Ethylene Oxide Oligomers Research Articles

Probing the Process of Electron Transfer in Microemulsions with Substituted Ferrocenes

Recently, we reported studies in which microemulsion-based electrolytes were used in redox flow batteries. That work built on studies of the electrochemistry of ferrocene in toluene/water/TWEEN® 20 microemulsions which showed the electron transfer to be remarkably facile, with reversible or quasi-reversible kinetics observed in cyclic voltammetry experiments with scan rates up ~20 V/sec. To rationalize these high rates, we speculated that the oxidation of ferrocene to ferricenium ion was accompanied by rather subtle changes in the ‘space charge’ region associated with ions in the aqueous sub-phase/hydrophilic interphase. (TWEEN® is a. non-ionic surfactant with multiple ethylene oxide oligomers as its head group.). However, it is also possible that the ferricenium ion is ejected into the aqueous phase. The latter process could lead to instability during cycling of the battery. To probe this question, we are exploring the electrochemistry and other associated dynamic processes in toluene/water/TWEEN® 20 microemulsions that contain various substituted ferrocene derivatives as electroactive components. Compounds were chosen using estimates of dipole moments from quantum mechanical calculations to provide an initial screen of polarity. Modifications ranging from mono- and di-carboxylic acid derivatives and a series of esters synthesized from the acids, to tertiary amines and to decamethyl ferrocene were probed. An overview of the outcomes of these studies will be presented, together with a discussion of implications for microemulsion ‘design’ to co-optimize electron transfer rate and cycling stability of the system when used batteries.

Deciphering the Formation and Accumulation of Solid-Electrolyte Interphases in Na and K Carbonate-Based Batteries.

The continuous solid-electrolyte interphase (SEI) accumulation has been blamed for the rapid capacity loss of carbon anodes in Na and K ethylene carbonate (EC)/diethyl carbonate (DEC) electrolytes, but the understanding of the SEI composition and its formation chemistry remains incomplete. Here, we explain this SEI accumulation as the continuous production of organic species in solution-phase reactions. By comparing the NMR spectra of SEIs and model compounds we synthesized, alkali metal ethyl carbonate (MEC, M = Na or K), long-chain alkali metal ethylene carbonate (LCMEC, M = Na or K), and poly(ethylene oxide) (PEO) oligomers with ethyl carbonate ending groups are identified in Na and K SEIs. These components can be continuously generated in a series of solution-phase nucleophilic reactions triggered by ethoxides. Compared with the Li SEI formation chemistry, the enhancement of the nucleophilicity of an intermediate should be the cause of continuous nucleophilic reactions in the Na and K cases.

Stabilizing SEI by cyclic ethers toward enhanced K+ storage in graphite

The poor cycling stability of graphite in traditional ester electrolyte limits its applications as anodes for potassium ion batteries (KIBs). Herein, we demonstrate that the introduction of cyclic ether co-solvents into ester electrolytes can remarkably enhance the cycling stability of graphite anodes. The graphite anode in ester electrolyte with cyclic ether could achieve a reversible capacity of 196.1 mAh g−1 after 100 cycles at 0.3 C (1 C = 280 mA g−1), about three times higher than those in ester electrolytes with or without linear ether. Compared with the SEI formed in ester electrolytes, the addition of tetrahydrofuran promotes the generation of K2CO3 and ethylene oxide oligomers (PEO), of which the K2CO3 is expected to be more conductive and PEO is mechanically robust. The more uniform, conductive and stable solid electrolyte interphases (SEIs) on graphite in electrolytes with cyclic ethers contribute to the enhancement of the electrochemical performances of graphite. This work provides a novel design of commercialized electrolytes to achieve high-performance anodes for KIBs, which potentially accelerates the development of KIBs.

