1,721,104 research outputs found
How long are polymer chains in poly(3,4- ethylenedioxythiophene):tosylate films? An insight from molecular dynamics simulations
No full text11 p.-7 fig.-1 graph. abst.Poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most important conductive polymers utilized in a
variety of applications in organic electronics and bioelectronics and energy storage. PEDOT chains are believed to be rather short, but detailed knowledge of their length is missing because of the challenges in its experimental determination due to insolubility of PEDOT films. Here, we report a molecular dynamics (MD) study of in situ oxidative chemical polymerization and simultaneous crystallization of molecularly doped PEDOT focusing on the determination of its chain lengths at different polymerization temperatures. We find the average chain length to be 6, 7, and 11 monomers for 298, 323 and 373 K, respectively. At the same time,
the length distribution is rather broad, for example, between 2 and 16 monomer units for T = 323 K. We demonstrate that the limiting factor determining the chain length is the diffusivity of the reactants (PEDOT monomers and oligomers). We also study the polymer film formation during solvent evaporation, and we find
that although crystallization starts and proceeds already during the polymerization and doping phases, it mostly occurs during the evaporation phase. Finally, we believe that our results providing the oligomer chain length and polymerization and crystallization mechanisms obtained by means of MD “computational microscopy” provide an important insight into the morphology of PEDOT that cannot be obtained by other means.This work was supported by the Swedish Research Council (2016-05990 and 2017-04474).Peer reviewe
Large scale mobility calculations in PEDOT (Poly(3,4- ethylenedioxythiophene)): Backmapping the coarse-grained MARTINI morphology
No full text8 p.-4 fig.Designing new high performances materials based on conducting polymers necessitates the development of multiscale models to investigate the charge transport in large realistic systems. In this work, we utilize Coarse-Grained (CG) Molecular Dynamics (MD) simulations to generate morphologies of Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with Tosylate (TOS) ions, and we develop a backmapping protocol to retrieve the atomistic details of the molecules afterwards. We demonstrate that the proposed protocol corrects for the nanostructure distortions induced by Coarse-Graining the system, namely a wrong density and an over-estimated stacking distance. Quantum chemical calculations are performed on the systems obtained after backmapping in order to calculate hopping rates for charge transport, and charge mobilities as a function of the PEDOT chain length and hydration level are then calculated by solving a master equation for transport. The results are identical to the calculations performed on PEDOT morphologies obtained by direct All-Atomistic (AA) MD simulations: the mobility increases with the chain length and decreases with the hydration level, this last effect being more pronounced for short chains. This definitely shows that the workflow CG MD backmapping mobility calculations is in position to calculate charge mobility in PEDOT based materials, paving the way for theoretical investigations of transport in more complex materials such as PEDOT doped with Polystyrene Sulfonate (PSS).This research was funded by KAW foundation grant Tail of the Sun,and the Swedish Research Council Grant No. 2016-05990 and 2017-04474, and the Advanced Functional Material center at Linköping University.Peer reviewe
Doping Efficiency of Poly(benzodifurandione) from First Principles [Elektronisk resurs]
No full textPoly(benzodifurandione) (PBFDO) has emerged as a promising n-type conductive polymer (n-CP) for organic electronic applications, particularly in thermoelectrics (TE), due to its high doping efficiency and environmental stability. Unlike most high-performance p-type polymers, high-efficiency n-CPs are limited, posing a bottleneck in the TE module performance. In this study, we use first-principles electronic structure calculations to investigate the thermodynamic conditions that favor n-doping in PBFDO, focusing on the role of the temperature, chain length, and doping concentration. We compute the change in Gibbs free energy, Delta G, upon doping and explore how it varies with temperature and polymer chain length. Our results show that doping becomes more thermodynamically favorable at lower temperatures and in longer chains, with a strong dependence of Delta G on the doping level emerging as chain length increases. Notably, PBFDO can achieve favorable doping levels across various chain lengths and temperatures, with specific doping thresholds identified for different molecular weights. These findings suggest that lower synthesis temperatures could lead to more heavily doped, higher-conductivity PBFDO, and that chain length significantly influences achievable doping efficiency. This work provides insights for optimizing PBFDO doping strategies to enhance its performance in TE applications, bridging a key gap in organic semiconductor research.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Anisotropic Lattice Thermal Conductivity in Highly Ordered PEDOT Fibers
No full textWhen it comes to sustainable and efficient energy solutions, organic semiconductors can play an important role in thermoelectric applications, since they are non-toxic, cheap, made of abundant chemical species, and show intrinsically low thermal conductivities. Their electrical conductivity can be optimized via doping. Yet, thermal conduction should be as low as possible and, to this end, the atomic scale mechanisms behind heat transport –e.g. the correlation between morphology and thermal conductivity or the role of doping– should be understood in detail. Fully atomistic molecular dynamics calculations of the lattice thermal conductivity of doped poly(3,4-ethylenedioxythiophene) (PEDOT) highly ordered, quasi-crystalline nanofibers are presented here. It is found that the conductivity along the backbone direction is not necessarily the highest, but it depends on the length of the PEDOT chains, thus the degree of anisotropy depends on the the aspect ratio of the nanofiber. Indeed, transport along the lamellar direction can be of the same order or higher than that of the backbone if their lengths are comparable. These results challenge the usual expectation that thermal conduction along the backbone largely exceeds those along the lamellar and π − π direction and have the important consequence that the anisotropy could be leveraged in thermal management applications.This work was financially supported by the European Commission through the Marie Skłodowska-Curie projects HORATES (GA-955837), by MCIN/AEI/10.13039/501100011033 under grant PID2020-119777GB-I00, and the Severo Ochoa Centres of Excellence Program under grant CEX2019-000917-S, and by the Generalitat de Catalunya under grant no. and 2017 SGR 1506. The work of PSF has been carried out within the PhD program in Physics of the Universitat Autònoma de Barcelona (UAB). We thank the Centro de Supercomputación de Galicia (CESGA) and National Academic Infrastructure for Supercomputing in Sweden (NAISS) for the use of their computational resources.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe
Variations on the Author
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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