the active electrode materials. It exhibits a desirable profile and maintains over 80% of its initial energy density after 1000 cycles. The hybrid supercapacitor also exhibit an excellent rate capability, even at a power density of 1000 W/kg, it has a specific energy 25 Wh/kg compared with 43 Wh/kg at the power density about 200 W/kg.     

Corrosion of Si3N4-ceramics in aqueous solutions Part I: Characterisation of starting materials and corrosion in 1 N H2SO4

The corrosion behaviour of silicon nitride materials in acids strongly depends on the composition and amount of the grain boundary. But there exist no systematic investigations of the relation between the corrosion behaviour and the composition and amount of the grain-boundary phase. The aim of the series of these papers is the systematic investigation of these relations. In the first part the methods of determination of the amorphous grain-boundary phases are described in detail. Additionally, the correlation between the corrosion behaviour and the composition of the grain-boundary phases are given. The structural reasons and the mechanisms behind the observed changes in the corrosion behaviour will be given in part II of this paper.     

Weak Gel Behaviour of Poly(vinyl alcohol)-Borax Aqueous Solutions

Thermal transition of PVA-borax aqueous gels with a PVA concentration of 60 g/L and a borax concentration of 0.28 M was investigated at temperatures ranging from 15 to 60C using static light scattering (SLS), dynamic light scattering (DLS), and dynamic viscoelasticity measurements. Three relaxation modes, i.e. two fast and one slow relaxation modes, were observed from DLS measurements. Two fast relaxation modes located around 10^–310¹ sec, with one fast mode (_f1) being scattering vector q-dependent and the other fast mode (_f2, with _f2>_f1) being q-independent. The _f1 mode was attributed to the gel mode whilst the _f2 mode could be due to the hydrodynamics of intra-molecular hydrophobic domains formed by uncharged segments of polymer backbones. The slow relaxation mode with relaxation time located around 10¹10³ sec in DLS data was due to the motion of aggregated clusters and was observed only at temperatures above 40C. The amplitude and relaxation time of slow mode decrease as temperature is increased from 40 to 60C. At temperatures below 40C, no slow relaxation mode was observed. The SLS measurements showed PVA-borax-water system had fractal dimensions D _f2.4 and D _f2.0 as temperature was below and above 40C, respectively. The simple tilting test indicated gel behaviour for the PVA-borax aqueous system at temperatures below 40C with a creep flow after a long time exposure in the gravity field. But the dynamic viscoelasticity measurements demonstrated a solution behaviour for PVA/borax/water at temperatures below 40C, the critical gel point behaviour for G() and G() was not observed in this system as those reported for chemical crosslinked gels. These results suggest that the PVA-borax aqueous system is a thermoreversible weak gel.     

Solubility of CO2 in aqueous solutions of NaCl, KCl, CaCl2 and their mixed salts at different temperatures and pressures

The solubility of CO₂ in water and aqueous solutions of NaCl, KCl, CaCl₂, NaCl + KCl (weight ratio = 1:1), NaCl + CaCl₂ (weight ratio = 1:1), KCl + CaCl₂ (weight ratio = 1:1), and NaCl + KCl + CaCl₂ (weight ratio = 1:1:1) was determined at 35.0, 45.0 and 55.0 °C up to 16 MPa, and the concentration of the salt was up to 14.3 wt%. It was demonstrated that solubility increased with increase in pressure, and decreased with increasing temperature. Addition of a salt or salt mixture resulted in reduction in the solubility due to the salting-out effect. At the same salt concentration (wt%), the salting-out effect of KCl was considerably smaller than those of NaCl and CaCl₂. The salting-out effect of a salt mixture is between those of its components.     

