We study the conformational and flow properties of sodium polystyrenesulfonate in aqueous NaCl solutions in the high polymer, high added-salt region using rheology and small angle neutron scattering (SANS). For low salt concentrations, the specific viscosity decreases with added salt as expected. At very high salt, however, the specific viscosity is found to rapidly increase with increasing added-salt concentration (c(s)). This indicates that addition of salt modifies the system in ways other than simply decreasing the electrostatic screening length. Beyond a critical shear stress of around 400 Pa, independent of molar mass, solutions display strong shear thickening reminiscent of shear-induced gelation. Scaling laws for the zero shear rate viscosity and critical shear rate with molar mass, polymer and added-salt concentration are established and compared to similar behavior observed for other systems. SANS experiments using the zero-average-contrast technique reveal that the chain size monotonically decreases with increasing added salt concentration, indicating that the increases in specific viscosity cannot be assigned to chain expansion. Our results indicate that NaPSS, usually thought to be a model polyelectrolyte system, displays complex and unexpected rheological behavior when both the polymer and added salt concentration approach the molar range, where the Debye screening length becomes smaller than the Bjerrum length.

Literature viscosity data are reviewed in both entangled solutions and semidilute unentangled solutions, with several examples of using de Gennes’ thermal blob to rationalize observations for flexible polymers dissolved in intermediate quality solvents. Some puzzling literature data in θ-solvents are also nicely understood with two-parameter scaling upon reanalysis (where the correlation length and the tube diameter concentration dependences differ). However, some literature data seem to not be understood with this simple scheme, suggesting that our understanding of neutral polymer solution viscosity is incomplete. Lastly, combinations of experiments are suggested to better examine the concept of the thermal blob.

The molecular level understanding of ion and polymer dynamics in nanoparticle-coupled hydrogel network polymer electrolytes is investigated by linear dielectric and viscoelastic measurements covering broad ranges of frequency and temperature. We prepare hydrogel polymer electrolytes (HPEs), composed of Li+ conducting hydrophilic poly(lithium acrylate) (PLiA) as the HPE matrix and vinyl-functionalized silica nanoparticles (NPs) as cross-linking points, via radical polymerization and sol-gel reaction. The NP content variation leads to changes in ionic conductivity (sigma(DC)), dielectric constant (epsilon(s)), relaxation frequency, and elastic modulus, which are important characteristic factors for understanding ion transport. From the physical model of electrode polarization (EP), allowing for the determination of the number density of simultaneously conducting ions and their mobility, the NP-containing HPEs (HPE-NP) have simultaneously higher conducting ion concentration (p) and mobility (mu), resulting in higher ionic conductivity (sigma(DC) similar to p mu), compared to the HPE without NPs. The temperature dependence of p and mu follows Arrhenius (thermally activated) and Vogel-Fulcher (segmentally driven) temperature dependences, respectively. In addition to the lower frequency EP, the HPEs show higher frequency relaxation (alpha(2)), attributed to ions rearranging. NP incorporation leads to faster alpha(2) relaxation and higher static dielectric constant epsilon(s) (shorter Bjerrum length l(B)). Time-temperature superposition (tTS) works well for these electrolytes and is applied to construct master curves of viscoelasticity and in-phase conductivity. In the end, the NP-containing HPE-based supercapacitor is fabricated using carbon nanotube yarn (CNTY) electrodes and shows stable electrochemical performance, demonstrating that our HPE can be a solid-state polymer electrolyte for energy storage devices.

Chain dynamics in the semidilute unentangled regime can be used to determine the molecular weight of polyelectrolytes based on the Rouse scaling model. Four methods enable determination of the number density of chains via measurements of correlation length (xi) by small-angle X-ray scattering, specific viscosity (eta(sp)) and relaxation time (tau) by rheometry, and diffusion coefficient (D) by NMR Five narrow dispersity cesium polystyrene sulfonate (CsPSS) solutions without salt are studied in water, anhydrous ethylene glycol, and anhydrous glycerol to test all methods. Combining viscosity and correlation length yields the weight-average molecular weight (M-w) from the Rouse model. Combining diffusion coefficient and correlation length in water provides number-average molecular weight (M-n) reliably for chains with N < 2000 repeat units. Glycerol slows relaxation dynamics, and the shear rate dependence of viscosity yields reliable tau for CsPSS with N > 100, which is governed by the product of z-average and z + 1 average molecular weight (MzMz+1) in the Rouse model. Terminal modulus G = (eta - eta(s))/tau via rheometry correlates with M-w/MzMz+1.

