PEO Chain Length Research Articles

Nanoscopic Interfacial Hydrogel Viscoelasticity Revealed from Comparison of Macroscopic and Microscopic Rheology.

Deviations between macrorheological and particle-based microrheological measurements are often considered to be a nuisance and neglected. We study aqueous poly(ethylene oxide) (PEO) hydrogels for varying PEO concentrations and chain lengths that contain microscopic tracer particles and show that these deviations reveal the nanoscopic viscoelastic properties of the particle-hydrogel interface. Based on the transient Stokes equation, we first demonstrate that the deviations are not due to finite particle radius, compressibility, or surface-slip effects. Small-angle neutron scattering rules out hydrogel heterogeneities. Instead, we show that a generalized Stokes-Einstein relation, accounting for an interfacial shell around tracers with viscoelastic properties that deviate from bulk, consistently explains our macrorheological and microrheological measurements. The extracted shell diameter is comparable to the PEO end-to-end distance, indicating the importance of dangling chain ends. Our methodology reveals the nanoscopic interfacial rheology of hydrogels and is applicable to different kinds of viscoelastic fluids and particles.

Lignin-Derived Mesoporous Carbon for Sodium-Ion Batteries: Block Copolymer Soft Templating and Carbon Microstructure Analysis.

The demand for versatile and sustainable energy materials is on the rise, given the importance of developing novel clean technologies for transition to a net zero economy. Here, we present the synthesis, characterization, and application of lignin-derived ordered mesoporous carbons with various pore sizes (from 5 to approximately 50 nm) as anodes in sodium-ion batteries. We have varied the pore size using self-synthesized PEOn-b-PHAm block copolymers with different PEO and PHA chain lengths, applying the "soft templating" approach to introduce isolated spherical pores of 20 to 50 nm in diameters. The pore structure was evaluated by transmission electron microscopy (TEM), nitrogen physisorption, and small-angle X-ray scattering (SAXS). We report the microstructure analysis of such mesoporous lignin-based carbons using Raman spectroscopy and wide-angle X-ray scattering (WAXS). In comparison with nontemplated carbon and carbons templated employing commercial Pluronic F-127 and PIB50-b-PEO45, which created accessible channels and spherical pores up to approximately 10 nm in diameter, the carbon microstructure analysis revealed that templating with all applied polymers significantly impedes graphitization upon thermal treatment. Furthermore, the gained knowledge of similar carbon microstructures regardless of the type of template allowed the investigation of the influence of different pore morphologies in carbon applied as an anode material in sodium-ion batteries, supporting the previous theories in the literature that closed pores are beneficial for sodium storage while providing insights into the importance of pore size.

Molecular Dynamics Study on the Aggregation Behavior of Triton X Micelles with Different PEO Chain Lengths in Aqueous Solution.

The aggregation structure of Triton X (TX) amphiphilic molecules in aqueous solution plays an important role in determining the various properties and applications of surfactant solutions. In this paper, the properties of micelles formed by TX-5, TX-114, and TX-100 molecules with different poly(ethylene oxide) (PEO) chain lengths in TX series of nonionic surfactants were studied via molecular dynamics (MD) simulation. The structural characteristics of three micelles were analyzed at the molecular level, including the shape and size of micelles, the solvent accessible surface area, the radial distribution function, the micelle configuration, and the hydration numbers. With the increase of PEO chain length, the micelle size and solvent accessible surface area also increase. The distribution probability of the polar head oxygen atoms on the surface of the TX-100 micelle is higher than that in the TX-5 or TX-114 micelle. In particular, the tail quaternary carbon atoms in the hydrophobic region are mainly located at the micelle exterior. For TX-5, TX-114, and TX-100 micelles, the interactions between micelles and water molecules are also quite different. These structures and comparisons at the molecular level contribute to the further understanding of the aggregation and applications of TX series surfactants.

