Poly Ethylene Oxide Chains Research Articles

Li+Transport in Poly(Ethylene Oxide) Based Electrolytes: Neutron Scattering, Dielectric Spectroscopy, and Molecular Dynamics Simulations

The dynamics of Li(+) transport in polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imde mixtures are investigated by combining neutron spin-echo (NSE) and dielectric spectroscopy with molecular dynamics (MD) simulations. The results are summarized in a relaxation time map covering wide ranges of temperature and time. The temperature dependence of the dc conductivity and the dielectric α relaxation time is found to be identical, indicating a strong coupling between both. The relaxation times obtained from the NSE measurements at 0.05 Å(-1)<q<0.2 Å(-1) are of similar magnitude as the relaxation time of Li(+) predicted by MD simulation. Our results suggest that the characteristic live times of the ions within the oxygen cages are mainly determined by the α relaxation that corresponds to local segmental motions of polymers, to a much lesser extent by the main chain relaxation, and not at all by the β relaxation or other faster processes. It is the first time decisive experimental evidence for a microscopic picture of the Li ion transportation process is shown in which the PEO chain forms EO cages over several monomer units and the Li ion "jump" from cage to cage. The role of the backbone of the polymer is discussed and contributes signifcantly to the Li ion transportation process. Moreover, detailed characteristic length and time scales of the Li(+) transport process in this polymer electrolyte are identified and interpreted.

Molecular dynamics in PBA/PEO miktoarm star copolymers

Molecular dynamics of miktoarm star copolymers consisting of poly(n-butyl acrylate) PBA and polyethylene oxide (PEO) arms was studied by means of Broadband Dielectric Spectroscopy (BDS) and Nuclear Magnetic Resonance (NMR) methods. The spectroscopic studies were performed for three types of copolymers differing in the composition, namely materials containing 76%, 46% and 16% molar fraction of PBA arms. The local processes, described by the Arrhenius law (e.g. the anisotropic rotation of methyl groups and the anisotropic local motions in the PEO chain), were observed for the studied systems below the glass transition temperature. It was found that the investigated PBA/PEO miktoarm star copolymers are characterized by single glass transition, which may result from similar values of glass transition temperatures of the PBA and PEO polymers. The segmental dynamics in the studied systems was quantitatively described by using the Vogel-Fulcher-Tammann (VFT) relation applied to combined NMR and BDS data. Moreover, above the glass transition temperature the interfacial polarization and conductivity phenomena were detected with the BDS method for all systems under study.

Exploring the Folding Pattern of a Polymer Chain in a Single Crystal by Combining Single-Molecule Force Spectroscopy and Steered Molecular Dynamics Simulations

Understanding the folding pattern of a single polymer chain within its single crystal will shed light on the mechanism of crystallization. Here, we use the combined techniques of atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS) and steered molecular dynamics (SMD) simulations to study the folding pattern of a polyethylene oxide (PEO) chain in its single crystal. Our results show that the folding pattern of a PEO chain in the crystal formed in dilute solution follows the adjacent re-entry folding model. While in the crystal obtained from the melt, the nonadjacent folding with large and irregular loops contributes to big force fluctuations in the force-extension curves. The method established here can offer a novel strategy to directly unravel the chain-folding pattern of polymer single crystals at single-molecule level.

Manipulating Crystal Orientation of Poly(ethylene oxide) by Nanopores

The confined crystallization behavior of a low molecular weight monodisperse polyethylene oxide (PEO) in anodic alumina oxide (AAO) templates was investigated. Homogeneous nucleation of polymer in AAO templates was confirmed. Within AAO with diameter larger than the contour length of PEO chains, the "kinetics selective growth" crystallization mechanism was confirmed based on the observation that the chain axis preferentially aligned perpendicular to the pore axis. However, when AAO diameter further decreases to a value smaller than the contour length of PEO, unique orientation with chain axis aligned parallel to the pore axis was observed for the first time. The results were discussed based on the competition between thermodynamics and kinetics during the crystallization process.