Background Traumatic peripheral nerve injury (TPNI) is a major medical problem with no universally accepted pharmacologic treatment. We hypothesized that encapsulation of pro-angiogenic erythropoietin (EPO) in amphiphilic PLGA-PEG block copolymers could serve as a local controlled-release drug delivery system to enhance neurovascular regeneration after nerve injury. Methods In this study, we synthesized an EPO-PLGA-PEG block copolymer formulation. We characterized its physiochemical and release properties and examined its effects on functional recovery, neural regeneration, and blood vessel formation after sciatic nerve crush injury in mice. Results EPO-PLGA-PEG underwent solution-to-gel transition within the physiologically relevant temperature window and released stable EPO for up to 18 days. EPO-PLGA-PEG significantly enhanced sciatic function index (SFI), grip strength, and withdrawal reflex post-sciatic nerve crush injury. Furthermore, EPO-PLGA-PEG significantly increased blood vessel density, number of junctions, and myelinated nerve fibers after injury. Conclusion This study provides promising preclinical evidence for using EPO-PLGA-PEG as a local controlled-release treatment to enhance functional outcomes and neurovascular regeneration in TPNI.

Materials with high dielectric constant, εs, are desirable in a wide range of applications including energy storage and actuators. Recently, zwitterionic liquids have been reported to have the largest εs of any liquid and, thus, have the potential to replace inorganic fillers to modulate the material εs. Although the large εs for zwitterionic liquids is attributed to their large molecular dipole, the role of chemical substituents attached to the zwitterion cation on εs is not fully understood, which is necessary to enhance the performance of soft energy materials. Here, we report the impact of zwitterionic liquid cation chemical substituents on εs (50 < εs < 300 at room temperature). Dielectric relaxation spectroscopy reveals that molecular reorientation is the main contributor to the high εs. The low Kirkwood factor g calculated for zwitterionic liquids (e.g., 0.1-0.2) suggests the tendency for the antiparallel zwitterion dipole alignment expected from the strong electrostatic intermolecular interactions. With octyl cation substituents, the g is decreased due to the formation of hydrophobic-rich domains that restrict molecular reorientation under applied electric fields. In contrast, when zwitterion cations are functionalized with ethylene oxide (EO) segments, g increases due to the EO segments interacting with the cations, allowing more zwitterion rotation in response to the applied field. The reported results suggest that high εs zwitterionic liquids require a large molecular dipole, compositionally homogeneous liquids (e.g., no aggregation), a maximized zwitterion number density, and a high g, which is achievable by incorporating polar chemical substituents onto the zwitterion cations.

Isotactic polypropylene (iPP) melts are industrial semicrystalline polymers whose processing typically involves strong shear flows. The study of the rheological response of iPP melts, well beyond the linear viscoelastic limit, is limited by edge fracture, which manifests in rotational rheometers. In this work, we used a reflection polariscope under shear to detect the onset shear rate at which edge fracture is observed for various rotational rheometry fixture diameters. The onset shear rate for edge fracture was found to correlate with the zero-shear viscosity, thereby enabling the prediction of edge fracture by only knowing the zero-shear viscosity; a quantity that is easier to measure compared to the second normal stress difference. Edge fracture is then mitigated by using a cone-partitioned plate, which enabled the study of the first normal stress difference, and in combination with capillary rheometry, allowed the measurement of flow curves with a very well-resolved shear thinning region. For strongly polydisperse iPPs at high shear rates, we found that viscosity scales as the −0.7 power of the shear rate, while primary normal stress difference scales as the square root of the shear rate. The dependence of the shear thinning of iPPs on polydispersity was then unravelled, offering a broad set of data to develop and test molecular models.

Polyelectrolyte solution dynamics have been carefully studied experimentally and theoretically for unentangled solutions and thought to be reasonably well understood. While theoretical models have been proposed for entangled polyelectrolyte solutions, there have been limited experimental data published to justify any understanding of entangled polyelectrolyte solution rheology. Herein, we study entangled nearly monodisperse carefully dialyzed cesium polystyrene sulfonate (M-n = 2.83 x 10(6) g/mol) solutions without salt in water, anhydrous ethylene glycol (T-g = -95 degrees C), and anhydrous glycerol (T-g = -80 degrees C) using rotational rheometry and X-ray scattering to determine the correlation length. For the glycerol solutions, time-temperature superposition was found to work between 25 and -5 degrees C, yielding linear viscoelastic (LVE) response of polyelectrolyte solutions over a wide frequency range. At concentrations where scaling predictions expect entanglements, the LVE response appears unentangled (no rubbery plateau), suggesting an underestimation of the entanglement concentration c(e) At higher concentrations in entangled solutions, the rubbery plateau width measured as the ratio of the two crossing points of storage and loss moduli (tau(rep)/tau(e)) in glycerol scales as c(4), suggesting that polyelectrolyte solutions behave like solutions of neutral polymers in the entangled concentration regime. Four methods for evaluating entanglement concentration are compared, and their relative orderings are similar to those of neutral polymer solutions.

