Crystallization Of PEO Research Articles

Molecular motifs for additives that retard PEO crystallization

We investigate the influence of several bifunctional phenol additives (resorcinol: RES, hydroquinone: HYD, p-hydroxybenzoic acid: PHBA, and p-nitrophenol: PNP) on the crystallization of matrix polymer, polyethyleneoxide. We employ solid state Nuclear Magnetic Resonance spectroscopy (NMR), Differential Scanning Calorimetry (DSC), optical microscopy, and Small Angle X-ray Scattering (SAXS) to investigate crystallization of the additivated PEO and compare with Density Functional Theory (DFT) calculations of additive-PEO interactions. Additive-polymer interactions are a function of the functional groups on the additive. Temperature-dependent spherulitic growth rate measurements from optical microscopy and SAXS lamellar long spacings indicate a distinct trend in the effect of additives on PEO crystallization. Change in PEO crystallization is most pronounced with PNP, followed by PHBA and finally RES and HYD. This trend correlates qualitatively with the binding energies of additive-PEO interactions from DFT studies. Our results suggest that DFT calculations might be a useful screening tool to evaluate the influence of additives on polymer crystallization. POLYM. ENG. SCI., 2016. © 2016 Society of Plastics Engineers

Structure and crystallization behavior of poly(ethylene oxide)/Ti3C2Tx MXene nanocomposites

MXenes represent a new family of 2D transition metal carbides and/or carbides that has attracted a great deal of attention in various applications because of their unique electrical, thermal, and mechanical properties. In this work, we report on the structure and crystallization behavior of poly(ethylene oxide)(PEO)/MXene nanocomposites. MXene Ti3C2Tx (where T is a surface termination) was synthesized and used as the nanofiller to form polymer nanocomposites using a solution blending method. Their morphologies, structures and crystallization behaviors were investigated using transmission electron microscopy, atomic force microscopy, polarized light microscopy, wide-angle X-ray diffraction and differential scanning calorimetry. Both non-isothermal and isothermal crystallization behaviors were studied. We show that the presence of 2D Ti3C2Tx accelerates PEO crystallization at very low MXene contents, while it inhibits PEO crystallization as the loading increases. The fastest crystallization rate was observed at 0.5 wt% MXene content. This was attributed to the competition of nucleation and confinement effect of the 2D filler.

Morphology and physical properties of electrospun polyethylene oxide/polyacrylonitrile mats and related graphene‐based nanocomposites

Highly porous bi‐component fibers from poly(ethylene oxide) (PEO)/polyacrylonitrile (PAN) blends with 90/10, 80/20, 70/30, and 50/50 PEO/PAN weight ratios were prepared. Electrospinning of the blends produced thin fibers with averaged diameters ranging from 275 to 190 nm. Incorporation of 1 wt% graphene sheets (GS) into the fibrous blends mats effectively increased the tensile modulus and electrical conductivity of the matrix. Differential scanning calorimetry (DSC) showed the lowered Tm and ΔHm of the PEO component in the bi‐component fibers, suggesting that the crystallization of PEO was hindered due to the presence of PAN. DSC results indicated a nucleation effect of GS on the crystallization of PEO. High porosity of the produced nanocomposite mats (about 93%) is a promising feature for their application as electrolytes. J. VINYL ADDIT. TECHNOL., 23:E152–E159, 2017. © 2016 Society of Plastics Engineers

Effect of miscibility state on crystallization behavior and polymorphism in crystalline/crystalline blends of poly(vinylidene fluoride)/poly(ethylene oxide)

