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Johansson, Tomas
Publications (10 of 14) Show all publications
Johansson, T., Persson, N.-K. & Inganäs, O. (2004). Moving Redox Fronts in Conjugated Polymers Studies from Lateral Electrochemistry in Polythiophenes. Journal of the Electrochemical Society, 151(4)
Open this publication in new window or tab >>Moving Redox Fronts in Conjugated Polymers Studies from Lateral Electrochemistry in Polythiophenes
2004 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 151, no 4Article in journal (Refereed) Published
Abstract [en]

The propagation speed of the front of electrochemical conversion, from semiconductor to highly doped polymer, in films of regioregular poly(3-hexylthiophene) spin cast on insulating substrates was analyzed. Propagation of the p-doped zone in polymer electrochromic devices was imaged simultaneously with recording of electrochemical data. The current is proportional to the propagation speed and has a Tafel-like behavior when taking the resistive drop in the film into account. The resistivity in the film, which gradually lowers the propagation speed, was used for determination of the conductivity of the p-doped polymer. By combining these values with the doping charge injected into the film during front migration we estimated the hole carrier mobility for different doping levels. © 2004 The Electrochemical Society.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-45745 (URN)10.1149/1.1649749 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Wang, X., Östblom, M., Johansson, T. & Inganäs, O. (2004). PEDOT surface energy pattern controls fluorescent polymer deposition by dewetting. Thin Solid Films, 449(1-2), 125-132
Open this publication in new window or tab >>PEDOT surface energy pattern controls fluorescent polymer deposition by dewetting
2004 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 449, no 1-2, p. 125-132Article in journal (Refereed) Published
Abstract [en]

An elastomeric stamp of poly(dimethylsiloxane) (PDMS) can modify the surface energy of some surfaces when brought into conformal contact with these for some time. The substrates under investigation are a conducting polymer poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) and a polyelectrolyte poly(sodium 4-styrenesulfonate) (NaPSS). The changes in surface wetting are characterized by contact angle measurement. Changes are due to the PDMS stamp, which leaves low molecular weight residues on the surface, as shown by infrared reflection absorption spectroscopy. This process may also be operating when other inks are transferred in microcontact printing. Patterning of fluorescent polymer film with feature size of 10–100 μm range is done by confining polymer solutions on the modified surface, by means of spin- or dip-coating. The profile of the patterned film and factors that influence the profile are discussed. This technique is a convenient way to build polymer microstructures for application in organic and biomolecular electronics and photonics.

Keywords
Surface energy, Surface modification by PDMS stamp, Contact angle analysis, IRA spectrum, Polymer patterning
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13884 (URN)10.1016/j.tsf.2003.10.153 (DOI)
Available from: 2006-07-07 Created: 2006-07-07 Last updated: 2018-10-08
Johansson, T., Mammo, W., Svensson, M., Andersson, M. & Inganäs, O. (2003). Electrochemical bandgaps of substituted polythiophenes. Journal of Materials Chemistry, 13(6), 1316-1323
Open this publication in new window or tab >>Electrochemical bandgaps of substituted polythiophenes
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2003 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 13, no 6, p. 1316-1323Article in journal (Refereed) Published
Abstract [en]

The electrochemical bandgaps for different soluble substituted polythiophenes have been measured by cyclic voltammetry. The effect of substituents on the oxidation/reduction potentials is discussed. Bandgaps obtained by cyclic voltammetry have been found to be in general higher than optical bandgaps. Among regioregular polymers substituted with a phenyl group at position 3 of the thiophene ring, examples are found that give very symmetric voltammograms. Rationalization for this behaviour is discussed from a conformational point of view.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46615 (URN)10.1039/b301403g (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Johansson, T., Pettersson, L. & Inganäs, O. (2002). Conductivity of de-doped poly(3,4-ethylenedioxythiophene). Synthetic metals, 129(3), 269-274
Open this publication in new window or tab >>Conductivity of de-doped poly(3,4-ethylenedioxythiophene)
2002 (English)In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 129, no 3, p. 269-274Article in journal (Refereed) Published
Abstract [en]

The conductivity of chemically and electrochemically de-doped poly(3,4-ethylenedioxythiophene) (PEDOT) has been investigated in situ. We observe a decrease in the conductivity by 4-5 orders of magnitude. The change of conductivity is correlated to the change of electronic structure. We obtain the dielectric function of the polymer by spectroscopic ellipsometry and note that anisotropy is observed in both doped and neutral states. © 2002 Elsevier Science B.V. All rights reserved.