Effects of chain length and anions on ion transport in PEO-lithium salt systems

ABSTRACT Understanding the transport mechanism of Li+ in solid polymer electrolytes is beneficial for improving the safety and energy density of lithium-ion batteries. In this work, we investigate the effects of chain length of poly (ethylene oxide) (PEO) and anions (TfO-, TFSI-, PFSI-) on ion transport properties in PEO-lithium salt systems using all-atom molecular dynamics simulations. We found that the Li+ and PEO monomers are co-diffusion, regardless of the PEO chain length and the type of anion. The diffusion of Li+ becomes slower with PEO chain length and reaches an asymptotic value. In addition, the motion of the Li+ is the slowest in PEO/LiTfO systems. We conclude that the free volume of the systems plays a decisive role in the transport properties of Li+.

Synthesis and characterization of poly(ethylene oxide) based copolymer membranes for efficient gas/vapor separation: Effect of PEO content and chain length

Due to their high CO2 selectivity, poly(ethylene oxide) (PEO)-based membranes have raised attention to CO2-related gas separations. Nevertheless, the fabrication of such membranes is quite challenging as PEO suffers from poor film forming ability and high crystallization tendency, which restricts gas transport. In this work, a new series of CO2 and water selective aromatic polyethers bearing flexible PEO side chains prepared via a polycondensation reaction is reported. The synthesized copolymers are mechanically and thermally robust, completely amorphous even at 49 wt% PEO and form flexible, soft membranes. As observed, membrane permeation properties are significantly influenced by both PEO chain length and PEO loading. CO2 permeability increases with PEO loading, which is assigned mainly to the enhanced CO2 solubility contribution of the PEO segments. In particular, when PEO content is higher than 39 wt%, copolymers go from the glassy to the rubbery state, thus resulting in increased CO2 permeability due to the significant contribution of favorable CO2-PEO interactions along with a minimal diffusivity increase. CO2 selectivities over H2 and CH4 also increase as a function of PEO content mainly due to the strong solubility contribution on CO2 permeability enhancement. The copolymer with the highest PEO loading (49 wt%) and the longer PEO chain (750) shows both a maximum CO2 permeability of 11.2 Barrer and maximum ideal CO2/H2 and CO2/CH4 selectivities of 9.6 and 68, respectively, at 30 °C. The CO2/H2 ideal selectivity of 9.6 surpasses the upper bound. Moreover, these copolymers show high water permeability that is also strongly dependent on the PEO weight content and PEO chain length. Likewise, the highest water permeability (30,100 Barrer) is delivered by the copolymer with the highest PEO loading (49 wt%) and the longer PEO chain (750) at 30 °C. The highest H2O selectivity over CO2 (2688) observed for this copolymer is comparable with other PEO-based copolymers having excellent separation performance. These results support the possible application of these copolymers in hydrogen purification and dehydration of CO2 gas streams.

Conformation and solubility of poly(ethylene oxide) in polymer-surfactant complex at high-temperature and high-salinity conditions

The solubility of poly(ethylene oxide) (PEO) with molecular weight (MW) ranging from 300,000 to 6,000,000 g/mol was studied in aqueous solution in the presence of salt (sodium chloride, [NaCl] = 1 M) at various temperatures by cloud point measurement. All PEO solutions exhibited phase separation at temperature above 78 ± 1 °C, the cloud point was independent of PEO chain length within the selected range of MW. An anionic surfactant sodium dodecyl sulfate (SDS), and a cationic surfactant dodecyl tri-methyl ammonium chloride (DTAC) was added into the PEO solutions, respectively, to successfully eliminate the precipitation of the polymer at higher temperature (up to 90 °C). However, the effects of SDS and DTAC on the cloud point of PEO at various surfactant concentrations, as well as the rheological behaviors of PEO/SDS and PEO/DTAC solutions were completely different. This observation leads to a study of the molecular structures formed by PEO and the surfactants. The interactions between a monodisperse and short-chain PEO (MW = 20,000 g/mol) and the surfactants at molecular level were investigated via two-dimensional NMR techniques. Based on these results, two different conformations of PEO in PEO/SDS and PEO/DTAC complex were proposed and a saturation concentration of SDS binding to PEO backbone was determined. The findings in this study provide evidences that molecular interaction between a polymer and a surfactant in solution strongly affect the solubility of the polymer and the rheological property of the solution.