Overall crystallization behavior and polymorphism of partially miscible blends of poly(vinylidene fluoride)/ poly(ethylene oxide) (PVDF/PEO) were systematically investigated. The PVDF/PEO blends were prepared from solution in the whole composition range. Isothermal and non-isothermal experiments were carried out using differential scanning calorimetry (DSC). Since the components of the blend crystallize separately due to high difference of the melting points, the changes in melting, crystallization, and equilibrium melting temperatures of PVDF and PEO as well as the degree of crystallization were evaluated. As the binary blends display an asymmetric lower critical solution temperature (LCST)-type phase diagram, the crystallization behavior and kinetics were strongly affected by the miscibility state of the blends in the melt. Particularly, the overall crystallization of PEO was accelerated in the blends with high level of PEO (>50 wt%) by two different mechanisms. The formation of phase separated domains at this composition range enhanced the nucleation ability due to the “spinodal decomposition/ interface assisted crystallization”. Moreover, presence of preexisting crystals of PVDF could act as a substrate for PEO crystallization and increased the crystallization growth rate. Wide angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR) were also utilized to study the crystalline polymorphism of PVDF and PEO in the blends.

Plasticization of NaX-PEO solid polymer electrolytes by Pyr13X ionic liquids

Addition of moderate contents (≤20wt%) of ionic liquids (ILs) to binary solid polymer electrolytes (SPEs) is made to alter the overall SPE properties, foremost to increase the room temperature ionic conductivity. Sodium conducting ternary electrolytes, based on sodium salts; NaTFSI and NaFSI, the polymer poly(ethylene oxide) (PEO), and pyrrolidinium ILs; Pyr13TFSI and Pyr13FSI, with different compositions: NaX(PEO)n – Pyr13X (X=TFSI, FSI), have been prepared. Raman and dielectric spectroscopy as well as differential scanning calorimetry have been used to evaluate the plasticizing effect of the Pyr13 IL cation and the accompanying TFSI and FSI IL anions via changes in ionic association, crystallinity, polymer chain dynamics, and total ionic conductivity. While all the TFSI based systems seem rather insensitive to the addition of IL with respect to speciation, the situation is much less clear for the FSI based systems. Furthermore, the addition of ILs seems beneficial for inhibiting PEO crystallization, especially for the FSI anion, and also for enhancing the polymer chain dynamics, but yet the FSI based ternary electrolytes show lower ion conductivities as compared to the analogous TFSI based systems.

Highly Elastic Fibers Made from Hydrogen-Bonded Polymer Complex

In this letter, we put forward an approach to prepare hydrogen-bonded complex fibers. First, a spinnable fluid is obtained by restricting hydrogen bonds, and then it is extruded through a spinneret into a coagulation bath where hydrogen bonds are built to induce fiber formation. The hydrogen-bonded poly(acrylic acid)/poly(ethylene oxide) (PAA/PEO) complex was prepared into fibers. PAA/PEO fiber shows excellent elastic behavior and can be drawn to more than 12× its original length without breaking, which is much higher than Spandex fiber or natural rubber fiber. In the fiber, PAA and PEO are miscible in the molecular level. Dynamic hydrogen bonding between PAA and PEO restricts the crystallization of PEO, retains flexibility of polymer chains, and also provides recovery forces when removing stress.

Improved self‐assembly of poly(dimethylsiloxane‐b‐ethylene oxide) using a hydrogen‐bonding additive

ABSTRACTBlock copolymers with increased Flory–Huggins interaction parameters (χ) play an essential role in the production of sub‐10 nm nanopatterns in the growing field of directed self‐assembly for next generation lithographic applications. A library of PDMS‐b‐PEO block copolymers were synthesized by click chemistry and their interaction parameters (χ) determined. The highest χ measured in our samples was 0.21 at 150 °C, which resulted in phase‐separated domains with periods as small as 7.9 nm, suggesting that PDMS‐b‐PEO is a prime candidate for sub‐10 nm nanopatterning. To suppress PEO crystallization, PDMS‐b‐PEO was blended with (l)‐tartaric acid (LTA) which allows for tuning of the self‐assembled morphologies. Additionally, it was observed that the order‐disorder transition temperature (TODT) of PDMS‐b‐PEO increased dramatically as the amount of LTA in the blend increased, allowing for further control over self‐assembly. To understand the mechanism of this phenomenon, we present a novel field‐based supramolecular model, which describes the formation of copolymer‐additive complexes by reversible hydrogen bonding. The mean‐field phase separation behavior of the model was calculated using the random phase approximation (RPA). The RPA analysis reproduces behavior consistent with an increase of the effective χ in the PDMS‐b‐(PEO/LTA suprablock). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 2200–2208

Self-Assembly of Telechelic Tyrosine End-Capped PEO and Poly(alanine) Polymers in Aqueous Solution.