C60(Cg) and C70(g): A computational study of the pressure and temperature dependence of their populations

Equilibrium mixtures of pure carbon gas-phase aggregates, C_n(g). are treated combining all available observational as well as computational thermodynamical data for n = 1, 2, 3, 4, 5, 60 and 70. A considerable sensitivity to temperature and pressure is pointed out, showing that there are both regions of a higher relative population of C₆₀(g) as well as of C₇₀(g). There can be significant competition between the formation of small and large clusters. Relations between the full-equilibrium situation (i.e., including graphite), gas-phase equilibrium, and the nonequilibrium situation are discussed.     

Role of adsorbed iodine into poly(vinyl alcohol) films drawn in KI/I2 solution

We have investigated the microstructure of the poly(vinyl alcohol) (PVA) films using small- and wide-angle X-ray scattering (SAXS and WAXS, respectively) techniques. The samples were uniaxially drawn in water or KI/I₂ aqueous solution and then dried in an air-oven at 333 K for 1 h prior to SAXS and WAXS measurements. It was found that for the films drawn in KI/I₂ solution PVA chains in the microfibrillar structure are more extended upon the film drawing compared to the case of the films drawn in pure water, which is resulted from the correlation function analysis on the SAXS data. Adsorbed iodines into the film were anticipated to act as junction points between the microfibrils via the formation of the PVA-iodine complexes.     

Diffusion of poly(ethylene oxide) in semidilute aqueous solution: Dynamic light scattering and gradient diffusion

Gradient diffusion measurements and dynamic light scattering data are presented for semidilute aqueous solutions of narrow distribution (molecular weight M: 2.5 × 10⁴ – 1.2 × 10⁶) poly(ethylene oxide) fractions. Resolution of the time correlation function using bimodal analysis gave: (a) a fast mode, identical within experimental error to the classical gradient diffusion values; (b) a slow mode, interpreted as reflecting the translational motions of clusters of entangled chains. The results are similar to those found for other aqueous polymer systems, probably reflecting the ease with which association occurs between extended, polar, chains.     

Thermal behavior of poly(acrylic acid)–poly(vinyl pyrrolidone) and poly(acrylic acid)–metal–poly(vinyl pyrrolidone) complexes

Thermal analysis (TGA and DTA) of samples of PAA, PVP, PAA–PVP complexes, containing different weight fractions of PAA and ternary polymer–metal–polymer complexes, were studied. The activation energy parameters for the thermal degradation were also calculated. The study of the effect of FeCl₃, NiCl₂, and Ni(NO₃)₂ on the TGA and DTA curves of the complexes showed that the decompositions are dependent on the concentrations and the nature of the metal ions. The DTA traces of PAA–PVP complex containing FeCl₃, NiCl₂, and Ni(NO₃)₂ showed that the treatment of the complex with these metal ions causes considerable changes in the thermal decomposition of PAA–PVP complex. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4049–4057, 2006     

Electrical conductivity properties of poly[(maleic acid)‐co‐(vinyl pyrrolidone)] salts in aqueous solutions

The interaction of alkaline ions with an anionic dicarboxylic polyelectrolyte is studied by means of electrical conductivity measurements. The results show that lithium, sodium and potassium counter‐ions interact in a very different way with this polyelectrolyte. The Kohlrausch plots bend downwards in the high‐dilution zone. The limiting equivalent conductivities of these polymers were then determined according to Vink's method by a polynomial adjustment of specific conductivity data. Whereas the dissociation order follows the sequence Li⁺ > Na⁺ > K⁺, the trend in equivalent conductivity follows the reverse order, and apparently is mainly determined by the equivalent conductivity of the counter‐ions. The interaction parameter f was determined using the Manning theory for the limiting equivalent conductivity of the polyion species. From the values of the latter parameters, the average distance between charges agrees well with that calculated from simple geometrical calculations for a mesomeric configuration. An alternative method was used to obtain the relative interaction parameter f* as a function of polymer concentration. The results can be explained in terms of the hydration parameters and the limiting equivalent conductivities of the counter‐ions. © 2001 Society of Chemical Industry