Fourier Transform IR Spectroscopy Measurements Research Articles

Titanium Carboxylate Molecular Layer Deposited Hybrid Films As Protective Coatings for Lithium-Ion Batteries

Thirty years after the release of the first commercial lithium-ion battery, capacity fading due to complex ageing mechanisms remains one of the major concerns in lithium-ion battery research. Lithium-ion battery cathodes age due to phenomena as transition metal dissolution, electrolyte oxidation and volume expansions.[1] To suppress these effects, a protective coating can be applied to the cathode’s surface to avoid direct contact with the liquid electrolyte. Many studies exist in literature, showing the protective effect of conformal and pinhole-free Atomical Layer Deposited (ALD) coatings. However, the inorganic coatings deposited by ALD are rigid and will crack upon volume expansion of the cathode.[2]Molecular Layer Deposition (MLD) offers the same benefits as ALD but can be used to deposit hybrid inorganic/organic flexible films that can accommodate potential volume expansions of the cathode. To our knowledge, apart from ‘metalcones’ i.e. MLD films grown using a metal containing precursor and an alcohol, MLD films remain to be explored as protective and flexible coatings for lithium-ion batteries.[3] In this work, hybrid MLD titanium carboxylate thin films are deposited using tetrakis(dimethylamido)titanium (TDMAT) and various dicarboxylic acid precursors: oxalic acid, malonic acid, succinic acid, glutaric acid and 3,6-dioxaoctanedioic acid. The latter containing two ethylene oxide units per molecule, potentially increasing the lithium-ion conductivity.[4]The growth of the titanium carboxylate MLD processes is studied using in situ ellipsometry at a substrate temperature of 100 °C and 160 °C. Only the TDMAT/oxalic acid process is found to display good saturation behavior, while a parasitic CVD component is present during the TDMAT pulse for the other processes. The structure of the as-deposited films is physically characterized using Fourier Transform IR spectroscopy (FTIR) and X-Ray Photoelectron Spectroscopy (XPS), confirming the successful deposition of titanium carboxylate films. The films are found to be stable in air up to 50 days as shown by FTIR. This is in contrast to many metalcone MLD films which are considered to be air sensitive as the organic backbone degrades upon air exposure. In addition, FTIR, X-Ray Reflectivity (XRR) and X-Ray Fluorescence (XRF) measurements show that the titanium carboxylate films remain intact upon immersion into a solution of 1 M LiClO4 in propylene carbonate, the liquid electrolyte used for electrochemical characterization.The electrochemical properties of a 5 nm TDMAT/oxalic acid, TDMAT/3,6-dioxaoctanedioic acid and TDMAT/glycerol film (conventional titanicone film [5]) are tested on top of three ideal electrode systems: anatase TiO2, TiN and LiMnO2 (LMO). The titanium carboxylate films are observed to have little to no effect on the lithium-ion kinetics of the TiO2 electrode system compared to the uncoated electrode. This is in contrast to the titanicone film displaying a detrimental effect on the kinetics. All films are observed to effectively suppress electrolyte oxidation when exposing the TiN electrode system to elevated potentials. On the LMO electrode an activation step is necessary for all films, after which a good lithium-ion mobility through the titanium carboxylate films is observed without the severe irreversible reactions detected in the potential profile for the titanicone films. Overall, the explorative tests on thin film electrodes in this work indicate that the electrochemical properties of the titanium carboxylate films seem promising candidates as protective and flexible coating of lithium-ion battery cathodes.[1] Vetter, J., Novák, P., Wagner, M. R., Veit, C., Möller, K. C., Besenhard, J. O., ... & Hammouche, A. (2005). Ageing mechanisms in lithium-ion batteries. Journal of power sources, 147(1-2), 269-281.[2] Ban, C., & George, S. M. (2016). Molecular layer deposition for surface modification of lithium‐ion battery electrodes. Advanced Materials Interfaces, 3(21), 1600762.[3] Zhao, Y., Zhang, L., Liu, J., Adair, K., Zhao, F., Sun, Y., ... & Sun, X. (2021). Atomic/molecular layer deposition for energy storage and conversion. Chemical Society Reviews, 50(6), 3889-3956.[4] Xue, Z., He, D., & Xie, X. (2015). Poly (ethylene oxide)-based electrolytes for lithium-ion batteries. Journal of Materials Chemistry A, 3(38), 19218-19253.[5] Van de Kerckhove, K., Mattelaer, F., Deduytsche, D., Vereecken, P. M., Dendooven, J., & Detavernier, C. (2016). Molecular layer deposition of “titanicone”, a titanium-based hybrid material, as an electrode for lithium-ion batteries. Dalton Transactions, 45(3), 1176-1184.

Effect of Nerolidol and/or Levulinic Acid on the Thermotropic Behavior of Lipid Lamellar Structures in the Stratum Corneum.

Permeation enhancers are required to deliver drugs through the skin efficiently and maintain effective blood concentrations. Studies of the barrier function of the stratum corneum using l-menthol, a monocyclic monoterpene widely used in medicines and foods, have revealed an interaction between characteristic intercellular lipid structures in the stratum corneum and permeation enhancers. The variety of permeation enhancers that can be used to contribute to transdermal delivery systems beyond l-menthol is increasing. In this study, we focused on nerolidol and levulinic acid and investigated their influence on stratum corneum lipid structures. Nerolidol, a sesquiterpene, has been reported to enhance the permeation of various drugs. Levulinic acid is reported to enhance the permeability of buprenorphine and is used as a component of the buprenorphine® patch. Synchrotron X-ray diffraction and attenuated total reflectance Fourier transform IR spectroscopy measurements revealed that nerolidol disturbs the rigidly arranged lipid structure and increases lipid fluidity. Levulinic acid had a smaller effect on stratum corneum lipid structures, but did increase lipid fluidity when co-administered with nerolidol or heat. We found that nerolidol has an effect on stratum corneum lipids similar to that of l-menthol, and levulinic acid had an effect similar to that of oleic acid.

