Unperturbed dimensions of branched chain,star and ring polymers

A novel Monte Carlo method has been applied to the calculation of the unperturbed dimensions of various monodisperse polymers, e.g. star polymers, branched polymers formed by the crosslinking of linear primary chains, and linear chains with some intramolecular cycles. Where results for the parameters h^?1 and g (representing the effect of branching upon the hydrodynamic radius and the radius of gyration, respectively) were known previously, agreement is good. The method can, however, be applied to furnish other statistical averages for polymers of any arbitrary branched structure, and the effects of polydispersity may also be included.     

The largest eigenvalue method for stereo-regular vinyl chains

We derived the analytical solution of the eigenvalue problem for stereo-regular vinyl chains, such as stereo-regular polypropylene chains. The solution is applicable to all stereo-regular polymers of the type (AB)_x which do not have symmetry between gauche⁺ and gauche⁻ states, and to polymers, such as polyoxymethylene or polydimethylsiloxane, for which symmetry between the gauche⁺ and gauche⁻ states does exist. For symmetric chains, the general solution of the eigenvalue problem is reduced to the known solution for polyoxymethylene chains. To illustrate the method the calculations have been performed for the three rotational states (trans, gauche⁺ and gauche⁻) model, but the general algebraic solution is applicable for any ν rotational states models of polymer chains. We used the analytical solution of the eigenvalue problem to calculate numerically elastic properties of stereo-regular polypropylene chains within the framework of Mark-Curro theory (J Chem Phys, 79, 5705, 1983).     

Sedimentation of large colloidal particles through semidilute polymer solutions

The sedimentation of various spherical particles with radii 25–175 Å in poly(ethylene oxide) aqueous polymer solutions have been investigated by analytical ultracentrifugation. As already observed by Laurent and Pietruszkiewicz (Biochim. Biophys. Acta 1961, 49, 258) the decrease in the sedimentation rate with polymer concentration, c, and particle radius, R, is of the form S ∝ exp(?Ac^y). Present experiments in semidilute solutions show that: (1) A is proportional to R but independent of polymer molecular weight; (2) y is $\text{? 0.62}$, significantly higher than the value of 0.5 claimed by previous authors; (3) polymer adsorption onto the particle surfaces has to be taken into account. Our results are in reasonable agreement with a simple form $\text{S ∝}\text{exp}\text{(}\text{?R}\text{ξ}\text{)}$ where ξ is the correlation length ∝_c^?v with v ?0.75. The semidilute polymer solution can thus be viewed as a statistical network of mesh ξ, the retardation factor being governed by the elastic distortion of the network due to the moving particles.     

Constrained nonlinear optimization for solubility parameters of poly(lactic acid) and poly(glycolic acid)—validation and comparison

An optimization technique has been proposed to determine Hansen solubility parameters (HSP) and radius of interaction (R) of PLA and PGA; objective function to be minimized being radius of interaction (R), and the constraints being that the solvents should be within and nonsolvents outside the interaction sphere. The proposed method has been validated and found to be most reliable. The values of HSP (δ_d, δ_p, δ_h) and R for PLA have been obtained as ((18.50, 9.70, 6.00) and 10.50) (J/cc)^0.5 at 25 °C; and those of PGA as ((17.70, 6.21, 12.50) and 1.92) (J/cc)^0.5 at 80 °C. For formulating the nonlinear inequality constraints known HSP data for 20 solvents and seven nonsolvents have been used for PLA at 25 °C; similarly HSP data for three newly found solvents (phenol, m-cresol and 4-chlorophenol), and five nonsolvents have been used for PGA at 80 °C. Established methods have been used for comparison. HSP and R have been directly compared using the 3D intrinsic viscosity and classical methods. Indirectly the total solubility parameter δ has been compared with the values obtained from the intrinsic viscosity 1D approach and group contribution method using Fedors and van Krevelen correlations. The 1D approach has led to an empirical correlation for intrinsic viscosities of PLA and PGA.     

