Suppression of crystallization in a plastic crystal electrolyte (SN/LiClO4) by a polymeric additive (polyethylene oxide) for battery applications

A basic problem with many promising solid electrolyte materials for battery applications is that crystallization in these materials at room temperature makes ionic mobilities plummet, thus compromising battery function. In the present work, we consider the use of a polymer additive (polyethylene oxide, PEO) to inhibit the crystallization of a promising battery electrolyte material, the organic crystal forming molecule succinonitrile (SN) mixed with a salt (LiClO₄). While SN spherulite formation still occurs at low PEO concentrations, the SN spherulites become progressively irregular and smaller with an increasing PEO concentration until a ‘critical’ PEO concentration (20% molar fraction PEO) is reached where SN crystallization is no longer observable by optical microscopy at room temperature. Increasing the PEO concentration further to 70% (molar fraction PEO) leads to a high PEO concentration regime where PEO spherulites become readily apparent by optical microscopy. Additional diffraction and thermodynamic measurements establish the predominantly amorphous nature of our electrolyte-polymer mixtures at intermediate PEO concentrations (20-60% molar fraction PEO) and electrical conductivity measurements confirm that these complex mixtures exhibit the phenomenology of glass-forming liquids. Importantly, the intermediate PEO concentration electrolyte-polymer mixtures retain a relatively high conductivity at room temperature in comparison to the semicrystalline materials that are obtained at low and high PEO concentrations. We have thus demonstrated an effective strategy for creating highly conductive and stable conductive polymer-electrolyte materials at room temperature that are promising for battery applications.     

Study of peptide fingerprints of parasite proteins and drug-DNA interactions with Markov-Mean-Energy invariants of biopolymer molecular-dynamic lattice networks

Since the advent of Molecular Dynamics (MD) in biopolymers science with the study by Karplus et al. on protein dynamics, MD has become the by foremost well established, computational technique to investigate structure and function of biomolecules and their respective complexes and interactions. The analysis of the MD trajectories (MDTs) remains, however, the greatest challenge and requires a great deal of insight, experience, and effort. Here, we introduce a new class of invariants for MDTs based on the spatial distribution of Mean-Energy values ξ_k(L) on a 2D Euclidean space representation of the MDTs. The procedure forces one MD trajectory to fold into a 2D Cartesian coordinates system using a step-by-step procedure driven by simple rules. The ξ_k(L) values are invariants of a Markov matrix (¹Π), which describes the probabilities of transition between two states in the new 2D space; which is associated to a graph representation of MDTs similar to the lattice networks (LNs) of DNA and protein sequences. We also introduce a new algorithm to perform phylogenetic analysis of peptides based on MDTs instead of the sequence of the polypeptide. In a first experiment, we illustrate this algorithm for 35 peptides present on the Peptide Mass Fingerprint (PMF) of a new protein of Leishmania infantum studied in this work. We report, by the first time, 2D Electrophoresis isolation, MALDI TOF Mass Spectroscopy characterization, and MASCOT search results for this PMF. In a second experiment, we construct the LNs for 422 MDTs obtained in DNA-Drug Docking simulations of the interaction of 57 anticancer furocoumarins with a DNA oligonucleotide. We calculated the respective ξ_k(L) values for all these LNs and used them as inputs to train a new classifier with Accuracy = 85.44% and 84.91% in training and validation respectively. The new model can be used as scoring function to guide DNA-Drug Docking studies in drug design of new coumarins for PUVA therapy. The new phylogenetics analysis algorithms encode information different from sequence similarity and may be used to analyze MDTs obtained in Docking or modeling experiments for any classes of biopolymers. The work opens new perspective on the analysis and applications of MD in polymer sciences.     

