| 1. |
- Pihl, Maria, 1978, et al.
(författare)
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Silica-based diffusion probes for use in FRAP and NMR-diffusometry
- 2019
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Ingår i: Journal of Dispersion Science and Technology. - : Informa UK Limited. - 0193-2691 .- 1532-2351. ; 40:4, s. 555-562
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Tidskriftsartikel (refereegranskat)abstract
- Development of multi-purpose probes for mass transport measurements is of importance to gain knowledge in diffusional behaviour in heterogeneous structures such as food, hygiene or pharamceuticals. By combining different techniques, such as Fluorescence Recovery After Photobleaching (FRAP) and Nuclear Magnetic Resonance Diffusometry (NMR-d), information of both local and global diffusion can be collected and used to gain insights on for example material heterogeneities and probe-material interactions. To obtain a FRAP-responsive probe, fluorescent silica particles were produced using fluorescent preconjugates added in a modified Stöber process. A NMR-d responsive moiety was introduced by derivatizing the fluorescent silica particles with polyethylene glycol. The particle size distributions were determined by dynamic light scattering and transmission electron microscopy and these measurements were compared to value extrapolated from diffusion measurements using FRAP and NMR-d. The good agreement between the FRAP and NMR-d measurements demonstrates the potential of multi-purpose probes for future applications concerning mass transport at local and global scale simultaneously. © 2018, © 2018 The Author(s).
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| 2. |
- Ben Hassine, Mohamed, 1985, et al.
(författare)
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Growth model for high-Al containing CVD TiAlN coatings on cemented carbides using intermediate layers of TiN
- 2021
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972. ; 421
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Tidskriftsartikel (refereegranskat)abstract
- This work concerns high Al-containing TixAl1-xN coatings prepared using low pressure-chemical vapour deposition (LP-CVD). The coatings were examined using electron microscopy techniques, such as scanning transmission electron microscopy (STEM), energy dispersive X-ray analysis (EDX) and transmission Kikuchi diffraction (TKD). An intermediate TiN-layer with a 〈211〉 texture consisting of twinned, needle-shaped grains influences the subsequent growth of the TiAlN layer. The TiAlN grains were columnar with a texture of 〈211〉. As the grains grow along 〈111〉, with {001} facets, this led to a tilted pyramid surface morphology. The grains developed an internal periodic epitaxial nanolamella structure. The thicknesses were 2 nm for the low (x = 0.6) and 6 nm for the high (x = 0.9) Al-containing lamellae. The TiAlN layer growth could be described by a “two-wing” model, where two TiAlN grains with a twin-related orientation grow on a twinned TiN grain, where the two TiAlN grains gradually switch sides, making the appearance of two wings of columnar grains. In general, this work shows that it should be possible to control the growth of TiAlN layers by controlling the texture and morphology of an intermediate layer, such as TiN.
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| 3. |
- Calcagno, Giulio, 1990, et al.
(författare)
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Fast charging negative electrodes based on anatase titanium dioxide beads for highly stable Li-ion capacitors
- 2020
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Ingår i: Materials Today Energy. - : Elsevier BV. - 2468-6069. ; 16
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid energy storage systems aim to achieve both high power and energy densities by combining supercapacitor-type and battery-type electrodes in tandem. The challenge is to find sustainable materials as fast charging negative electrodes, which are characterized by high capacity retention. In this study, mesoporous anatase beads are synthetized with tailored morphology to exploit fast surface redox reactions. The TiO2-based electrodes are properly paired with a commercial activated carbon cathode to form a Li-ion capacitor. The titania electrode exhibits high capacity and rate performance. The device shows extremely stable performance with an energy density of 27 mWh g-1 at a specific current of 2.5 A g−1 for 10,000 cycles. The remarkable stability is associated with a gradual shift of the potential during cycling as result of the formation of cubic LiTiO2 on the surface of the beads. This phenomenon renews the interest in using TiO2 as negative electrode for Li-ion capacitors.
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| 4. |
- Hashemi, Seyed Ehsan, 1986, et al.