Polymer Functionalized Nanoparticles in Blue Phase LC: Effect of Particle Shape

Ethylene oxide oligomers and polymers, free and tethered to gold nanoparticles, were dispersed in blue phase liquid crystals (BPLC). Gold nanospheres (AuNPs) and nanorods (AuNRs) were functionalized with thiolated ethylene oxide ligands with molecular weights ranging from 200 to 5000 g/mol. The BPLC mixture (ΔTBP ~6 °C) was based on the mesogenic acid heterodimers, n-hexylbenzoic acid (6BA) and n-trans-butylcyclohexylcarboxylic acid (4-BCHA) with the chiral dopant (R)-2-octyl 4-[4-(hexyloxy)benzoyloxy]benzoate. The lowest molecular weight oligomer lowered and widened the BP range but adding AuNPs functionalized with the same ligand had little effect. Higher concentrations or molecular weights of the ligands, free or tethered to the AuNPs, completely destabilized the BP. Mini-AuNRs functionalized with the same ligands lowered and widened the BP temperature range with longer mini-AuNRs having a larger effect. In contrast to the AuNPs, the mini-AuNRs with the higher molecular weight ligands widened rather than destabilized the BP, though the lowest MW ligand yielded the largest BP range, (ΔTBP > 13 °C). The different effects on the BP may be due to the AuNPs accumulating at singular defect sites whereas the mini-AuNRs, with diameters smaller than that of the disclination lines, can more efficiently fill in the BP defects.

A Phase-Changing Polymer Film for Broadband Smart Window Applications.

Smart windows (SWs) with tunable opacity are sought to regulate solar-irradiation and privacy protection. A new smart window material based on a phase-changing polymer that can be reversibly switched between a semicrystalline, opaque state and an amorphous, transparent state is introduced. The polymer film is a network of the phase-changing poly(stearyl acrylate) crosslinked with a poly(ethylene oxide) oligomer. The two constituent polymers show strong phase separation. The transmission switching of the resulting copolymer film is resulted from the combination of three different mechanisms: reversible phase changing of the poly(stearyl acrylate) component, phase separation between the two distinct constituent polymers, and a large change of refractive index of the phase-changing polymer during the amorphous-to-semicrystalline transition. The opaqueness switching can be reversed and repeated for more than 500 cycles of heating and cooling. A silver nanowire (AgNW)-based transparent heater is combined with the SW film to control the semicrystalline-to-amorphous phase transition. The resulting smart window exhibits a high infrared transmittance modulation (ΔTIR ) of 80.4% and solar transmittance modulation (ΔTsolar ) of 70.2%, which significantly outperform existing thermochromic smart windows.

High‐Safety All‐Solid‐State Lithium‐Ion Battery Working at Ambient Temperature with In Situ UV‐Curing Polymer Electrolyte on the Electrode

AbstractThe development of wearable electronic devices prompts the demand for high‐safety all‐solid‐state lithium‐ion batteries (ASSLIBs), which can work at ambient temperature with comparable performance to traditional commercial lithium‐ion batteries. In this work, a three‐dimensional network design to overcome the contradiction between ionic conductivity and mechanical strength in polymer electrolytes is proposed. The designed solid polymer electrolyte (SPE) has the ion‐conducting group (oligomeric ethylene oxide) fixed on the side chains, whereas the main chain is crosslinked polyacrylate, providing good mechanical strength. Succinonitrile (SN) is uniformly dispersed in the cross‐linked network as an additive. The prepared SN−SPE shows a high ionic conductivity of 4.6×10−4 S cm−1 at 25 °C with a Li+‐ion transference number of 0.45 and an excellent electrochemical stability window up to 4.6 V (vs. Li+/Li). The preparation method allows that the electrolyte can be UV‐cured in situ on the cathode to achieve a cathode‐electrolyte integrated electrode, which enhances the interface contact and decreases the interface resistance. As‐fabricated LiFePO4//Li4Ti5O12 cathode‐electrolyte integrated ASSLIBs can deliver a discharge capacity of 155.88 mAh g−1 at 0.2 C at room temperature and a capacity retention up to 93.62 % after 100 charge‐discharge cycles. The reported polymer electrolyte and advanced assembly process provided a promising strategy for the wearable ASSLIBs.

Effect of Solvent Polarity on Enthalpies of Solvation of Ethylene Oxide Oligomers

The enthalpies of dissolution, ΔsolHm∞, and solvation, ΔsolvHm∞, of ether oligomers CH3O(CH2CH2O)nCH3 (n = 1–4) in ethyl acetate, pyridine, N,N-dimethylformamide, and acetonitrile have been determi...

