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- Härdelin, Linda, 1977, et al.
(författare)
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Electrospinning of cellulose nanofibers from ionic liquids: The effect of different cosolvents
- 2012
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 125:3, s. 1901-1909
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose was electrospun with various concentrations of ionic liquid and cosolvent. Three different cosolvents were used in this study; dimethylacetamide (DMAc), dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO). The cosolvents were added to modify the viscosity, electrical conductivity, and surface tension of the solutions. The solubility of cellulose in ionic liquids is highly affected by changes in solvent properties on the molecular level in the binary solvent systems. The difference in molecular structure of the cosolvents and the interactions between cosolvent and ionic liquid can explain the difference in dissolution power of the cosolvents. Scanning electron microscope (SEM) was used to characterize electrospun cellulose fibers. For the systems tested the importance of having a rather high viscosity and high surface tension, and some degree of shear thinning to produce fibers is shown.
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| 5. |
- Härdelin, Linda, 1977, et al.
(författare)
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Influence of molecular weight and rheological behavior on electrospinning cellulose nanofibers from ionic liquids
- 2013
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 130:4, s. 2303-2310
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Tidskriftsartikel (refereegranskat)abstract
- Dissolving pulp was depolymerized with 2.5M HCl into cellulose fractions with decreasing molecular weight relative to acid treatment time. The cellulose fractions were dissolved at various concentrations in the ionic liquid 1-ethyl-3-methylimidazolium acetate (EmimAc) with co-solvent DMSO at ratio 1 : 1 (w/w) and electrospun. Size exclusion chromatography was used to evaluate the molecular weight distributions and the rheological properties were characterized with a cone-and-plate rheometer. Scanning electron microscope was used to evaluate the fiber morphology, and thereby spinnability. Zero shear viscosity as a function of cellulose concentration show that all the solutions in this study are in the entangled semi-dilute regime; where the polymer concentration is large enough for significant overlap necessary for chain entanglement. However, within the intervals studied, neither cellulose concentration nor molecular weight seems to be decisive for if a solution can be electrospun into fibers or not. It is rather the viscosity of the solution that is decisive for electrospinnability, even though the solution is in the entangled semi-dilute regime.
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| 6. |
- Lindgren, Lars Johan, 1977, et al.
(författare)
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Synthesis, Characterization, and Devices of a Series of Alternating Copolymers for Solar Cells
- 2009
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Ingår i: CHEMISTRY OF MATERIALS. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 21:15, s. 3491-3502
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Tidskriftsartikel (refereegranskat)abstract
- In this study we report the synthesis, characterization. and photovoltaic properties of a series of six Conjugated polymers based on donor-acceptor-donor (DAD) structure. The polymers are obtained via Suzuki polymerization of different alkoxy-substituted DAD monomers together with a substituted fluorene or phenylene monomer. Application of polymers as light-harvesting and electron-donating materials in solar cells, in conjunction with both [60]PCBM and [70]PCBM as acceptors, show power-conversion efficiencies (PCEs) up to 2.9%, values obtained without extensive optimization work. Furthermore, atomic force microscopy and field-effect transistor (FET) mobility measurements of acceptor-polymer mixtures show that differences in substitution on the polymers affect morphology, mobility, and device performance. Within the series of polymers, all showing similar optical absorption and redox behavior, substituents play an important role in phase separation on a micrometer scale, which in turn has a large impact on device performance. The phase-separation behavior is clearly seen in [70]PCBM devices where the best-performing devices are obtained using the polymers with short alkoxy groups or no substituents together with a high speed of spin coating during device preparation.
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| 7. |
- Admassie, Shimelis, et al.
(författare)
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Electrochemical and optical studies of the band gaps of alternating polyfluorene copolymers
- 2006
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Ingår i: Synthetic Metals. ; 156:7-8, s. 614-623
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Tidskriftsartikel (refereegranskat)abstract
- The electrochem. and optical properties of alternating polyfluorene copolymers with low band gaps were detd. These polymers incorporated fluorene units alternating with groups including electron-withdrawing (A) and electron-donating (D) groups in donor-acceptor-donor (DAD) sequence to achieve the lowering of band gaps. The polymers were solvent-casted on Pt disk electrode and the band gaps were estd. from cyclic voltammetry (CV). These values were compared with values obtained from optical absorption measurements. Although the electrochem. detd. band gaps are slightly higher than the optical band gap in most cases, values are well correlated. The values of the band gaps detd. range from 2.1 to 1.3 eV. [on SciFinder (R)]
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| 8. |
- 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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| 9. |
- Gadisa, Abay, et al.
(författare)
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Red and near infrared polarized light emissions from polyfluorene copolymer based light emitting diodes
- 2007
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Ingår i: Appl. Phys. Lett. FIELD Full Journal Title:Applied Physics Letters. ; 90:11, s. 113510/1-113510/3
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Tidskriftsartikel (refereegranskat)abstract
- The authors report polarized red, electroluminescence peak at 705 nm and near IR, electroluminescence peak at 950 nm, light emission from light emitting diodes based on two polyfluorene copolymers. The copolymers are synthesized from a fluorene monomer combined with donor-acceptor-donor comonomers and designed to have a low band gap and form birefringent liq. cryst. phases. Emission occurs from aligned thin films of polymer layers. The emissive layers are aligned by spin coating on a layer of rubbed conducting polymer poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) and thermally converted into glassy nematic liq. cryst. state. [on SciFinder (R)]
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| 10. |
- Gadisa, Abay, et al.
(författare)
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Stoichiometry dependence of charge transport in polymer/methanofullerene and polymer/C70 derivative based solar cells
- 2006
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Ingår i: Organic Electronics. ; 7:4, s. 195-204
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Tidskriftsartikel (refereegranskat)abstract
- Charge transport in a near IR absorbing polyfluorene copolymer (APFO-Green1) and its blends with methanofullerene [6,6]-Ph C61-butyric acid Me ester (PCBM), and 3'-(3,5-bis-trifluoromethylphenyl)-1'-(4-nitrophenyl)pyrazolino[70]fullerene (BTPF70) is reported. PCBM and BTPF70 are electron acceptor and transporting mols. in polymer based solar cells. The BTPF70 has emerged as a new electron acceptor mol. that provides adequate exciton dissocn. when blended with the low band gap polyfluorene copolymer APFO-Green1. Electron transport in both net PCBM and BTPF70 films are subjected to positional and energetic disorder, with the degree of disorder being more pronounced in BTPF70. On the other hand, mixing PCBM with conjugated polymers usually leads to increased hole mobility. We have investigated and compared the acceptor concn. dependence of charge transport in APFO-Green1/PCBM and APFO-Green1/BTPF70 blend films. For better understanding of the charge transport in the heterojunction films, the field and temp. dependence of hole transport in pure APFO-Green1 films has also been studied. It is obsd. that the behavior of hole mobility in the blend layer is sensitive to the acceptor type. For APFO-Green1/PCBM hole only devices, the hole mobility attains a local max. at 67 wt.% of PCBM, while on the contrary mixing any amt. of BTPF70 with APFO-Green1 results into degrdn. of hole transport. Electron transport in both blends, however, increases monotonically as a function of acceptor loading. [on SciFinder (R)]
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