Effects of interedge scattering on the Wigner crystallization in graphene nanoribbons

We investigate the effects of coupling between the two zigzag edges of graphene nanoribbons on the Wigner crystallization of electrons and holes using a combination of tight-binding, mean field Hubbard and many-body configuration interaction methods. We show that the thickness of the nanoribbon plays a crucial role in the formation of Wigner crystal. For ribbon widths smaller than 16 \mbox{\AA}, increased kinetic energy overcomes the long-range Coulomb repulsion and suppresses the Wigner crystallization. For wider ribbons up to 38 \mbox{\AA} wide, strong Wigner localization is observed for even number of electrons, revealing an even-odd effect also found in Coulomb blockade addition spectrum. Interedge correlations are found to be strong enough to allow simultaneous crystallization on both edges, although an applied electric field can decouple the two edges. Finally, we show that Wigner crystallization can also occurs for holes, albeit weaker than for electrons.Comment: Accepted for publication in PR

Morphology and ion diffusion in PEDOT:Tos. A coarse grained molecular dynamics simulation

A Martini coarse-grained Molecular Dynamics (MD) model for the doped conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is developed. The morphology of PEDOT:Tos (i.e. PEDOT doped with molecular tosylate) and its crystallization in aqueous solution for different oxidation levels were calculated using the developed method and compared with corresponding all atomistic MD simulations. The diffusion coefficients of Na+ and Cl- ions in PEDOT:Tos are studied using the developed coarse-grained MD approach. It is shown that the diffusion coefficients decrease exponentially as the hydration level is reduced. It is also predicted that the diffusion coefficients decrease when the doping level of PEDOT is increased. The observed behavior is related to the evolution of water clusters and trapping of ions around the polymer matrix as the hydration level changes. The predicted behavior of the ionic diffusion coefficients can be tested experimentally, and we believe that molecular picture of ionic diffusion in PEDOT unraveled in the present study is instrumental for the design of polymeric materials and devices for better and enhanced performance.This work was supported by the Troëdssons foundation (896/16), Knut and Alice Wallenberg Foundation through the project The Tail of the Sun, and the Swedish Research Council via ‘‘Research Environment grant’’ on ‘‘Disposable paper fuel cells’’ (201605990). IZ thanks the Advanced Functional Material center at Linköping University for financial support

Why does solvent treatment increase the conductivity of PEDOT : PSS? Insight from molecular dynamics simulations

Poly(3,4-ethylenedioxythiophene) : polystyrene sulfonate (PEDOT : PSS) is one of the most important conducting polymers. In its pristine form its electrical conductivity is low, but it can be enhanced by several orders of magnitude by solvent treatment, e.g. dimethyl sulfoxide (DMSO). There are various (and often conflicting) explanations of this effect suggested in the experimental literature, but its theoretical understanding based on simulation and modelling accounting for the complex realistic morphology of PEDOT : PSS is missing. Here, we report Martini coarse-grained molecular dynamics simulation for the DMSO solvent treatment of the PEDOT : PSS film. We show that during solvent treatment a part of the deprotonated PSS chains are dissolved in the electrolyte. After the solvent treatment and subsequent drying, the PEDOT-rich regions become closer to each other, with a part of the PEDOT chains penetrating into the PSS-rich regions. This leads to an efficient coupling between PEDOT-rich regions, leading to the enhancement of the conductivity. Another factor leading to the conductivity improvement is the pi-pi stacking enhancement resulting in more pi-pi stacks in the film and in the increased average size of PEDOT crystallites. Our results demonstrate that course-grained molecular dynamics simulations of a realistic system represent a powerful tool enabling theoretical understanding of important morphological features of conducting polymers, which, in turn, represents a prerequisite for materials design and improvement.Funding Agencies|Swedish Research Council [2016-05990, 2017-04474]; Aforsk</p

Loneliness and Its Related Factors among Elderly People in Yazd

Introduction: Old people appear to be most prone to loneliness and depression perhaps because of decrease in their ability in daily livings, increase in morbidity, loss of close ties caused by loss of friends and spouses. This study was conducted for investigation of the loneliness and its related factors in elderly people in Yazd. Methods: In this cross sectional study, 200 old people (over 60 years old) from three zone; health centers, nursing home and retirement center by convenient sampling method. Data was collected by UCLA Loneliness Scale that was consisting of 20 items for loneliness measurement. Scores 41 and more defined as loneliness. Collected data was analyzed by proper statistical tests with SPSS software. Results: Results showed that 71 % of subjects had Not Feel Lonely, 24 % moderate and 5 % severe felling of loneliness. Factors such as level of education, marital status, numbers of daughter and sons, previous job, residence site, current job status, living in nursing home, insufficient income, place of praying, sleep quantity and quality of sleep and feeling of healthy were associated with&nbsp; loneliness status (p < 0.05). Conclusion: Our findings showed loneliness is common in elderly that support needs for more investigations and attention to loneliness related factors, educational courses conduction for family to take care of their elders, preparing of recreational measures and social support groups to decrease the loneliness in old people and so they spend this period by good and healthy sensation.&nbsp