Keywords
Conductivity, Electrochemical doping, Ellipsometry, PEDOT, Spectroscopy
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46927 (URN)10.1016/S0379-6779(02)00086-3 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Duineveld, P., Lilja, M., Johansson, T. & Inganäs, O. (2002). Diffusion of solvent in PDMS elastomer for micromolding in capillaries. Langmuir, 18(24), 9554-9559
Open this publication in new window or tab >>Diffusion of solvent in PDMS elastomer for micromolding in capillaries
2002 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, no 24, p. 9554-9559Article in journal (Refereed) Published
Abstract [en]

Micromolding in capillaries is a soft lithography method for patterning materials. We have studied the diffusion of solvent from the excavated microsized channels in the stamp into the PDMS material, both theoretically and experimentally. It was demonstrated that a model of 1-D diffusion of solvent through a PDMS stamp, coupled with a mass conservation of the solvent in the channels, leads to a quantitatively accurate model for the velocity of the boundary between liquid-filled and vapor-filled microchannels in the stamp. With the model the diffusion coefficient of the solvent into PDMS was successfully determined.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46852 (URN)10.1021/la025831s (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Jonforsen, M., Johansson, T., Spjuth, L., Inganäs, O. & Andersson, M. (2002). Synthesis and characterization of poly(quinoxaline vinylene)s and poly(pyridopyrazine vinylene)s with phenyl substituted side-groups. Synthetic metals, 131(1-3), 53-59
Open this publication in new window or tab >>Synthesis and characterization of poly(quinoxaline vinylene)s and poly(pyridopyrazine vinylene)s with phenyl substituted side-groups
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2002 (English)In: Synthetic metals, ISSN 0379-6779, E-ISSN 1879-3290, Vol. 131, no 1-3, p. 53-59Article in journal (Refereed) Published
Abstract [en]

Poly(quinoxaline vinylene) and poly(pyridopyrazine vinylene) with 3(2'-ethylhexyloxy)phenyl side-groups have been synthesized and compared with similar polymers with purely aliphatic side-chains. The new polymers had smaller bandgaps, and from cyclic voltammetry it was seen that the phenyl substituted side-groups made the polymers easier to reduce, with half wave potentials of -1.02 and -1.33 V versus Ag/AgCl for the poly(pyridopyrazine vinylene) and poly(quinoxaline vinylene) respectively. The attachment of the phenyl substituted side-groups had counteracting effects on the stability towards photo-oxidation, which resulted in improved stability of the poly(pyridopyrazine vinylene) compared to its equivalent with purely aliphatic side-chains, while the poly(quinoxaline vinylene) showed decreased stability. © 2002 Elsevier Science B.V. All rights reserved.

Keywords
Cyclic voltammetry, N-Doping, Pyrido[3, 4-b]pyrazine, Quinoxaline, Small bandgap, Stability
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-46854 (URN)10.1016/S0379-6779(02)00137-6 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Jonforsen, M., Johansson, T., Inganäs, O. & Andersson, M. (2002). Synthesis and characterization of soluble and n-dopable poly(quinoxaline vinylene)s and poly(pyridopyrazine vinylene)s with relatively small band gap. Macromolecules, 35(5), 1638-1643
Open this publication in new window or tab >>Synthesis and characterization of soluble and n-dopable poly(quinoxaline vinylene)s and poly(pyridopyrazine vinylene)s with relatively small band gap
2002 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 35, no 5, p. 1638-1643Article in journal (Refereed) Published
Abstract [en]