When a semicrystalline polymer melt is processed in intense flow, the nucleation rate can be accelerated and the resultant morphology is transformed to anisotropic structures. These cumulative changes to the crystallization process are referred to as flow-induced crystallization (FIC). In this study, shear flow-induced crystal formations of poly(ether ether ketone) (PEEK) are investigated after applying a short-term shear (gamma = 20 s(-1) and t(s) < 230 s) via rheology and ex situ small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). Using rheology, three types of dynamic response are monitored during FIC: no flow effect, nucleation acceleration, and instant crystal growth without crystallization induction time. Ex situ SAXS is employed with sheared PEEK disks to evaluate the flow-induced lamellar structure and orientation. The short-term shear changes the fraction and degree of lamellar stack orientation, whereas the lamellar structure is barely affected by shear, in terms of the long spacing (L* = 14.6 nm), linear crystallinity (chi(c) = 0.34), and crystalline and amorphous layer thicknesses (L-c = 5.0 nm and L-a = 9.6 nm). Ex situ WAXS patterns indicate that PEEK chains (c-axis) are aligned in the shear direction within crystalline domains.

Cellulose nanocrystals (CNCs) are rod-shaped particles that can self-assemble into a chiral nematic phase at certain contents. Due to their negative diamagnetic susceptibility and high aspect ratio, the structure of the chiral nematic phase of CNC suspensions can be manipulated using a magnetic field, which is a promising path to extending local order to a larger scale. The ability to manipulate CNCs in non-aqueous solvents is critically needed to incorporate them in a wide range of polymers. So far, magnetic field-induced manipulation of CNCs in suspension was reported for aqueous suspensions only, whereas a much-needed similar study for non-aqueous solvents has not been reported to the best of our knowledge. In this paper, we investigate the CNC ordering in n-methylformamide (NMF) under a 0.7 T magnetic field and compare it to the order achieved in H2O. The formation of a well-defined chiral nematic phase and its viscosity have a significant influence on the rate and extent of the field-induced orientation of CNCs. A clearly formed chiral nematic phase has a high potential for increased levels of field-induced ordering. And the chiral nematic phase with the lowest viscosity showed the largest increase in ordering when the magnetic field is applied before reaching equilibrium and plateauing. In contrast, the higher viscosity suspensions exhibited limited temporal changes after the initial field effect. These findings will facilitate the fabrication of globally ordered CNCs in a variety of polymers under a magnetic field, which is a necessary step to expanding the engineering applications of large-scale cellulose-based composites with anisotropic properties.

The development of all-solid-state Li-ion batteries requires solid electrolyte materials with many desired properties, such as ionic conductivity, chemical and electrochemical stability, and mechanical durability. Computation-guided materials design techniques are advantageous in designing and identifying new solid electrolytes that can simultaneously meet these requirements. In this joint computational and experimental study, a new family of fast lithium ion conductors, namely, LiTaSiO5 with sphene structure, are successfully identified, synthesized, and demonstrated using a novel computational design strategy. First-principles computation predicts that Zr-doped LiTaSiO5 sphene materials have fast Li diffusion, good phase stability, and poor electronic conductivity, which are ideal for solid electrolytes. Experiments confirm that Zr-doped LiTaSiO5 sphene structure indeed exhibits encouraging ionic conductivity. The lithium diffusion mechanisms in this material are also investigated, indicating the sphene materials are 3D conductors with facile 1D diffusion along the [101] direction and additional cross-channel migration. This study demonstrates a novel design strategy of activating fast Li ionic diffusion in lithium sphenes, a new materials family of superionic conductors.

With rapidly increasing demand of Li-ion batteries (LIBs) triggered by the widespread proliferation of mobile devices and electric vehicles, a comprehensive and clean recycling strategy is greatly desired to alleviate the pressure of waste treatment and raw material supply. In this study, a novel method is developed for the recovery of semi-precious metals (Li, Co and Ni) from spent LIBs based on low temperature solution reactions, which is different from conventional acid leaching or high temperature smelting recycling methods. This novel recycling method can be applied to most of the prevailing commercial cathode materials, including LiCoO2(LCO), LiNixMnyCozO2 (NMC), and LiNi0.8Co0.15Al0.05O2 (NCA), with high recovery rates of 93%~99%. In situ synchrotron XRD is conducted to reveal the reaction mechanism and optimize the reaction conditions. A scaled-up recycling test towards industrial applications is also proposed based on the solution reactions. The experimental results suggest this novel method can be easily adopted for industry-level LIB recycling processes in an efficient and environmentally friendly way. A life cycle analysis has also been conducted to confirm the economic and energy/emission feasibility of this approach. Therefore, this approach shows great promise as a next-generation scenario for the recycling of high-value metals from spent commercial LIBs in the near future. Figure 1

