Accelerated Fabrication of Fiber-Welded Mesoporous Cotton Composites

Natural fiber-welded (NFW) biopolymer composites are rapidly garnering industrial and commercial attention in the textile sector, and a recent disclosure demonstrating the production of mesoporous NFW materials suggests a bright future as sorbents, filters, and nanoparticle scaffolds. A significant roadblock in the mass production of mesoporous NFW composites for research and development is their lengthy preparation time: 24 h of water rinses to remove the ionic liquid (IL) serving as a welding medium and then 72 h of solvent exchanges (polar to nonpolar), followed by oven drying to attain a mesoporous composite. In this work, the rinsing procedure is systematically truncated using the solution conductivity as a yardstick to monitor IL removal. The traditional water immersion rinses are replaced by a flow-through system (i.e., infinite dilution) using a peristaltic pump, reducing the required water rinse time for the maximum removal of IL to 30 min. This procedure also allows for easy in-line monitoring of solution conductivity and reclamation of an expensive welding solvent. Further, the organic solvent exchange is minimized to 10 min per solvent (from 24 h), resulting in a total combined rinse time of 1 h. This process acceleration reduces the overall solvent exposure time from 96 to 1 h, an almost 99% temporal improvement.

Interrogating the Latent Porosity Within Natural Fiber Welded Composites

Seemingly nonporous biopolymer composites prepared by natural fiber welding (NFW) possess latent pores that can be exfoliated by conscientious solvation. We present a seminal demonstration of this concept for cellulose and explore the impact of latent pores on the manufacture and commercialization of NFW products.

Physical and Electrochemical Analysis of N-Alkylpyrrolidinium-Substituted Boronium Ionic Liquids

In this work, a series of novel boronium-bis(trifluoromethylsulfonyl)imide [TFSI-] ionic liquids (IL) are introduced and investigated. The boronium cations were designed with specific structural motifs that delivered improved electrochemical and physical properties, as evaluated through cyclic voltammetry, broadband dielectric spectroscopy, densitometry, thermogravimetric analysis, and differential scanning calorimetry. Boronium cations, which were appended with N-alkylpyrrolidinium substituents, exhibited superior physicochemical properties, including high conductivity, low viscosity, and electrochemical windows surpassing 6 V. Remarkably, the boronium ionic liquid functionalized with both an ethyl-substituted pyrrolidinium and trimethylamine, [(1-e-pyrr)N111BH2][TFSI], exhibited a 6.3 V window, surpassing previously published boronium-, pyrrolidinium-, and imidazolium-based IL electrolytes. Favorable physical properties and straightforward tunability make boronium ionic liquids promising candidates to replace conventional organic electrolytes for electrochemical applications requiring high voltages.

Elucidating the interplay of local and mesoscale ion dynamics and transport properties in aprotic ionic liquids

Ion dynamics and charge transport in 1-methyl-3-octylimidazolium ionic liquids with chloride, bromide, tetrafluoroborate, tricyanomethanide, hexafluorophosphate, triflate, tetrachloroaluminate, bis(trifluoromethylsulfonyl)imide, and heptachlorodialuminate anions are investigated by broadband dielectric spectroscopy, rheology, viscometry, and differential scanning calorimetry. A detailed analysis reveals an anion and temperature-dependent separation of characteristic molecular relaxation rates extracted from various representations of the dielectric spectra. The separation in rates extracted from the electric modulus and conductivity formalisms is interpreted as an experimental signature of significant heterogeneity in the local ion dynamics associated with the structural glass transition, viscosity, and dc ion conductivity. It is further found that the degree of dynamic heterogeneity correlates with the strengths of slow dielectric and mechanical relaxations previously attributed to the dynamics of mesoscale solvophobic aggregates. Increasing local dynamic heterogeneity correlates with an increase in the strength of the slow, aggregate dielectric relaxation and a decrease in the strength of the slow, aggregate mechanical relaxation. Accordingly, increasing local dynamic heterogeneity, brought about by change in temperature and/or cation/anion chemical structure, correlates with an increase in the static dielectric permittivities and a decrease in the contribution of aggregate dynamics to the zero-shear viscosities. The established correlation provides a new ability to distinguish between the influence of mesoscale aggregate shape/morphology versus local and mesoscale ion dynamics on the transport properties of ionic liquids.

Dissolution of Biopolymers Using Ionic Liquids

Ionic liquids represent a unique class of solvents that offer unprecedented versatility and tunability. Nature has developed a wide variety of materials based upon both proteins and polysaccharides. Many of these materials have unique properties that are a function not only of the material identity but are also largely dictated by processing conditions. Recent work has shown the potential of ionic liquids as solvents for the dissolution and processing of biopolymers. In this research we have expanded upon the limited data available to date using several biopolymers including: silk, chitin, collagen and elastin.