Effect of Chemical Reaction and Mass Transfer on Ozonation of the Azo Dyes Reactive Black 5 and Reactive Orange 96

Ozonation of wastewater containing azo dye has been studied to evaluate the enhancement of ozone mass transfer from O₂O₃ gas into water with the presence of chemical reactions in a bubble column reactor. Experiments were performed at different initial dye concentrations and at various gas flow rates. C.I. Reactive Black 5 (RB 5) and C.I. Reactive Orange 96 (RO 96) have been chosen as representative model substances being found in wastewater from textile-finishing wastewater. Results show that the rate of ozone mass transfer increases with increasing initial dye concentration and gas flow rate. Consequently, an enhancement factor E for ozone mass transfer with chemical reaction could be calculated which increases with dye concentration. The chemical reaction between ozone and dye enhanced the mass transfer within the liquid film of the gas liquid boundary. The greatest enhancement factor for wastewater containing RO 96 of 2050 mgL^?1 is E = 15.4 compared with E = 9.1 for RB 5 of 3800 mgL^?1, both for gas flow rates of 19 Lh^?1. For lower gas flow rates, higher enhancement factors were observed, particularly for RO 96.     

Four chiral Ag(I) complexes with dual chiral components: Effect of positional isomerism,luminescence and SHG response

Four chiral Ag(I) complexes with dual chiral components have been synthesized by using a series of (1R,2R)-N¹,N²-bis(pyridinylmethyl)cyclohexane-1,2-diamine ligands with different N-positions of pyridyl rings. The circular dichroism (CD) spectra and second-harmonic generation (SHG) efficiency measurements confirmed that they are of structural chirality in the bulk samples. The luminescence properties indicated that they may have potential applications as optical materials. The formation of discrete mononuclear and binuclear complexes and one-dimensional chains may be attributed to positional isomerism of the ligands.     

Electrochemical reduction and oxidation pathways for Reactive Black 5 dye using nickel electrodes in divided and undivided cells

The cathodic reduction and anodic OH-mediated oxidation of the azo dye Reactive Black 5 (RB5) have been studied potentiostatically by using undivided and divided cells with a Ni-polyvinylchloride (Ni-PVC) composite cathode and a Ni wire mesh anode. Solutions of 50–100 cm³ of 20–80 mg dm^?3 RB5 in 0.1 mol dm^?3 KOH were degraded to assess the effect of electrolysis time and electrode potentials on the infrared and absorbance spectra, as well as on the decay of the total organic carbon and chemical oxygen demand. Reversed-phase high performance liquid chromatography (RP-HPLC) with ion-pairing and diode array detection (ion pair chromatography), along with coupling to tandem mass spectrometry (LC–MS/MS), were used for the identification of the aromatic degradation by-products and monitoring their time course. These analyses revealed the progressive conversion of the RB5 dye to simpler molecules with m/z 200, 369.5 and 547 under the direct action of the electron at the cathode and the formation of polar compounds such as alkylsulfonyl phenol derivatives with m/z 201, 185 and 171 by the OH mediation at the anode. From these results, the electrochemical reduction and oxidation pathways for the RB5 dye were elucidated.     

Structure and dynamics of thin polymer films: a case study with the bond-fluctuation model

This paper reports Monte Carlo simulation results of a polymer melt of short, non-entangled chains which are embedded between two impenetrable walls. The melt is simulated by the bond-fluctuation lattice model under athermal conditions, i.e. only excluded volume interactions between the monomers and between the monomers and the walls are taken into account. In the simulations, the wall separation is varied from about one to about 15 times the bulk radius of gyration R_g. The confinement influences both static and dynamic properties of the films: Chains close to the walls preferentially orient parallel to it. This parallel orientation decays with increasing distances from the wall and vanishes for distances larger than about 2R_g. Strong confinement effects are therefore observed for film thicknesses D?4R_g. The preferential alignment of the chains with respect to the walls suppresses reorientations in perpendicular direction, whereas parallel reorientations take place in an environment of high monomer density. Therefore, they have a relaxation time larger than that of the bulk. On the other hand, the influence of confinement on the translation motion of the chains parallel to the walls is very weak. It almost coincides with the bulk behavior even if D≈1.5R_g. Despite these differences between translational and reorientational dynamics, their behavior can be well reproduced by a variant of Rouse theory which only assumes orthogonality of the Rouse modes and determines the necessary input from the simulation.     

