| 31. |
- Dussauze, M., et al.
(författare)
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Lithium Ion Conducting Boron-Oxynitride Amorphous Thin Films: Synthesis and Molecular Structure by Infrared Spectroscopy and Density Functional Theory Modeling
- 2013
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:14, s. 7202-7213
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Tidskriftsartikel (refereegranskat)abstract
- Li ion containing oxynitride amorphous thin films are promising materials for electrochemical applications due to their high ionic conductivity, mechanical stability and chemical durability. Here we report on the preparation of Li boron-oxynitride (LiBON) amorphous thin films by rf sputtering of Li-diborate and Li-pyroborate targets in nitrogen atmosphere. The materials produced were subsequently studied by infrared transmittance spectroscopy assisted by density functional theory calculations using representative Li boron-oxide and boron-oxynitride clusters. The combination of experiments and calculations allows us to propose accurate vibrational assignments and to clarify the complex infrared activity of the LiBON films. Both experimental and calculated spectra show that nitrogen incorporation induces significant structural rearrangements, manifested mainly by a change in boron coordination number from four to three, and by the formation of boron-nitrogen-boron bridges. The nature of boron-nitrogen bonding depends on the composition of the sputtering target, with an exponential relationship adequately describing the dependence of B-N stretching frequency on bond length. Besides bonding to two boron atoms by covalent bonds, the nitrogen atoms interact also with Li ions by participating in their coordination sphere together with oxygen atoms. Likely, boron-nitrogen bonding in LiBON films facilitates Li ion transport due to induced charge delocalization within the boron-nitrogen-boron bridges and reduced electrostatic interaction with the Li ions.
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| 32. |
- Eliasen, K. L., et al.
(författare)
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High-frequency dynamics and test of the shoving model for the glass-forming ionic liquid Pyr14-TFSI
- 2021
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Ingår i: Physical Review Materials. - 2475-9953. ; 5:6
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Tidskriftsartikel (refereegranskat)abstract
- In studies of glass-forming liquids, one of the important questions is to understand to which degree chemically different classes of liquids have the same type of dynamics. In this context, room-temperature ionic liquids are interesting because they exhibit both van der Waals and Coulomb interactions. In this work we study the α relaxation and faster relaxation dynamics in the room-temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14-TFSI). The paper presents quasielastic neutron and shear mechanical spectroscopy data measured over seven decades in frequency (10-3-104 Hz). The use of these two methods in combination reveal the α relaxation and four separate, faster modes. Two of these faster modes, based on the partial deuterations, can be assigned to the methyl group and the methyl end of the butyl chain of the cation. The neutron data are also used to determine the mean-square displacement (MSD) on the nanosecond timescale. It is shown that the temperature dependence of the MSD can account for the super-Arrhenius behavior of the α relaxation as predicted by the shoving model [Dyre, Rev. Mod. Phys. 78, 953 (2006)RMPHAT0034-686110.1103/RevModPhys.78.953], similarly to what is seen in simpler glass-forming liquids.
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| 33. |
- Flores, Eibar, 1990, et al.
(författare)
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PRISMA: A Robust and Intuitive Tool for High-Throughput Processing of Chemical Spectra
- 2022
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Ingår i: Chemistry-Methods. - : Wiley. - 2628-9725. ; 2:10
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Tidskriftsartikel (refereegranskat)abstract
- Here we introduce PRISMA, an open-source tool to rapidly analyse large numbers of spectra into meaningful spectroscopic trends. PRISMA follows a human-in-the-loop workflow, where the user interacts with an intuitive graphical user interface to control multiple steps in the spectrum analysis process: trimming, baseline correction, and peak fitting. The tool outputs the results in an easy-to-read csv format within seconds. We describe the functionalities implemented in PRISMA and test its capabilities with three experimental cases relevant to the study of Electrochemical energy storage and conversion devices: a temperature-dependent Raman measurement of phase transitions, a linear Raman mapping of a graphite composite electrode, and an operando X-ray diffraction experiment of lithium nickel oxide composite battery electrode. The case studies demonstrate the robustness of the app and its ability to unearth insightful trends in peak parameters, which are easier to represent, interpret and further analyse with more advanced techniques.
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| 34. |
- Fretz, Samuel Joseph, 1987, et al.