Water‐Soluble Fluorescent Probes Based on Dendronized Polyfluorenes for Cell Imaging

Novel water-soluble dendronized fluorescent polyfluorenes (DFPFs) are prepared from hydrophilic monomers and hydrophobic comonomers. Incomplete energy transfer is found to result in a two-color emission of the DFPFs at around 410 and 650 nm. The incomplete energy transfer can be attributed to the poor compatibility between the fluorene and benzothiadiazole units. Polyethylene oxide (PEO) encapsulation of the DFPFs shows over 90% cell viability, indicating good biocompatibility. These DFPFs show differential cellular uptake. P1 with fewer PEO chains exhibits limited cellular membrane uptake and low brightness in cells. By contrast, P3 with more PEO chains is efficiently internalized by cells and accumulated in the cytoplasm. A strong fluorescence from whole cells is also observed.

Quantifying nisin adsorption behavior at pendant PEO layers

The antimicrobial peptide nisin shows potent activity against Gram-positive bacteria including the most prevalent implant-associated pathogens. Its mechanism of action minimizes the opportunity for the rise of resistant bacteria and it does not appear to be toxic to humans, suggesting good potential for its use in antibacterial coatings for selected medical devices. A more quantitative understanding of nisin loading and release from polyethylene oxide (PEO) brush layers will inform new strategies for drug storage and delivery, and in this work optical waveguide lightmode spectroscopy was used to record changes in adsorbed mass during cyclic adsorption-elution experiments with nisin, at uncoated and PEO-coated surfaces. PEO layers were prepared by radiolytic grafting of Pluronic® surfactant F108 or F68 to silanized silica surfaces, producing long- or short-chain PEO layers, respectively. Kinetic patterns were interpreted with reference to a model accounting for history-dependent adsorption, in order to evaluate rate constants for nisin adsorption and desorption, as well as the effect of pendant PEO on the lateral clustering behavior of nisin. Nisin adsorption was observed at the uncoated and F108-coated surfaces, but not at the F68-coated surfaces. Nisin showed greater resistance to elution by peptide-free buffer at the uncoated surface, and lateral rearrangement and clustering of adsorbed nisin was apparent only at the uncoated surface. We conclude peptide entrapment at the F108-coated surface is governed by a hydrophobic inner region of the PEO brush layer that is not sufficient for nisin entrapment in the case of the shorter PEO chains of the F68-coated surface.

ポリカルボン酸系分散剤の化学構造が炭酸カルシウムへの吸着挙動と懸濁液の粘性に及ぼす影響

ポリカルボン酸系分散剤（以下、PC）の化学構造が、炭酸カルシウム（以下、CC）懸濁液の粘性低減効果とPC吸着量との関係に及ぼす影響を検討した。この結果、水和反応を生じないCC系においては、モノマーユニット換算でのPC吸着量あたりの粘性低減効果はPCの主鎖長に依らず等しく、側鎖に関しては長いPC程高い効果を発揮することが明らかとなった。さらに、レオロジー的アプローチによる吸着層厚の推定および、CC表面錯体反応の考慮によるPC吸着サイト分布の計算の併用によりPCの吸着形態を検討した結果、側鎖の短いPCはPC同士が凝集した状態でCC表面に吸着することで厚い吸着層を形成している可能性が示唆された。

A mechanistic study explaining the synergistic viscosity increase obtained from polyethylene oxide (PEO) and β-naphthalene sulfonate (BNS) in shotcrete

In shotcrete, a combination of polyethylene oxide (PEO) and β-naphthalene sulfonate (BNS) is commonly applied to reduce rebound. Here, the mechanism for the synergistic viscosity increase resulting from this admixture combination was investigated via x-ray diffraction (XRD), infrared and nuclear magnetic resonance (NMR) spectroscopy. It was found that the electron-rich aromatic rings present in BNS donate electrons to the alkyl protons of PEO and thus increase the electron density there. This rare interaction is known as CH–π interaction and leads to the formation of a supramolecular structure whereby PEO chains bind weakly to BNS molecules. Through this mechanism a polymer network exhibiting exceptionally high molecular weight and thus viscosity is formed. Among polycondensates, sulfanilic acid–phenol–formaldehyde (SPF) provides even higher synergy with PEO than BNS while melamine (PMS), acetone (AFS) or polycarboxylate (PCE) based superplasticizers do not work at all. Effectiveness of lignosulfonates is dependent on their degree of sulfonation.

