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Bollstrom R.,Center for Functional Materials | Bollstrom R.,Åbo Akademi University | Tobjork D.,Center for Functional Materials | Tobjork D.,Åbo Akademi University | And 12 more authors.
International Conference on Digital Printing Technologies | Year: 2011

New value-added, intelligent products with novel functionalities, e.g., sensors and simple displays have recently received much attention in the research community. For these types of products to come into everyday use, devices with reasonable electrical performance and negligible production cost are required. One way to reduce the manufacturing cost is to fabricate the electronics on inexpensive paper substrates by using roll-to-roll techniques ("Paper Electronics"), as an alternative to conventional electronics manufactured with batch processes on glass or polymer film substrates. The current work discusses printing of electronics on paper and demonstrates, as a proof-of-concept, a hygroscopic insulator field effect transistor device (HIFET) printed on paper with a custom-built roll-to-roll hybrid printer. ©2011 Society for Imaging Science and Technology.


Bollstrom R.,Center for Functional Materials | Bollstrom R.,Åbo Akademi University | Tobjork D.,Center for Functional Materials | Tobjork D.,Åbo Akademi University | And 10 more authors.
Chemical Engineering and Processing: Process Intensification | Year: 2013

Printability of functional inks on multilayer curtain coated substrates was investigated. The inks represent those commonly used to produce solution processable electronic devices, such as organic transistors. The substrate, which combines sufficient barrier and printability properties for printed functional devices, was manufactured utilizing high speed curtain coating technique. The coating structure consists of a mineral pigment layer coated on top of a barrier layer. The combination of the two layers allows for controlling the absorption of ink solvents. By adjusting the thickness, porosity and surface energy of the top-coating the printability can be tuned for various functional inks. Focus was set on printing conducting silver and carbon inks, both with nano- and micrometer sized particles, as well as printing of an organic semiconductor, poly(3-hexylthiophene). The pore volume in the top-coating determined the spreading of the micrometer sized silver ink as well as the amount semiconductor per area required, whereas the pore size was the determining factor regarding penetration of the nano-sized silver ink. As a proof of concept hygroscopic insulator field effect transistors were printed on the multi-layer curtain coated paper using a custom-built roll to roll hybrid printer. © 2012 Elsevier B.V.


Bollstrom R.,Center for Functional Materials | Bollstrom R.,Åbo Akademi University | Pettersson F.,Center for Functional Materials | Pettersson F.,Åbo Akademi University | And 7 more authors.
Nanotechnology | Year: 2014

A multilayer coated paper substrate, combining barrier and printability properties was manufactured utilizing a pilot-scale slide curtain coating technique. The coating structure consists of a thin mineral pigment layer coated on top of a barrier layer. The surface properties, i.e. smoothness and surface porosity, were adjusted by the choice of calendering parameters. The influence of surface properties on the fine line printability and conductivity of inkjet-printed silver lines was studied. Surface roughness played a significant role when printing narrow lines, increasing the risk of defects and discontinuities, whereas for wider lines the influence of surface roughness was less critical. A smooth, calendered surface resulted in finer line definition, i.e. less edge raggedness. Dimensional stability and its influence on substrate surface properties as well as on the functionality of conductive tracks and transistors were studied by exposure to high/low humidity cycles. The barrier layer of the multilayer coated paper reduced the dimensional changes and surface roughness increase caused by humidity and helped maintain the conductivity of the printed tracks. Functionality of a printed transistor during a short, one hour humidity cycle was maintained, but a longer exposure to humidity destroyed the non-encapsulated transistor. © 2014 IOP Publishing Ltd.


Tobjork D.,Åbo Akademi University | Tobjork D.,Center for Functional Materials | Aarnio H.,Åbo Akademi University | Aarnio H.,Center for Functional Materials | And 18 more authors.
Thin Solid Films | Year: 2012

Sintering of printed metal nanoparticles can be made not only by conventional heating, but also by, e.g., electrical, microwave, plasma, laser and flash lamp annealing. We demonstrate sintering by using low-cost incandescent lamps as an effective way of obtaining highly conductive contacts of two types of ink-jet printed metal-nanoparticle inks on paper; both alkanethiol protected gold nanoparticles and a commercially available silver nanoparticle ink. This low-cost roll-to-roll compatible sintering process is especially suitable on paper substrates because of the high diffuse reflectance, relatively high thermal stability and low thermal conductivity of paper. A volume resistivity of around 10 μΩ cm was achieved of the inkjetted silver nanoparticles within 15 s of exposure to an IR lamp, which corresponds to a conductivity of 10-20% of that of bulk silver. Too long exposure time and too high intensity, however, lead to darkening of the paper fibers. Both the crack formation and the coffee ring effect of the inkjet printed gold nanoparticles were, furthermore, found to be reduced on paper as compared to glass or plastic substrates. © 2011 Elsevier B.V. All rights reserved.


Bober P.,Process Chemistry Center | Bober P.,Czech Institute of Macromolecular Chemical | Liu J.,Process Chemistry Center | Mikkonen K.S.,University of Helsinki | And 8 more authors.
Biomacromolecules | Year: 2014

In this work, flexible and free-standing composite films of nanofibrillated cellulose/polypyrrole (NFC/PPy) and NFC/PPy-silver nanoparticles (NFC/PPy-Ag) have been synthesized for the first time via in situ one-step chemical polymerization and applied in potential biomedical applications. Incorporation of NFC into PPy significantly improved its film formation ability resulting in composite materials with good mechanical and electrical properties. It is shown that the NFC/PPy-Ag composite films have strong inhibition effect against the growth of Gram-positive bacteria, e.g., Staphylococcus aureus. The electrical conductivity and strong antimicrobial activity makes it possible to use the silver composites in various applications aimed at biomedical treatments and diagnostics. Additionally, we report here the structural and morphological characterization of the composite materials with Fourier-transform infrared spectroscopy, atomic force microscopy, and scanning and transmission electron microscopy techniques. © 2014 American Chemical Society.