Computational microscopy study of the granular structure and pH dependence of PEDOT:PSS

Computational microscopy based on Martini coarse grained molecular dynamics (MD) simulations of a doped conducting polymer poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (best known as PEDOT:PSS) was performed focussing on the formation of the granular structure and PEDOT crystallites, and the effect of pH on the material morphology. The PEDOT:PSS morphology is shown to be sensitive to the initial distribution of PEDOT and PSS in the solution, and the results of the modelling suggest that the experimentally observed granular structure of PEDOT:PSS can be only obtained if the PEDOT/PSS solution is in the dispersive state in the initial crystallization stages. Variation of the pH is demonstrated to strongly affect the morphology of PEDOT:PSS films, altering their structure between granular-type and homogeneous. It also affects the size of crystallites and the relative arrangement of PEDOT and PSS chains. It is shown that the crystallites in PEDOT:PSS are smaller than those in PEDOT with molecular counterions such as PEDOT:tosylate, which is consistent with the available experimental data. The predicted changes of the PEDOT:PSS morphology with variation of the pH can be tested experimentally, and the calculated atomistic picture of PEDOT:PSS films (not accessible by conventional experimental techniques) is instrumental for understanding the material structure and building realistic models of PEDOT:PSS morphology.Funding Agencies|Troedssons foundation [896/16]; Peter Wallenberg foundation [PWS-2016-0010]; Swedish Research Council via "Research Environment grant" on "Disposable paper fuel cells" [2016 05990]; Swedish Research Council [2017-04474]; Swedish Energy Agency [43561-1]; Advanced Functional Material center at Linkoping University</p

Morphology and ion diffusion in PEDOT:Tos. A coarse grained molecular dynamics simulation

A Martini coarse-grained Molecular Dynamics (MD) model for the doped conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is developed. The morphology of PEDOT:Tos (i.e. PEDOT doped with molecular tosylate) and its crystallization in aqueous solution for different oxidation levels were calculated using the developed method and compared with corresponding all atomistic MD simulations. The diffusion coefficients of Na+ and Cl- ions in PEDOT:Tos are studied using the developed coarse-grained MD approach. It is shown that the diffusion coefficients decrease exponentially as the hydration level is reduced. It is also predicted that the diffusion coefficients decrease when the doping level of PEDOT is increased. The observed behavior is related to the evolution of water clusters and trapping of ions around the polymer matrix as the hydration level changes. The predicted behavior of the ionic diffusion coefficients can be tested experimentally, and we believe that molecular picture of ionic diffusion in PEDOT unraveled in the present study is instrumental for the design of polymeric materials and devices for better and enhanced performance.Funding Agencies|Troedssons foundation [896/16]; Knut and Alice Wallenberg Foundation through the project The Tail of the Sun; Swedish Research Council [201605990]; Advanced Functional Material center at Linkoping University</p

Bundeshaushalt 1988 [neunzehnhundertachtundachtzig]: verlaessl. u. vertrauensbildende Finanzpolitik ; Rede d. Bundesministers ... Gerhard Stoltenberg am 9. September 1987 im Dt. Bundestag ; mit Erlaeuterungen

SIGLEAvailable from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, Duesternbrook Weg 120, D-24105 Kiel A 169173 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

What Can We Learn about PEDOT:PSS Morphology from Molecular Dynamics Simulations of Ionic Diffusion?

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate(PEDOT:PSS)is one of the most important mixed electron-ion conducting polymers,where the efficiency of the ion transport is crucial for many of itsapplications. Despite the impressive experimental progress in thedetermination of ionic mobilities in PEDOT:PSS, the fundamentals ofion transport in this material remain poorly understood, and the theoreticalinsight into the ion diffusion on the microscopical level is completelymissing. In the present paper, a Martini 3 coarse-grained moleculardynamics (MD) model for PEDOT:PSS is developed and applied to calculatethe ion diffusion coefficients and ion distribution in the film. Wefind that the ion diffusion coefficients for Na+ ions arepractically the same in the PEDOT-rich and PSS-rich regions and donot show sensitivity to the oxidation level. We compare the calculateddiffusion coefficients with available experimental results. Basedon this comparison and based on the MD morphology simulation of PEDOT:PSSrevealing the formation of pores inside the film, we revise a commonlyaccepted granular morphological model of PEDOT:PSS. Namely, we arguethat PEDOT:PSS films, in addition to PEDOT-rich and PSS-rich regions,must contain a network of pores where the ion diffusion takes place.Funding Agencies|Wallenberg Wood Science Center; Knut and Alice Wallenberg Foundation (project "H2O2"); Swedish e-Science Research Centre (SeRC)</p