Synthesis of Hydrophilic Polyamide Copolymers Based on Nylon 6 and Nylon 46

Hydrophilic polyamide copolymers were successfully synthesized based on Nylon 6 and Nylon 46. This study aims to synthesize hydrophilic polyamides with moisture regain ability comparable to that of cotton. Random copolymers of nylon 6 and nylon 46 did not exhibit moisture regain rates higher than 6 %. A limited introduction of trifunctional monomer, diethylenetriamine (TA) produced the polyamides with higher mechanical strengths but failed to enhance the moisture regain. The incorporation of poly(ethylene oxide) oligomer with amine end groups increased the moisture regain but resulted in poor hydro-thermal and mechanical strength. A synergic effect was observed for copolymers which contain both nylon 46 units and PEO oligomer in regards to moisture regain capacity. Furthermore, the poor hydro-thermal and mechanical strength of Nylon/PEO segmented polyamides were drastically improved by the introduction of diethylenetriamine (TA). This study demonstrated that the polyamide copolymers comprising both PEO oligomer and TA unit record tensile moduli over 3 GPa and moisture regain rates of 8–10 wt%.

Understanding the Electrode/Electrolyte Interface Layer on the Li-Rich Nickel Manganese Cobalt Layered Oxide Cathode by XPS.

Layered lithium-rich nickel manganese cobalt oxide (LR-NMC) represents one of the most promising cathode materials for application in high energy density lithium-ion batteries. The extraordinary capacity delivered derives from a combination of both cationic and anionic redox processes. However, the latter ones lead to oxygen evolution which triggers structural degradation and electrode/electrolyte interface (EEI) instability that hinders the use of LR-NMC in practical application. In this work, we investigate the surface chemistry of LR-NMC and its evolution upon different conditions to give further insights into the processes occurring at the EEI. X-ray photoelectron spectroscopy studies reveal that once the organic component of the layer is formed, it remains stable independently on the higher cutoff voltage applied, while continuous growth of inorganics along with oxygen evolution occurs. The results performed on lithiated and delithiated LR-NMC surfaces indicate an instability of the EEI layer formed at high voltages, which undergoes a partial decomposition. Furthermore, the tris(pentafluorophenyl)borane electrolyte additive simultaneously prevents excess LiF formation and changes the chemical composition of the EEI layer. The latter is characterized by a higher amount of poly(ethylene oxide) oligomer species and LixPOyFz formation. In addition, the presence of boron-containing compounds in the EEI layer cannot be excluded, which may be also responsible of the increased thickness of the EEI layer. Finally, fast kinetics at elevated temperatures exacerbate the salt decomposition which results in the formation of an EEI which is thicker and richer in LiF.

Noncontact Imaging of Ion Dynamics in Polymer Electrolytes with Time-Resolved Electrostatic Force Microscopy.

Ionic-transport processes govern performance in many classic and emerging devices, ranging from battery storage to modern mixed-conduction organic electrochemical transistors (OECT). Here, we study local ion-transport dynamics in polymer films using time-resolved electrostatic force microscopy (trEFM). We establish a correspondence between local and macroscopic measurements using local trEFM and macroscopic electrical impedance spectroscopy (EIS). We use polymer films doped with lithium bis(trifluoromethane)sulfonimide (LiTFSI) as a model system where the polymer backbone has oxanorbornenedicarboximide repeat units with an oligomeric ethylene oxide side chain of length n. Our results show that the local polymer response measured in the time domain with trEFM follows stretched-exponential relaxation kinetics, consistent with the Havriliak-Negami relaxation we measure in the frequency-domain EIS data for macroscopic samples of the same polymers. Furthermore, we show that the trEFM results capture the same trends as the EIS results-changes in ion dynamics with increasing temperature, increasing salt concentration, and increasing volume fraction of ethylene oxide side chains in the polymer matrix evolve with the same trends in both measurement techniques. We conclude from this correlation that trEFM data reflect, at the nanoscale, the same ionic processes probed in conventional EIS at the device level. Finally, as an example application for emerging materials syntheses, we use trEFM and infrared photoinduced force microscopy (PiFM) to image a diblock copolymer electrolyte for next-generation solid-state energy storage applications.