The self-assembly in aqueous solution of three novel telechelic conjugates comprising a central hydrophilic polymer and short (trimeric or pentameric) tyrosine end-caps has been investigated. Two of the conjugates have a central poly(oxyethylene) (polyethylene oxide, PEO) central block with different molar masses. The other conjugate has a central poly(L-alanine) (PAla) sequence in a purely amino-acid based conjugate. All three conjugates self-assemble into β-sheet based fibrillar structures, although the fibrillar morphology revealed by cryogenic-TEM is distinct for the three polymers--in particular the Tyr5-PEO6k-Tyr5 forms a population of short straight fibrils in contrast to the more diffuse fibril aggregates observed for Tyr5-PEO2k-Tyr5 and Tyr3-PAla-Tyr3. Hydrogel formation was not observed for these samples (in contrast to prior work on related systems) up to quite high concentrations, showing that it is possible to prepare solutions of peptide-polymer-peptide conjugates with hydrophobic end-caps without conformational constraints associated with hydrogelation. The Tyr5-PEO6k-Tyr5 shows significant PEO crystallization upon drying in contrast to the Tyr5-PEO2k-Tyr5 conjugate. Our findings point to the remarkable ability of short hydrophobic peptide end groups to modulate the self-assembly properties of polymers in solution in model peptide-capped "associative polymers". Retention of fluidity at high conjugate concentration may be valuable in potential future applications of these conjugates as bioresponsive or biocompatible materials, for example exploiting the enzyme-responsiveness of the tyrosine end-groups.

Highly CO2-Selective Gas Separation Membranes Based on Segmented Copolymers of Poly(Ethylene oxide) Reinforced with Pentiptycene-Containing Polyimide Hard Segments.

Poly(ethylene oxide) (PEO)-containing polymer membranes are attractive for CO2-related gas separations due to their high selectivity toward CO2. However, the development of PEO-rich membranes is frequently challenged by weak mechanical properties and a high crystallization tendency of PEO that hinders gas transport. Here we report a new series of highly CO2-selective, amorphous PEO-containing segmented copolymers prepared from commercial Jeffamine polyetheramines and pentiptycene-based polyimide. The copolymers are much more mechanically robust than the nonpentiptycene containing counterparts due to the molecular reinforcement mechanism of supramolecular chain threading and interlocking interactions induced by the pentiptycene structures, which also effectively suppresses PEO crystallization leading to a completely amorphous structure even at 60% PEO weight content. Membrane transport properties are sensitively affected by both PEO weight content and PEO chain length. A nonlinear correlation between CO2 permeability with PEO weight content was observed due to the competition between solubility and diffusivity contributions, whereby the copolymers change from being size-selective to solubility-selective when PEO content reaches 40%. CO2 selectivities over H2 and N2 increase monotonically with both PEO content and chain length, indicating strong CO2-philicity of the copolymers. The copolymer film with the longest PEO sequence (PEO2000) and highest PEO weight content (60%) showed a measured CO2 pure gas permeability of 39 Barrer, and ideal CO2/H2 and CO2/N2 selectivities of 4.1 and 46, respectively, at 35 °C and 3 atm, making them attractive for hydrogen purification and carbon capture.