Synthesis and characterization of poly(quinoxaline vinylene)s and poly(pyridopyrazine vinylene)s with linear and branched aliphatic side chains are reported. The electron affinity of the polymers was measured with cyclic voltammetry (CV) and found to be highest for the pyridopyrazine vinylene polymers, Compared to CN-MEH-PPV, the pyridopyrazine vinylene polymers were easier to reduce, while the quinoxaline derivatives were harder. UV-vis absorption measurements showed that the polymers have relatively small band gaps.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47896 (URN)10.1021/ma0111111 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Johansson, D., Wang, X., Johansson, T., Inganäs, O., Yu, G., Srdanov, G. & Andersson, M. (2002). Synthesis of soluble phenyl-substituted poly(p-phenylenevinylenes) with a low content of structural defects. Macromolecules, 35(13), 4997-5003
Open this publication in new window or tab >>Synthesis of soluble phenyl-substituted poly(p-phenylenevinylenes) with a low content of structural defects
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2002 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 35, no 13, p. 4997-5003Article in journal (Refereed) Published
Abstract [en]

The synthesis and characterization of two new soluble poly(p-phenylenevinylenes) (PPVs) are reported. The polymers are poly(2-2',5'-bis(octyloxy)benzene)-1,4-phenylenevinylene) (BOP-PPV) and poly(2-(2',5'-bis(octyloxy)benzene)-5-methoxy-1,4-phenylenevinylene) (BOPM-PPV). Both polymers have been polymerized at high and low temperatures to study the formation of structural defects. It is shown that both methoxy groups as side chains and low polymerization temperatures decrease the content of defects in the final polymer. As a consequence, the polymers with lower concentration of defects exhibit higher electroluminescence yields in light-emitting diodes. In addition to this, the polymers with a low content of defects exhibited longer operational lifetimes in these devices. The highest photoluminescence quantum yield in the solid state and electroluminescence efficiency were found to be 72% and 1.74%, respectively.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47880 (URN)10.1021/ma011768m (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Redhe, M., Forsberg, J., Johansson, T. & Marklund, P.-O. (2002). Using the response surface methodology and the D-optimality criterion in crashworthiness related problems. Structural and multidisciplinary optimization (Print), 24(3), 185-194
Open this publication in new window or tab >>Using the response surface methodology and the D-optimality criterion in crashworthiness related problems
2002 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 24, no 3, p. 185-194Article in journal (Refereed) Published
Abstract [en]

The aim of this paper is to determine the efficient number of experimental points when using the response surface methodology in crashworthiness problems.

The D-optimality criterion is used as experimental design method. Two application models have been studied, one square tube and one front rail from Saab Automobile AB. Both models were fully parameterized in the preprocessor LS-INGRID but only two design variables were used. The optimization package LS-OPT was used to determine the design of experiments using the D-optimality criterion. Both models were subjected to an impact into a rigid wall and the simulations were carried out using LS-DYNA. A general recommendation is to to use 1.5 times the minimum number of experimental points. A more specialized recommendation is for linear surfaces 1.5, elliptic surfaces 2.2 and for quadratic surfaces 1.6 times the minimum number of experimental points.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-35584 (URN)10.1007/s00158-002-0228-9 (DOI)27810 (Local ID)27810 (Archive number)27810 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
Inganäs, O., Johansson, T. & Ghosh, S. (2001). Phase engineering for enhanced electrochromism in conjugated polymers. Electrochimica Acta, 46(13-14), 2031-2034
Open this publication in new window or tab >>Phase engineering for enhanced electrochromism in conjugated polymers
2001 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 46, no 13-14, p. 2031-2034Article in journal (Refereed) Published
Abstract [en]

Development of nanostructured blends of electrochromic polymers formed by self-assembly is reported. We have prepared blends of a polythiophene derivative, poly(3,4-ethylenedioxythiophene) and polypyrrole, combining optical and electrochemical properties of the two polymers. The route towards these blends is based on self-assembly of the former polymer into a hydrogel, and subsequent electrochemical polymerisation of the latter using the conducting hydrogel matrix as a template. When used as electrodes, these materials show very fast electrochromic response. The route used in the present work is generic and may be extended to other polymers. © 2001 Elsevier Science Ltd.

Keywords
Conjugated polymer, Electrochromism, Hydrogel electrode, Morphology, Polymer blend
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47423 (URN)10.1016/S0013-4686(01)00420-0 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
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