(författare)
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Effect of compositional interlayers on the vertical electrical conductivity of Si-doped AlN/GaN distributed Bragg reflectors grown on SiC''
- 2017
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Ingår i: Applied Physics Express. - 1882-0786 .- 1882-0778. ; 10:5, s. 055501-
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the effect of strain-compensating interlayers on the vertical electrical conductivity of Si-doped AlN/GaN distributed Bragg reflectors (DBRs). Samples with 10.5 mirror pairs were grown through plasma-assisted molecular beam epitaxy on SiC. Room-temperature current–voltage characteristics were measured vertically in mesas through 8 of the 10.5 pairs. The sample with no interlayers yields a mean specific series resistance of 0.044 Ω cm2 at low current densities, while three samples with 5/5-Å-thick, 2/2-nm-thick, and graded interlayers have resistivities between 0.16 and 0.34 Ω cm2. Thus, interlayers impair vertical current transport, and they must be designed carefully when developing conductive DBRs.
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| 5. |
- Kumar Rajasekharan, Anand, 1990, et al.
(författare)
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Bioinspired Structural Hierarchy within Macroscopic Volumes of Synthetic Composites
- 2018
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Ingår i: Advanced healthcare materials. - : Wiley. - 2192-2640 .- 2192-2659. ; 7:18
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Tidskriftsartikel (refereegranskat)abstract
- A key challenge in developing bioinspired composites is the fabrication of well-defined 3D hierarchical structures ranging from nano to the macroscale. Herein, the development of a synthetic polymer–apatite composite realized by integrating bottom-up self-assembly and additive manufacturing (AM) is described. The resulting composite exhibits a bioinspired hierarchical structure over its 3D macroscopic volume. The composite is assembled in a bottom-up manner, where periodic nanoscale assemblies of organic micellar fibrils and inorganic apatite nanocrystals are organized as bundles of mineralized microstructures. These microstructural bundles are preferentially oriented throughout the macroscopic volume of the material via extrusion based AM. The obtained structural hierarchy is investigated in 3D using electron microscopy and small angle X-ray scattering tensor tomography and correlated to the structural hierarchy and anisotropy observed in biological tissues such as bone and the bone–cartilage interface. This work demonstrates the possibility to form polymer–apatite composites with a well-defined hierarchical structure throughout its macroscopic volume, which is crucial for the development of mechanically optimized materials for applications such as bone and osteochondral implants.
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| 6. |
- Lotsari, Antiope, 1981, et al.
(författare)
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Transformation of amorphous calcium phosphate to bone-like apatite
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 9:1
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Tidskriftsartikel (refereegranskat)abstract
- Mineralisation of calcium phosphates in bone has been proposed to proceed via an initial amorphous precursor phase which transforms into nanocrystalline, carbonated hydroxyapatite. While calcium phosphates have been under intense investigation, the exact steps during the crystallisation of spherical amorphous particles to platelet-like bone apatite are unclear. Herein, we demonstrate a detailed transformation mechanism of amorphous calcium phosphate spherical particles to apatite platelet-like crystals, within the confined nanodomains of a bone-inspired nanocomposite. The transformation is initiated under the presence of humidity, where nanocrystalline areas are formed and crystallisation advances via migration of nanometre sized clusters by forming steps at the growth front. We propose that such transformation is a possible crystallisation mechanism and is characteristic of calcium phosphates from a thermodynamic perspective and might be unrelated to the environment. Our observations provide insight into a crucial but unclear stage in bone mineralisation, the origins of the nanostructured, platelet-like bone apatite crystals.
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| 7. |
- Peterson, Anna, 1988, et al.
(författare)
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Dynamic Nanocellulose Networks for Thermoset-like yet Recyclable Plastics with a High Melt Stiffness and Creep Resistance
- 2019
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 20:10, s. 3924-3932
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Tidskriftsartikel (refereegranskat)abstract
- Many polymers, including polyethylene, feature a relatively low melting point and hence must be cross-linked to make them viable for applications that demand a high stiffness and creep resistance at elevated temperatures. The resulting thermoset plastics cannot be recycled, and therefore alternative materials with a reconfigurable internal network structure are in high demand. Here, we establish that such a thermoset-like yet recyclable material can be realized through the addition of a nanocellulose reinforcing agent. A network consisting of cellulose nanocrystals, nano- or microfibrils imparts many of the characteristics that are usually achieved through chemical cross-linking. For instance, the addition of only 7.5 wt % of either nanocellulose material significantly enhances the melt stiffness of an otherwise molten ethylene-acrylate copolymer by at least 1 order of magnitude. At the same time, the nanocellulose network reduces the meltcreep elongation to less than 10%, whereas the neat molten matrix would rupture. At high shear rates, however, the molten composites do not display a significantly higher viscosity than the copolymer matrix, and therefore retain the processability of a thermoplastic material. Repeated re-extrusion at 140 °C does not compromise the thermomechanical properties, which indicates a high degree of recyclability. The versatility of dynamic nanocellulose networks is illustrated by 3D printing of a cellulose composite, where the high melt stiffness improves the printability of the resin.