Structure and surface properties of chitosan/PEO/gelatin nanofibrous membrane

Present paper deals with the effect of gelatin on the structure, phase composition, and morphology of the electrospun chitosan/PEO nanofibers. Special attention is paid to the surface chemistry, surface structure and surface morphology of nanocomposite fibers, as these parameters are crucial for biomedical applications and for eventual subsequent surface modification. Gelatin prevents the crystallization of PEO and chitosan and has significant effect on the surface properties of chitosan/PEO/gelatin nanofibers, especially after the cross-linking. During the heating at 130 °C, gelatin appears on the surface of the nanofibers, what results in a large amount of the surface cracks, as well as in the dramatic changes of the surface chemistry and consequently surface adhesion properties. In addition, we observe regions with a continuous gelatin layer between fibers after the cross-linking, what leads to a significant decrease of the porosity of the nanofiber textile. Special attention has been paid to the complex characterization of the structure and surface chemistry of composite nanofibrous materials in order to predict their surface properties, crucial for wound dressing and tissue engineering.

Crystallization behaviour of poly(ethylene oxide) under confinement in the electrospun nanofibers of polystyrene/poly(ethylene oxide) blends.

We have studied the confined crystallization behaviour of poly(ethylene oxide) (PEO) in the electrospun nanofibers of the phase-separated blends of polystyrene (PS) and PEO, where PS was present as the major component. The size and shape of PEO domains in the nanofibers were considerably different from those in the cast films, presumably because of the nano-dimensions of the nanofibers and the extensional forces experienced by the polymer solution during electrospinning. The phase-separated morphology in turn influenced the crystallization behaviour of PEO in the blend nanofibers. At a PEO weight fraction of ≥0.3, crystallization occurred through a heterogeneous nucleation mechanism similar to that in cast blend films. However, as the PEO weight fraction in the blend nanofibers was reduced from 0.3 to 0.2, an abrupt transformation of the nucleation mechanism from the heterogeneous to predominantly homogenous type was observed. The change in the nucleation mechanism implied a drastic reduction of the spatial continuity of PEO domains in the nanofibers, which was not encountered in the cast film. The melting temperature and crystallinity of the PEO crystallites developed in the nanofibers were also significantly lower than those in the corresponding cast films. The phenomena observed were reconciled by the morphological observation, which revealed that the phase separation under the radial constraint of the nanofibers led to the formation of small-sized fibrillar PEO domains with limited spatial connectivity. The thermal treatment of the PS/PEO blend nanofibers above the glass transition temperature of PS induced an even stronger confinement effect on PEO crystallization.

Confined PEO crystallisation in immiscible PEO/PLLA blends

PEO/PLLA blends are immiscible. PEO phase is confined into PLLA interlamellar and interspherulitic regions and a confined and fractional crystallisation of PEO occurs as the density of the PLLA crystalline phase increases.

High Ionic Conductivity of Composite Solid Polymer Electrolyte via In Situ Synthesis of Monodispersed SiO2 Nanospheres in Poly(ethylene oxide).

High ionic conductivity solid polymer electrolyte (SPE) has long been desired for the next generation high energy and safe rechargeable lithium batteries. Among all of the SPEs, composite polymer electrolyte (CPE) with ceramic fillers has garnered great interest due to the enhancement of ionic conductivity. However, the high degree of polymer crystallinity, agglomeration of ceramic fillers, and weak polymer-ceramic interaction limit the further improvement of ionic conductivity. Different from the existing methods of blending preformed ceramic particles with polymers, here we introduce an in situ synthesis of ceramic filler particles in polymer electrolyte. Much stronger chemical/mechanical interactions between monodispersed 12 nm diameter SiO2 nanospheres and poly(ethylene oxide) (PEO) chains were produced by in situ hydrolysis, which significantly suppresses the crystallization of PEO and thus facilitates polymer segmental motion for ionic conduction. In addition, an improved degree of LiClO4 dissociation can also be achieved. All of these lead to good ionic conductivity (1.2 × 10(-3) S cm(-1) at 60 °C, 4.4 × 10(-5) S cm(-1) at 30 °C). At the same time, largely extended electrochemical stability window up to 5.5 V can be observed. We further demonstrated all-solid-state lithium batteries showing excellent rate capability as well as good cycling performance.