Structure and dynamics of water in nonionic reverse micelles: A combined time-resolved infrared and small angle x-ray scattering study

We study the structure and reorientation dynamics of nanometer-sized water droplets inside nonionic reverse micelles (water/Igepal-CO-520/cyclohexane) with time-resolved mid-infrared pump-probe spectroscopy and small angle x-ray scattering. In the time-resolved experiments, we probe the vibrational and orientational dynamics of the O-D bonds of dilute HDO:H(2)O mixtures in Igepal reverse micelles as a function of temperature and micelle size. We find that even small micelles contain a large fraction of water that reorients at the same rate as water in the bulk, which indicates that the polyethylene oxide chains of the surfactant do not penetrate into the water volume. We also observe that the confinement affects the reorientation dynamics of only the first hydration layer. From the temperature dependent surface-water dynamics, we estimate an activation enthalpy for reorientation of 45 ± 9 kJ mol(-1) (11 ± 2 kcal mol(-1)), which is close to the activation energy of the reorientation of water molecules in ice.

Convenient Approach to Polypeptide Copolymers Derived from Native Proteins

A convenient approach for the synthesis of narrowly dispersed polypeptide copolymers of defined compositions is presented. The controlled denaturation of the proteins serum albumin and lysozyme followed by an in situ stabilization with polyethylene(oxide) chains yields polypeptide side chain copolymers of precisely defined backbone lengths as well as the presence of secondary structure elements. Supramolecular architectures are formed in solution because of the presence of hydrophobic and hydrophilic amino acids along the polypeptide main chain. Polypeptide copolymers reported herein reveal excellent solubility and stability in aqueous media and no significant cytotoxicity at relevant concentrations, and they can be degraded via proteolysis, which is very attractive for biomedical applications. This "semi-synthetic chemistry" approach is based on a novel and convenient concept for producing synthetic polypeptides from native protein resources, which complements traditional polypeptide synthesis and expression approaches and offers great opportunities for the preparation of diverse polypeptides with unique architectures.

Investigating the effectiveness of PEO/PPO based copolymers as dispersing agents for graphitic carbon black aqueous dispersions

The dispersability of graphitic carbon black, selected as a model for carbon nanotubes, has been investigated using a combination of rheological, conductivity and atomic force microscopy (AFM) techniques. The effectiveness of three PEO/PPO based non-ionic dispersants, namely polyethylene oxide polypropylene oxide ABA copolymers (synperonic PE/F 103 with 2×16 ethylene oxide units and PE/F 108 with 2×148 ethylene oxide units) and NPE1800 (nonyl phenyl polypropylene oxide-polyethylene oxide with 27 ethylene oxide units), is reported. Adsorption isotherms were determined for these dispersants. The adsorption isotherms of PE/F 103 in comparison with PE/F 108 revealed that in molar terms (μmol/m2) the adsorption decreases for PE/F 108 with more ethylene oxide units, indicating that adsorption is governed by size of the PEO (polyethylene oxide) chain length. Also, the synperonic PE series which has polypropylene oxide as an anchor group and does not contain any aromatic ring in their anchoring group, gave lower adsorption amounts (in moles) as compared to the NPE 1800 which contains an aromatic ring (nonyl phenyl) in its anchoring group as well as propyleneoxide. The relative viscosity-effective volume fraction Φ′ curves are compared with the theoretical curves for the hard sphere dispersions calculated using Krieger–Dougherty equation. For the graphitic carbon black studied here, in an aqueous medium, neither PE/F 103, nor PE/F 108 showed good agreement with the Krieger–Dougherty equation; the viscosities were all much higher than that predicted by that equation. Whilst NPE 1800 produced dispersions of lower viscosity and the viscosity values showed a good agreement with the Krieger–Dougherty equation. The results achieved from oscillatory measurements showed that PE/F 103 and PE/F 108 dispersants showed a frequency cross-over of G′ and G″ at lower volume fractions. Also they produced dispersions of high electrical conductivity, suggesting that these systems are aggregated. In the AFM force spectroscopy measurements, the interactions between the adsorbed layers of PE/F103 were initially attractive, whilst somewhat surprisingly the PE/F 108 adsorbed layers only showed repulsive interactions on approach and separation. NPE 1800 stabilised systems exhibited much lower viscosity and elastic modulus than the PE/F stabilised dispersions; produced dispersions of lower electrical conductivity and showed repulsive interactions in AFM, suggesting that these systems are much more stable than the carbon black dispersions bearing adsorbed PE/F polymers.The results indicated that synperonics (PE/F 103 and PE/F 108) are not a good dispersants for graphitic carbon black and by consequence for carbon nanotubes; whilst NPE 1800 is a suitable dispersant for these dispersions and could be a good dispersant for carbon nanotubes.