Cyclization dynamics of polymers: 7. Applications of the pyrene excimer technique to the internal dynamics of poly(dimethylsiloxane) chains

Poly(dimethylsiloxane) (PDMS) polymers end-capped on both ends with pyrene chromophores have been synthesized. Rate constants for end-to-end cyclization 〈 k₁ 〉 have been determined for dilute solutions of these polymers in toluene solution using a combination of fluorescence decay and steady-state fluorescence measurements. While precise values of the critical exponent for the chain length (N¯) dependence of 〈 k₁ 〉 are not yet available, these results are consistent with the N¯^{? 3/2} dependence predicted by Wilemski-Fixman theory. PDMS chains cyclize somewhat more than two times faster than polystyrene chains of the same length in solvents of similar solvating power and viscosity. These results provide strong support for similar predictions made several years ago by Perico and Cuniberti, who used intrinsic viscosity data to parametrize the Rouse-Zimm model for analysis of polymer cyclization dynamics.     

Improvement of electrochemical properties of PEO–LiTFSI electrolyte by incorporation of boroxine polymers with different backbone lengths

A series of boroxine polymers (BP) with different backbone lengths were synthesized. Polymer electrolytes prepared by blending poly(ethylene oxide) (PEO) and BP with Li(N(SO ₂CF₃)₂) (LiTFSI) were evaluated. Better performance was observed by addition of BP in the PEO based polymer electrolyte. The effect of the backbone length of BP on electrochemical properties of PEO–BP–LiTFSI electrolyte systems was investigated. Compared with the PEO–LiTFSI system, about five times higher ionic conductivity at low temperature and five times higher lithium ion transference number at 70°C were achieved by incorporation of long chain BP in the electrolyte. Short chain BP exhibited outstanding performance in decreasing interfacial resistances on both anode and cathode surfaces. Good battery performance was also observed for these BP containing hybrid polymer electrolytes.     

Investigation of gas properties, design, and operational parameters on hydrodynamic characteristics, mass transfer, and biomass production from natural gas in an external airlift loop bioreactor

An external airlift loop bioreactor (EALB) was used for production of biomass from natural gas. The effect of riser to downcomer cross sectional area ratio (A_r/A_d), volume of gas-liquid separator, superficial gas velocity (U_sgr), and physical properties of gases and their mixtures [υ_g (μ/ρ) and D_g] were investigated on mixing time, gas hold-up, and volumetric gas liquid mass transfer coefficients (k_La). It was found that A_r/A_d has remarkable effects on gas hold-up and k_La due to its influence on mixing time. Kinematic viscosity (υ_g) showed its significant role on mixing time, gas hold-up and k_La when different gases used (mixing time changes directly whereas gas hold-up and k_La change indirectly). Moreover, it was found that diffusion coefficient of gas in water (D_g) has remarkable effect on k_La. The volumetric mass transfer coefficients for methane and its mixtures with oxygen (three different mixtures) were determined at different geometrical and operational factors. In average, the rate of oxygen utilization is approximately 1.8 times higher than that of methane. A gas mixture of 25 vol% methane and 75 vol% oxygen was the best gas mixture for biomass production in the EALB. The correlations developed for predicting the mixing time, gas hold-up, and k_La in terms of U_sgr, A_r/A_d, volume of gas-liquid separator, and gas phase properties have been found to be encouraging.     

Depletion potential between two attractive plates mediated by polymers

Depletion interactions in polymer-colloid mixtures in the presence of the attraction between polymers and particle surfaces are computed from the simulation data on polymer partitioning. The gap between two large colloid particles is approximated by the slit plates immersed in a dilute polymer solution. The difference between the intra-slit and bulk pressures of polymers Δp (net pressure) and the effective pair potential of plates W is calculated as a function of the plate separation D and the attraction strength ε of plates to polymer segments. Weak attraction strengths ε are considered, including the region around the compensation point ε_c (the depletion/adsorption threshold) where the partition coefficient of polymers K=1. A fit of the simulation data for the free energy confinement ΔA=−k_BT ln K served as a base of computations of the above depletion characteristics. The analytical functions deduced for Δp(D,ε) and W(D,ε) predict a reduction of the range and depth of depletion interaction by an increase in the attraction strength |ε|. Variation of the thickness δ of depletion layers near the plates with attraction ε was also determined. Consequences of reduced depletion interaction for the effective second virial coefficient B₂ and for the stability of colloidal suspensions were discussed. At the compensation point ε_c the depletion effect disappears and the stability of polymer-colloid mixtures in dilute solution is not affected by the polymer concentration.     