(författare)
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Amine- and Amide-Functionalized Mesoporous Carbons: A Strategy for Improving Sulfur/Host Interactions in Li-S Batteries
- 2020
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Ingår i: Batteries and Supercaps. - : Wiley. - 2566-6223. ; 3:8, s. 757-765
-
Tidskriftsartikel (refereegranskat)abstract
- Lithium-sulfur (Li-S) batteries are of great interest due to their potentially high energy density, but the low electronic conductivity of both the sulfur (S-8) cathode active material and the final discharge product lithium sulfide (Li2S) require the use of a conductive host. Usually made of relatively hydrophobic carbon, such hosts are typically ill-suited to retain polar discharge products such as the intermediate lithium polysulfides (LiPs) and the final Li2S. Herein, we propose a route to increase the sulfur utilization by functionalizing the surface of ordered mesoporous carbon CMK3 with polar groups. These derivatized CMK3 materials are made using a simple two-step procedure of bromomethylation and subsequent nucleophilic substitution with amine or amide nucleophiles. We demonstrate that, compared to the unfunctionalized control, these modified CMK3 surfaces have considerably larger binding energies with LiPs and Li2S, which are proposed to aid the electrochemical conversion between S-8 and Li2S by keeping the LiPs species in close proximity to the carbon surface during Li-S battery cycling. As a result, the functionalized cathodes exhibit significantly improved specific capacities relative to their unmodified precursor.
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| 35. |
- Fu, Yifeng, 1984, et al.
(författare)
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Selective growth of double-walled carbon nanotubes on gold films
- 2012
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Ingår i: Materials Letters. - : Elsevier BV. - 1873-4979 .- 0167-577X. ; 72, s. 78-80
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Tidskriftsartikel (refereegranskat)abstract
- Growth of high-quality vertical aligned carbon nanotube (CNT) structures on silicon supported gold (Au) films by thermal chemical vapor deposition (TCVD) is presented. Transmission electron microscopy (TEM) images show that the growth is highly selective. Statistical study reveals that 79.4% of the as-grown CNTs are double-walled. The CNTs synthesized on Au films are more porous than that synthesized on silicon substrates under the same conditions. Raman spectroscopy and electrical characterization performed on the as-grown double-walled CNTs (DWNTs) indicate that they are competitive with those CNTs grown on silicon substrates. Field emission tests show that closed-ended DWNTs have lower threshold field than those open-ended.
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| 36. |
- Fu, Yifeng, 1984, et al.
(författare)
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Templated Growth of Covalently Bonded Three-Dimensional Carbon Nanotube Networks Originated from Graphene
- 2012
-
Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 24:12, s. 1576-1581
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Tidskriftsartikel (refereegranskat)abstract
- A template-assisted method that enables the growth of covalently bonded three-dimensional carbon nanotubes (CNTs) originating from graphene at a large scale is demonstrated. Atomic force microscopy-based mechanical tests show that the covalently bonded CNT structure can effectively distribute external loading throughout the network to improve the mechanical strength of the material.
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| 37. |
- Ghai, Viney, 1989, et al.
(författare)
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Achieving Long-Range Arbitrary Uniform Alignment of Nanostructures in Magnetic Fields
- 2024
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Ingår i: Advanced Functional Materials. - 1616-3028 .- 1616-301X. ; In Press
-
Tidskriftsartikel (refereegranskat)abstract
- For magnetic field orientation of nonstructures to become a viable method to create high performance multifunctional nanocomposites, it is of paramount importance to develop a method that is easy to implement and that can induce long-range uniform nanostructural alignment. To overcome this challenge, inspired by low field nuclear magnetic resonance (NMR) technology, a highly uniform, high field strength, and compact magnetic-field nanostructure orientation methodology is presented for polymeric nanocomposites using a Halbach array, for the first time. Potential new advances are showcased for applications of graphene polymer composites by considering their electro-thermal and antibacterial properties in highly oriented orthogonal morphologies. The high level of anisotropy induced in the graphene nanocomposites studied stands out through: 1) up to four decades higher electrical conductivities recorded in comparison to their randomly oriented counterparts, at concentrations where the latter show minimal improvements compared to the unfilled polymer; 2) over 1200% improvement in thermal conductivity, 3) antibacterial surfaces at field benchmark levels with lower filler content and with the added versatility of arbitrary orientation of the nanofillers. Overall, the new method and variations thereof can open up new horizons for tailoring nanostructure and performance for virtually all major nanocomposite applications based on graphene and other types of fillers.
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| 38. |
- Ghanbari, Reza, 1984, et al.
