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The utilization of ionic liquids (ILs) for future electrochemical applications shows great promise. Recently ILs have been investigated for many electrochemical systems however, further characterization and development of ILs remains as they are utilized in devices such as batteries, capacitors, fuel cells, sensors, and other applications. In this study, we present time resolved (TRS) FTIR spectroscopy data as a means to characterize interfaces between IL-based electrolytes and gold electrodes. These data are important in that dynamic interactions at the electrode/electrolyte interface are crucial to device efficiency, power density, sensitivity, et cetera.

Inkjet printing has become an increasingly popular tool for materials science research due to its ability to rapidly create small devices with excellent precision and reproducibility. Recent studies have utilized inkjet printing for the construction of inexpensive devices using ink-mimicking solutions containing various materials of interest (magnetic, sensing, electronic)[i],[ii],[iii]. By varying the chemical nature of these inks, inkjet printing becomes a robust, versatile, and accessible tool for small scale material fabrication. Ionic liquids (IL) have been the focus of materials research for some time due to their unique physical and chemical properties. Of significant interest is their ability to solubilize biopolymers such as cellulose and silk[iv]. When paired with inkjet printing, these ILs allow for variable, reproducible modification of biopolymers. By incorporating materials of interest into these IL inks, inkjet printing presents an extremely powerful tool for small scale fabrication with a myriad of applications. In this research we will discuss the modification of surface structures through the inkjet printing of neat IL, IL’s containing nano and micro-scale particles, and IL/polymer solutions. [i] Delaney, J. T., Jr.; Smith, P. J.; Schubert, U. S. Inkjet Printing of Proteins. Soft Matter, 2009, 24, 4866. [ii] Singh, M.; Haverinen, H. M.; Dhagat, P.; Jabbour, G. E. Inkjet Printing – Process and Its Applications. Adv. Materials, 2010, 22, 673. [iii] Hu, C.; Bai, X.; Wang, Y.; Jin, W.; Zhang, X.; Hu, S. Inkjet Printing of Nanoporous Gold Electrode Arrays. Anal. Chem. 2012, 84, 3745. [iv] Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D. Dissolution of Cellulose with Ionic Liquids. J. Am. Chem. Soc., 2002, 18, 4974.

Batteries are one of the most impactful inventions humankind has ever developed. Lithium-ion energy cells represent a significant advance in battery technology. Electrolytes used in batteries are still not well understood in terms of solution structure. We investigate electrolyte solvate structure with the aid of differential scanning calorimetry, Raman spectroscopy, and X-ray diffraction. Here is a report on the solvate structure(s) present in mixtures of propylene carbonate (PC) and lithium trifluoromethanesulfonate (LiTf). Mixtures of racemic PC with LiTf form glasses whereas enantiomerically pure PC, both R and S isomers, forms mixtures with more complex phase behavior. At concentrations approaching a 1:1 molar ratio of solvent to salt, a solvate that melts at ~150 °C was detected. A crystal of the 1:1 solvate of the R-(+)-PC:LiTf was successfully grown and analyzed by X-ray diffraction. This solvate has an aggregated structure where the Li+ cations are tetrahedrally coordinated. Three directions of coordination come from Tf– anions acting as a bridging ligand between three different Li+ cations and the 4th direction of coordination comes from the carbonyl oxygen of the solvent molecule.

Extruded organically modified layered silicate (OMLS) - poly(lactic acid) (PLA) composites exhibit a mixed intercalated/exfoliated morphology. To explore effects of surfactant hydrophobicity and polarity on the quality of dispersion, a series of OMLS were prepared from quaternary ammonium, phosphonium, and imidazolium salts, including some synthesized hexadecanoic acid containing ionic liquids. The alkyl chains were modified to include aromatic and oxygen moieties while keeping the same long alkyl chain length. Nile Blue was co-exchanged to add a fluorescent tag to the layered silicates. The effectiveness of this technique for PLA and different Nile Blue salts were assessed. Degree of exfoliation was monitored using x-ray diffraction and fluorescence spectroscopy. Thermal characteristics of the new OMLS were measured.

Ionic liquids (ILs) represent a class of printable material for use in the inkjet technique. Additionally, some ILs are effective solvents for biopolymers (i.e., cellulose and silk). The combination of the ILs ability to solvate biopolymers and the highly controllable delivery of liquids utilized in inkjet printing technology provide a means to pattern substrates and build structures. In this report, the delivery of IL-based solvents to cellulosic papers by inkjet printing is demonstrated. In particular, imaging data that characterize morphological alterations to cellulosic paper substrates are discussed. Results suggest that printed materials with unique properties are possible for a wide range of applications.

