| 1. |
- Sillrén, Per, 1982, et al.
(author)
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A statistical model of hydrogen bond networks in liquid alcohols
- 2012
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In: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 136:9, s. 094514-094521
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Journal article (peer-reviewed)abstract
- We here present a statistical model of hydrogen bond induced network structures in liquid alcohols. The model generalises the Andersson-Schulz-Flory chain model to allow also for branched structures. Two bonding probabilities are assigned to each hydroxyl group oxygen, where the first is the probability of a lone pair accepting an H-bond and the second is the probability that given this bond also the second lone pair is bonded. The average hydroxyl group cluster size, cluster size distribution, and the number of branches and leaves in the tree-like network clusters are directly determined from these probabilities. The applicability of the model is tested by comparison to cluster size distributions and bonding probabilities obtained from Monte Carlo simulations of the monoalcohols methanol, propanol, butanol, and propylene glycol monomethyl ether, the di-alcohol propylene glycol, and the tri-alcohol glycerol. We find that the tree model can reproduce the cluster size distributions and the bonding probabilities for both mono- and poly-alcohols, showing the branched nature of the OH-clusters in these liquids. Thus, this statistical model is a useful tool to better understand the structure of network forming hydrogen bonded liquids. The model can be applied to experimental data, allowing the topology of the clusters to be determined from such studies.
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| 2. |
- Fu, Yifeng, 1984, et al.
(author)
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Selective growth of double-walled carbon nanotubes on gold films
- 2012
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In: Materials Letters. - : Elsevier BV. - 1873-4979 .- 0167-577X. ; 72, s. 78-80
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Journal article (peer-reviewed)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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| 3. |
- Fu, Yifeng, 1984, et al.
(author)
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Templated Growth of Covalently Bonded Three-Dimensional Carbon Nanotube Networks Originated from Graphene
- 2012
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In: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 24:12, s. 1576-1581
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Journal article (peer-reviewed)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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| 4. |
- Zhang, Zhfei, et al.
(author)
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Characterization of CNT Enhanced Conductive Adhesives in Terms of Thermal Conductivity
- 2012
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In: ECS Transactions. - : The Electrochemical Society. - 1938-5862 .- 1938-6737. - 9781607683186 ; 44:1, s. 1011-1017
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Conference paper (peer-reviewed)abstract
- CNTs have excellent thermal, electrical and mechanical properties. They can be used in various ways. One researched field of application is CNT-polymer composites which combine common technologies with advanced materials. This paper will focus on the thermal property of CNT-Ag-filled adhesives and compares the new materials with conventional, electrical Ag-filled conductive adhesives. Several analytical methods, FTIR, Raman analysis, SEM and TEM have been carried out to examine the different surface conditions after physicval and chemical modification of CNTs. The thermal conductivities of composites containing different types of CNTs were investigated. The incorporation of CNTs into polymers resulted in enhancement of the thermal conductivity compared to Ag-filler. The increase of thermal conductivity with addition of CNT filler is obvious, especially for the purified CNT. The value of thermal conductivity is about two times higher than the Ag-filled conductive adhesive. However, improvement on thermal conductivity of the surface modified CNT-filled conductive adhesives is not so obvious. Since the thermal conduction in CNT is by phonon transfer, the nanometric size and the huge interface lead to strong phonon-scattering at the interface. Thus, a relatively low interfacial area, weak interfacial adhesion promotes the conduction of phonons and minimizes coupling losses. According to this, the non-treated MWCNTs seem to have the highest potential to improve the thermal conductivity of epoxies.
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| 5. |
- Bielecki, Johan, 1982, et al.
(author)
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Femtosecond optical reflectivity measurements of lattice-mediated spin repulsions in photoexcited LaCoO3 thin films
- 2014
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In: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969 .- 1098-0121 .- 1550-235X. ; 89:3, s. art. no. 035129-
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Journal article (peer-reviewed)abstract
- We present results on the temperature dependence of ultrafast electron and lattice dynamics, measured with pump-probe transient reflectivity experiments, of an epitaxially grown LaCoO3 thin film under tensile strain. Probing spin-polarized transitions into the antibonding e(g) band provides a measure of the low-spin fraction, both as a function of temperature and time after photoexcitation. It is observed that femtosecond laser pulses destabilize the constant low-spin fraction (similar to 63%-64%) in equilibrium into a thermally activated state, driven by a subpicosecond change in spin gap Delta. From the time evolution of the low-spin fraction, it is possible to disentangle the thermal and lattice contributions to the spin state. A lattice mediated spin repulsion, identified as the governing factor determining the equilibrium spin state in thin-film LaCoO3, is observed. These results suggests that time-resolved spectroscopy is a sensitive probe of the spin state in LaCoO3 thin films, with the potential to bring forward quantitative insight into the complicated interplay between structure and spin state in LaCoO3.
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| 6. |
- Bielecki, Johan, 1982, et al.
