1,720,992 research outputs found
Ordering kinetics in two-dimensional hexagonal pattern of cylinder-forming PS-b-PMMA block copolymer thin films: Dependence on the segregation strength
No full textEnabling data-driven design of block copolymer self-assembly
Full text linkHere we present a database composed of scanning electron microscope images of self-assembled block copolymers. The fabrication process parameters, structural properties and microscope information are all contained in the image metadata, making a group of images a database on its own. This approach has numerous advantages including ease of sharing, reusability of information and resilience against user errors. This database follows the digital International System of Units principles and is complemented by a graphical user interface for process metadata insertion and an automated algorithm for image analysis to retrieve structural properties of the nanostructures. Databases such as this one, together with data-driven approaches, enable users to rationally design new materials with the desired properties by understanding the relationship between fabrication parameters and material structure. The here reported database, that contains around 1747 images of lamellar phase and lying down cylinders self-assembled block copolymers along with associated metadata, is structured so it can be continuously expanded by the research community including also samples with different block copolymers morphologies
Composition of ultrathin binary polymer brushes by thermogravimetry-gas chromatography-mass spectrometry
No full textIn the present paper, a reliable and rugged thermogravimetry-gas chromatography-mass spectrometry (TGA-GC-MS) method was developed to determine the composition of ultrathin films consisting of binary blends of functional polystyrene (PS) and polymethylmethacrylate (PMMA) grafted to a silicon wafer. A general methodology will be given to address the composition determination problem for binary or even multicomponent polymer brush systems using the PS/PMMA-based samples as a paradigmatic example. In this respect, several distinct tailor-made materials were developed to ensure reliable calibration and validation stages. The analytical method was tested on unknown samples to follow the composition evolution in PS/PMMA brushes during the grafting reaction. A preferential grafting of the PMMA was revealed in full agreement with its preferential interaction with the SiO2 polar surface
Enhanced Lateral Ordering in Cylinder Forming PS-b-PMMA Block Copolymers Exploiting the Entrapped Solvent
No full textCharacterization of ultra-thin polymeric films by Gas chromatography-Mass spectrometry hyphenated to thermogravimetry
No full textPolymeric materials are widely employed to build up tunable nanomasks for nano-patterning technologies. Ultrathin polymer layers are involved in this process. A Thermo Gravimetric Analysis-Mass Spectrometry (TGA-GC-MS) method was optimised, validated and successfully applied to investigate the thermal behavior of ultrathin poly(styrene-r-methylmethacrylate) random copolymer layers P(S-r-MMA) grafted to a silicon wafer surface. The interface between TGA and MS is highly versatile since many instrumental parameters (i.e. loop volumes, pulsed sampling frequencies, acquisition modalities, carrier gases, flow rates) can be easily tuned. Samples featuring substantial scale difference, i.e. bulk materials, thick films (few μm thickness), thin and ultrathin films (few nm thickness) can be analyzed without any instrumental modification or sample pretreatments. The TGA-GC-MS analysis was used to highlight subtle differences in samples featuring different thicknesses, in the 2-6 nm range, and subjected to various thermal treatments, thus indicating that this hyphenated technique could be successfully applied to the investigation of ultrathin polymer films
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
TGA-GC-MS quantitative analysis of phosphorus-end capped functional polymers in bulk and ultrathin films
No full textAn hyphenated method based on thermal gravimetric, gas chromatographic and mass spectrometric analyses (TGA-GC-MS) is proposed for the quantitative analysis of diethylphosphate-end capped polymers with varying chain length, in bulk and as ultra thin film. The method fully calibrated and validated, revealed a powerful and affordable tool in the determination of the amount of phosphorous in polymeric samples but also it allows the determination of the number of repeating units per chain end.
Compared to the common techniques, namely NMR spectroscopy and ICP-MS, no sample pretreatments are required. Consequently, polymeric films supported on inert substrates can be directly analyzed. The quantitative calibration, obtained for bulk materials, was demonstrated to be accurate also for films of different thickness. In this frame, the method revealed highly sensitive thus allowing the phosphorous determination even in ultrathin films with thickness of few tens of nanometers.
Finally, the chromatographic profile of the species evolving during the thermal degradation was found to depend on the polymeric film thickness. This implies that information concerning the polymer stability and degradation mechanism at different size scale can be obtained.
Considering the widespread interest for thin and ultrathin films of polymers containing phosphorous groups for brush-based technologies, the proposed method can be helpful in various areas, including flame retardant material, healthcare and medicine, microelectronic, for facile and precise characterization of functional interfaces
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