Phase morphology and crystallinity of poly(vinylidene fluoride)/poly(ethylene oxide) piezoelectric blend membranes

Polymer blends based on poly(vinylidene fluoride), PVDF, and poly(ethylene oxide), PEO, with varying compositions, have been prepared by solvent casting, the polymer blend films being obtained from solutions in dimethyl formamide at 70°C. Under these conditions PVDF crystallizes from solution while PEO remains in the molten state. Then, PEO crystallizes from the melt confined by PVDF crystals during cooling to room temperature. PVDF crystallized from DMF solutions adopts predominantly the electroactive β-phase (85%). Nevertheless when PEO is introduced in the polymer blend the β-phase content decreases slightly to 70%. The piezoelectric coefficient (d33) in pristine PVDF is −5pC/N and decreases by increasing PEO content in the PVDF/PEO blends. Blend morphology, observed by electron and atomic force microscopy, shows the confinement of PEO between the already formed PVDF crystals. On the other hand, the sample contraction when PEO is extracted from the blend with water (which is not a solvent for PVDF) allows proving the co-continuity of both phases in the blend. PEO crystallization kinetics have been characterized by DSC both in isothermal and cooling scans experiments showing important differences in crystalline fraction and crystallization rate with sample composition.

Lithium-Salt-Containing High-Molecular-Weight Polystyrene-block-Polyethylene Oxide Block Copolymer Films.

Ionic conductivity in relation to the morphology of lithium-doped high-molecular-weight polystyrene-block-polyethylene oxide (PS-b-PEO) diblock copolymer films was investigated as solid-state membranes for lithium-ion batteries. The tendency of the polyethylene (PEO) block to crystallize was highly suppressed by increasing both the salt-doping level and the temperature. The PEO crystallites completely vanished at a salt-doping ratio of Li/EO>0.08, at which the PEO segments were hindered from entering the crystalline unit of the PEO chain. A kinetically trapped lamella morphology of PS-b-PEO was observed, due to PEO crystallization. The increase in the lamella spacing with increasing salt concentration was attributed to the conformation of the PEO chain rather than the volume contribution of the salt or the previously reported increase in the effective interaction parameter. Upon loading the salt, the PEO chains changed from a compact/highly folded conformation to an amorphous/expanded-like conformation. The ionic conductivity was enhanced by amorphization of PEO and thereby the mobility of the PEO blocks increased upon increasing the salt-doping level.

A study of crystallisation of poly (ethylene oxide) and polypropylene on graphene surface

Crystallisation behaviour of poly (ethylene oxide) (PEO) and isotactic polypropylene (iPP) on graphene surface was investigated by means of polarized microscopy, wide angle X-ray diffraction (WAXD), and Raman techniques. Results indicated that graphene influences the crystallisation and crystal structure of iPP and PEO. WAXD peaks shifting toward lower diffraction angle, i.e. increase in d-pacing, was observed in both PEO and iPP crystallised on the surface of graphene. The change of d-spacing of both PEO and iPP could result from the compressive stress caused by graphene. A shift of 2D band in graphene was observed from Raman spectra. The Raman spectra indicated the big shift in the 2D band is due to the presence of stress induced strain in the polymer attached graphene. The residual stress was generated during crystallization of the polymers on the surface of graphene. Due to the interactions between the graphene and the polymers, the stress was transferred to the graphene which leads to a strain of the graphene. Raman spectra proved the presence of stress generated by the crystallization of the polymers on the surface of graphene.