A review of the effects of covapors on adsorption rate coefficients of organic vapors adsorbed onto activated carbon from flowing gases

Published breakthrough time, adsorption rate, and capacity data for components of organic vapor mixtures adsorbed from flows through fixed activated carbon beds have been analyzed. Capacities (as stoichiometric centers of constant pattern breakthrough curves) yielded stoichiometric times τ, which are useful for determining elution orders of mixture components. Where authors did not report calculated adsorption rate coefficients k_v of the Wheeler (or, more general, Reaction Kinetic) breakthrough curve equation, we calculated them from breakthrough times and τ. Ninety-five k_v (in mixture)/k_v (single vapor) ratios at similar vapor concentrations were calculated and averaged for elution order categories. For 43 first-eluting vapors the average ratio (1.07) was statistically no different (standard deviation 0.21) than unity, so that we recommend using the single-vapor k_v for such. Forty-seven second-eluting vapor ratios averaged 0.85 (standard deviation 0.24), also not significantly different from unity; however, other evidence and considerations lead us to recommend using k_v (in mixture)=0.85k_v (single vapor). Five third- and fourth-eluting vapors gave an average of 0.56 (standard deviation 0.16) for a recommended k_v (in mixture)=0.56k_v (single vapor) for such.     

Effect of molecular architecture on the self-diffusion of polymers in aqueous systems: A comparison of linear, star, and dendritic poly(ethylene glycol)s

Star polymers with a hydrophobic cholane core and four poly(ethylene glycol) (PEG) arms, CA(EG_n)₄, have been synthesized by anionic polymerization. Pulsed-gradient spin-echo NMR spectroscopy was used to study the diffusion behavior of the star polymers, ranging from 1000 to 10,000 g/mol, in aqueous solutions and gels of poly(vinyl alcohol) (PVA) at 23 °C. The star polymers have a lower self-diffusion coefficient than linear PEGs at equivalent hydrodynamic radius. In water alone, the star polymers and their linear homologues have a similar diffusion behavior in the dilute regime, as demonstrated by the similar concentration dependence of the self-diffusion coefficients. In the semidilute regime, the star polymers tend to aggregate due to their amphiphilic properties, resulting in lower self-diffusion coefficients than those of linear PEGs. ¹H NMR T₁ measurements at 10-70 °C revealed that the PEG arms of the star polymers are more mobile than the core, suggesting the star polymers in solution have a conformation similar to that of poly(propylene imine) dendrimers.     

Coatings of Conducting Polymers for Corrosion Protection of Mild Steel

The investigation of electrochemical behavior of different conducting polymers, polythiophene (PTh), polypyrrole (PPy) and polyterthiophene (PTTh) on a mild steel (MS) electrode were done. Moreover, the combinations of the conducting polymers PTh and PPy was investigated. The synthesis of all polymeric coatings was done by the cyclic voltammetry technique. The electrochemical impedance spectroscopy (EIS) measurements were used to evaluate the corrosion performance of coated mild steel by different polymers in 0.5 M of different acid solutions (HCl, HClO₄, H₂ C ₂ O ₄, H₃PO₄ and HNO₃). The protection of all polymeric coatings against corrosion of the substrate was promising and the bilayer coating PPy/PTh gave the best protection efficiency in all used acids. The order of efficiency for the different coatings in HCl and HNO₃ solutions was MS/PPy/PTh > MS/PPy > MS/PTTh > MS/PTh but the order in HClO₄, H₃PO₄ and H₂ C ₂ O ₄ solutions was MS/PPy/PTh > MS/PTTh > MS/PPy > MS/PTh.     

