| 1. |
- Carmeli, Enrico, et al.
(författare)
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Crystallization kinetics of melt-mixed 3D hierarchical graphene/polypropylene nanocomposites at processing-relevant cooling rates
- 2022
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Ingår i: Composites Part B: Engineering. - : Elsevier BV. - 1359-8368. ; 247
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the solidification behaviour of isotactic polypropylene (iPP) composites with reduced graphene oxide nanoplatelets is key to open the possibility to widespread use of these high performing nanocomposites. The crystallization behaviour of these systems, with filler content in the range of 0.2–3.5 wt% has been investigated by differential scanning calorimetry (up to 100 °C/min) and ex-situ structural and morphological characterization of samples prepared at processing-relevant cooling conditions (up to 2000 °C/s). Compared to the self-nucleated neat iPP, the nucleation efficiency was estimated to vary from 44 to 93% when increasing the filler content. Such a high nucleating efficiency has not been reported yet for a nanocomposite with iPP matrix. This result is due to the very good dispersion of the filler in these melt-mixed graphene-based polypropylene systems. The nucleation ability of the graphene filler does not reach a saturation in the concentration range studied. The gap between laboratory and industrial cooling rate scale is here reduced thanks to the information achieved from the fast-cooling experiments. By varying the filler amount in the investigated range, a significant shift of the cooling rate window in which the transition from α-to mesophase dominated crystallization takes place was detected. Notably, with 3.5 wt% graphene platelets, α-phase crystals are predominantly present in the material even after quenching at 1000 °C/s, similar to highly nucleated commercial iPP grades.
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| 2. |
- Deribew, Dargie, et al.
(författare)
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Crystallization-Driven Enhancement in Photovoltaic Performance through Block Copolymer Incorporation into P3HT:PCBM Blends
- 2013
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 46:8, s. 3015-3024
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Tidskriftsartikel (refereegranskat)abstract
- We report the increased crystallization of poly(3-hexylthiophene)(P3HT) in the donor−acceptor mixture of [6,6]-phenyl-C61-butyric acid methylester (PCBM) with P3HT by the addition of a block copolymer, P3HT-b-PI, where PI refers to polyisoprene. The photovoltaic performance of devices created using this blendis markedly improved by the addition of the diblock copolymer. We have characterizedthe structure of thin films of the P3HT-b-PI containing mixtures using opticalmicroscopy, scanning force microscopy, UV−vis absorption spectroscopy, neutronreflectometry, and grazing incidence X-ray diffraction (GIXD). The GIXD data providethe information on the crystallinity of the films, the absorption data were used toconfirm that the addition of the diblock was responsible for the increase in crystallization, neutron reflectometry data reveal a PCBM-rich region near the hole injection layer, and the two microscopy techniques revealed the structural effect of the crystallization at the surface of the films.
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| 3. |
- Erothu, Harikrishna, et al.
(författare)
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Synthesis, Thermal Processing, and Thin Film Morphology of Poly(3-hexylthiophene)-Poly(styrenesulfonate) Block Copolymers
- 2015
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:7, s. 2107-2117
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Tidskriftsartikel (refereegranskat)abstract
- A series of novel block copolymers, processable from single organic solvents and subsequently rendered amphiphilic by thermolysis, have been synthesized using Grignard metathesis (GRIM) and reversible addition-fragmentation chain transfer (RAFT) polymerizations and azide-alkyne click chemistry. This chemistry is simple and allows the fabrication of well-defined block copolymers with controllable block lengths. The block copolymers, designed for use as interfacial adhesive layers in organic photovoltaics to enhance contact between the photoactive and hole transport layers, comprise printable poly(3-hexylthiophene)-block-poly(neopentyl p-styrenesulfonate), P3HT-b-PNSS. Subsequently, they are converted to P3HT-b-poly(p-styrenesulfonate), P3HT-b-PSS, following deposition and thermal treatment at 150 degrees C. Grazing incidence small- and wide-angle X-ray scattering (GISAXS/GIWAXS) revealed that thin films of the amphiphilic block copolymers comprise lamellar nanodomains of P3HT crystallites that can be pushed further apart by increasing the PSS block lengths. The approach of using a thermally modifiable block allows deposition of this copolymer from a single organic solvent and subsequent conversion to an amphiphilic layer by nonchemical means, particularly attractive to large scale roll-to-roll industrial printing processes.
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| 4. |
- Jansen, Karin A., et al.
(författare)
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Molecular packing structure of fibrin fibers resolved by X-ray scattering and molecular modeling
- 2020
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 16:35, s. 8272-8283
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Tidskriftsartikel (refereegranskat)abstract
- Fibrin is the major extracellular component of blood clots and a proteinaceous hydrogel used as a versatile biomaterial. Fibrin forms branched networks built of laterally associated double-stranded protofibrils. This multiscale hierarchical structure is crucial for the extraordinary mechanical resilience of blood clots, yet the structural basis of clot mechanical properties remains largely unclear due, in part, to the unresolved molecular packing of fibrin fibers. Here the packing structure of fibrin fibers is quantitatively assessed by combining Small Angle X-ray Scattering (SAXS) measurements of fibrin reconstituted under a wide range of conditions with computational molecular modeling of fibrin protofibrils. The number, positions, and intensities of the Bragg peaks observed in the SAXS experiments were reproduced computationally based on the all-atom molecular structure of reconstructed fibrin protofibrils. Specifically, the model correctly predicts the intensities of the reflections of the 22.5 nm axial repeat, corresponding to the half-staggered longitudinal arrangement of fibrin molecules. In addition, the SAXS measurements showed that protofibrils within fibrin fibers have a partially ordered lateral arrangement with a characteristic transverse repeat distance of 13 nm, irrespective of the fiber thickness. These findings provide fundamental insights into the molecular structure of fibrin clots that underlies their biological and physical properties.
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| 5. |
- Liu, Jian, et al.
(författare)
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Amphipathic Side Chain of a Conjugated Polymer Optimizes Dopant Location toward Efficient N-Type Organic Thermoelectrics
- 2021
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 33
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Tidskriftsartikel (refereegranskat)abstract
- There is no molecular strategy for selectively increasing the Seebeck coefficient without reducing the electrical conductivity for organic thermoelectrics. Here, it is reported that the use of amphipathic side chains in an n-type donor-acceptor copolymer can selectively increase the Seebeck coefficient and thus increase the power factor by a factor of approximate to 5. The amphipathic side chain contains an alkyl chain segment as a spacer between the polymer backbone and an ethylene glycol type chain segment. The use of this alkyl spacer does not only reduce the energetic disorder in the conjugated polymer film but can also properly control the dopant sites away from the backbone, which minimizes the adverse influence of counterions. As confirmed by kinetic Monte Carlo simulations with the host-dopant distance as the only variable, a reduced Coulombic interaction resulting from a larger host-dopant distance contributes to a higher Seebeck coefficient for a given electrical conductivity. Finally, an optimized power factor of 18 mu W m(-1) K-2 is achieved in the doped polymer film. This work provides a facile molecular strategy for selectively improving the Seebeck coefficient and opens up a new route for optimizing the dopant location toward realizing better n-type polymeric thermoelectrics.
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| 6. |
- McKibbin, Sarah R., et al.
(författare)
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In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering
- 2019
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Ingår i: Nano Research. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 12:1, s. 25-31
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Tidskriftsartikel (refereegranskat)abstract
- In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N2 gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5–100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 105 particles/cm3) corresponding to a volume fraction below 3 × 10–10, which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions. [Figure not available: see fulltext.].
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| 7. |
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