In situ Evolved Gas Analysis of TMOS-based Gel Electrolytes Containing Guanidinium Thiocyanate for Quasi-solid-state Dye-sensitized Solar Cells by TG-FTIR and TG-MS

A comparative study on thermal stability of hybrid (organic / inorganic) electrolytes for dye-sensitized solar cells (DSSCs) in various ethylene oxide oligomers / silica based gelly matrices, containing also some efficiency-promoter additives is presented. Using thermogravimetry combined with two evolved gas analytical (EGA-FTIR and EGA-MS) techniques, the released gases and volatile decomposition products from the composite electrolytes during dynamic heating programs have been identified and monitored. First methanol (arising from condensation of tetramethoxysilane, TMOS) and acetonitrile (solvent) are evolved followed by elongated release of 4-tert-butylpyridine, than carbonyl sulfide, which is one of the degradation products of guanidinium thiocyanate, and various alkyl iodides, as well as iodine, later various oxidized species with >C=O groups (arising from oxidative degradation of oligo(ethylene glycolic) parts, ammonia (originated from guanidine) have been observed and traced during the accelerated heating tests, before final burning out of the organic residue with CO2 evolution. Thermal behavior of pure guanidinium thiocyanate, one of the most important additives improving thermal stability of Grätzel type solar cells (DSSCs), combined with identification of its eight gaseous decomposition products and their release pattern is also reported.

Synthesis of amphiphilic comb-like liquid crystalline diblock polyethers and their self-assembly in solution

We have designed and synthesized a series of novel polyether based amphiphilic liquid crystalline (LC) diblock copolymers composed of pendent hydrophobic LC mesogens and hydrophilic ethylene oxide (EO) oligomers by using sequential anionic polymerization. The majority of this comb-like diblock copolymer is constituted by EO segments except the mesogenic groups which generate the chemical dissimilarity and drive the phase segregation. We have investigated the morphology evolution of the diblock copolymers in dioxane/water co-solvent with continuous tuning of the quality of the solvent, and discovered a systematic morphological transformation from a spherical micelle to a spherical vesicle, and finally to a faceted vesicle with increase of the water content above a critical value. The formation of the structured vesicle is related to the emerging of LC order within the membranes as revealed by in situ wide-angle X-ray diffraction experiments on the polymer solution. The elastic instability imparted from collective LC interactions which is incommensurate with the global topological geometry dictates this unique behavior. This type of faceted capsules on the tens of nanometer scale are expected to be potentially useful in biotechnological applications or drug delivery.

Wettability Alteration of Calcite by Nonionic Surfactants.

The process of selecting an effective surfactant for wettability alteration is dependent on a number of factors, including mineral type, temperature, salinity, and nature of adsorbed oil and ultimately how the molecular structure of the surfactant interacts with all of these. Here, we present an experimental study of the effectiveness of nonionic surfactants with different hydrophobic groups and different lengths of hydrophilic ethylene oxide oligomers. The surfactants selected alter the wettability of the rock primarily by acting on the water-rock and oil-rock interfaces. The dynamics of wettability alteration is measured by the evolution of contact angles of oil drops on initially oil-wet surfaces at three different temperatures. Wettability alteration is found to be enhanced by surfactants with shorter hydrophilic units and increased temperatures. Experimental observations are efficiently summarized by a few thermodynamic and kinetic parameters. Qualitative experiments are performed to study surfactant-induced dewetting of oil films. Finally, a model involving "coating" and "sweeping" mechanisms is proposed to explain the mechanism of surfactant action.

Electrochemical stability of ether based salt-in-polymer based electrolytes: Computational investigation of the effect of substitution and the type of salt

The electrochemical stability window (EW) of polyether based salt-in-polymer electrolytes was investigated using density functional theory (DFT) calculations. The electrolyte systems investigated consisted of polyethylene oxide (PEO) in either lithium-bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium-hexafluorophosphate (LiPF6) salt and the EW was determined by performing calculations of reduction and oxidation potentials of isolated ethylene oxide (EO) oligomer and the respective salt species in a continuum solvent. The simulations suggest that the cathodic limit of the polymer-salt system is defined by the reduction potential of the salt anion and that both salt anions considered are unstable against Li anode. The anodic limit is defined by EO and it is stable against most commercial cathodes. Including explicit salt molecules in the calculations shows that the predicted EW is changed by ∼0.4 V. The calculations further reveal that the EW is dependent on the type of the salt molecule. Perfluoropolyether, a perfluorinated analog of PEO that has lower reduction potential and higher oxidation potential in isolation as compared to PEO, improved both oxidation and reduction stability of the polymer-salt system. Substitution of other functional groups to PEO improved the electrochemical stability to potentially accommodate higher voltage window requirements.

