Electrolytes for Zn Batteries: Deep Eutectic Solvents in Polymer Gels

Gel polymer electrolytes composed of deep eutectic solvent acetamide₄ :Zn(TFSI)₂ and poly(ethylene oxide) (PEO) are prepared by using a fast, solvent-free procedure. The effect of the PEO molecular weight and its concentration on the physicochemical and electrochemical properties of the electrolytes are studied. Gels prepared with ultrahigh molecular-weight PEO present pseudo-solid behavior and ionic conductivity even higher than that of the original liquid electrolyte. A decrease in the dendritic growth in soft gels with PEO contents up to 1 wt % is demonstrated. The changes in the chemical structure of the electrolyte produced by the strong interactions between ethylene oxide units and Zn²⁺ have also been studied. The addition of PEO takes the electrolyte out of its original eutectic composition, producing blend crystallization. However, it is possible to retain the eutectic point of the electrolyte in a gel form if the addition of PEO is accompanied by the reduction of acetamide.

Highly Stable Hierarchically Structured All-Polymeric Lubricant-Infused Films Prevent Thrombosis and Repel Multidrug-Resistant Pathogens

Thrombus formation and infections caused by bacterial adhesion are the most common causes of failure in blood-contacting medical devices. Reducing the interaction of pathogens using repellent surfaces has proven to be a successful strategy in preventing device failure. However, designing scale-up methodologies to create large-scale repellent surfaces remains challenging. To address this need, we have created an all-polymeric lubricant-infused system using an industrially viable swelling-coagulation solvent (S-C) method. This induces hierarchically structured micro/nano features onto the surface, enabling improved lubricant infusion. Poly(3,3,3-trifluoropropylmethylsiloxane) (PTFS) was used as the lubricant of choice, a previously unexplored omniphobic nonvolatile silicone oil. This resulted in all-polymeric liquid-infused surfaces that are transparent and flexible with long-term stability. Repellent properties have been demonstrated using human whole blood and methicillin-resistant Staphylococcus aureus (MRSA) bacteria matrices, with lubricated surfaces showing 93% reduction in blood stains and 96.7% reduction in bacterial adherence. The developed material has the potential to prevent blood and pathogenic contamination for a range biomedical devices within healthcare settings.

Ionic Conductivity Enhancement in UHMW PEO Gel Electrolytes Based on Room-Temperature Ionic Liquids and Deep Eutectic Solvents

Physical gels made of poly(ethylene oxide) (PEO) and deep eutectic solvents urea-Li bis(trifluoromethanesulfonyl)imide (TFSI) and ethylene glycol/LiTFSI, or pyrrolidinium ionic liquid solutions PYR13TFSI-LiTFSI and PYR14TFSI-LiTFSI, are prepared by a fast, single-step process, which involves no auxiliary solvents or intermediates and is reproducible and scalable. The properties of these gels are studied as a function of the PEO content and its molecular weight and the nature of the liquid electrolyte. The gels prepared with a low concentration (1-5 wt %) of ultrahigh molecular weight (UHMW) PEO are tough, stretchable materials which resemble soft elastomers and are also self-healing and transparent. Their rheology shows the conventional behavior of physical polymer gels, so that the higher the molecular weight of PEO, the lower the polymer concentration needed to produce the gel. However, the ion conductivities and diffusivities of the gels are striking, in many cases being equal to or significantly higher than those of pure liquid electrolytes. This ion conductivity enhancement is the highest for the lowest PEO concentration with the highest molecular weight. This unprecedented molecular weight dependence of conductivity and diffusivity is the result of two combined effects: the liquid electrolyte chemical structure modification as a consequence of the addition of PEO and the development of elastic networks, where ion mobility and rheology are uncoupled when the PEO added is of UHMW.