Determination of mass transfer coefficients for packing materials used in biofilters and biotrickling filters for air pollution control. 1. Experimental results

Gas film mass transfer coefficients (k_Ga_t,k_Ga_w) and liquid film mass transfer coefficients (k_La_w) for packing materials used in biofilters and biotrickling filters for air pollution control were determined experimentally. Lava rock, polyurethane foam cube (PUF), Pall ring, porous ceramic beads, porous ceramic Raschig rings and compost-woodchips mixtures were investigated. The experiments were performed at gas velocities ranging from 100 to and liquid velocities of , i.e., a wide range that covers most biofilters and biotrickling filters. k_Ga_t in biofilter packings ranged from about 500 to , while k_Ga_w and k_La_w in biotrickling filters ranged from 100 to , and 1 to , respectively, depending on the packings and the conditions. This is markedly lower than mass transfer coefficients usually observed for conventional wet scrubbing. The gas film mass transfer coefficient (k_Ga_t) of 50:50% vol compost-woodchips mixture, a common biofilter packing, was greater than this of a 20% vol compost and 80% woodchips mixture, though the mass transfer was not increased by increasing further the volume fraction of compost. All compost mixtures exhibited a greater gas film mass transfer coefficient than lava rock or other synthetic materials. The mass transfer coefficients of compost mixtures was also influenced by packing method and it was directly proportional to the surface area of the bulking agents added. The gas film mass transfer coefficient (k_Ga_w) of five biotrickling filter packing materials increased linearly with gas velocity. The effect of liquid on the gas film mass transfer coefficient was not significant. Of all the biotrickling filter packings, the porous ceramic beads had the highest gas and liquid film mass transfer coefficients followed by lava rock, porous ceramic rings, 1 in Pall ring and PUF cubes. The liquid film mass transfer coefficient (k_La_w) was directly proportional to liquid velocity and the effect of gas velocity was negligible. Several correlations allowing prediction of mass transfer coefficients are presented in Part 2 of this paper.     

Electrochemical impedance spectroscopy and cyclic voltammetry of ferrocene in acetonitrile/acetone system

The oxidation of ferrocene (FeCp₂) to ferrocenium cation (FeCp ₂ ⁺ ) (where Cp: cyclopentadienyl anion, C₅H₅ ^?) was investigated by means of electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) on either platinum (Pt) or glassy carbon (G-C) electrodes in acetonitrile (ACN), acetone (ACE), and acetonitrile (ACN)/acetone (ACE) binary mixtures with n-tetrabutylammonium hexafluorophosphate (TBAPF₆) as background electrolyte at T = 294.15 K. The half-wave potentials (E _1/2), the diffusion coefficients (D), and the heterogeneous electron-transfer rate constants (k _s) were derived. The activation free energies for electron transfer (ΔG _exp ^≠ ) were experimentally determined and compared with the theoretical values (ΔG _cal ^≠ ). The electron-transfer process was reversible and diffusion-controlled in all investigated solvent mixtures. The changes on the metal–ligand bond lengths upon electron transfer were almost insignificant. The E _1/2 values were shifted to less positive potentials with the increase of the ACN content. The k _s values obtained on Pt electrode were slightly larger compared to k _s measured on G-C electrode, while in both cases the k _s values were diminished with the enrichment of the mixtures in ACN. The EIS spectra confirmed that the rate-determining step in the whole process is the diffusion of the FeCp₂ species and thus the process can be properly characterized as diffusion-controlled.     

Voltammetric study of the cyanide complexes of osmium—I. The reduction of the cyanide complex of Os(VI) on a platinum rde

Two forms of cyanide complexes of hexavalent osmium were found in alkaline KCN solutions. The initially formed complex, OsO₂(OH)₂(CN)^2?₂, is stable only in solutions with at least a ten-fold excess of OH^? ions over CN^? ions. At higher cyanide concentrations it is converted into the OsO₂(CN)^2?₄ complex. Both these complexes are reduced to tervalent osmium. A more detailed study of complex OsO₂(OH)₂(CN)^2?₂ has shown that it is reduced electrochemically according to the scheme of a consecutive electrochemical reaction.OsO₂(OH)₂(CN)^2?₂ + 2e(k₁,α₁) → Os(IV) + e(k₂,α₂) → Os(OH)₄(CN)^3?₂The values α₁ = 0.65 and α₂ = 0.40 and the potential dependences of constants k₁ and k₂ were determined.     