Concurrent zero-dimensional and one-dimensional biomineralization of gold from a solution of Au3+ and bovine serum albumin

A technique was developed for preparing a novel material that consists of gold nanoparticles trapped within a fiber of unfolded proteins. These fibers are made in an aqueous solution that contains HAuCl4 and the protein, bovine serum albumin (BSA). By changing the ratio of gold to BSA in solution, two different types of outcomes are observed. At lower gold to BSA ratios (30-120), a purple solution results after heating the mixture at 80 °C for 4 h. At higher gold to BSA ratios (130-170), a clear solution containing purple fibers results after heating the mixture at 80 °C for 4 h. UV-Vis spectroscopy and light scattering techniques show growth in nanocolloid size as gold to BSA ratio rises above 100. Data indicate that, for the higher gold to BSA ratios, the gold is sequestered within the solid material. The material mass, visible by eye, appears to be an aggregation of smaller individual fibers. Scanning electron microscopy and transmission electron microscopy indicate that these fibers are primarily one-dimensional aggregates, which can display some branching, and can be as narrow as 400 nm in size. The likely mechanism for the synthesis of the novel material is discussed.

Fluorescence monitoring of ionic liquid-facilitated biopolymer mobilization and reorganization

Ionic liquid-facilitated mobilization and reorganization of biopolymers in natural fibrous materials is visualized by confocal fluorescent spectromicroscopy. Ionic liquid-based processes controllably fuse adjacent fibres while simultaneously leaving selected amounts of biopolymers in their native states. These processes generate congealed materials with extended intermolecular hydrogen bonding networks and enhanced properties.

3-(1-Methyl-3-imidazolio)propane-sulfonate: a precursor to a Brønsted acid ionic liquid

The title compound, C₇H₁₂N₂O₃S, is a zwitterion precursor to a Brønsted acid ionic liquid with potential as an acid catalyst. The C—N—C—C torsion angle of 100.05 (8)° allows the positively charged imidazolium head group and the negatively charged sulfonate group to inter­act with neighboring zwitterions, forming a C—H⋯O hydrogen-bonding network; the shortest among these inter­actions is 2.9512 (9) Å. The C—H⋯O inter­actions can be described by graph-set notation as two R²₂(16) and one R²₂(5) hydrogen-bonded rings.

Comparison of the quality of aqueous dispersions of single wall carbon nanotubes using surfactants and biomolecules

The use of single wall carbon nanotubes (SWCNTs) in current and future applications depends on the ability to process SWCNTs in a solvent to yield high-quality dispersions characterized by individual SWCNTs and possessing a minimum of SWCNT bundles. Many approaches for the dispersion of SWCNTs have been reported. However, there is no general assessment which compares the relative quality and dispersion efficiency of the respective methods. Herein we report a quantitative comparison of the relative ability of "wrapping polymers" including oligonucleotides, peptides, lignin, chitosan, and cellulose and surfactants such as cholates, ionic liquids, and organosulfates to disperse SWCNTs in water. Optical absorption and fluorescence spectroscopy provide quantitative characterization (amount of SWCNTs that can be suspended by a given surfactant and its ability to debundle SWCNTs) of these suspensions. Sodium deoxy cholate (SDOCO), oligonucleotides (GT)(15), (GT)(10), (AC)(15), (AC)(10), C(10-30), and carboxymethylcellulose (CBMC-250K) exhibited the highest quality suspensions of the various systems studied in this work. The information presented here provides a good framework for further study of SWCNT purification and applications.

Use of a polyhedral oligomeric silsesquioxane (POSS)-imidazolium cation as an organic modifier for montmorillonite

Recent studies on organically modified clays (OMCs) have reported enhanced thermal stabilities when using imidazolium-based surfactants over the typical ammonium-based surfactants. Other studies have shown that polyhedral oligomeric silsesquioxanes (POSS) also improve the thermal properties of composites containing these macromers. In an attempt to utilize the beneficial properties of both imidazolium surfactants and POSS macromers, a dual nanocomposite approach to prepare OMCs was used. In this study, the preparation of a new POSS-imidazolium surfactant and its use as an organic modifier for montmorillonite are reported. The purity, solubility, and thermal characteristics of the POSS-imidazolium chloride were evaluated. In addition, several OMCs were prepared by exchanging the Na+ with POSS imidazolium cations equivalent to 100%, 95%, 40%, 20%, and 5% of the cation exchange capacity of the clay. The subsequent OMCs were characterized using thermal analysis techniques (DSC, SDT, and TGA) as well as 29Si NMR to determine the POSS content in the clay interlayer both before and after thermal oxidation degradation. Results indicate the following: (1) the solvent choice changes the efficiency of the ion-exchange reaction of the clay; (2) self-assembled crystalline POSS domains are present in the clay interlayer; (3) the d-spacing of the exchanged clay is large (3.6 nm), accommodating a bilayer structure of the POSS-imidazolium; and (4) the prepared POSS-imidazolium exchanged clays exhibit higher thermal stabilities than any previously prepared imidazolium or ammonium exchanged montmorillonite.