Chloroaluminate Gel Electrolytes Prepared with Copolymers Based on Imidazolium Ionic Liquids and Deep Eutectic Solvent AlCl3:Urea

Polymer gel electrolytes (PGEs) have been prepared with copolymers based on imidazolium ionic liquids and the deep eutectic mixture of AlCl₃:urea (uralumina) as liquid electrolyte. The copolymers were synthesized by photopolymerization of vinylpirrolidone or methylmethacrylate with imidazolium bis (trifluoromethane sulfonyl) imide (TFSI) ionic liquid monomer and mixed in an increasing range of wt.% with uralumina. The rheology and electrochemical activity of PGEs were highly dependent on the molar ratio of charged groups and copolymer content. Structure of the PGEs was studied by FTIR and Raman spectroscopy and a correlation between interactions polymer/uralumina and changes in speciation of uralumina was established. Despite the low molecular weight of the copolymers, the resulting polymer electrolytes develop elastomeric character associated with the binding ionic species. Although there is room to improve the electrochemical activity, in this study these new gels provide sufficient electroactivity to make them feasible alternatives as electrolytes in secondary aluminum batteries.

Understanding the Molecular Structure of the Elastic and Thermoreversible AlCl3 : Urea/Polyethylene Oxide Gel Electrolyte

It is possible to prepare elastic and thermoreversible gel electrolytes with significant electroactivity by dissolving minimal weight fractions of ultra-high molecular weight polyethylene oxide (UHMW PEO) in an aluminum deep eutectic solvent (DES) electrolyte composed of AlCl₃ and urea at a molar ratio of 1.5 : 1 (AlCl₃ /urea). The experimental vibrational spectra (FTIR and Raman) provide valuable information on the structure and composition of the gel electrolyte. However, the complexity of this system requires computational simulations to help interpretation of the experimental results. This combined approach allows us to elucidate the speciation of the DES liquid electrolyte in the gel and how it interacts with the polymer chains to give rise to an elastic network that retains the electroactivity of the liquid electrolyte to a very great extent. The observed reactions occur between the ether in the polymer and both the amine groups in urea and the aluminum species. Thus, similar elastomeric gels may likely be prepared with other aluminum liquid electrolytes, making this procedure an effective way to produce families of gel aluminum electrolytes with tunable rheology and electroactivity.

High Performance Polymer/Ionic Liquid Thermoplastic Solid Electrolyte Prepared by Solvent Free Processing for Solid State Lithium Metal Batteries

A polymer/ionic liquid thermoplastic solid electrolyte based on poly(ethylene oxide) (PEO), modified sepiolite (TPGS-S), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and 1-Butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) ionic liquid is prepared using solvent free extrusion method. Its physical-chemical, electrical, and electrochemical properties are comprehensively studied. The investigated solid electrolyte demonstrates high ionic conductivity together with excellent compatibility with lithium metal electrode. Finally, truly Li-LiFePO₄ solid state coin cell with the developed thermoplastic solid electrolyte demonstrates promising electrochemical performance during cycling under 0.2 C/0.5 C protocol at 60 °C.

Ionic Liquid-Based Thermoplastic Solid Electrolytes Processed by Solvent-Free Procedures

A series of thermoplastic polymer electrolytes have been prepared employing poly(ethylene oxide) (PEO) as a polymer matrix, bis(trifluoromethane sulfonimide) (LiTFSI), and different room-temperature ionic liquids (RTIL) with bis(fluorosulfonyl)imide (FSI) or TFSI anions. This formulation makes them safe and non-flammable. The electrolytes have been processed in the absence of solvents by melt compounding at 120 °C, using sepiolite modified with d-α-tocoferol-polyethyleneglycol 1000 succinate (TPGS-S) as a physical cross-linker of PEO. Several concentrations of RTILs, lithium salt, and TPGS-S have been tested in order to obtain the highest ionic conductivity (σ) without losing electrolytes’ mechanical stability. The materials’ rheology and ionic conductivity have been extensively characterized. The excellent crosslinking ability of TPGS-S makes the electrolytes behave as thermoplastic materials, even those with the highest liquid concentration. The electrolytes with the highest concentrations of FSI anion present a σ over 10⁻³ S·cm⁻¹ at 25 °C and close to 10⁻² S·cm⁻¹ at 70 °C, and notably behave as solids at temperatures up to 90 °C despite over 65 wt % of their formulation being liquid. The electrolytes thus obtained are safe solid thermoplastics prepared by industrially scalable procedures and are suitable for energy storage devices, proving the adequacy of polymer-based materials as solid electrolytes for batteries or supercapacitors.