Molecular Dynamics Simulations of Strain-Induced Phase Transition of Poly(ethylene oxide) in Water.

We study the dilute aqueous solutions of poly(ethylene oxide) (PEO) oligomers that are subject to an elongating force dipole acting on both chain ends using atomistic molecular dynamics. By increasing the force, liquid-liquid demixing can be observed at room temperature far below the lower critical solution temperature. For forces above 35 pN, fibrillar nanostructures are spontaneously formed related to a decrease in hydrogen bonding between PEO and water. Most notable is a rapid decrease in the bifurcated hydrogen bonds during stretching, which can also be observed for isolated single chains. The phase-segregated structures display signs of chain ordering, but a clear signature of the crystalline order is not obtained during the simulation time, indicating a liquid-liquid phase transition induced by chain stretching. Our results indicate that the solvent quality of the aqueous solution of PEO depends on the conformational state of the chains, which is most likely related to the specific hydrogen-bond-induced solvation of PEO in water. The strain-induced demixing of PEO opens the possibility to obtain polymer fibers with low energy costs because crystallization starts via the strain-induced demixing in the extended state only.

Short-chained oligo(ethylene oxide)-functionalized gold nanoparticles: realization of significant protein resistance.

Protein corona formed on nanomaterial surfaces play an important role in the bioavailability and cellular uptake of nanomaterials. Modification of surfaces with oligoethylene glycols (OEG) are a common way to improve the resistivity of nanomaterials to protein adsorption. Short-chain ethylene oxide (EO) oligomers have been shown to improve the protein resistance of planar Au surfaces. We describe the application of these EO oligomers for improved protein resistance of 30nm spherical gold nanoparticles (AuNPs). Functionalized AuNPs were characterized using UV-Vis spectroscopy, dynamic light scattering (DLS), and zeta potential measurements. Capillary electrophoresis (CE) was used for separation and quantitation of AuNPs and AuNP-protein mixtures. Specifically, nonequilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) was employed for the determination of equilibrium and rate constants for binding between citrate-stabilized AuNPs and two model proteins, lysozyme and fibrinogen. Semi-quantitative CE analysis was carried out for mixtures of EO-functionalized AuNPs and proteins, and results demonstrated a 2.5-fold to 10-fold increase in protein binding resistance to lysozyme depending on the AuNP surface functionalization and a 15-fold increase in protein binding resistance to fibrinogen for both EO oligomers examined in this study. Graphical abstract Using capillary electrophoresis, the addition of short-chained oligo(ethylene oxide) ligands to gold nanoparticles was shown to improve protein binding resistance up to 15-fold.

Chain Tilt and Crystallization of Ethylene Oxide Oligomers with Midchain Defects.

Many text books and publications do not focus on the necessity of chain tilting in crystalline lamellae of oligomers and polymers, a fundamental aspect of their crystallization already discussed by Flory. Herein we investigate the chain tilt of ethylene oxide oligomers (EOs) containing various midchain defects by WAXS, SAXS and solid state 13C MAS NMR spectroscopy. At low temperatures, one out of the two EO chains of EO9-meta-EO9 and EO11-TR-EO11 containing a 1,3-disubstituted benzene or a 1,4-disubstituted 1,2,3-triazole defect in central position of the oligomer chain forms crystals and the other EO chain as well as the defect remain in the amorphous phase. The aromatic midchain defect of these two oligomers can be incorporated into the crystalline lamella upon heating below Tm. Then, the adjoining amorphous EO chain crosses from the lamellae to the amorphous regions at an angle ξ, which is preordained by the substitution pattern of the aromatic defect, revealing that the chain tilt angle ranges between 36° ≤ ϕ ≤ 60°.