Electrochimie du polynitrure de soufre dans les solvants non aqueux—II. Comportement dans le carbonate de propylene

The electrochemical behaviour of polysulfur nitride and (SN)_x modified by bromine or lithium has been studied by cyclic voltametry in MClO₄, KPF₆, and MBr with M = Li⁺, Na⁺, K⁺, Et₄N⁺, propylene carbonate solutions. The cathodic reaction could produce (SN)_x alkaline insertion compounds. The buthyllithium chemical reaction could also give partially reversible (SN)_x alkaline insertion compounds.The products obtained could have the following formula: [SN(LiBu₄)_0.2]_x. Both compounds obtained by chemical and electrochemical reactions have similar electrochemical properties. A decomposition of the electrode material at a cathodic voltage of about ?2 V for the AgAg⁺ reference electrode occurred producing turquoise blue ions that could be oxidized to give a red coloration. (SN)_x bromine derivatives are the center of reversible oxido-reduction reaction in polysulfur nitride and its derivatives seem limited by the species diffusion in the solid.     

Preparation of star polymers based on polystyrene or poly(styrene-b-N-isopropyl acrylamide) and divinylbenzene via reversible addition-fragmentation chain transfer polymerization

Star polymers based on styrene/divinyl benzene (St/DVB) and PSt-b-poly(N-isopropyl acrylamide) (NIPAAM)/DVB have been successively prepared by ‘arm-first’ method via reversible addition-fragmentation chain transfer (RAFT) polymerization. The linear macro RAFT agent PSt-SC(S)Ph was prepared by RAFT polymerization of St using benzyl dithiobenzoate and AIBN as RAFT agent and initiator. Successive RAFT polymerization of NIPAAM with PSt-SC(S)Ph as macro RAFT agent to afford diblock copolymer, PSt-b-PNIPAAM-SC(S)Ph. The coupling reactions of PSt-SC(S)Ph or PSt-b-PNIPAAM-SC(S)Ph in the presence of DVB produced the star copolymers, C(PSt)_n or C(PSt-b-PNIPAAM)_n. The molar ratio of DVB/PSt-SC(S)Ph and polymerization time influenced the yields, molecular weight and distribution of the star-shaped polymers, which was characterized by ¹H NMR and IR spectra, GPC measurements as well as DLS.     

Dimension of heterogeneous network architecture formed in emulsion cross-linking copolymerization

The mean-square radius of gyration Rg² and the graph diameter D of highly heterogeneous network polymers formed in emulsion vinyl/divinyl copolymerization are investigated to find a linear relationship, Rg² = a D. The proportionality coefficient, a, is dominated by the cycle (circuit) rank, k_c, or the number of intramolecular cross-links. The magnitude of a is slightly larger than that for the random cross-linked network polymers, but the functional form of a (k_c) is simply proportional to that for the random networks proposed earlier. This relationship makes it possible to determine Rg² based on D and k_c, enabling quick estimation of Rg² for large network polymers. It is found that the contraction factor g of the present heterogeneous network polymer is larger than that for the homogeneous networks formed through random cross-linking of polymer chains. The ratio of these two contraction factors is kept constant, irrespective of the magnitude of k_c.     

Effect of coordination number on the formation of silver nanoparticles in polymer/silver salt complex membranes