Molecular orientation and mechanical property size effects in electrospun polyacrylonitrile nanofibers

Electrospinning of polymeric solutions entails high jet velocities which could orient the polymer molecules along the jet direction. Polarized Fourier Transform IR spectroscopy (FTIR), Wide angle X-ray diffraction (WAXD) and Microelectromechanical System (MEMS)-based single nanofiber mechanical property experiments were employed to investigate the molecular orientation and crystallinity in electrospun polyacrylonitrile (PAN) nanofibers produced under different electrospinning conditions with diameters mainly varying between 100 and 300nm. FTIR measurements with nanofibers fabricated at three different electrospinning distances, but under the same electric field intensity, revealed an enhanced molecular orientation only for the longest electrospinning distance. At long electrospinning distances the fiber solvent content is substantially reduced resulting in high viscosity, and, therefore, sustained shear stresses, which, in turn, allows for permanent molecular orientation. The orientation factors from polarized FTIR were in good agreement with the mechanical property trends obtained from individual nanofibers, where high elastic moduli and yield strengths were recorded from nanofibers with diameters smaller than 300nm, which were fabricated at the longest electrospinning distance. WAXD studies on bundles of aligned PAN nanofibers showed small crystallinity which did not follow the trends in the mechanical properties and varied rather non-monotonically from 7%, for fibers spun at the shortest distance, to 17% for fibers spun at the longest distance used in this study.

Mechanistic Study of Lean NO2 Reduction by Propane Over HZSM-5 in the Presence of Water

This study focuses on the mechanism of lean NO2 redn. by propane in the presence of water, over an acidic zeolite (HZSM-5). Fourier Transform IR spectroscopy measurements with NO2 and propane in excess oxygen show formation of surface bound NO+, isocyanate, unsatd. hydrocarbons and traces of amine species. Upon addn. of water the isocyanate species disappear and amine species are formed. Hence, it seems likely that the isocyanate species are hydrolyzed to amine species, which are possible reaction intermediates in the HC-SCR reaction over HZSM-5.

Formation of hydroxyapatite/biopolymer biomaterials. I. Microporous composites from solidified emulsions

Microporous materials of controlled pore size were prepared by means of a three-step process involving in situ hydrochemical preparation of a hydroxyapatite-sodium caseinate (HAp-Cas) composite material into a Cas-stabilized oil-in-water emulsion, subsequent concentration and drying of the composite-emulsion, and removal of the oil by means of supercritical carbon dioxide extraction. The resulting composite materials were found to contain micron-sized pores in the space previously occupied by the oil droplets. In order to elucidate the structure of the resulting porous product, its Cas-HAp composition was studied in the corresponding nonporous composite material. In nonporous samples, a protein assay by means of visible spectroscopy suggested equilibrium between the Cas that was trapped in the composite structure and the Cas that remained in solution after precipitation. This observation was confirmed by separate thermogravimetric analysis and Fourier transform IR spectroscopy measurements.

Ligand binding to synthetic mutant myoglobin (His-E7----Gly): role of the distal histidine.

Low-temperature flash photolysis with IR and visible spectroscopy was used to probe the influence of the distal histidine His-64(E7) of sperm-whale myoglobin (Mb) on the orientation of bound carbon monoxide (CO) and on the kinetics of CO rebinding. The synthesis and high-level expression of a sperm-whale myoglobin gene in Escherichia coli permits the efficient substitution of the distal histidine through site-directed mutagenesis. Substitution of His-E7 with glycine [GlyE7]Mb bound with CO (CO[GlyE7]Mb) results in one broad bound-CO IR stretch band, v(C-O), centered at 1973 cm-1 at 10 K, in contrast to three distinct bands for native and synthetic wild-type MbCO at 1966, 1945, and 1929 cm-1. After flash photolysis at 10 K, the unbound state of CO[GlyE7]Mb exhibits two CO stretch bands, whereas MbCO has three. Fourier transform IR spectroscopy measurements of the linear dichroism after photoselective flash photolysis of CO bound to [GlyE7]Mb at 10 K reveals the bound CO to be oriented at an angle of alpha = 20 degrees +/- 2 degrees with respect to the heme normal. Flash photolysis data from 10 to 300 K provide evidence for a larger distal pocket and a smaller enthalpy barrier (by approximately 4 kJ/mol) for [GlyE7]MbCO as compared with wild-type MbCO. These results reinforce the notion that the dominant control of the binding step at the heme iron comes from the proximal side through the protein structure.

Characterization of deformation phenomena in polymers by rapid-scanning fourier transform IR (FTIR) spectroscopy and mechanical measurements

The uniaxial deformation and recovery of primarily amorphous poly(butylene terephthalate) (PBT) has been investigated by simultaneous FTIR spectroscopy and stress-strain measurements. Contrary to annealed, crystalline samples the stress-induced transformation of the polymer chains to a conformation deviating slightly from the planar all-trans crystalline β-form has been found almost irreversible.