Decoupling of ion conductivity from segmental dynamics in oligomeric ethylene oxide functionalized oxanorbornene dicarboximide homopolymers

In order to design more effective solid polymer electrolytes, it is important to decouple ion conductivity from polymer segmental motion. To that end, novel polymers based on oxanorbornene dicarboximide monomers with varying lengths of oligomeric ethylene oxide side chains have been synthesized using ring opening metathesis polymerization. These unique polymers have a fairly rigid and bulky backbone and were used to investigate the decoupling of ion motion from polymer segmental dynamics. Ion conductivity was measured using broadband dielectric spectroscopy for varying levels of added lithium salt. The conductivity data demonstrate six to seven orders of separation in timescale of ion conductivity from polymer segmental motion for polymers with shorter ethylene oxide side chains. However, commensurate changes in the glass transition temperatures Tg reduce the effect of decoupling in ion conductivity and lead to lower conductivity at ambient conditions. These results suggest that both an increase in decoupling and a reduction in Tg might be required to develop solid polymer electrolytes with high ion conductivity at room temperature.

Air-operating polypyrrole actuators based on poly(vinylidene fluoride) membranes filled with poly(ethylene oxide) electrolytes

To develop air-operating conducting polymer (CP) actuators with enhanced performance, polymer electrolyte membranes with high ionic conductivity and mechanical endurance are necessary. Poly(ethylene oxide) oligomers penetrate into porous poly(vinylidene fluoride) membranes and sequentially undergo crosslinking to produce polymer electrolyte membranes. The properties of the electrolyte membranes are regulated by varying the degree of crosslinking. Polypyrrole layers are constructed on the surfaces of the membranes by chemical polymerization, creating CP actuators. CP actuators based on the resulting polymer electrolyte membranes operate properly in air and show highly enhanced performance such as a large displacement and long operation time. This approach, therefore, has great potential to extend the applications of CP actuators.

GC-MS Headspace and Comparative Computational Studies in the Formation and Follow-up Reactions of Nucleophiles in Li-Ion Battery Electrolytes

As societal needs move towards more sustainable and efficient energy landscapes, electrical energy storage is taking a center stage. The need for devices with greater safety, higher energy and power densities, and longer lifetimes is ever increasing, with applications ranging from stationary storage for intermittent sources (e.g. wind and solar) and grid load-leveling, to electrification of transportation and consumer electronics. The development of longer cycle life Li-ion batteries is an important goal for the large-scale deployment of electrified transportation. A key requirement for these devices is an improved solvent-electrolyte system, capable of withstanding the extreme potentials and temperature ranges expected for modern Li-ion cells. We have undertaken fundamental experimental and computational studies to determine the significance of decompositions of linear and cyclic carbonates to commonly observed nucleophilic species in cycled Li-ion battery electrolytes. The formation of these nucleophiles has been widely reported, as have the straightforward follow-up reactions.1 , 2 , 3, although, the mechanism(s) by which these nucleophiles are formed has not been settled. Moreover, the relevant kinetic aspects of these nucleophilic reactions have not been widely explored, nor have possible reactions that proceed at higher temperature or longer timescales. Since these reactions are generally in competition with one another, and Li-ion electrolyte formulations contain multiple solvents in varying concentrations, a view of the relative rates of these reactions is an important piece of formulating a long cycle life electrolyte. Rather than allow these species to react in multiple experimental studies, across temperatures and concentration ranges, computational methods are well suited to determine the relevant reaction kinetics and thermodynamics with a high degree of confidence. For example, products can be oxidized at relatively low cathode potentials, or they can attack cyclic and linear solvents to generate a host of oligomers and other small molecules.4 , 5 Many of the products of these reactions can also be soluble and electrochemically unstable.6 In this report, we will present headspace GC-MS data for a cycled EC-EMC + LiPF6 electrolyte, with consideration toward species found at the anode and cathode. The observed products will then be compared with data from computational studies of electrochemical and chemical reactions of Li-ion battery solvents. From the computational data, we may conclude the most likely pathways for nucleophile generation and follow up solvent decompositions under typical operating conditions of a Li-ion cell. The focus will be on reasonable routes to observed products, many of which have been proposed as the product of solvent oxidation. Solvent transesterfiications, and formation of lithium ethylene dicarbonate (LEDC), poly(ethylene oxide) oligomers and poly(ethylene carbonate-co-ethylene oxide) oligomers will be discussed. Figure 2. Cycle of chemical / electrochemical solvent decompositions.