Revisiting of dimensional scaling of linear chains in dilute solutions

The dimensions of linear polymer chains are scaled to their molar mass (M) as R = kM^α with α = 1/2 and 3/5 in a theta and an athermal solvent, respectively. In a good solvent, both k and α are a function of the solvent quality and chain length range. A high-temperature laser light-scattering spectrometer was used to measure the average radius of gyration (〈R_g〉) and hydrodynamic radius (〈R_h〉) of a set of narrowly distributed linear polystyrene chains in decalin over a wide temperature range. k and α in the scaling experimentally varying with T over a chain length range was analyzed. The results reveal that for 〈R_g〉, α = 0.59 − 0.09exp(−τ/0.066) and k = 0.60τ^2α−1, reasonably agreeing with the thermal blob theory. For 〈R_h〉, α = 0.59 − 0.09exp(−τ/0.106), but k deviates from the relationship of k ∝ τ^2α−1, reflecting that the hydrodynamic interaction and chain draining are not considered in the thermal blob theory.     

Single-chain scattering in heterogeneous block copolymers

Diblock copolymers consisting of polystyrene (S) attached to a polybutadiene (B) block (which is either hydrogenous or perdeuterated) have been synthesized and blended in such a way that the microphase-separated S and B domains have equal scattering-length densities, thus eliminating the component of small-angle neutron scattering (SANS) due to the domain structure. Two samples were studied: one with small spherical polybutadiene microdomains whose size was in essential agreement with calculations assuming equilibrium, and a second one of larger molecular weight in which the sphere size, while larger, was considerably smaller than predicted from equilibrium theory. The SANS spectra of these samples were analysed to give the radii of gyration R_g and molecular weights M_w of the labelled polybutadiene blocks from plots of I^?1versusQ² and least-square fits to the single-chain scattering function proposed by Debye. Results for the first sample agreed with the molecular weight obtained from chromatography and u.v. absorption and with the R_g found in bulk polybutadiene of similar M_w. The SANS estimates of both M_w and R_g for the second sample were anomallously large; these deviations may be due to (a) non-Gaussian conformations of the polybutadiene chains imposed by the nonequilibrium state of the microdomain, or (b) clustering of the deuterated polybutadiene chains within the microdomain due to small isotopic differences in chemical potential, enhanced by the larger M_w. Observations on other systems suggest that the second effect is the dominant one.     

Configurational properties of model lattice chains under varying solvent conditions

Configurational properties, viz mean squares of the end-to-end distance (〈R²〉) and the radius of gyration (〈S²〉), probability distribution of R and the ratio between mean squares of the principal axes of equivalent ellipsoid (〈XX²〉: 〈YY²〉:〈ZZ²〉), have been calculated for model polymer molecules under differing solvent conditions. The present study follows a computational statistical approach which is based on the Metropolis sampling technique. The molecules are represented by tetrahedral chains with trans/gauche bond conformational energy difference equal to 1.0 kT. The solvent condition is characterised by the intersegmental interactions which are assumed to be given by a square-well potential. The depth of the potential well, Δε_s, serves to define the solvent parameter. It is shown that in the region Δε_s ～?0.4 kT the configurational criteria for the existence of the theta condition are fulfilled (the chains assumed 〈R²〉 and 〈S²〉 values that correspond to the random-walk state and the limiting probability function governing the end-to-end distance distribution is gaussian). The calculated values of 〈R²〉,〈S²〉 and 〈XX²〉 〈YY²〉:〈ZZ²〉 indicate that the chains in “good” solvents (Δε_s < ?0.4 kT) exist in highly extended configurations. As the system assumes the below-theta conditions (Δε_s <?0.4 kT) the extended configurations collapse into compact ones. Such compact configurations are not spherical but retain an appreciable degree of elongation. The probability distribution of R in the limit of infinite chain length deviates significantly from the gaussian behaviour in both the above and below-theta conditions. The present calculations suggest that the introduction of the trans/gauche conformational energy difference leads to the reduction of the long-range excluded volume in the chains.     

On the ionic conductivity of some zirconia-derived high-entropy oxides

The reported High Entropy Oxides (HEOs) up to now exhibit lower ionic conductivity values than those of classical SOFC electrolytes. Multi-cations oxides, stabilized with the fluorite-type structure are investigated here in order to examine whether the high entropy is relevant to enhance the anionic conductivity of such HEOs, or not. The two synthesis routes that are used do not show significant impact on material properties. Based on configurational entropy (≥ 1.5 k_B/f.u. for HEOs) and ionic radius difference calculations, new compositions are designed and prepared: i) the (Hf_1/3Ce_1/3Zr_1/3)_1-x(Gd_1/2Y_1/2)_xO_2-x/2 series in which the x ratio is increased so as to promote a high vacancy concentration, ii) the (Hf_xCe_yZr_1-x-y)_0.85Yb_0.15O_1.93 series based on the critical radius concept. The ionic conductivity of these HEOs is slightly improved compared to previously reported data but does not exceed 4 × 10^?4 S.cm^?1 at 600 °C. Possible causes of such a low ionic conductivity value are discussed.     