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| 8. |
- Vavra, Szilvia, 1990, et al.
(författare)
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An imidazolium ionic liquid as effective structure-directing agent for the fabrication of silica thin films with vertically aligned nanochannels
- 2020
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- In parallel to the increasing variety of ionic liquids that show different kinds of nanometer-scale structuration in their pure and solved forms, there is a raising interest in exploring the possibility of using ionic liquids as soft-templates for the synthesis of mesoporous materials. We report the case of 1-hexadecyl-3-methylimidazolium chloride (C16MIMCl), a surface active ionic liquid (SAIL), here used as an excellent soft-template for the formation of vertically aligned, uniform mesochannels, with a well defined pore width of 2.5 nm in silica thin films deposited with the electrochemically assisted self-assembly (EASA) method. The obtained mesochannels run through the entire thickness of the films and after removal of the ionic liquid the emptied mesochannels ensure a thorough mass transport to the substrate, here monitored by the redox-active electrochemical probe Ru(II)/Ru(III) during cyclic voltammetry (CV). Moreover, the mechanism of pore formation is explained; unlike the mechanisms reported for short chain imidazolium ionic liquid silica templates, in the case of C16MIMCl the dominating so-called cooperative interaction is the electrostatic attraction between the C16MIM+ and the network-forming negatively charged silicate oligomers. Therefore, this study provides a better understanding of the templating behavior of long chain imidazolium ionic liquids and motivates further research on the synthesis of ionic liquid-based functional hybrid materials.
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| 9. |
- Örn Simonarson, Gunnar, 1986, et al.
(författare)
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Electrochemical and structural characterization of lithiation in spray deposited ordered mesoporous titania as an anode for Li ion batteries
- 2020
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 10:34, s. 20279-20287
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Tidskriftsartikel (refereegranskat)abstract
- Ordered mesoporous titania, preparedvialow-temperature spray deposition, was examined as an anode material for lithium ion batteries. The material exhibits an exceptionally high electrochemical capacity of 680 mA h g-1during the first discharge, which rapidly decreases over the following cycles. The capacity stabilizes at around 170 mA h g-1after 50 cycles and the material delivers 83 mA h g-1at high charge/discharge rates (10C). A combination of electrochemical and structural characterization techniques were used to study the charge/discharge behavior of the material and the origin of the irreversible capacity. To determine the effect of cycling on the structure of the material, X-ray absorption spectroscopy (XAS) and energy filtered TEM were carried out on pristine and cycled samples in intercalated and deintercalated states. Titanium K-edge XAS measurements showed that intercalated lithium affects the NEXAFS region. By comparing peak intensity ratios, we propose a method to quantify the amount of lithium inserted into the titania structure and to differentiate between lithium bound in close proximity to titanium, and lithium bound further away from titanium. Additionally, we suggest that the irreversible loss in capacity is due to the formation of phases that are stable, and thereby electrochemically inactive, over the electrochemical cycling conditions applied.
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| 10. |
- Örn Simonarson, Gunnar, 1986, et al.
(författare)
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Evolution of the Polymorph Selectivity of Titania Formation under Acidic and Low-Temperature Conditions
- 2019
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 4:3, s. 5750-5757
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Tidskriftsartikel (refereegranskat)abstract
- Evolution of the polymorph selectivity of titanium dioxide was studied under acidic and low-temperature synthesis conditions. Short synthesis times resulted in high relative amounts of the rutile phase, and long synthesis times resulted in high relative amounts of the brookite and anatase phases. The effect of titania precursor concentration was investigated and found to have a large impact on the polymorph selectivity. As the reaction proceeds with time, changes in the chemical environment, caused in particular by the gradually decreasing titania precursor concentration, are therefore likely the cause of the change in polymorph selectivity observed.
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