1,720,978 research outputs found
Polymer-dispersed liquid crystal elastomers
Full text linkThe need for mechanical manipulation during the curing of conventional liquid crystal elastomers diminishes their applicability in the field of shape-programmable soft materials and future applications in additive manufacturing. Here we report on polymer-dispersed liquid crystal elastomers, novel composite materials that eliminate this difficulty. Their thermal shape memory anisotropy is imprinted by curing in external magnetic field, providing for conventional moulding of macroscopically sized soft, thermomechanically active elastic objects of general shapes. The binary soft-soft composition of isotropic elastomer matrix, filled with freeze-fracture-fabricated, oriented liquid crystal elastomer microparticles as colloidal inclusions, allows for fine-tuning of thermal morphing behaviour. This is accomplished by adjusting the concentration, spatial distribution and orientation of microparticles or using blends of microparticles with different thermomechanical characteristics. We demonstrate that any Gaussian thermomechanical deformation mode (bend, cup, saddle, left and right twist) of a planar sample, as well as beat-like actuation, is attainable with bilayer microparticle configurations
Actuation of Gold-Coated Liquid Crystal Elastomers
No full textWe demonstrate that gold layers are a promising candidate for resistive heating actuation of liquid crystalline elastomers at moderate strains of around 10% and with good repeatability up to a few 10 kilocycles. These composites are easy to manufacture and have suitable resistivity to be actuated with low-voltage power supplies. The mechanical and electrical properties of such materials are investigated and the observed resistance changes are explained in terms of a percolation model
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
Liquid single crystal elastomer/conducting polymer bilayer composite actuator: Modelling and experiments
No full textIn order to integrate electroconductive properties in a Liquid Single Crystal Elastomer (LSCE) and to test direct actuation of the LSCE by Joule heating, we present a new bi-layered all-organic composite actuator based on the coupling of a nematic LSCE with a conductive polymer. The bending actuator is fabricated by depositing a thin conductive polymer layer of poly(3,4- ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) over the surface of a polysiloxane-based monodomain nematic LSCE film. Mechanical properties of PEDOT:PSS, better matched with LSCE ones compared with metals or inorganic nanoparticles used in other approaches, allowed us to develop an all-organic reliable millimetre-scale actuating composite. The thermally induced elongation/compression of the LSCE over 30% is exploited for the fabrication of bending actuators with curvature up to κ = 0.64 mm-1. The LSCE and the composite material are characterized as regards their thermo-mechanical and electrical properties. A model is introduced to describe bending of the composite as a function of the thermo-mechanical properties of the LSCE, and the model is assessed by comparing the model results with the experimental findings. Bending actuation via direct Joule heating of the composite is also assessed by supplying the necessary current (50 mA at 1.3 V) through wires connected to the composite. These results open new possibilities for the application of LCEs in the micro and soft robotics fields, as well as in the biomedical field. © 2013 The Royal Society of Chemistry
Brief overview on 2H NMR studies of polysiloxane-based side-chain nematic elastomers
No full textThis is a brief overview on recent studies on liquid crystalline elastomers (LCEs) based on polysiloxane chain, in the form of monodomain films, selectively H-2-labeled in different parts of the LCE samples, i.e. on the crosslinker or mesogenic units. H-2 NMR spectroscopic techniques were used to measure the temperature dependence of the quadrupolar splittings, line widths and relaxation times, T-1 and T-2. From these data, several information about the orientational order parameter, S, of various LCE fragments, thermodynamic features of the isotropic-nematic transition and main motional processes could be generalized for this type of elastomers
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
A Photosensitive Liquid Crystal Studied by 14N NMR, 2H NMR, and DFT Calculations
No full textAn azobenzene derivative, namely diheptylazobenzene, showing the nematic and smectic A liquid crystalline phases, was investigated by means of a combined approach based on NMR and DFT calculations. 14N NMR quadrupole- and chemical-shift-perturbed spectra were acquired in the whole mesophasic range, providing both experimental quadrupolar splittings and chemical shift anisotropy values. On the same mesogen, deuterium labelled at the α-position of the hydrocarbon chain, 2H NMR quadrupole-perturbed spectra were recorded. The analysis of these NMR data was performed with the help of ab initio calculations, in vacuo and by taking into account the effect of the anisotropic environment typical of liquid crystals, by using the IEF-PCM model. The geometry optimizations of the azomesogen in the trans and cis configurations were performed by DFT calculations employing the combination of B3LYP functional with the 6-311G(d) basis set. The analysis of experimental NMR data was performed by considering the trans configuration as the most populated one and the corresponding quadrupolar tensors and chemical shielding tensors were determined at the DFT level of theory. The main result of this work is the determination of a relatively high and temperature-dependent molecular biaxiality of the trans state of this azomesoge
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