Forced translocation of polymer chains through a nanotube: A case of ultrafiltration

Translocation of polymer chains under the application of an external force has been studied through coarse-grained Monte Carlo simulations. The chains are pulled through a nanotube of finite length and diameter and their translocation times measured. The average translocation time, τ follows a scaling relation involving the chain length, N and applied force, F as, τ ∼ N^ν′F^−μ, where ν′ and μ are two different exponents (ν′ = 0.674, and μ = 0.95 ± 0.05). The scaling law is closely similar to the nanopore translocation scaling law reported by Milchev et al. [Ann N Y Acad Sci 2009;1161:95]. Characteristic signatures of the chain escape time have been exhibited by the square of end-to-end distance R², axial radius of gyration R_g−x and other constituent properties. The behavior of the linear polymers under the application of a pulling force has been exploited to gain insights into the ultrafiltration process of unentangled polymers in dilute solution. The generic pulling force-translocation time (F, τ) data obtained through simulation can be matched reasonably well with the hydrodynamic force-critical macroscopic flow time (f_h, Q_c⁻¹) data and also with the hydrodynamic force-reduced critical microscopic flow time (f_h, q_c⁻¹) data obtained in the ultrafiltration experiment on long linear polystyrene chains in cyclohexane, as recently reported by Ge et al. [Macromolecules 2009;42:4400] The simulation technique reported here may be extended to study biomolecular transports occurring in long protein channels, as studied experimentally through current-time or voltage-time traces.     

Etude voltamperometrique de la n-acetyl l-tyrosine amide sur electrode a pate de graphite en milleux aqueux I—comportement dans les domaines de balayage superieurs a 0,5 v/enh

Graphite paste electrode allows to determine elementary processes of the electrochemical oxidation in aqueous media of an electrochemical probe such as: N-acetyl L-tyrosine amide. Mathematical analysis of voltammograms gives the following EC mechanism: R?C₆H₅OH?R?C₆H₅O^. + H⁺ + e 2 R?C₆H₅O^. → R?C₆H₅O⁺ + R?C₆H₅O^?, R?C₆H₅O^? + H⁺ → R?C₆H₅OH, R?C₆H₅O⁺ → [R?C₆H₄O]^.. + H⁺, n[R?C₆H₄O]^.. → ?[R?C₆H₄O]^?_n.     

Three-dimensional diamond growth film simulations: correlations between nucleation and surface parameters

The development of a three-dimensional simulation of the diamond nucleation and growth presented in a previous paper has been used in this study to determine surface parameters such as the roughness, R_a, and porosity (filling factor Q) of diamond film, according to the crystal size (via the radius R) and the nucleation density N. Evolutions of these surface parameters are compared to values obtained by a statistical treatment (Poisson's law) based on the random nucleation and subsequent growth of hemispheres. In particular, we study the roughness variations with the parameter λ=πR²N, which seems to be the key variable in the case of coatings whose nucleation and growth are in agreement with the Volmer–Weber mechanism. From these results, it is possible to calculate some surface parameters that are useful for tribological and optical applications and whose evolutions with synthesis time have not been reported to our knowledge.     

Laser light-scattering studies of soluble high performance fluorine-containing polyimides

