1,721,035 research outputs found
SLE3S-water system: a linear rheological characterisation
No full textSurfactant-water mixtures display a complex rheological behaviour, with changes in parameters such as viscosity and moduli of several orders of magnitude as a consequence of phase changes, depending on their concentration and temperature: this criticism heavily affects different industrial processes. In our work, linear rheological behaviour of aqueous mixtures of a commercial anionic surfactant, sodium lauryl ether sulphate, is investigated in a range of temperature (30-60 ?) and surfactant concentration (20-72%wt) of technological relevance. Four phases with different texture are identified by polarised light microscopy: micellar, hexagonal, cubic and lamellar, all showing a shear-thinning behaviour. Rheological parameters of cubic phase show a net jump in a relatively narrow temperature range, suggesting a temperature-induced phase change. The systematic analysis of the rheological behaviour of this widely used surfactant system, reported here for the first time, can be of fundamental support for many industrial applications
Methodology for the investigation of surfactant dissolution in water
No full textConcentrated aqueous solutions of surfactants pastes are widely used in industrial productions. The dissolution phenomena of these fluids in water is difficult to optimize, given the thermodynamic complexity of the system, that adds further resistance to the mass transport efficiency. One of the most common anionic surfactants is Sodium Lauryl Ether Sulphate (SLE3S). Depending on the SLE3S-water composition, surfactant nano-molecules can assume different morphologies, such as micellar phases (30%wt), cubic structures (~60%wt), or lamellar liquid crystals (>60%wt), which are characterized by nanoscale ordered structures. Different phases show strongly different rheological behaviour. All phases are non-Newtonian, with a shear-thinning viscosity as function of imposed shear rate. A novel methodology is here proposed to investigate the dynamic evolution of the phase changes during surfactant dissolution using Time-lapse microscopy. Samples are observed trough crossed polarizers. Differences in nano-morphology, due to molecules rearrangement during phase changes, can be easily monitored by measuring light intensity profiles
Microconfined shear deformation of a droplet in an equiviscous non-Newtonian immiscible fluid: Experiments and modelling
No full textA Low-Cost, User-Friendly Rheo-Optical Compression Assay to Measure Mechanical Properties of Cell Spheroids in Standard Cell Culture Plates
Get PDFThe mechanical characterization of cell spheroids, one of the most widely used 3D biology models in vitro, is a hotspot of current research on the role played by the mechanical response of cells and tissues. The techniques proposed so far in the literature, while providing important scientific insights, require specialized equipment and technical skills that are not usually available in cell biology facilities. Here, an innovative rheo-optical compression assay is presented: it is based on microscopy glass coverslips as the load is applied to cell spheroids in standard cell culture plates and on image acquisition with an optical microscope or even a smartphone equipped with adequate magnification lenses. Mechanical properties can be simply obtained by correlating the applied load to the deformation of cell spheroids measured by image analysis. The low-cost, user-friendly features of the proposed technique can boost mechanobiology research making it easily affordable to any biomedical lab equipped with cell culture facilities
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
Compressional stress stiffening & softening of soft hydrogels - how to avoid artefacts in their rheological characterisation
No full text: Hydrogels have been successfully employed as analogues of the extracellular matrix to study biological processes such as cells' migration, growth, adhesion and differentiation. These are governed by many factors, including the mechanical properties of hydrogels; yet, a one-to-one correlation between the viscoelastic properties of gels and cell fate is still missing from literature. In this work we provide experimental evidence supporting a possible explanation for the persistence of this knowledge gap. In particular, we have employed common tissues' surrogates such as polyacrylamide and agarose gels to elucidate a potential pitfall occurring when performing rheological characterisations of soft-materials. The issue is related to (i) the normal force applied to the samples prior to performing the rheological measurements, which may easily drive the outcomes of the investigation outside the materials' linear viscoelastic regime, especially when tests are performed with (ii) geometrical tools having unbefitting dimensions (i.e., too small). We corroborate that biomimetic hydrogels can show either compressional stress softening or stiffening, and we provide a simple solution to quench these undesired phenomena, which would likely lead to potentially misleading conclusions if they were not mitigated by a good practice in performing rheological measurements, as elucidated in this work
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
Use of common gamma-chain cytokines for the visualization, isolation and genetic modification of memory T lymphocytes
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