Long-Term Underwater Hydrophobicity: Exploring Topographic and Chemical Requirements

A family of hybrid organoinorganic silica-based particles with varied chemical natures and morphologies has been synthesized to test their ability to develop coatings with underwater hydrophobicity. The particles were characterized by elemental microanalysis, scanning electron microscopy, and dynamic light scattering to evaluate the organic content, observe the morphology, and estimate the aggregate size, respectively. These morphologies were transferred into surface topographies by spraycoating dispersions made from the particles onto glass supports, resulting in coatings with an ample range of profiles and roughness but all of them being superhydrophobic. Atomic force microscopy and optical profilometry were used to map the coating surfaces and analyze the topography. Then, underwater hydrophobicity endurance was tested by immersion under a 2 cm 20 °C water column perpendicular to circular glass supports coated with the particles. The so-called mirror effect derived from the occurrence of the primary plastron (continuous air layer occluded between the surface and the water) was observed on the surface of all of the coatings tested. Apart from the dependency of plastrons on the water temperature and substrate shape, the plastron quality and lifetime is notably different depending on the particle morphology and thus on the coating topography. These experiments have demonstrated that the most persistent mirror effects, and therefore underwater superhydrophobicity, were produced on coatings that exhibited the smoothest topographies at the micrometric scale. In addition, these particle-only coatings can be made mechanically stable and robust by blending with a polymer matrix.

Superhydrophobic and highly luminescent polyfluorene/silica hybrid coatings deposited onto glass and cellulose-based substrates

Neat poly(9,9-dioctyl-9H-fluorene) (PFO) and composites of PFO and a modified organonanosilica P(7) at weight ratios 90/10, 70/30, and 50/50 have been employed to prepare fluorescent and superhydrophobic coatings by spraying onto three different substrates: glass, Whatman paper, and a filtration membrane of mixed cellulose esters. The water repellency of the coatings and their photophysical properties are therein studied. It is found that, irrespective of the substrate and the composite composition, all coatings remain fluorescent. In some of the coatings prepared, confined morphologies are created, which fluoresce with a wavelength distribution resembling that of an ordered planar β-phase. Among the coatings prepared in this work, those with a ratio PFO/P(7) of 50/50 are the ones with the strongest chain confinement and the highest surface roughness, being highly emissive at the β-phase wavelengths and also superhydrophobic. Depending on the substrate these materials are also tough and flexible (cellulose based substrates) or display a remarkable light transmittance (glass). A final merit of these multifunctional materials is the simplicity of the preparation procedure, adequate for large surfaces and industrial applications.

Multipurpose ultra and superhydrophobic surfaces based on oligodimethylsiloxane-modified nanosilica

Nonfluorinated hydrophobic surfaces are of interest for reduced cost, toxicity, and environmental problems. Searching for such surfaces together with versatile processing, A200 silica nanoparticles are modified with an oligodimethylsiloxane and used by themselves or with a polymer matrix. The goal of the surface modification is controlled aggregate size and stable suspensions. Characterization is done by NMR, microanalysis, nitrogen adsorption, and dynamic light scattering. The feasibility of the concept is then demonstrated. The silica aggregates are sprayed in a scalable process to form ultrahydrophobic and imperceptible coatings with surface topographies of controlled nanoscale roughness onto different supports, including nanofibrillated cellulose. To improve adhesion and wear properties, the organosilica was mixed with polymers. The resulting composite coatings are characterized by FE-SEM, AFM, and contact angle measurements. Depending on the nature of the polymer, different functionalities can be developed. Poly(methyl methacrylate) leads to almost superhydrophobic and highly transparent coatings. Composites based on commercial acrylic car paint show "pearl-bouncing" droplet behavior. A light-emitting polyfluorene is synthesized to prepare luminescent and water repellent coatings on different supports. The interactions between polymers and the organosilica influence coating roughness and are critical for wetting behavior. In summary, the feasibility of a facile, rapid, and fluorine-free hydrophobization concept was successfully demonstrated in multipurpose antiwetting applications.

Surface modification of sepiolite in aqueous gels by using methoxysilanes and its impact on the nanofiber dispersion ability

Surface modification reactions on needle-like sepiolite using alkyl and functional silanes have been carried out in the form of aqueous gels. In contrast with modifications in organic solvents, reactions in water make it possible to modify the surface of almost-individual sepiolite fibers and produce either a continuous coating or a nanotexturization of the sepiolite fiber surface, depending on the reaction conditions. This clean procedure substitutes advantageously organic solvent surface modifications and allows the tuning of surface properties such as specific surface area, wetting behavior, and chemical functionalization. A consequence of such tuning is, for example, the excellent dispersion of modified sepiolite nanofibers in a great variety of polymers by routine compounding and processing techniques.