Langmuir-Blodgett Films of C60-end-capped Poly(ethylene oxide)

Buckyballs (C60) are linked to one end and two ends of linear poly(ethylene oxide) (PEO) chains through highly efficient click chemistry to obtain giant amphiphilic molecules C60-PEO and C60-PEO-C60, respectively. C60-PEO and C60-PEO-C60 molecules are spread on water surface and then transferred to solid substrates with Langmuir-Blodgett (LB) film deposition approach. C60-PEO and C60-PEO-C60 exhibit fractal growth behavior on the solid substrate under certain conditions owing to the crystallization ability of PEO segment. PEO chain length and the end capped mode both affect the fractal growth pattern.

Molecular weight fractionation by confinement of polymer in one-dimensional pillar[5]arene channels

Confinement of polymers in nano-spaces can induce unique molecular dynamics and properties. Here we show molecular weight fractionation by the confinement of single polymer chains of poly(ethylene oxide) (PEO) in the one-dimensional (1D) channels of crystalline pillar[5]arene. Pillar[5]arene crystals are activated by heating under reduced pressure. The activated crystals are immersed in melted PEO, causing the crystals to selectively take up PEO with high mass fraction. The high mass fractionation is caused by the greater number of attractive CH/π interactions between PEO C-H groups and the π-electron-rich 1D channel of the pillar[5]arene with increasing PEO chain length. The molecular motion of the confined PEO (PEO chain thickness of ~3.7 Å) in the 1D channel of pillar[5]arenes (diameter of ~4.7 Å) is highly restricted compared with that of neat PEO.

Accumulation of Glassy Poly(ethylene oxide) Anchored in a Covalent Organic Framework as a Solid-State Li+ Electrolyte.

Design of molecular structures showing fast ion conductive/transport pathways in the solid state has been a significant challenge. The amorphous or glassy phase in organic polymers works well for fast ion conductivity because of their dynamic and random structure. However, the main issue with these polymers has been the difficulty in elucidating the mechanisms of ion conduction and thus low designability. Furthermore, the amorphous or glassy state of ion conductive polymers often confronts the problems of structural/mechanical stabilities. Covalent organic frameworks (COFs) are an emerging class of crystalline organic polymers with periodic structure and tunable functionality, which exhibit potential as a unique ion conductor/transporter. Here, we describe the use of a COF as a medium for all-solid-state Li+ conductivity. A bottom-up self-assembly approach was applied to covalently reticulate the flexible, bulky, and glassy poly(ethylene oxide) (PEO) moieties that can solvate Li+ for fast transport by their segmental motion in the rigid two-dimensional COF architectures. Temperature-dependent powder X-ray diffraction and thermogravimetric analysis showed that the periodic structures are intact even above 300 °C, and differential scanning calorimetry and solid-state NMR revealed that the accumulated PEO chains are highly dynamic and exhibit a glassy state. Li+ conductivity was found to depend on the dynamics and length of PEO chains in the crystalline states, and solid-state Li+ conductivity of 1.33 × 10-3 S cm-1 was achieved at 200 °C after LiTFSI doping. The high conductivity at the specified temperature remains intact for extended periods of time as a result of the structure's robustness. Furthermore, we demonstrated the first application of a COF electrolyte in an all-solid-state Li battery at 100 °C.

Hydrogen Bonding Induced Co-Ordering and Interfacial Curvature Controlled Crystallization Behavior of Binary Copolymer Blends

We investigated the effects of the hydrogen-bonding interaction and molecular architecture on the phase and crystallization behaviors of binary copolymer blends. In blends comprising polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and polystyrene-block-poly(acrylic acid) (PS-b-PAA) block copolymers, the hydrogen bonding between PEO and PAA block chains improved their miscibility so that they shared the common domains and microphase-separated against the domains composed of PS block chains, keeping their junctions at the common interfaces. However, hydrogen bonds reduced the crystallizable chain length of PEO, causing crystallization to occur within a more confined region and at a lower temperature. In the PS-b-PEO and polystyrene-graft-poly(acrylic acid) (PS-g-PAA) blends, the junctions between the PS main chain and the branched PAA block chains in PS-g-PAA were also localized at the PS-b-PEO interface with the PS main chains segregated into PS microdomains and the PAA branches hydrogen-bonded with the ...

