| 11. |
- Andersson Trojer, Markus, et al.
(författare)
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Elastic strain-hardening and shear-thickening exhibited by thermoreversible physical hydrogels based on poly(alkylene oxide)-grafted hyaluronic acid or carboxymethylcellulose
- 2020
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 22:26, s. 14579-14590
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Tidskriftsartikel (refereegranskat)abstract
- The formation of strongly elastic physical gels based on poly(alkylene oxide)-grafted hyaluronan or carboxymethylcellulose, exhibiting both shear-thickening and strain-hardening have been studied using rheometry and explained using a slightly different interpretation of the transient network theory. The graft copolymers were prepared by a quantitative coupling reaction. Their aqueous solutions displayed a thermoreversible continuous transition from Newtonian fluid to viscoelastic solid which could be controlled by the reaction conditions. The evolution of all material properties of the gel could be categorized into two distinct temperature regimes with a fast evolution at low temperatures followed by a slow evolution at high temperatures. The activation energy of the zero shear viscosity and the relaxation time of the graft inside the interconnecting microdomains were almost identical to each other in both temperature regimes. This suggests that the number of microdomains remained approximately constant whereas the aggregation number inside the microdomains increased according to the binodal curve of the thermosensitive graft.
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| 12. |
- Andersson Trojer, Markus, 1981, et al.
(författare)
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Quantitative Grafting for Structure-Function Establishment: Thermoresponsive Poly(alkylene oxide) Graft Copolymers Based on Hyaluronic Acid and Carboxymethylcellulose
- 2019
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 20:3, s. 1271-1280
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 American Chemical Society. A series of thermoresponsive graft copolymers, gelling at physiological conditions in aqueous solution and cell growth media, have been synthesized using quantitative coupling between a small set of amino-functionalized poly(alkylene oxide) copolymers (PAO) and the carboxylate of the biologically important polysaccharides (PSa) carboxymethylcellulose and the less reactive hyaluronate. Quantitative grafting enables the establishment of structure-function relationship which is imperative for controlling the properties of in situ gelling hydrogels. The EDC/NHS-mediated reaction was monitored using SEC-MALLS, which revealed that all PAOs were grafted onto the PSa backbone. Aqueous solutions of the graft copolymers were Newtonian fluids at room temperatures and formed reversible physical gels at elevated temperatures which were noncytotoxic toward chondrocytes. The established structure-function relationship was most clearly demonstrated by inspecting the thermogelling strength and the onset of thermogelling in a phase diagram. The onset of the thermogelling function could be controlled by the global PAO concentration, independent of graft ratio.
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| 13. |
- Anselmo, Ana Sofia, 1980-, et al.
(författare)
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Tuning the Vertical Phase Separation in Polyfluorene: Fullerene Blend Films by Polymer Functionalization
- 2011
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Ingår i: Chemistry of Materials. - Washington : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 23:9, s. 2295-2302
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Tidskriftsartikel (refereegranskat)abstract
- Achieving control over the nanomorphology of blend films of the fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester, PCBM, with light-absorbing conjugated polymers is an important challenge in the development of efficient solution-processed photovoltaics. Here, three new polyfluorene copolymers are presented, tailored for enhanced miscibility with the fullerene through the introduction of polymer segments with modified side chains, which enhance the polymer's polar character. The composition of the spincoated polymer:PCBM films is analyzed with dynamic secondary ion mass spectrometry (dSIMS). The dSIMS depth profiles demonstrate compositional variations perpendicular to the surface plane, as a result of vertical phase separation, directed by the substrate. These variations propagate to a higher degree through the film for the polymers with a larger fraction of modified side chains. The surface composition of the films is studied by Near-edge X-ray absorption fine structure spectroscopy (NEXAFS). Quantitative analysis of the NEXAFS spectra through a linear combination fit with the spectra of the pure components yields the surface composition. The resulting blend ratios reveal polymer-enrichment of the film surface for all three blends, which also becomes stronger as the polar character of the polymer increases. Comparison of the NEXAFS spectra collected with two different sampling depths shows that the vertical composition gradient builds up already in the first nanometers underneath the surface of the films. The results obtained with this new series of polymers shed light on the onset of formation of lamellar structures in thin polymer:PCBM films prepared from highly volatile solvents.
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| 14. |
- Barrau, Sophie, et al.
(författare)
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Nanomorphology of Bulk Heterojunction Organic Solar Cells in 2D and 3D Correlated to Photovoltaic Performance
- 2009
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 42:13, s. 4646-4650
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Tidskriftsartikel (refereegranskat)abstract
- Control of the nanoscale morphology of the donor-acceptor material blends inorganic solar Cells is critical for optimizing the photovoltaic performances. The influence of intrinsic (acceptor materials) and extrinsic (donor:acceptor weight ratio, substrate, solvent) parameters was investigated, by atomic force microscopy (AFM) and electron tomography (ET), on the nanoscale phase separation of blends of a low-band-gap alternating polyfluorene copolymers (APFO-Green9) with [6,6]-phenyl-C-71-butyric acid methyl ester ([70]PCBM). The photovoltaic performances display an optimal efficiency for the device elaborated with a 1:3 APFO-Green polymer:[70][PCBM weight ratio and spin-coated from chloroform solution. The associated active layer morphology presents small phase-separated domains which is a good balance between as a large interfacial donor-acceptor area and Continuous paths of the donor and acceptor phases to the electrodes.
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| 15. |
- Bjorstrom, C. M., et al.
