1,720,966 research outputs found
Multi-walled carbon nanotubes plastic actuator
No full textCarbon nanotubes (CNTs) have electrical and mechanical properties that make them highly attractive for actuators. They have the ability to deform elastically by several percent, thus storing very large amounts of energy, thanks to their crystalline nature and to their morphology. A bimorph actuator composed of single-walled carbon nanotubes (SWCNTs), polyvinylidene difluoride (PVdF) and the ionic liquid (IL) 1-butyl 3-methylimidazolium tetrafluoroborate [BMIM][BF4] with a polymer-supported internal IL electrolyte was previously demonstrated by Aida and coworkers. While several experiments were carried out using SWCNTs, PVdF and a number of ILs, the use of multi-walled carbon nanotubes (MWCNTs) instead of SWCNTs is, to our knowledge, a new result that will be presented here. Electrochemical characterizations by cyclic voltammetry (CV), and actuation tests performed applying a square wave of 4 V peak-to-peak at frequencies between 0.3 and 2 Hz are reported and discussed. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Improvement of polypyrrole and carbon nanotube co-deposition techniques for high charge-transfer electrodes
No full textBoth carbon nanotubes (CNTs) and polypyrrole (PPy) have been investigated as materials for manufacturing high charge transfer electrodes due to their outstanding performances. The combination of their complementary properties via an electro chemical co-deposition route has been already shown to achieve interesting results. In this work, PPy and chemically functionalized multi walled CNTs (COOH-MWCNT) were potentiostatically, galvanostatically and potentiodynamically electrodeposited from an aqueous solution to form a nanocomposite on the surface of a variety of metal electrodes. A study of the influence of experimental parameters such as temperature, current, and growth rate in the different electro-deposition methods was performed. The electronic and electro-chemical properties of the nanocomposite films have been studied by cyclic voltammetry and electrochemical impedance spectroscopy, while a morphological study has been performed via scanning electron microscopy. A comparison between the different techniques and guidelines for best results will be reported. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Performance improvement in bucky gel actuators by chemical modifications of carbon nanotubes
No full textSingle walled carbon nanotubes functionalized with an aromatic diamine have been successfully used to prepare bucky gel layers by mixing with an imidazolium based ionic liquid, allowing to build bimorph actuators that significantly outperform those prepared by using the pristine or oxidized carbon nanotubes. The carbon nanotube gravimetric specific capacitance doubles, the actuator maximum operating frequency becomes five times higher and for same injected charge the strain reaches a fourfold increase. The origin of such dramatic effects is most probably due to an enhanced binding between the carbon nanotubes induced by their chemical modification. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Strategies for tuning carbon nanotube plastic actuator performance through material hybridization and the thickness effect: A proof of principle
No full textBucky gel actuators are a kind of electrochemical actuator based on carbon nanotubes having interesting features. They are intrinsically safe because are operated at low voltage, they are lightweight and they are able to work in air without any liquid electrolyte. One key aspect that needs improvement is their actuation speed which is strongly dependent on their ability of being efficiently charged and discharged without exceeding the electrochemical stability window of the electrolyte. By proper material processing, we have successfully addressed this issue. An actuator thickness reduction to one third of the original size results in a one order of magnitude increase of both the strain at higher frequencies and the maximum operating frequency. The strain improvement at high frequency due to thinning has the sole drawback of decreasing the maximum strain that can be achieved in quasi-static conditions. We addressed this second issue by using a proper combination of actuating materials. Oxidative polymerization of pyrrole was carried out directly on preformed bucky gel slurry in order to combine the remarkable properties of ionic actuators based on carbon nanotubes and polypyrrole. A small amount of polypyrrole is sufficient to dramatically improve the overall actuator performance, and by using this hybrid it is possible to obtain thin actuators (about 0.1 mm) with superior performance even at lower frequencies. © 2013 IOP Publishing Ltd
Study on Different Water-Based Binders for Li4Ti5O12 Electrodes
Full text linkIn this study, Li4Ti5O12 (LTO) electrodes with different types of water-soluble binders are successfully coated upon aluminum foil. Electrodes containing solely sodium alginate (SA) as a binder or a mixed PVDF/carboxymethyl cellulose (CMC) binder show the most stable performance in 1 M LiPF6 in EC/DMC 1:1 in half cell vs. Li, with respect to cycle stability over 100 cycles at 1 C. The electrodes processed with a mixture of PVDF/SA show considerable fading and slightly worse values for rate capability. Each one of the different binders used is eco-friendly, and the whole processing can be performed without the use of organic solvents. Further advantages covering the whole production and recycling process, as well as safety issues during operation, encourage deeper research in this area
A Method to Measure the Swelling of Water-Soluble PVDF Binder System and Its Electrochemical Performance for Lithium Ion Batteries
Full text linkWater-soluble CMC/PVDF binder systems were used to prepare graphite anodes and compared mechanically and electrochemically with CMC/SBR binder systems. The effect of crystallinity of PVDF binder on the mechanical and electrochemical performance of the anodes is studied. A contact free method easy to operate and equipped with high accuracy was developed by using capacitance measurement. The swelling of graphite electrodes was controlled and showed different results for different binder crystallinities (no swelling of binder with high crystallinity vs 12% for medium crystallinity and 17% for low crystallinity binder). The discharge capacity depends on the crystallinity of the binders and half-cells delivered a capacity in the range of 230-360 mAh g(-1). The binder with medium crystallinity in particular exhibited the best mechanical and electrochemical performance and showed an excellent C-rate stability with specific capacities up to 10 C. Full cell tests showed good cycling stability over 180 cycles. The water-based PVDF binders seem to be a promising alternative to solvent-based binders. (C) 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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