Aggregation equilibria of amphiphilic phthalocyanines substituted by polyethylene oxide in dichloromethane

The aggregation equilibria of metal-free and copper(II) phthalocyanine compounds substituted by polyethylene oxide at β (2 or 3, 9 or 10, 16 or 17, 23 or 24) positions, TDEO6-MPc, in deuterated dichloromethane were studied by means of 1H NMR spectroscopy. Where the side chain polyethylene oxide is hexaethyleneglycolmonododecylether (DEO6). The results of concentration dependence of 1H NMR signals reveal that the metal-free phthalocyanine TDEO6-H2Pc and copper complex TDEO6-CuPc successively form the aggregates up to trimer and tetramer in the concentration range of Pc, C Pc = 10-5.5–10-1.5 M , respectively. Formation constants and chemical shifts of each aggregate were determined by non-linear regression analysis of chemical shift change. The structures of TDEO6-MPc aggregates were estimated as TDEO6-MPc is successively stacked face to face. The phthalocyanine rings in the aggregate is slipped between them, the slippage, however, is not so large. DEO6 side chains are flexible and move freely.

Molecular dynamics simulation study of solvent effects on conformation and dynamics of polyethylene oxide and polypropylene oxide chains in water and in common organic solvents

In this paper, the conformation and dynamics properties of polyethylene oxide (PEO) and polypropylene oxide (PPO) polymer chains at 298 K have been studied in the melt and at infinite dilution condition in water, methanol, chloroform, carbon tetrachloride, and n-heptane using molecular dynamics simulations. The calculated density of PEO melt with chain lengths of n = 2, 3, 4, 5 and, for PPO, n = 7 are in good agreement with the available experimental data. The conformational properties of PEO and PPO show an increasing gauche preference for the O-C-C-O dihedral in the following order water>methanol>chloroform>carbon tetrachloride = n-heptane. On the contrary, the preference for trans conformation has a maximum in carbon tetrachloride and n-heptane followed in the order by chloroform, methanol, and water. The PEO conformational preferences are in qualitative agreement with results of NMR studies. PEO chains formed different types of hydrogen bonds with polar solvent molecules. In particular, the occurrence of bifurcated hydrogen bonding in chloroform was also observed. Radii of gyration of PEO chains of length larger than n = 9 monomers showed a good agreement with light scattering data in water and in methanol. For the shorter chains the observed deviations are probably due to the enhanced hydrophobic effects caused by the terminal methyl groups. For PEO the fitting of end-to-end distance distributions with the semi-flexible chain model at 298 K provided persistence lengths of 0.375 and 0.387 nm in water and methanol, respectively. Finally, the radius of gyration of Pluronic P85 turned out to be 2.25 ± 0.4 nm at 293 K in water in agreement with experimental data.