ABA Triblock Brush Polymers: Synthesis, Self-Assembly, Conductivity, and Rheological Properties

The synthesis, self-assembly, conductivity, and rheological properties of ABA triblock brush polymers (BBCPs) with grafted polystyrene (A block, NPS = 21) and poly(ethylene oxide) (B block, NPEO = 45) side chains are reported. Two backbone molecular weights (NA:NB:NA = 11:78:11 and 15:119:15) were investigated with lithium bis(trifluoromethane)sulfonimide (LiTFSI) doping ratios 2 ≤ [EO]:[Li+] ≤ 20. Blends with 2 ≤ [EO]:[Li+] ≤ 10 suppress PEO crystallization and self-assemble into hexagonally packed cylinders of the minority gPS component. Conductivity is on the order of 10–3 S/cm at 105 °C with a corresponding elastic modulus ca. 104 Pa. The optimum conductivity occurs at a blend ratio near 10:1 [EO]:[Li+], similar to that reported for linear block copolymer analogues.

Anisotropic Ion Transport in a Poly(ethylene oxide)–LiClO4 Solid State Electrolyte Templated by Graphene Oxide

Solid polymer electrolytes (SPEs) have attracted intensive attention due to their potential applications in all-solid-state lithium batteries. Tailoring crystallization is crucial to the design of high performance poly(ethylene oxide) (PEO)–based SPEs. In this paper, we demonstrate that PEO crystal orientation in a PEO–lithium electrolyte results in anisotropic ionic conductivity along and through the crystalline lamellae. This conductivity anisotropy can be further enhanced by incorporating two-dimensional graphene oxide (GO) nanosheets, which retard PEO crystallization, template the crystal orientation, and guide the ion transport, leading to highly anisotropic and conductive nanocomposite polymer electrolytes.

Cooperative and Sequential Phase Transitions in it-Poly(propylene oxide)-b-poly(ethylene oxide)-b-it-poly(propylene oxide) Triblock Copolymers

Sequential phase transitions were investigated in detail for a set of newly designed poly(propylene oxide)-b-poly(ethylene oxide)-b-poly(propylene oxide) (PPO–PEO–PPO) triblock copolymers, where the PPO blocks have isotactic, (R)- or (S)-, or atactic configurations. Microphase separation and thermal composition fluctuations were studied near the order–disorder transition temperature (133 ± 1 °C), and the interaction parameters χ(T) were determined. A unique feature of these materials is the cooperative and sequential nature of phase transitions, which leads to the inversion of the crystallization/melting sequence of PEO and isotactic PPO blocks. The PEO blocks crystallize quickly (ca. 50 °C) within a soft, confined lamellar template, which is followed by slow crystallization of the isotactic PPO blocks (ca. 40 °C) under hard confinement. However, in the melting process, PEO crystals melt first (ca. 60 °C) affording soft confinement which enables isotactic PPO crystals to undergo recrystallization and lame...

Mechanisms and kinetics of the crystal thickening of poly(butadiene)-block-poly(ethylene oxide) during annealing within the melting range

Self-assembled nanostructures of crystallizable block copolymers can be tuned by controlled crystal thickening during annealing. In this contribution, we present a strategy, based on time- and temperature-dependent DSC, SAXS and WAXS measurements, which enables to study, both, the mechanisms and kinetics of crystal thickening and the respective morphological development, exemplarily discussed for the soft-confined PB-b-PEO block copolymer. Thereby, DSC based PEO crystal thickness distributions yield qualitative information about the mechanisms during annealing. Conclusions on the kinetics and the absolute long-period growth due to crystal thickening can be drawn from the time- and temperature-dependent SAXS investigations, by calculating the average long-period and its deviations from the SAXS reflection position and shape, respectively. By this combined study, three annealing regimes were observed. (i) At low annealing temperatures Ta, steady lamellae-thickening was found, due to defect healing of the PEO crystals. (ii) Thermal fractionation was observed at intermediate Ta, due to the exclusion of shorter PEO chains from the crystals. (iii) Annealing close to and above the peak melting temperature, self-nucleation of the molten PEO fractions dominated. The combination of the applied techniques provides deeper insights into the kinetics and ordering mechanisms of the controlled long-period growth by crystal thickening under variable confinements, which enables to tailor the morphology of the block copolymer within several nanometers, without changing the degree of polymerization.