News Article | December 1, 2016
Site: phys.org

For the first time in the world, a NIMS research team represented by Yuka Kobayashi, Principal Researcher, Research Center for Functional Materials, designed and fabricated single-component organic molecules that are conductive like metal under normal pressure, despite the fact that the molecules contain neither multiple molecules nor metal elements. Because the molecules are completely pure, they are more durable and stable compared to conventional chemically doped organic conductive materials. The new molecules may be applied to solar cell electrodes and touch panels. Organic molecules consisting solely of light elements essentially do not have carriers by which an electric charge can pass through. As such, they are not high quality conductors. To address this issue, pure organic metals have been synthesized for over 50 years by combining molecules with different properties, thereby altering their individual properties and generating charge carriers. It is well known that Professor Hideki Shirakawa won a Nobel Prize for discovering conductive polymers from among these molecules studied. However, multiple molecules combined together have issues in terms of stability and durability. On the other hand, regarding pure organic materials made of a single component, it was necessary to apply high pressure of at least 1 giga pascal(GPa) in order to make them conductive like metal. In line with this practice, for many years, it had been thought to be extremely difficult to make these materials conductive like metal under ambient pressure. Recently, the research team designed new molecules that spontaneously generate holes that can serve as charge carriers. Then the team fabricated pure organic molecules that conduct electricity like metal at a wide range of temperatures under normal pressure. Electrical conductivity of the film that was made exclusively of these molecules (TED as a short name) was 530 S/cm (S = siemens, which is an inverse of resistivity) at room temperature and 1,000 S/cm at 50 K. The conductivity is at the highest level among organic metals. In addition, through molecular orbital calculations, the team found that TED has a prominent spin density gradient which had not been seen in other radical molecules. This electronic state may correlate with the mechanism by which single-component molecules exhibit metallic-conduction properties. These findings may set two general directions in the design of highly conductive organic materials. First, a step of adding a chemical dopant for making materials conductive (post-doping) can be eliminated, and consequently, it becomes feasible to design molecules that make it possible to drastically enhance the durability and chemical stability of organic conductive materials. Second, from the viewpoint of practical application, a printable method, a derived printing technique, can be used to easily fabricate highly conductive organic materials. This research was conducted as a follow-up of a previous study carried out in line with the Funding Program for Next Generation World-Leading Researchers (NEXT Program; Yuka Kobayashi, project leader) sponsored by the Japan Society for the Promotion of Science. This study was published in the online version of Nature Materials on October 10, 2016. More information: Yuka Kobayashi et al. Carrier generation and electronic properties of a single-component pure organic metal, Nature Materials (2016). DOI: 10.1038/nmat4768


Pykonen M.,Center for Functional Materials | Johansson K.,Ytkemiska Institutet AB | Bollstrom R.,Center for Functional Materials | Fardim P.,Åbo Akademi University | Toivakka M.,Center for Functional Materials
Industrial and Engineering Chemistry Research | Year: 2010

SocietyFluorocarbon, organosilicon, and hydrocarbon plasma coatings were used to modify the surface of permeable pigment-coated paper, and their impact on UV-varnish absorption was investigated. According to mercury porosimetry results, the plasma coatings had no influence on the porous structure of the paper. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) results showed characteristic surface chemical compositions for each plasma coating. The fluorocarbon plasma coating increased the UV-varnish contact angles significantly, whereas the hydrocarbon plasma coating had no clear influence. When the UV varnish was applied with a flexography unit including nip pressure, the role of surface chemical composition seemed to become minimal. The viscosity of the UV varnish was shown to impact the absorption rate with and without external pressure. © 2010 American Chemical.


Sarfraz J.,Åbo Akademi University | Tobjork D.,Åbo Akademi University | Osterbacka R.,Åbo Akademi University | Osterbacka R.,Center for Functional Materials | Linden M.,University of Ulm
Proceedings of IEEE Sensors | Year: 2011

Drop-casted deprotonated Emeraldine base (poly)aniline (PANI) - copper chloride films on paper substrates containing ink-jet printed silver electrodes have been prepared and are shown to be promising low-cost gas-sensors for H2S at room temperature. These films showed large changes in the conductivity (three to four orders of magnitude) upon exposure to low concentrations of H 2S (10ppm) due to the formation of CuS and concurrent protonation of PANI. This large response of the sensor can be explained by the relatively large roughness and porosity of the paper substrate. Furthermore, the minimum resistances are low enough to allow LED lamps to be switched on using a low-voltage battery, thus serving as a proof-of-concept for mass-produced H 2S-sensors for, for example, the food packaging industry. © 2011 IEEE.


Saarinen J.J.,Center for Functional Materials | Ihalainen P.,Center for Functional Materials | Maattanen A.,Center for Functional Materials | Bollstrom R.,Center for Functional Materials | Peltonen J.,Center for Functional Materials
Nordic Pulp and Paper Research Journal | Year: 2011

Two new printed functionalities on a recently developed natural fibre based substrate are demonstrated. All-printed UV-A illumination detector is obtained using conductive polyaniline or poly(3,4)-ethylenedioxythiophene/ polystyrenesulfonate polymers, which change resistance under UV-A illumination. Electric field assisted wetting is characterized using flexographically printed silver electrodes. Detailed topographical characterization of porous, permeable, and rough fibre substrate is crucial for optimizing electric functionality of such devices. Printed functionality on a natural fibre based substrate is expected to provide a more sustainable approach for applications such as sensors and displays that are currently printed on plastic films.

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