(författare)
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Painting Taylor vortices with cellulose nanocrystals: supercritical spectral dynamics
- 2023
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We study the flow stability and spatio-temporal spectral dynamics of cellulose nanocrystal (CNC) suspensions in a custom Taylor-Couette flow cell using the intrinsic shear induced birefringence and liquid crystalline properties of CNC suspensions for flow visualizations for the first time. The analysis is performed at constant ramped speed inputs of the independently rotating cylinders for several cases ranging from only inner or outer rotating cylinders to three counter-rotation cases. All CNC suspensions have measurable elastic and shear thinning, both increasing with CNC concentration. We show that the flow patterns recorded are essentially Newtonian-like, with non-Newtonian effects ranging from a decrease in wavenumbers to altering the critical parameters for the onset of instability modes. Outer cylinder rotation flow cases are stable for all concentrations whereas inner cylinder rotation flow cases transition to axisymmetric and azimuthally periodic secondary flows. However, unstable counter-rotation cases become unstable to asymmetric spiral modes. With increasing CNC concentration a counter-rotation case was found where azimuthally periodic wavy patterns transition to asymmetric spiral modes. In contrast to polymeric solutions of similar low to moderate elasticity and shear thinning, the shear-thinning region of CNC suspensions is expected to lead to the breakdown of the chiral nematic phase, whose elastic constants constitute the dominant structural elasticity mechanism. Thus, we interpret the Taylor-Couette stability of the CNC suspensions as dominated by their shear-thinning character due to the expected loss of elasticity in nonlinear flow conditions.
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| 39. |
- Ghanbari, Reza, 1984, et al.
(författare)
-
Painting Taylor vortices with cellulose nanocrystals: Suspension flow supercritical spectral dynamics
- 2024
-
Ingår i: Physics of Fluids. - 1089-7666 .- 1070-6631. ; 36:4
-
Tidskriftsartikel (refereegranskat)abstract
- We study the flow stability and spatiotemporal spectral dynamics of cellulose nanocrystal (CNC) suspensions in a custom Taylor-Couette flow cell using the intrinsic shear induced birefringence and liquid crystalline properties of CNC suspensions for flow visualizations, for the first time. The analysis is performed at constant ramped speed inputs of the independently rotating cylinders for several cases ranging from only inner or outer rotating cylinders to three counter-rotation cases. All CNC suspensions have measurable elasticity and shear thinning, both increasing with CNC concentration. We show that the flow patterns recorded are essentially Newtonian-like, with non-Newtonian effects ranging from a decrease in wavenumbers to altering the critical parameters for the onset of instability modes. Outer cylinder rotation flow cases are stable for all concentrations whereas inner cylinder rotation flow cases transition to axisymmetric and azimuthally periodic secondary flows. However, counter-rotation cases become unstable to asymmetric spiral modes. With increasing CNC concentration, a counter-rotation case was found where azimuthally periodic wavy patterns transition to asymmetric spiral modes. Based on rheo-SAXS measurements, the shear-thinning region of CNC suspensions is expected to lead to the breakdown of the chiral nematic phase, whose elastic constants constitute the dominant structural elasticity mechanism. Thus, we interpret the Taylor-Couette stability of the CNC suspensions as dominated by their shear-thinning character due to the expected loss of elasticity in nonlinear flow conditions.
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| 40. |
- Gkourmpis, Thomas, et al.
(författare)
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Melt-Mixed 3D Hierarchical Graphene/Polypropylene Nanocomposites with Low Electrical Percolation Threshold
- 2019
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 9:12
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Tidskriftsartikel (refereegranskat)abstract
- Graphene-based materials are a family of carbonaceous structures that can be produced using a variety of processes either from graphite or other precursors. These materials are typically a few layered sheets of graphene in the form of platelets and maintain some of the properties of pristine graphene (such as two-dimensional platelet shape, aspect ratio, and graphitic bonding). In this work we present melt mixed graphene-based polypropylene systems with significantly reduced percolation threshold. Traditionally melt-mixed systems suffer from poor dispersion that leads to high electrical percolation values. In contrast in our work, graphene was added into an isotactic polypropylene matrix, achieving an electrical percolation threshold of similar to 1 wt.%. This indicates that the filler dispersion process has been highly efficient, something that leads to the suppression of the beta phase that have a strong influence on the crystallization behavior and subsequent thermal and mechanical performance. The electrical percolation values obtained are comparable with reported solution mixed systems, despite the use of simple melt mixing protocols and the lack of any pre or post-treatment of the final compositions. The latter is of particular importance as the preparation method used in this work is industrially relevant and is readily scalable.
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