1,721,096 research outputs found
Monte Carlo Simulation of Coarse Grain Polymeric Systems
No full textWe introduce a particle-based Monte Carlo formalism for the study of polymeric melts, where the interaction energy is given by a local density functional, as is done in traditional field-theoretic models. The method enables Monte Carlo simulations in arbitrary ensembles and direct calculation of free energies. We present results for the phase diagram and the critical point of a binary homopolymer blend. For a symmetric diblock copolymer, we compute the distribution of local stress in lamellae and locate the order-disorder transition
Defect Removal in the Course of Directed Self-Assembly is Facilitated in the Vicinity of the Order-Disorder Transition
No full textThe stability of prototypical defect morphologies in thin films of symmetric diblock copolymers on chemically patterned substrates is investigated by self-consistent field theory. The excess free energy of defects and barriers of defect-removal mechanisms are obtained by computing the minimum free-energy path. Distinct defect-removal mechanisms are illustrated demonstrating that (i) defects will become unstable at a characteristic value of incompatibility chi N- above the order-disorder transition and (ii) the kinetics is accelerated at weak segregation. Numerical findings are placed in the context of physical mechanisms, and implications for directed self-assembly are discussed
Simulations of theoretically informed coarse grain models of polymeric systems
No full textSimulations of theoretically informed coarse grain models, where the interaction energy is given by a functional of the local density, are discussed in the context of polymeric melts. Two different implementations are presented by addressing two examples. The first relies on a grid-based representation of non-bonded interactions and focuses on the concept of density multiplication in block copolymer lithography. Monte Carlo simulations are used in a high-throughput manner to explore the parameter space, and to identify morphologies amenable to lithographic fabrication. In the second example, which focuses on the order disorder transition of block copolymers, the constraints imposed by a grid are removed, thereby enabling simulations in arbitrary ensembles and direct calculation of local stresses and free energies
Morphology of multi-component polymer systems: single chain in mean field simulation studies
No full textRecent work exploring phase separation and self-assembly in multicomponent polymer fluids using a particle-based self-consistent field simulation method is reviewed. The computational method is placed in the context of classical molecular dynamics and Monte Carlo simulations as well as field-theoretic approaches. Its potential is illustrated by applications ranging from spinodal decomposition in symmetric polymer blends and the ordering of diblock copolymers in the bulk to more complex phenomena such as solvent evaporation from thin polymer films and the fabrication of three-dimensional bicontinuous diblock copolymer morphologies via reconstruction on patterned substrates
Free Energy of Defects in Ordered Assemblies of Block Copolymer Domains
No full textWe investigate commonly occurring defects in block copolymer thin films asembled on chemically nanopatterned substrates. and predict their probability of occurence by computing their free energies. A theoretically informed 3D coarse. grain model is used to describe the system. These defects substrate increases and when partial defects occur close to the top surface of the flim. The results presented defects. here reveal an extraordinarily large thermodynamic driving force for the elimination of defects. When the characteristics of the substrate are commensurate with the morphology of the block copolymer, the probability of creating a defect is extremely small and well below the specifications of the semiconductor industry for fabrication of features having characteristic dimensions on the scale of nanometers. We also investigate how the occurrence of defect change's when imperfections arise in the underlysing patterns and find that, while defects continue to be remarkably unstable, stretched patterns are more permissive than compressed patterns
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
Dimensions and shapes of block copolymer domains assembled on lithographically defined chemically patterned substrates
No full textThin films of a nearly symmetric lamellae-forming diblock copolymer of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) having a bulk repeat period, L-O, were directed to assemble vertically away from chemically nanopatterned striped substrates (having a periodicity L-S) that consisted of alternating stripes that were preferentially wet by the two blocks of the copolymer. The relative widths of the adjacent stripes were systematically varied such that the normalized line width of the chemical surface pattern, defined as the width of the stripe that was wet by the styrene block of the block copolymer, W, divided by the constant chemical surface pattern period, L-s had values between 0.30 and 0.65. On chemical surface patterns with L-S approximate to L-O the diblock copolymer domains formed defect-free perpendicular arrays if the normalized line width W/L-S, was between 0.36 and 0.63. On chemical surface patterns with L-S not equal L-O, the range of W/L-S capable of inducing defect free arrays decreased as the difference between L-S and L-O increased. Single-chain-in-mean-field (SCMF) simulations provided information on the dimensions and shapes of the block copolymer domains. The SCMF simulations indicated that the widths of the lamellae at half film thickness were 0.47L(S) independent of W/L-S and the angle of the interface between the vertically oriented domains remained within 11 degrees of the substrate normal over the range of experimentally relevant values of W/L-S
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