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 <i>p</i>-phenylene diisocyanate is a small hard segment, the ionomers were found to be single phase with only one DSC <i>T</i>_g 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 <i>T</i>_g, 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 <i>T</i>_g and are related to ion rearrangement. Lower ion content creates lower <i>T</i>_g, lower activation energy for conducting ions, and higher ion mobility, as sodium cations interact strongly with both PEO and the urethane linkage

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

PEO600-based polyurethane ionomers with various hard segment contents were synthesized and characterized by both linear viscoelastic (LVE) properties and dielectric relaxation spectroscopy. The ions were placed in the soft segment to achieve better ionic conductivity while the hard phase can provide mechanical strength. Microphase separation was observed in all samples with more than 23 wt % hard segment. The samples that show evidence of microphase separation share similar soft phase glass transition temperature, but the degree of microphase separation and ionic conductivity were found to be significantly affected by specimen preparation method (hot pressed or solution cast). Both ionic conductivity and polymer chain mechanical relaxation show VFT or WLF temperature dependence. At 150 °C, the microphase-separated samples were found preserving both the ionic conductivity and mechanical modulus. While most literature focuses on gel polymer electrolytes or block copolymers to obtain both high modulus and high conductivity in single-ion conductors, our polyurethane ionomers demonstrate an alternative path to simultaneously high modulus and ionic conductivity

The Effect of Water on Rheology of Native Cellulose/Ionic Liquids Solutions

Cellulose coagulates upon adding water to its solutions in ionic liquids. Although cellulose remains in solution with much higher water contents, here we report the effect of 0–3 wt % water on solution rheology of cellulose in 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium acetate. Fourier transform infrared spectroscopy, thermal gravimetric analysis, and polarized light microscopy were also used to study water absorbance to the solutions. Tiny amounts of water (0.25 wt %) can significantly affect the rheological properties of the solutions, imparting a yield stress, while dry solutions appear to be ordinary viscoelastic liquids. The yield stress grows linearly with water content and saturates at a level that increases with the square of cellulose content. Annealing the solutions containing small amounts of water at 80 °C for 20 min transforms the samples to the fully dissolved “dry” state

Linear Viscoelasticity and Swelling of Polyelectrolyte Complex Coacervates

Mixing oppositely charged hydrophilic polyelectrolytes is the simplest path to constructing a polyampholyte gel that is useful as a soft tissue scaffold for binding enzymes in their native state. The swelling and viscoelastic properties of such a synthetic polyampholyte gel coacervate, constructed from polyions of different charge density, are reported in water with various amounts of NaCl salt. When constructed, this coacervate is roughly 70% water and 15% of each polyion, nearly charge balanced. If salt is removed from the surrounding supernatant, the gel swells owing to the weak charge imbalance because small amounts of salt screen electrostatic repulsions. If instead more salt is added to this coacervate, the gel behaves as any polyampholyte gel, swelling as salt is added because the excess salt screens the electrostatic attractions and eventually this leads to redissolving the coacervate. The amount of salt needed to redissolve the coacervate increases with polyion molecular weight. To our surprise, we discovered that the small charge imbalance within the coacervate grows with the molecular weight of the more strongly charged polyion

Flow-Induced Crystallization of PEEK: Isothermal Crystallization Kinetics and Lifetime of Flow-Induced Precursors during Isothermal Annealing

The role of an interval of shear flow in promoting the flow-induced crystallization (FIC) for poly­(ether ether ketone) PEEK was investigated by melt rheology and calorimetry. At 350 °C, just above the melting temperature of PEEK (<i>T</i>_m), a critical shear rate to initiate the formation of flow-induced precursors was found to coincide with the shear rate at which the Cox–Merz rule abruptly begins to fail. In cooling the sheared samples to 320 °C, FIC can be up to 25× faster than quiescent crystallization. Using rheology and differential scanning calorimetry, the stability of FIC-induced nuclei was investigated by annealing for various times at different temperatures above <i>T</i>_m. The persistence of shear-induced structures slightly above <i>T</i>_m, along with complete and rapid erasure of FIC-induced nuclei above the equilibrium melting temperature, suggests that FIC leads to thicker lamellae compared with the quiescently crystallized samples

Viscosity and Scaling of Semiflexible Polyelectrolyte NaCMC in Aqueous Salt Solutions