(author)
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Short-range structure of the brownmillerite-type oxide Ba2In2O5 and its hydrated proton-conducting form BaInO3H
- 2014
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In: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 2:40, s. 16915-16924
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Journal article (peer-reviewed)abstract
- The vibrational spectra and short-range structure of the brownmillerite-type oxide Ba2In2O6 and its hydrated form BaInO3H, are investigated by means of Raman, infrared, and inelastic neutron scattering spectroscopies together with density functional theory calculations. For Ba2In2O6, which may be described as an oxygen deficient perovskite structure with alternating layers of InO6 octahedra and InO4 tetrahedra, the results affirm a short-range structure of Icmm symmetry, which is characterized by random orientation of successive layers of InO4 tetrahedra. For the hydrated, proton conducting, form, BaInO3H, the results suggest that the short-range structure is more complicated than the P4/mbm symmetry that has been proposed previously on the basis of neutron diffraction, but rather suggest a proton configuration close to the lowest energy structure predicted by Martinez et al. [J.-R. Martinez, C. E. Moen, S. Stoelen, N. L. Allan, J. Solid State Chem., 180, 3388, (2007)]. An intense Raman active vibration at 150 cm(-1) is identified as a unique fingerprint of this proton configuration.
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| 7. |
- Bielecki, Johan, 1982, et al.
(author)
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Structural and magnetic properties of isovalently substituted multiferroic BiFeO3 : Insights from Raman spectroscopy
- 2012
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In: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 86:184422
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Journal article (peer-reviewed)abstract
- Raman spectra, supplemented by powder x-ray diffraction and magnetization data of isovalently A- and B-site substituted BiFeO3 in the Bi1−xLaxFeO3 (0≤x≤1), Bi1−xTbxFeO3 (0≤x≤0.2), and Bi0.9Sm0.1Fe1−xMnxO3 (0≤x≤0.3) series, are presented. A good agreement between the structural transitions observed by x-ray diffraction and the vibrational modes observed in the Raman spectra is found over the whole substitutional ranges, and in particular we find spectroscopic signatures of a PbZrO3-type structure for Bi0.8La0.2FeO3. Mode assignments in the substituted materials are made based on Raman spectra of the end-members BiFeO3 and LaFeO3. Moreover, by comparing spectra from all samples with R3c structure, the phonon assignment in BiFeO3 is revisited. A close connection between the degree of octahedral tilt and the Raman shift of the A1 oxygen a−a−a− tilt mode is established. An explanation for the strong second-order scattering observed in Bi1−xLaxFeO3 and Bi1−xTbxFeO3 is suggested, including the assignment of the previously mysterious BiFeO3 mode at 620 cm−1. Finally, the magnetization data indicates a transition from a cycloidal modulated state towards a canted antiferromagnet with increasing A-site substitution, while Bi0.9Sm0.1Fe1−xMnxO3 with x=0 and 0.15 exhibit an anomalous closing of the hysteresis loop at low temperatures. For low A-site substitution levels (x≤0.1) the decreasing Raman intensity of the Fe derived modes correlates with the partial destruction of the spin cycloid as the substitution level increases.
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| 8. |
- He, Wenxiao, 1985, et al.
(author)
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Biomimetic nanocrystalline apatite resembling bone
- 2010
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In: European Cells and Materials: 3rd International NanoBio Conference 2010, ETH Zurich, Switzerland August 24-27 2010. - 1473-2262. ; 20:suppl. 3, s. 106-
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Conference paper (peer-reviewed)
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| 9. |
- He, Wenxiao, 1985, et al.
(author)
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Formation of Bone-like Nanocrystalline Apatite Using Self-Assembled Liquid Crystals
- 2012
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 24:5, s. 892-902
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Journal article (peer-reviewed)abstract
- A two-step process using liquid crystalline phases combined with controlled postcrystallization for the preparation of bone-like apatite has been developed. First, amorphous calcium phosphate (ACP) spherules with a diameter of 10.8 +/- 1.4 nm and specific surface area (SSA) in the range of 150-170 m(2)/g were synthesized within a reverse hexagonal liquid crystalline (LC) phase. Second, the ACP spherules were dispersed and aged in Milli-Qwater, where they crystallized into poorly crystalline apatite (PCA). The addition of heparin during aging was explored, which was shown to retard the ACP - PCA conversion. The particle formation within the LC phase was monitored using synchrotron small-angle X-ray scattering, and the formed materials were characterized by X-ray diffraction, conventional and high-resolution transmission electron microscopy, nitrogen adsorption, thermogravimetry with infrared-coupled analysis, and Raman spectroscopy. The PCA formed using the LC aging route presented bone-resembling features, such as,Ca2+ and OH- deficiency, CO32- substitution, poor crystallinity; and ultrahigh SSA of 356 m(2)/g. The resulting particles were compared to hydroxyapatite synthesized via a conventional water-based precipitation method. The LC-aging route exhibited excellent controllability over the CaP crystallization, which enabled facile tailoring of the resulting material properties for different types of application.
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| 10. |
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