(författare)
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Vertical phase separation in spin-coated films of a low bandgap polyfluorene/PCBM blend - Effects of specific substrate interaction
- 2007
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Ingår i: Applied Surface Science. - Amsterdam : Elsevier BV. - 0169-4332 .- 1873-5584. ; 253:8, s. 3906-3912
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Tidskriftsartikel (refereegranskat)abstract
- We report on the effect of the substrate on the vertical phase separation in spin-coated thin films of poly [(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-4',7'-di-2-thienyl-2',1',3'-benz othiadiazole] (APFO-3) blended with [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM). Compositional depth profiles of the films are measured by dynamic secondary ion mass spectrometry (SIMS). We found that changing the substrate from silicon to gold affects the composition profile near the substrate interface. This is caused by a specific interaction between the polymer (APFO-3) and the gold surface, as confirmed by X-ray photoelectron spectroscopy (XPS). The composition profile in the area away from the substrate interface, as well as the enrichment of the free surface with APFO-3, remain however unaffected by the choice of substrate. The vertical composition was also analysed for APFO-3:PCBM films spin-coated on indium tin oxide (ITO) coated with a thin layer of (3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS). (c) 2006 Elsevier B.V. All rights reserved.
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| 16. |
- Chen, Miaoxiang, 1962-, et al.
(författare)
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High carrier mobility in low band gap polymer-based field-effect transistors
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 87:25, s. 252105-1-252105-3
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Tidskriftsartikel (refereegranskat)abstract
- A conjugated polymer with a low band gap of 1.21 eV, i.e., absorbing infrared light, is demonstrated as active material in field-effect transistors (FETs). The material consists of alternating fluorene units and low band gap segments with electron donor-acceptor-donor units composed of two electron-donating thiophene rings attached on both sides of a thiadiazolo-quinoxaline electron-acceptor group. The polymer is solution-processable and air-stable; the resulting FETs exhibit typical p-channel characteristics and field-effect mobility of 0.03 cm2 V−1 s−1.
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| 17. |
- Gadisa, Abay, et al.
(författare)
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A new donor-acceptor-donor polyfluorene copolymer with balanced electron and hole mobility
- 2007
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Ingår i: Adv. Funct. Mater. FIELD Full Journal Title:Advanced Functional Materials. ; 17:18, s. 3836-3842
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Tidskriftsartikel (refereegranskat)abstract
- A new alternating polyfluorene copolymer poly[2,7-(9,9-dioctylfluoren)-alt-5,5-(5',8'-di-2-thienyl-(2',3'-bis-(3''-octyloxyphenyl)-quinoxaline))] (APFO-15), which has electron donor-acceptor-donor units in between the fluorene units, is synthesized and characterized. This polymer has a strong absorption and emission in the visible range of the solar spectrum. Its electroluminescence and photolumin escence emissions extend from about 560 to 900 nm. Moreover, solar cells with efficiencies in excess of 3.5 % have been realized from blends of APFO-15 and an electron acceptor mol., a mathanofullerene [6,6]-phenyl-C61-butyric acid Me ester (PCBM). It has also been obsd. that electron and hole transport is balanced both in the pure polymer phase and in polymer/PCBM bulk heterojunction films, which makes this material quite attractive for applications in opto-electronic devices. [on SciFinder (R)]
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| 18. |
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| 19. |
- George, Zandra, 1985, et al.
(författare)
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Two-in-one : Cathode modification and improved solar cell blend stability through addition of modified fullerenes
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:7, s. 2663-2669
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of dual purpose modified fullerenes with pyridine-as well as amine-functional groups is reported. Addition of these fullerenes to a polymer : fullerene bulk-heterojunction blend based on a thiophene-quinoxaline donor polymer is found to modify the active layer/cathode interface of inverted solar cells (glass/ITO/active layer/MoO3/Al). In particular the open-circuit voltage of devices is increased from 0.1 V to about 0.7 V, which results in a drastic rise in photovoltaic performance with a power conversion efficiency of up to 3%. At the same time, presence of the functionalised fullerene additives prevents the detrimental formation of micrometre-sized fullerene crystals upon annealing at 140 degrees C. As a result, the device performance is retained, which promises significantly increased thermal stability of the bulk-heterojunction blend nanostructure.
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| 20. |
- Hedman, Erik, et al.
(författare)
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Psychometric properties of Internet-administered measures of health anxiety : an investigation of the Health Anxiety Inventory, the Illness Attitude Scales, and the Whiteley Index
- 2015
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Ingår i: Journal of Anxiety Disorders. - : Elsevier BV. - 0887-6185 .- 1873-7897. ; 31, s. 32-37
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The Health Anxiety Inventory (HAI), the Illness Attitude Scales (IAS), and the Whiteley Index (WI) are three of the most widely used health anxiety measures, but their psychometric properties have not been investigated when administered via the Internet.METHODS: We investigated the three instruments' test-retest reliability, internal consistency, convergent, and discriminant validity and sensitivity to change using one sample (n=111) of participants with severe health anxiety and one sample of healthy controls (n=92).RESULTS: The HAI, IAS, and WI showed high test-retest reliability (rs≥.80), good convergent, and discriminant validity and were sensitive to detect change. The HAI and IAS (αs≥.85), but not the WI (αs≤.60) demonstrated high internal consistency.CONCLUSIONS: The HAI, IAS, and WI have good psychometric properties, except for the low internal consistency of WI, when used as Internet-administered measures of health anxiety. Using these measures over the Internet offers highly important advantages such as increased ease of administration, reduced attrition, and cost-efficient treatment evaluation.
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