A Study of the Deformation, Network, and Aging of Polyethylene Oxide Films by Infrared Spectroscopy and Calorimetric Measurements

The calorimetric and infrared (IR) spectroscopy measurements of polyethylene oxide (PEO) are used to evaluate the deformation and relaxation that films experience during a temperature cycle (30°C–90°C–30°C). After melting, the intensity of some bands decreases by 10 to 70%. During the temperature cycle, the C–O band in the 1100 cm−1 region and the C–C–O deformation bands at 650 and 500 cm−1 show some new features. A network of cooperative oxygen-hydrogen interactions between the PEO chains form in films with special history, namely, in thermally treated films, in thin films prepared from gel forming solutions, and in thick films after aging. The interchain interaction network is suggested from the IR absorption bands in the 1200 and 900 cm−1 region and also from small bands at 1144 and 956 cm−1. The network seems absent or reduced in thin films. IR spectroscopy appears a sensitive technique to study chain conformations in PEO films and in other materials where order, disorder, and the formation of intermolecular interactions coexist.

Host–guest interactions in polycationic human serum albumin bioconjugates

Polycationic human serum albumin, cHSA, as well as cHSA conjugates with multiple polyethylene(oxide) chains of two different lengths were synthesized, and the uptake and release of spin-labeled fatty acid (FA) ligands were quantitatively analyzed by continuous wave (CW) electron paramagnetic resonance (EPR) spectroscopy and nanoscale distance measurements with double electron–electron resonance (DEER) spectroscopy. It is found that the seven FA binding pockets of native HSA are less well accessible by FAs in cHSA and its PEO-conjugates. A large number (at least 25) of FAs can diffusely and electrostatically be bound to the surface of all highly cationic serum albumin variants. These bound FAs show a remarkable resilience against release from both cHSA and PEO conjugates. Conjugation of PEO chains to cHSA had only minute effects on all EPR data, indicating that PEO grafts can be used without reduction of effectiveness in the ligand binding.

Preparation of PEO/clay nanocomposites using organoclay produced via micellar adsorption of CTAB.

The aim of this study was the preparation of polyethylene oxide (PEO)/clay nanocomposites using organoclay produced via micellar adsorption of cethyltrimethyl ammonium bromide (CTAB) and their characterisation by X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectra, and the investigation of certain mechanical properties of the composites. The results show that the basal distance between the layers increased with the increasing CTAB/clay ratio as parallel with the zeta potential values of particles. By considering the aggregation number of CTAB micelles and interlayer distances of organo-clay, it could be suggested that the predominant micelle geometry at lower CTAB/clay ratios is an ellipsoidal oblate, whereas, at higher CTAB/clay ratios, sphere-ellipsoid transition occurs. The increasing tendency of the exfoliation degree with an increase in clay content may be attributed to easier diffusion of PEO chains to interlayer regions. FT-IR spectra show that the intensity of Si-O stretching vibrations of the organoclays (1050 cm−1) increased, especially in the ratios of 1.0 g/g clay and 1.5 g/g clay with the increasing CTAB content. It was observed that the mechanical properties of the composites are dependent on both the CTAB/clay ratios and clay content of the composites.

Modification of Polyurethane Surface with an Antithrombin–Heparin Complex for Blood Contact: Influence of Molecular Weight of Polyethylene Oxide Used as a Linker/Spacer