Highly controllable ambient atmosphere spray deposition of water dispersible poly(benzimidazobenzophenanthroline) films

Thin films of water dispersible poly(ethylene oxide) (PEO) functionalized poly(benzimidazobenzophenanthroline) (BBL) polymers have been prepared by a pulse spray technique on a spinning substrate in ambient atmosphere. The deposition method is advantageous for generating ultra-thin films of nanometer thicknesses. A single spray pulse was found in a reproducible manner to generate a layer of ca. 2 nm thickness. The PEO-chain length in the BBL functionalization had an essential influence on the building mechanism of the films. The polymers functionalized by short PEO chains induced the formation of very smooth films while longer PEO chains induced rough films and notable nanostructuration. The BBL-PEO film deposited using spray pulse deposition was found to be electro- and photoactive. The electron transfer processes observed are slightly different from earlier reported results for similar polymers, which is probably due to the very thin film. The films exhibited photocurrent generation when transformed into conducting form.

Hydrophobic and Elastic Forces Experienced by a Series of Pyrene End-Labeled Poly(ethylene oxide)s Interacting with Sodium Dodecyl Sulfate Micelles

A series of pyrene end-labeled poly(ethylene oxide)s (Py2-PEO(x) with x equal to 2, 3.4, 5, 6, 7.8, and 10 kg mol–1) were synthesized, and their interactions with SDS micelles were characterized by steady-state and time-resolved fluorescence. Pyrene excimer formation (PEF) indicated that both pyrenyl ends were located in the same SDS micelle whereas the absence of PEF reflected bridging of two SDS micelles by a Py2-PEO molecule having its pyrenyl end groups in separate micelles. PEF efficiency was characterized from the excimer-to-monomer fluorescence intensity ratio (IE/IM) which was determined as a function of PEO chain length and salt concentration. More detailed information about the PEF process was obtained by fitting the monomer and excimer fluorescence decays globally according to the model free analysis (MFA). MFA yielded the average rate constant ⟨k⟩ of PEF and the molar fraction (ffree) of pyrenyl labels that did not form excimer, thus reflecting the extent of bridging undergone by the Py2-PEO c...

Linear Viscoelasticity and Cation Conduction in Polyurethane Sulfonate Ionomers with Ions in the Soft Segment–Single Phase Systems

PEO-based polyurethane sulfonate ionomers with various PEO chain lengths and sodium counterions were synthesized and characterized by both linear viscoelasticity (LVE) and dielectric relaxation spectroscopy (DRS). Since p-phenylene diisocyanate is a small hard segment, the ionomers were found to be single phase with only one DSC Tg which increases with both ion content and hard segment content. An electrode polarization model was used to simultaneously determine the temperature dependence of conducting ion concentration and their mobility, which show Arrhenius and Vogel–Fulcher–Tammann (VFT) temperature dependences, respectively. The polymer dipole relaxation probed by DRS was found to be between 103 and 106 times faster than the mechanical segmental relaxation observed in LVE data near Tg, suggesting that most polymer modes need to wait for the ions to rearrange. The dielectric relaxation, mechanical relaxation, and ionic conductivity all show good correlation with DSC Tg and are related to ion rearrange...

Effect of Side Chains on the Low-Dimensional Self-Assembly of Polyphenylene-Based “Rod–Coil” Graft Copolymers in Solution

We synthesized a series of “rod–coil” graft copolymers containing a laterally expanded poly-p-phenylene (PPP) backbone grafted with nonionic poly(ethylene oxide) (PEO) or ionic poly(acrylic acid) (PAA) side chains (denoted as PPP-g-PEO or PPP-g-PAA). The effect of the side chains on the self-assembly of the graft copolymers in THF–water mixed solvents was investigated. The PPP-g-PEO copolymers exhibited temperature-dependent self-assembly behavior, which is affected by the grafting percentage (GP) and the degree of polymerization (DP) of PEO. At 25 °C, which is higher than the crystallization temperature (Tc) of the PEO chains, PPP-g-PEO self-assembled into ultralong helices with controlled pitches when PN > 6lm/4b, where P represents GP, N denotes DP of PEO, lm expresses the length of a repeating unit in PPP, and b is Kuhn monomer length of a free jointed PEO chain; when PN < 6lm/4b, only nonhelical nanowires were observed. At 10 °C, which is below Tc of PEO, PPP-g-PEO self-assembled into polygonal multi...