Polymer/silver salt complex membranes consisting of AgBF₄ dissolved in poly(2-ethyl-2-oxazoline) (POZ) exhibited higher separation performance for propylene/propane mixtures but gradual decrease of separation properties, primarily due to the reduction of silver ions to silver nanoparticles. In this study, the effect of salt concentration on the formation of silver nanoparticles in POZ/AgBF₄ complex membranes was investigated. Separation test showed that 1/0.5 POZ/AgBF₄ complex membrane exhibited improved long-term stability on the membrane separation performance for propylene/propane mixtures compared to 1/1 POZ/AgBF₄ complex membrane. The stability improvement would be attributed to the suppression of the reduction of silver ions to silver metal nanoparticles, resulting from the higher coordination number of silver ions to carbonyl oxygens of POZ in 1/0.5 POZ/AgBF₄ membrane than 1/1 membrane. Transmission electron microscopy (TEM) and UV–visible spectra results confirmed that the rate of silver metal nanoparticle formation in the 1/0.5 POZ/AgBF₄ complex membrane was significantly retarded compared to that of 1/1 POZ/AgBF₄ complex membrane. It is therefore concluded that the coordination number of silver ions for carbonyl oxygens is of pivotal importance in controlling the reduction reaction of silver ions to silver metals and consequently improving the membrane separation performance for propylene/propane mixtures.     

Low band gap Schiff base polymers obtained by complexation with Lewis acids

Two Schiff base polymers were prepared from the respective monomers by condensation method using toluene and N-methyl-2-pyrrolidinone as solvent. They were complexed with Al(III), In(III), and Cu(II) trifluoromethane sulfonates (triflates), and AlCl₃ Lewis acids and characterized by FT-IR, UV–Vis spectroscopy, and scanning electron microscopy (SEM). Homogeneous films were prepared by spin coating in the presence and absence of Lewis acids. Polymer–Lewis acid interaction was confirmed by FT-IR, UV–Vis spectroscopy, and SEM. Lewis acid composition in polymers was determined by FT-IR spectroscopy. Absorption spectra of these conjugated Schiff base polymer complexes exhibited smaller optical band gap than pristine polymers. These variations ranged from 2.4 to 1.4 and 3.3 to 2.0 eV. Absorption depends on the Lewis acid in the polymer and band gap on the nature of the metal incorporated in the polymeric backbone. Solubility increased by complexation. The obtained complexes were soluble in trifluoroacetic and formic acids and in m-cresol. Polymer–Lewis acid solutions in m-cresol were stable for 98 h; the others remained stable over several months. The results of this study revealed that optical, solubility, and band-gap properties of conjugated Schiff base polymers can be modified by Lewis acids and these could be studied by optoelectronics.     

Kinetics of ligand exchange reaction of Cu(II)-ammine complex with poly(vinyl alcohol) in aqueous solution

The kinetics of the ligand exchange reaction of the Cu(II)-ammine complex with poly(vinyl alcohol) (PVA) has been studied by a stopped-flow method at pH 9–10, at μ=0.1 (NH₄Cl) and at 25°C. The reaction is initiated by the formation of unstable [Cu(NH₃)₃]²⁺ by the attack of H⁺ on Cu(II)-ammine complex, and proceeds through the mixed complex {[Cu(NH₃)₃(O?PVA)]²⁺}. This step may be rate-determining, followed by a rapid reaction. Finally, the Cu(II) ion is taken up by PVA. The rate is given by d[Cu(II)?PVA]/dt=k[H⁺]{[Cu(NH₃)₄]²⁺}[PVA]/[NH₄Cl], where k=k₁ + k′₂[H⁺], k₁=4.25× 10s^?1 and k′₂=5.20× 10¹¹l mol^?1s^?1.     

Glass transition temperature prediction of polymers through the mass-per-flexible-bond principle

A semi-empirical method based on the mass-per-flexible-bond (M/f) principle was used to quantitatively explain the large range of glass transition temperatures (T_g) observed in a library of 132 l-tyrosine derived homo, co- and terpolymers containing different functional groups. Polymer class specific behavior was observed in T_g vs. M/f plots, and explained in terms of different densities, steric hindrances and intermolecular interactions of chemically distinct polymers. The method was found to be useful in the prediction of polymer T_g. The predictive accuracy was found to range from 6.4 to 3.7 K, depending on polymer class. This level of accuracy compares favorably with (more complicated) methods used in the literature. The proposed method can also be used for structure prediction of polymers to match a target T_g value, by keeping the thermal behavior of a terpolymer constant while independently choosing its chemistry. Both applications of the method are likely to have broad applications in polymer and (bio)material science.