Vinyl trimethoxysilane (VTMS)-modified hexagonal mesoporous silica (HMS-3) has been synthesized at varied loading concentrations of VTMS to determine the effect of VTMS loading on hydrogen adsorption capacity. Materials were synthesized with 0, 10, 20, and 31.5 mol percent starting VTMS with respect to total silica precursor. In the modified VTMS(X)-HMS-3 silica submicron particles (X = 0%, 10%, 20%, and 31.5%), hydrogen adsorption capacity increased with a maximum of 0.72 wt% adsorbed by VTMS(31.5)-HMS-3 at 77.3 K and 825 mmHg. This adsorption surpass the adsorption capacity of the unmodified VTMS(0)-HMS-3, which attained 0.50 wt% adsorption at the same temperature and pressure. The correlative increasing trend in adsorption capacity following increased organic modification provides inspiration for similar modifications to periodic mesoporous organosilicas (PMO), which exhibit higher adsorption capacity than traditionally modified particles. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Compared to rechargeable batteries, electrochemical double-layer capacitors (EDLCs) are normally considered to be higher power but lower electrical energy density charge storage devices. To increase the energy density, one can enlarge the interfacial area between electrodes and electrolyte through the introduction of nanopores and employ electrolytes that are stable over wider voltage ranges, such as ionic liquids. However, due to the relatively high viscosity of ionic liquids and large ion sizes, these measures can result in diminished power performance. Here, we describe the synthesis of carbon electrodes that overcome these limitations and simultaneously provide high specific energies and high specific powers in EDLCs using the ionic liquid EMI-TFSI as an electrolyte. A colloidal crystal templating method was optimized to synthesize three-dimensionally ordered mesoporous (3DOm) carbons with well-defined geometry, three-dimensionally interconnected pore structure and tunable pore size in the range from 8 to 40 nm. To achieve precise control over the pore sizes in the carbon products, parameters were established for direct syntheses or seed growth of monodisperse silica nanospheres with specific sizes, using L-lysine-assisted hydrolysis of silicon alkoxide precursors. Porous carbons were then templated from these materials using phenol formaldehyde (PF) or resorcinol-formaldehyde (RF) precursors. The pore structures of the nanoporous carbon products were characterized in detail, and the materials were tested as electrodes for EDLCs. Optimal pore sizes were identified that provided a large interface between the electrode and the electrolyte while maintaining good ion transport through the relatively viscous electrolyte. 3DOm PF-carbons with pore diameters in the 21-29 nm range exhibited similar high specific capacitance values (146-178 F g(-1) at 0.5 A g(-1), with respect to the mass of carbon in a single electrode) as typical large-scale activated-carbon-based EDLCs but showed significantly better high-rate performance (80-123 F g(-1) at 25 A g(-1)), a result of the more accessible pore space in which ion diffusion was less restricted.

Organosilicon complexes were synthesized via a green chemical process using silica nanoparticles derived from rice husk (RH) biomass. By controlling the pre-treatment of RHs and pyrolysis conditions, silica samples with various surface areas and degrees of crystallinity were synthesized. Such silica can be converted to silicon complexes via a low temperature approach. The synthesized silicon complexes were characterized by 1H, 13C, 29Si nuclear magnetic resonance and elemental analysis. Overall, the biogenic silica nanoparticles with high surface area and low crystallinity exhibit high reactivity, comparable to commercial fumed silica. Considering their high reactivity and low cost, such biogenic silica nanoparticles from RHs are ideal starting materials to produce organosilicon compounds.

Biogenic silica. nanoparticles (25-30 nm in diameter). were synthesized from rice husks. The characterizations revealed that the silica nanoparticles were composed of smaller primary particles (ca. 4.2 nm in diameter), and their clustering led to a porous structure with a surface area of 164 m(2)/g. Under the controlled melting catalyzed by K+, such silica nanoparticle clusters can gradually fuse to form semicrystalline porous silica frameworks with tunable pore size and structural integrity.

With the addition of copper microparticles, the electrical conductivity of a hexagonal mesoporous silica (HMS) disk can be enhanced. As an electric field is applied across the interface of the HMS–Cu mixture and an electrolyte solution, the liquid infiltration pressure increases considerably, which is also dependent on the nanopore size. It may be attributed to the surface charge effect, which is amplified by the large surface to volume ratio.

Abstract The inner surfaces of a hexagonal mesoporous silica (HMS) are treated by chlorotrimethylsilane, either directly or through vapor or liquid endcapping. The directly treated inner surfaces have the highest effective interfacial tension, and the liquid endcapping treated surfaces have the largest accessible nanopore volume. The difference in the treatment results may be attributed to the distinct surface structures.