Dependence of Morphology, Shear Modulus, and Conductivity on the Composition of Lithiated and Magnesiated Single-Ion-Conducting Block Copolymer Electrolytes

Single-ion-conducting block copolymers are of considerable interest as electrolytes for battery systems, as they eliminate overpotentials due to concentration gradients. In this study, we characterize a library of poly(ethylene oxide) (PEO)-based diblock copolymers where the second block is poly(styrene-4-sulfonyltrifluoromethylsulfonyl)imide with either cation: univalent lithium or divalent magnesium counterions (PEO–PSLiTFSI or PEO–P[(STFSI)2Mg]). The PEO chain length is held fixed in this study. Polymers were synthesized in matched pairs that were identical in all aspects except for the identity of the counterion. Using rheology, SAXS, DSC, and AC impedance spectroscopy, we show that the dependence of morphology, modulus, and conductivity on composition in these charged copolymer systems is fundamentally different from uncharged block copolymers. At a given frequency and temperature, the shear moduli of the magnesiated copolymer systems were approximately 3–4 orders of magnitude higher than those of th...

Effect of sodium gluconate on dispersion of polycarboxylate superplasticizer with different grafting density in side chain

Abstract Sodium gluconate is a commonly used retarder, and the incorporation of SG has been accepted as the most efficient way to improve the basic performance of polycarboxylate superplasticizer (PCE) system in real concrete. However, this improvement cannot be always achieved, and the main reason for this uncertainty is because the interaction between PCE and SG has not completely understood. In order to gain deeper insight into this interaction, adsorption behavior and dispersion mechanism of PCE-SG system involved in two kinds of PCE with different grafting density of carboxyl groups in side chain have been investigated. Specifically, the dispersion was assessed with the fluidity of the cement paste, and adsorption behavior was estimated with total organic carbon and zeta potential. The combination between PCE and SG was characterized with conductivity, dynamic light scattering, and X-ray photoelectron spectroscopy. Finally, several models were proposed to illustrate the mechanism behind. The results show that gluconate grafted as side chain of PCE and the increase in length of PEO chain caused by addition of SG can provide contribution to dispersion. Competitive adsorption between SG and PCE would take place to reduce the dispersion, and the declining degree depends on the relative adsorption between PCE and SG. Dispersion of PCE-SG is not only dependent on added dosage of SG, but also decided by molecular structure of PCE. This result provides guidance on how to promote the basic performance of the PCE-retarder system in real engineering practice.

Soft segment length controls morphology of poly(ethylene oxide) based segmented poly(urethane-urea) copolymers in a binary solvent

It is known that morphology and structure-property behavior of poly(ethylene oxide) (PEO) based poly(urethane-urea) copolymers are affected by soft segment (SS) chain length. Here, a multi-scale computational study is carried out to determine the origins of this behavior, supported by atomic force microscopy (AFM) imaging. First, single PEO chains of varying lengths are comparatively examined by molecular dynamics and dissipative particle dynamics (DPD) simulations in THF:DMF solvent mixture to verify that the coarse graining strategy is applicable to the system at hand. In the second step, hard segment (HS) beads are attached to PEO chains to study their effect on the overall morphology. We find that the critical chain length of PEO plays a key role on the structure-property behavior of these copolymers. Density fields obtained from DPD calculations reveal a stable channel formation by SS beads in the copolymers if their length is below a threshold value. HS-SS interactions drive this behavior by promoting phase mixing. The role of the binary solvent is essential as the channel-like structures are not stable in the pure solvents. In contrast, for chains having long enough PEO segments, spontaneous clustering of the PEO units controls morphology development. This behavior gives rise to the formation of globular SS clusters surrounded by HS units. The dual solvent acts as a lubricant, with THF preferring the PEO clusters. Results obtained from DPD studies are corroborated by AFM images obtained for the corresponding copolymers. The strategy employed lays the foundations for developing systems having novel morphologies and macroscopic-properties using designs based on HS-SS cooligomers.