Polyurethane (PU) was modified using isocyanate chemistry to graft polyethylene oxide (PEO) of various molecular weights (range 300-4600). An antithrombin-heparin (ATH) covalent complex was subsequently attached to the free PEO chain ends, which had been functionalized with N-hydroxysuccinimide (NHS) groups. Surfaces were characterized by water contact angle and X-ray photoelectron spectroscopy (XPS) to confirm the modifications. Adsorption of fibrinogen from buffer was found to decrease by ~80% for the PEO-modified surfaces compared to the unmodified PU. The surfaces with ATH attached to the distal chain end of the grafted PEO were equally protein resistant, and when the data were normalized to the ATH surface density, PEO in the lower MW range showed greater protein resistance. Western blots of proteins eluted from the surfaces after plasma contact confirmed these trends. The uptake of ATH on the PEO-modified surfaces was greatest for the PEO of lower MW (300 and 600), and antithrombin binding from plasma (an indicator of heparin anticoagulant activity) was highest for these same surfaces. The PEO-ATH- and PEO-modified surfaces also showed low platelet adhesion from flowing whole blood. It is concluded that for the PEO-ATH surfaces, PEO in the low MW range, specifically MW 600, may be optimal for achieving an appropriate balance between resistance to nonspecific protein adsorption and the ability to take up ATH and bind antithrombin in subsequent blood contact.

Four-dimensional structural dynamics of sheared collagen networks

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AFM IMAGING AND SINGLE-MOLECULE FORCE SPECTROSCOPY STUDIES ON MACROMOLECULAR INTERACTIONS AT SINGLE-MOLECULE LEVEL

The investigations on macromolecular interactions at the single-molecule level using atomic force microscopy(AFM) imaging and AFM-based single-molecule force spectroscopy(SMFS),with an emphasis on the combination of these two methods,have been discussed on the base of the author's recent work in related fields.First,AFM imaging(including static air phase and in situ liquid phase AFM imaging) is used to detect the effect of protein-binding on the topology of double stranded DNA(dsDNA) based on the characteristic(spaghetti-like) AFM image of dsDNA.Then,SMFS study on the nature of force-induced conformation transition of dsDNA is demonstrated.The force-fingerprint of dsDNA can then be used to study protein-DNA interactions revealing the effects of protein-binding on the dynamic conformation of dsDNA.In addition,the application of AFM-based SMFS in the investigation of RNA-protein coat interactions in an intact plant virus,tobacco mosaic virus(TMV),has been demonstrated.To realize this,a TMV particle is immobilized perpendicularly on a gold-coated substrate.The genetic RNA can then be pulled step-by-step out of the TMV particle through its 5′ opening.This study extends the force spectroscopy technique to the investigation of nucleic acid-protein interactions in more complicated biological systems(i.e.,in the virus particle).Finally,the attempt in the quantitative study of polymer interactions in a polyethylene oxide(PEO) single crystal is successfully accomplished by pulling a single PEO chain via its thiol-labelled end out of its single crystal by a good in situ combination of AFM imaging and SMFS.The generality of the established method in the investigation of crystallization of other polymers is discussed.This quantitative information on inter-and intramolecular interactions of macromolecules is useful in revealing the mechanism of many important biological processes(such as DNA replication) as well as in the design of high-performance polymer materials.

Lithium ion transport and ion–polymer interaction in PEO based polymer electrolyte plasticized with ionic liquid

The polyethylene oxide (PEO) based lithium ion conducting polymer electrolytes complexed with lithium trifluoromethanesulfonate (LiCF 3SO 3 or LiTf) plasticized with an ionic liquid 1-ethyl 3-methyl imidazolium trifluoromethanesulfonate (EMITf) have been reported. Morphological, spectroscopic, thermal and electrochemical investigations demonstrate promising characteristics of the polymer films, suitable as electrolyte in various energy storage/conversion devices. Significant structural changes have been observed in the polymer electrolyte due to the ionic liquid addition, investigated by X-ray diffraction (XRD) and optical microscopy. The ion-polymer interaction, particularly the interaction of imidazolium cation with PEO chains, has been evidenced by IR and Raman spectroscopic studies. The optimized composition of the polymer electrolyte i.e. PEO 25.LiTf + 40 wt.% EMITf offer room temperature ionic conductivity of ~ 3 × 10 − 4 S cm − 1 with wide electrochemical stability window and excellent thermal stability. The ‘σ versus 1/T’ curves show apparent Arrhenius behavior below and above melting temperature. The ionic conductivity has been observed due to Li + ions, as confirmed from 7Li-NMR studies, though the component ions of ionic liquid and anions also contribute significantly to the overall conductivity.