We investigate the viscosity dependence on concentration and molecular weight of semiflexible polyelectrolyte sodium carboxy­methylcellulose (NaCMC) in aqueous salt-free and NaCl solutions. Combining new measurements and extensive literature data, we establish relevant power laws and crossovers over a wide range of degree of polymerization (<i>N</i>) as well as polymer (<i>c</i>) and salt (<i>c</i>_s) concentrations. In salt-free solution, the overlap concentration shows the expected <i>c</i>* ∝ <i>N</i>^–2 dependence, and the entanglement crossover scales as <i>c</i>_e ∝ <i>N</i>^–0.6±0.3, in strong disagreement with scaling theory for which <i>c</i>_e ∝ <i>c</i>* is expected, but matching the behavior found for flexible polyelectrolytes. A second crossover, to a steep concentration dependence for specific viscosity (η_sp ∝ <i>c</i>^3.5±0.2), commonly assigned to the concentrated regime, is shown to follow <i>c</i>** ∝ <i>N</i>^–0.6±0.2 (with <i>c</i>**/<i>c</i>_e ≃ 6) which thus suggests instead a dynamic crossover, possibly related to entanglement. The scaling of <i>c</i>* and <i>c</i>_e in 0.01 and 0.1 M NaCl shows neutral polymer in good solvent behavior, characteristic of highly screened polyelectrolyte solutions. This unified scaling picture enables the estimation of viscosity of ubiquitous NaCMC solutions as a function of <i>N</i>, <i>c</i>, and <i>c</i>_s and establishes the behavior expected for a range of semiflexible polyelectrolyte solutions

Synthesis and Lithium Ion Conduction of Polysiloxane Single-Ion Conductors Containing Novel Weak-Binding Borates

Three borate monomers: lithium triphenylstyryl borate (B1), a variant with three ethylene oxides between the vinyl and the borate (B2) and a third with perfluorinated phenyl rings (B3) were synthesized and used to prepare polysiloxane ionomers based on cyclic carbonates via hydrosilylation. B1 ion content variations show maximum 25 °C conductivity at 8 mol %, reflecting a trade-off between carrier density and glass transition temperature (<i>T</i>_g) increase. Ethylene oxide spacers (B2) lower <i>T</i>_g, and increase the dielectric constant, both raising conductivity. Perfluorinating the four phenyl rings (B3) lowers the ion association energy, as anticipated by ab initio estimations. This increases conductivity, a direct result of 3 times higher measured carrier density. The ∼9 kJ/mol activation energy of simultaneously conducting ions is less than half that of ionomers with either sulfonate or bis­(trifluoromethanesulfonyl) imide anions, suggesting that ionomers with weak-binding borate anions may provide a pathway to useful single-ion Li⁺ conductors, if their <i>T</i>_g can be lowered

Segmental Dynamics of Polymer Melts with Spherical Nanoparticles

The impact of spherical nanoparticles (NPs) on the segmental dynamics of polymer melts is investigated. The addition of NPs broadens the segmental dynamics with effects of both particle size and loading. Interfacial bound layer thickness is calculated by the difference in magnitude of the segmental dynamics of pure polymer and nanocomposites. These theoretical models suggest that the bound layer thickness in the case of strongly adsorbing polymer matrices may increase with particle size

Self-Assembly of Doublets from Flattened Polymer Colloids

Bottom-up fabrication methods are used to assemble strong yet flexible colloidal doublets. Part of a spherical particle is flattened, increasing the effective interaction area with another particle having a flat region. In the presence of a moderate ionic strength, the flat region on one particle will preferentially “bond” to a flat region on another particle in a deep (≥10 <i>kT</i>) secondary energy minimum. No external field is applied during the assembly process. Under the right conditions, the flat–flat bonding strength is ≥10× that of a sphere–sphere interaction. Not only can flat–flat bonds be quite strong, but they are expected to remain freely rotatable and flexible, with negligible energy barriers for rotation because particles reside in a deep secondary energy minimum with a ∼20–30 nm layer of fluid between the ∼1 μm radius particles. We present a controlled technique to flatten the particles at room temperature, the modeling of the interparticle forces for flattened spheres, and the experimental data for the self-assembly of flat–flat doublets

Isothermal Flow-Induced Crystallization of Polyamide 66 Melts

When the molten state of a semicrystalline polymer is subjected to sufficiently intense flow before crystallization, the crystallization kinetics are accelerated and the crystalline superstructure is transformed from spherulites to smaller anisotropic structures. In this study, flow-induced crystallization (FIC) of polyamide 66 (PA 66) was investigated using rheology and polarized optical microscopy. After an interval of shear flow at 270 °C, above the melting temperature (<i>T</i>_<i>m</i> = 264 °C) and below the equilibrium melting temperature, small-amplitude oscillatory shear time sweeps at 245 °C were used to monitor FIC kinetics. As specific work was imposed on a PA 66 melt at 270 °C from 10 Pa to 40 kPa, the onset of crystallization at 245 °C did not change. Above the critical work of 40 kPa up to 100 MPa, the onset of crystallization at 245 °C was progressively shifted from 628 to 26 s, as the applied specific work was increased. For quantitative analysis of the acceleration, the Avrami equation was used with Pogodina’s storage modulus normalization method, revealing the transition of Avrami exponent from ∼3 to ∼2 at the critical specific work of ∼40 kPa. Strong FIC acceleration was observed after the transition. After applying very low shear rates, large spherulites were observed without cylindrites, while a mixture of small spherulites and large anisotropic cylindrites was seen after applying a shear rate of 10 s^–1