Comparison between protein repulsions by diblock PLA-PEO and albumin nanocoatings using OWLS

A previous investigation suggested that a surface bearing a rinsing-resistant depot (nanocoating) of albumin is more protein-repulsive than the same surface physically pegylated by a poly(D,L-lactic acid)-poly(ethylene oxide) diblock copolymer. To complement the study, Optical Waveguide Lightmode Spectroscopy was used to compare the mass and the thickness of protein depots from different systems, namely albumin alone at different concentrations, a mixture of albumin + fibrinogen + γ-globulin at their physiological concentrations, and sheep serum. The same standard OWLS protocol was applied to compare data for bare sensor chips, for chips covered by an albumin nanocoating, and for chips physically pegylated using poly(D,L-lactic acid)-poly(ethylene oxide) diblock copolymers with different compositions and block lengths. The strategy and the conditions being rather different from those generally used to study pegylation-related antifouling properties; the literature was first reviewed critically. Then full coverage of sensor chips by albumin was demonstrated. The comparative study confirmed that albumin was more protein-repulsive than any of the diblock copolymers, irrespective of the protein system. Furthermore, it was found that pegylated surfaces were albumin-repulsive only when the concentration of the protein solution flowing over the surface was very low (0.1 g/L). It was not possible to correlate the copolymer data to PEO chain density, chain length and existence of brush. The in vitro repulsive activity of albumin was not affected by drying and rehydration, a feature of interest for storage of albumin-coated surfaces. All these observations confirmed our preliminary findings and showed that considering model proteins individually or in mixtures at concentrations far from physiological concentrations are not suitable to reflect the reality of full blood-surface interactions.

Successive RAFT polymerization of poly(ethylene oxide) methyl ether methacrylates with different length of PEO chains giving diblock brush copolymers

Synthesis of diblock brush copolymers by RAFT polymerization of poly(ethylene oxide) methyl ether methacrylates with different length of PEO chains (PEOxMEMA, x=5, 9, 19, and 43) is reported. Polymerization products were characterized by SEC with tetra detection array (RI, LS, DP and UV) which enabled to get not only molecular characteristics but also estimate “livingness” of the polymers. Kinetics of polymerization of PEOxMEMA and characteristics of the polymers were dependent on the length of PEO chains but the differences were not large. Diblock brush copolymers synthesized by chain extension had higher dispersity compared to that of the homopolymers, and the copolymers with the longest PEO chains contained a fraction of the “died” chains. Synthesis of diblock brush copolymers by “one pot” RAFT polymerization was preferential over polymerization with isolation of the first block.

PEO hot melt extrudates for controlled drug delivery: Importance of the molecular weight

Poly(ethylene oxide) (PEO)-based hot melt extrudates offer an interesting potential as oral controlled drug delivery systems and can provide additional advantages, such as reducing the risk of drug abuse. Different polymer molecular weight PEOs are commercially available and can be used to prepare drug-loaded hot melt extrudates. Importantly, the macromolecular chain length impacts crucial system features, including the swelling and erosion kinetics of the systems, which determine the conditions for drug release. The aim of this study was to monitor the effects of changes in the PEO molecular weight (100, 200, 300, 600, 900, 1,000, 2,000, 4,000, 5,000, vs. 7000 kDa) on theophylline release from hot melt extrudates and to try to better understand the observed tendencies. The drug loading was kept constant at 10%. Interestingly, theophylline release substantially slowed down when increasing the PEO polymer molecular weight from 100 kDa to 600 kDa, but a further increase to 7000 kDa led only to a slight additional decrease in the drug release rate. Upon exposure to the release medium, a more or less important gel layer formed (depending on the PEO chain length), consisting of a transparent and a non-transparent part (due to the presence of non-dissolved theophylline crystals). These gel layers surrounded (solid) cores, which decreased in size with time. No clear correlation was found between: (i) the impact of the PEO polymer molecular weight on the drug release kinetics and (ii) the impact of the PEO polymer molecular weight on the dynamic changes in the thicknesses of the transparent and non-transparent gel layers, the dimensions of the (solid) cores, the dry mass (%), remaining PEO (%) or water content (%) of the different system portions. Interestingly, such a correlation was only observed with respect to the changes in the volume of the “(solid) cores + non-transparent gels” (dominated by the changes in their diameters).