New Disordering Mode for TFSI- Anions: The Nonequilibrium, Plastic Crystalline Structure of Et4NTFSI

A new TFSI- anion disordering mode has been discovered in a supercooled plastic crystalline phase of Et4NTFSI, which may, in part, account for the low melting points of TFSI- salts with organic cations, thereby forming ionic liquids, and the intriguing properties of LiTFSI for lithium battery applications.

Alkyl vs. alkoxy chains on ionic liquid cations

The crystal structures and thermal behavior of the 1-(2-methoxyethyl)-2,3-dimethylimidazolium chloride and hexa-fluorophosphate salts are compared with the analogous 1-butyl-2,3-dimethylimidazolium salts to examine the influence of the ether oxygen on salt thermal properties for a typical constituent cation used in the preparation of ionic liquids.

Dissolution and Regeneration of Bombyx mori Silk Fibroin Using Ionic Liquids

In this work, the suitability of imidazolium-based ionic liquid solvents is investigated for the dissolution and regeneration of silkworm (Bombyx mori) silk. Within an ionic liquid the anion plays a larger role in dictating the ultimate solubility of the silk. The dissolution of the silk in the ionic liquid is confirmed using wide-angle X-ray scattering. The dissolved silk is also processed into 100 mum-thick, two-dimensional films, and the structure of these films is examined. The rinse solvent, acetonitrile or methanol, has a profound impact on both the topography of the films and the secondary structure of the silk protein. The image depicts a silkworm cocoon dissolved in 1-butyl-3-methylimidazolium chloride and then regenerated as a film with birefringence.

Physical Properties of Substituted Imidazolium Based Ionic Liquids Gel Electrolytes

The physical properties of solid gel electrolytes of either polyvinylidene diflurohexafluoropropylene or a combination of polyvinylidene hexafluoropropylene and polyacrylic acid, and the molten salts 1-ethyl-3-methylimidazolium tetrafluoroborate, 1,2-dimethyl-3-n-propylimidazolium tetrafluoroborate, and the new molten salts 1,2-dimethyl-3-n-butylimidazolium tetrafluoroborate, and 1,2-dimethyl-3-n-butylimidazolium hexafluorophosphate were characterized by temperature dependent ionic conductivity measurements for both the pure molten salt and of the molten salt with 0.5 M Li+ present. Ionic conductivity data indicate that for each of the molten salts, the highest concentration of molten salt allowable in a single component polymer gel was 85%, while gels composed of 90%molten salt were possible when using both polyvinylidene hexafluorophosphate and polyacrylic acid. For polymer gel composites prepared using lithium containing ionic liquids, the optimum polymer gel composite consisted of 85% of the 0.5 M Li+/ionic liquid, 12.75% polyvinylidene hexafluoropropylene, and 2.25% poly (1-carboxyethylene). The highest ionic conductivity observed was for the gel containing 90%1-ethyl-3-methyl-imidazolium tetrafluoroborate, 9.08 mS/cm. For the lithium containing ionic liquid gels, their ionic conductivity ranged from 1.45 to 0.05 mS/cm, which is comparable to the value of 0.91 mS/cm, observed for polymer composite gels containing 0.5 M LiBF4 in propylene carbonate.

Gutmann Acceptor Properties of LiCl, NaCl, and KCl Buffered Ambient-Temperature Chloroaluminate Ionic Liquids

Gutmann acceptor numbers have been determined using (31)P nuclear magnetic resonance (NMR) for AlCl(3)/EMIC melts as well as LiCl, NaCl, and KCl neutral buffered melts. In AlCl(3)/EMIC melts, where EMIC is 1-ethyl-3-methylimidazolium chloride, the change in Gutmann acceptor number as a function of the AlCl(3):EMIC melt ratio is attributed to an equilibrium between a monoadduct of triethylphosphine oxide.AlCl(3) and a diadduct of triethylphosphine oxide.2AlCl(3). Observed acceptor numbers for the neutral buffered melts appear linear with respect to the melt's initial mole ratio of AlCl(3):EMIC prior to buffering. The lithium cation appears to be the most Lewis acidic alkali metal cation followed by the sodium and potassium cations. Possible reasons for the change in acceptor number as a function of changing alkali metal cation concentration are presented.