In the past decade, ionic liquid solvents have been developed for a wide variety of biopolymers such as cellulose and silk. During this time ionic liquids have also been shown to enhance the interactions of micromaterials and nanomaterials (i.e., clays, carbon nanotubes, magnetic materials, et cetera) with polymeric materials. Recently, our group has demonstrated an ionic liquid-based technique, “Natural Fiber Welding”, by which functionalized composite materials are generated from (often fibrous) biopolymer substrates. Fiber welding processes leverage many of the advantageous properties of ionic liquids as solvents and compatibilization media. A distinctive characteristic of the fiber welding process is the selective mobilization and restructuring of biopolymers to create composite materials that retain native biopolymer microstructures and mesostructures. As ionic liquid solvents penetrate fiber surfaces, biopolymers are opened to chemical derivatization; simultaneously, hydrogen bonding networks are reorganized (and extended).

Certain ionic liquids (ILs) are known to be efficient solvents for biopolymers. That said, solvent efficacy is strongly impacted by the presence of both adventitious as well as other molecular components that may be added deliberately. For example, 1-ethyl-3-methylimidazolium acetate often contains water and acetic acid (polar protic) impurities (by-products of IL synthesis) that can have significant effects upon the dissolution of biopolymers. Additionally, ILs can be mixed with solvents such as acetonitrile (polar aprotic) that also impact the dissolution process. Data are presented that explore the effect of IL-based solvent composition on fiber welding: the controlled, partial dissolution of fibrous materials to create composite materials. Results suggest that IL-based solvents can be modified for specific outcomes. Additionally, the fiber welding processes and material analysis techniques utilized are themselves useful to quantify solvent efficacy.

Electrospinning is a technique commonly used to produce nano to micro sized fibers with a high surface area to volume ratio. Of particular interest are electrospun natural fibers, such as cellulose, with high biocompatibility allowing for applications in biosensors, membranes and biomedical devices. Unfortunately, cellulose is naturally recalcitrant and insoluble in common solvents due to high crystallinity arising from a strong hydrogen bonding network making processing of this fiber difficult. Currently, processing techniques such as wet or dry-wet spinning and electrospinning have been investigated with known cellulose solvent such as Nmethyl-morpholine N-oxide/water, salt/solvent systems such as lithium chloride/dimethyl acetamide or ethylene diamine/potassium thiocyanate, ionic liquids (ILs) and from IL/dimethylsulfoxide systems.

Fossil fuels are being rapidly depleted and a novel and renewable source of hydrocarbons needs to be found. One source of untapped energy is cellulose. Work has shown that ionic liquids can dissolve and enable the facile processing of cellulose. This research shows that 1-methylimidazolum-3-ethylsulfonic acid triflate, an ionic liquid catalyst, can be used as a catalyst for the depolymerization of cellulose in an ionic liquid at greater than 50% conversion to reducing sugars. It also shows the main product of the reaction is glucose which is further dehydrated into 5-(Hydroxy-methyl) furfural. This investigation evaluated the effects of time, temperature, and co-catalyst on the reaction products and rate of the reaction.

Preliminary data are shown for a systematic study of the variables that control the fiber welding process. Cotton cloth samples are treated with various amounts of 1-ethyl-3-methylimidazolium acetate for a series of times and temperatures. Processed materials are characterized by scanning electron microscopy, infrared spectroscopy, x-ray diffraction, and mechanical (tensile) testing. Chemical and physical properties are shown to be controllably modified with careful management of process variables.

Ionic liquids are effective solvents for the dissolution of biopolymers such as cellulose and silk. New materials can be created from these natural feedstocks by processes that involve the full dissolution of biomaterials. Many reports show that the dissolution and reconstitution processes eliminate the native polymer structure, often with deleterious consequences to the physical properties of the material. Recently, it has been shown that robust biopolymer based structures may be created without full dissolution of the material by a method we call “Natural Fiber Welding”. The welding process generates modified natural fiber structures while leaving much of the material in its native state. As a result, natural fiber welding enables tunable preservation of native microstructure while also affording manipulation of important material properties.

Preliminary data are shown for the mechanical properties of cellulose and silk composite blends with and without nanomodifiers. Composite strength increases with increasing cellulose concentration for samples created with two different coagulation solutions. In general, samples containing > 30% silk are difficult to handle and test because they are extremely brittle. The addition of nanocomposites may increase overall strength of samples, but is dependent on the morphology of the nanomaterial added.