Microwave versus conventional heating in the grafting of alkyltrimethoxysilanes onto silica particles

The scope of this work is the comparative analysis in terms of grafting rate, structure of the grafted layer, and wetting behavior of three series of silica nanoparticles modified with alkyltrimethoxysilanes by using conventional heating with and without acid catalysis, and microwave irradiation. A comprehensive characterization of the grafted layer by means of Fourier transform infrared (FTIR), microanalysis, and solid state NMR techniques has shown that microwave irradiation provokes a pronounced increase in the loading rate compared to conventional heating. This microwave effect is outstanding in the case of the reactions with methyltrimethoxysilane, because of the acceleration of the condensation rate. Moreover, solid state NMR spectra ((29)Si and (13)C) strongly suggest structural differences in the grafted layer obtained by the two heating sources. The wetting behavior of the modified nanoparticles was studied, concluding that these changes in the structure of the grafted layer induced by the synthetic procedure do not determine the values of the dynamic water contact angles.

Effect of microstructure on the thermo-oxidation of solid isotactic polypropylene-based polyolefins

In the present work we aim to clarify the role of the microstructure and the crystalline distribution from the thermo-oxidation of solid isotactic PP (iPP) and ethylene-propylene (EP) copolymers. The effects of the content and quality of the isotacticity interruptions, together with the associated average isotactic length, on the induction time (t_i) as well as on the activation energy (E_act) of the thermo-oxidation are analysed. Both parameters have been found to change markedly at an average isotactic length (n₁) of 30 propylene units. While t_i reaches a minimum when n₁ is approximately 30 units, E_act increases quasi-exponentially as the number of units decreases from 30. This variation can be explained in terms of changes induced in the crystalline interphase, i.e. local molecular dynamics, which are closely linked to the initiation of the thermo-oxidation of isotactic PP-based polyolefins.

Use of p-Toluenesulfonic Acid for the Controlled Grafting of Alkoxysilanes onto Silanol Containing Surfaces: Preparation of Tunable Hydrophilic, Hydrophobic, and Super-Hydrophobic Silica

The modification of Aerosil 200 has been carried out using methoxysilanes in toluene reflux, with p-toluenesulfonic acid as the catalyst. Both trimethoxyalkyl silanes (methyl, ethyl, propyl, butyl, hexyl, octyl, and octadecyl) and trialkylmethoxy silanes (trimethyl and dimethyloctyl) have been used. The surface has been studied by 29Si NMR, 13C NMR, elemental analysis, thermogravimetry, water contact angle, and BET analysis. When incorporating trimethoxysilanes, a plateau of modification was achieved after 1 h of reflux, while when using trialkylmethoxy silanes, a longer time of about 7 h was required. The average number of molecules incorporated in both cases has been well above those reported by other authors in similar reactions and in much shorter times. Depending on the modification agent and on the experimental conditions, the resulting organosilicas are in seven cases superhydrophobic, in three cases hydrophobic, and in two cases hydrophilic. Two structural origins for superhydrophobicity have been identified in these samples: almost complete disappearance of water accessible surface silanols (smallest methoxysilanes) and shielding of would-be water accessible surface silanols by long aliphatic tails. These features can be very precisely controlled.

A potentiostatic study of oxygen transport through poly(2-ethoxyethyl methacrylate-co-2,3-dihydroxypropylmethacrylate) hydrogel membranes

The oxygen permeability and diffusion coefficients of hydrogel membranes prepared with copolymers of 2-ethoxyethyl methacrylate (EEMA)/2,3-dihydroxypropylmethacrylate (MAG) with mole fraction of the second monomer in the range between 0 and 0.75 are described. Values of the permeability and diffusion coefficients of oxygen are determined by using electrochemical procedures involving the measurement of the steady-state current in membranes prepared by radical polymerization of the monomers. The results obtained for the transport properties were analyzed taking into account the fractional free volumes, the cohesive energy densities and the glass transition temperatures of the hydrogels.