Two sets of soluble high performance polyimides synthesized from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′-(trifluoromethyl)-4,4′-diaminobiphenyl diamine (PFMB), and from 2,2′-bis(trifluoromethyl)-4,4′,5,5′-biphenyl-tetracarboxylic dianhydride (HFBPDA) and 2,2′-(trifluoromethyl)-4,4′-diaminobiphenyl diamine (PFMB) have been investigated by static and dynamic laser light scattering (LLS) in tetrahydrofuran (THF) at 30°C. The calibrations, for 6FDA-PFMB: <R_g> (nm) = 3.87 × 10^?2 <M_w> ^0.568, <R_h> (nm) = 2.38 × 10^?2 <M_w>^0.560 and <D> (cm²/s) = 2.13 × 10^?4 <M_w>^?0.560; for HFBPDA-PFMB: <R_g> (nm) = 2.24 × 10^?2 <M_w>^0.626, <R_h> (nm) = 1.27 × 10^?2 <M_w>^0.621 and <D> (cm²/s) = 3.99 × 10^?4 <M_w>^?0.621, have been established, where <M₂>, <R_g>, <R_h> and <D> are the weight-average molar mass, the root mean square z-average radius of gyration, the z-average hydrodynamic radius and the z-average translational diffusion coefficient, respectively. A combination of <M_w> and the translational diffusion coefficient distribution G(D) leads to the calibrations of D (cm²/s) = 2.41 × 10^?4M^?0.564 and D (cm²/s) = 6.16 × 10^?4M^?0.656 for 6FDA-PFMB and HFBPDA-PFMB, respectively, where D and M correspond to monodisperse species. With these calibrations, we can convert a translational diffusion coefficient distribution G(D) into a corresponding molar mass distribution f_w(M). On the basis of the Kratky-Porod wormlike chain model, the persistence lengths (q) were found to be ? 3.3 nm and ? 4.5 nm, respectively, for 6FDA-PFMB and HFBPDA-PFMB, which indicates that both polyimide chains have an extended conformation. In addition, <R_g> / <R_h> ? (1.7-1.9) shows that they are in coil conformation. Therefore, we conclude that both polyimides have an extended coil conformation.     

Size evolution of ion beam synthesized Pb nanoparticles in Al

The size evolution of Pb nanoparticles (NPs) synthesized by ion implantation in an epitaxial Al film has been experimentally investigated. The average radius R of Pb NPs was determined as a function of implantation fluence f. The R(f) data were analyzed using various growth models. Our observations suggest that the size evolution of Pb NPs is controlled by the diffusion-limited growth kinetics (R²∝f). With increasing implantation current density, the diffusion coefficient of Pb atoms in Al is evident to be enhanced. By a comparative analysis of the R(f) data, values of the diffusion coefficient of Pb in Al were obtained.     

The automation of electrode kinetics — III. The dissolution of Mg in Cl−, F− and OH− containing aqueous solutions

The dissolution of Mg in Cl^?, F^?, and OH^? containing aqueous solutions has been investigated over a large potential range, from far into H₂ evolution at ? 3000 mV (sce) to the passive state at ? 1400 mV (sce). The steady state current-potential and the impedance have been measured using a new automatic electrochemical measurement system. An equivalent circuit and a least squares fitting procedure have been used to analyse the data. The resulting C_dl-E, θ-E, σ_Mg-E, R_w,-E, and the primary i-E and Z(ω)-E data are compared for each anion, and reveal details of the electrode kinetics of these complex dissolution reactions.     

Defect modes for (200), GGTGG,tight fold re-entry in polyethylene single crystals

Lattice dynamical calculations on trans-planar polyethylene chains containing conformational defects of the type GGTGG have been carried out. The purpose of the work is to predict the points in the vibrational infra-red and/or Raman spectrum at which a tight, (200) type, fold should show absorptions and/or scattering. Calculations are verified for the cyclic hydrocarbon C₃₄H₆₈ which contains two GGTGG defects. The usefulness and limitations of the vibrational spectrum as evidence for the existence of (200) tight folds are discussed. Two infra-red bands near 1342 cm^?1 and a third near 700 cm^?1 may indicate GGTGG defects in single crystals. Raman spectra seem insensitive to such defects.     

Characterization of poly(1,4-phenyleneterephthalamide) in concentrated sulphuric acid. 2: Determination of molecular weight distributions

By combining static and dynamic properties (M_w, A₂, k_dR_g and R_h) of poly(1,4-phenyleneterephthalamide), PPTA (commercially known as Kevlar), with a detailed analysis of measured time correlation functions at different scattering angles in dilute solution, we have been able to estimate the molecular weight dependence of the radius of gyration, R_g(M), the persistence length ? ($\text{≈ 290}\text{A}\text{?}$), and the molecular weight distribution (M_z:M_w:M_n ≈ 6.2:1.8:1) using an unfractionated PPTA sample (M_w = 4.3 × 10⁴ g/mole). Laplace inversion of the time correlation function was accomplished independently by means of two different algorithms: the singular value decomposition technique with discrete multi-exponentials to approximate the normalized characteristic linewidth distribution function G(г) and the method of regularization whereby a linearized smoothing operator was used. The non-intrusive laser light scattering technique permits us to characterize, for the first time, the molecular weight distribution of PPTA which has been difficult to perform by means of other more established methods, such as size exclusion chromatography, because of the corrosive nature of solvents used in preparing PPTA solutions.