Academic and industrial research on nanofibres is an area of increasing global interest, as seen in the continuously multiplying number of research papers and patents and the broadening range of ...chemical, medical, electrical and environmental applications. This in turn expands the size of the market opportunity and is reflected in the significant rise of entrepreneurial activities and investments in the field. Electrospinning is probably the most researched top-down method to form nanofibres from a remarkable range of organic and inorganic materials. It is well known and discussed in many comprehensive studies, so why this review? As we read about yet another "novel" method producing multifunctional nanomaterials in grams or milligrams in the laboratory, there is hardly any research addressing how these methods can be safely, consistently and cost-effectively up-scaled. Despite two decades of governmental and private investment, the productivity of nanofibre forming methods is still struggling to meet the increasing demand. This hinders the further integration of nanofibres into practical large-scale applications and limits current uses to niche-markets. Looking into history, this large gap between supply and demand of synthetic fibres was seen and addressed in conventional textile production a century ago. The remarkable achievement was accomplished via extensive collaborative research between academia and industry, applying ingenious solutions and technological convergence from polymer chemistry, physical chemistry, materials science and engineering disciplines. Looking into the present, current advances in electrospinning and nanofibre production are showing similar interdisciplinary technological convergence, and knowledge of industrial textile processing is being combined with new developments in nanofibre forming methods. Moreover, many important parameters in electrospinning and nanofibre spinning methods overlap parameters extensively studied in industrial fibre processing. Thus, this review combines interdisciplinary knowledge from the academia and industry to facilitate technological convergence and offers insight for upscaling electrospinning and nanofibre production. It will examine advances in electrospinning within a framework of large-scale fibre production as well as alternative nanofibre forming methods, providing a comprehensive comparison of conventional and contemporary fibre forming technologies. This study intends to stimulate interest in addressing the issue of scale-up alongside novel developments and applications in nanofibre research.
Extracts of the Quillaja saponaria tree contain natural surfactant molecules called saponins that very efficiently stabilize foams and emulsions. Therefore, such extracts are widely used in several ...technologies. In addition, saponins have demonstrated nontrivial bioactivity and are currently used as essential ingredients in vaccines, food supplements, and other health products. Previous preliminary studies showed that saponins have some peculiar surface properties, such as a very high surface modulus, that may have an important impact on the mechanisms of foam and emulsion stabilization. Here we present a detailed characterization of the main surface properties of highly purified aqueous extracts of Quillaja saponins. Surface tension isotherms showed that the purified Quillaja saponins behave as nonionic surfactants with a relatively high cmc (0.025 wt %). The saponin adsorption isotherm is described well by the Volmer equation, with an area per molecule of close to 1 nm(2). By comparing this area to the molecular dimensions, we deduce that the hydrophobic triterpenoid rings of the saponin molecules lie parallel to the air-water interface, with the hydrophilic glucoside tails protruding into the aqueous phase. Upon small deformation, the saponin adsorption layers exhibit a very high surface dilatational elasticity (280 ± 30 mN/m), a much lower shear elasticity (26 ± 15 mN/m), and a negligible true dilatational surface viscosity. The measured dilatational elasticity is in very good agreement with the theoretical predictions of the Volmer adsorption model (260 mN/m). The measured characteristic adsorption time of the saponin molecules is 4 to 5 orders of magnitude longer than that predicted theoretically for diffusion-controlled adsorption, which means that the saponin adsorption is barrier-controlled around and above the cmc. The perturbed saponin layers relax toward equilibrium in a complex manner, with several relaxation times, the longest of them being around 3 min. Molecular interpretations of the observed trends are proposed when possible. Surprisingly, in the course of our study we found experimentally that the drop shape analysis method (DSA method) shows a systematically lower surface elasticity, in comparison with the other two methods used: Langmuir trough and capillary pressure tensiometry with spherical drops. The possible reasons for the observed discrepancy are discussed, and the final conclusion is that the DSA method has specific problems and may give incorrect results when applied to study the dynamic properties of systems with high surface elasticity, such as adsorption layers of saponins, lipids, fatty acids, solid particles, and some proteins. The last conclusion is particularly important because the DSA method recently became the preferred method for the characterization of fluid interfaces because of its convenience.
We present a genome assembly from an individual male
(the malaria mosquito; Arthropoda; Insecta; Diptera; Culicidae), from a wild population in Cameroon. The genome sequence is 271 megabases in span. ...The majority of the assembly is scaffolded into three chromosomal pseudomolecules with the X sex chromosome assembled. The complete mitochondrial genome was also assembled and is 15.5 kilobases in length.
We present a genome assembly from an individual female
(the malaria mosquito; Arthropoda; Insecta; Diptera; Culicidae), Ifakara strain. The genome sequence is 264 megabases in span. Most of the ...assembly is scaffolded into three chromosomal pseudomolecules with the X sex chromosome assembled. The complete mitochondrial genome was also assembled and is 15.4 kilobases in length.
Ultra fine short fibres have a variety of applications. Short aligned fibres or a mixture of short and long fibres can reinforce brittle materials, alter the appearance, texture and durability of ...synthetic fibres, and adjust the strength, toughness and stiffness of a composite material. Among electrospun products, short fibres are usually produced by secondary processing of continuous as-spun fibres. However, this is not entirely straightforward or cost-effective due to the efficiency of the secondary process and the relatively low tensile strength of the electrospun ultrafine fibres. Besides, sub-micrometre size fibres with an average aspect ratio (AR) <200 have not been directly produced without further processing by changing collector geometry in electrospinning. Using a model polymer, polymethylsilsesquioxane (PMSQ), short micro-fibres with 10 < AR < 200 were electrospun directly in this work, i.e. without the need for a secondary process. The AR and particularly fibre length were shown to be strongly influenced by the solvent system used for electrospinning and the molecular weight (
) of the polymer. When using PMSQ1 (
=7500) in methanol instead of acetone, short fibres with AR <200 were produced instead of continuous fibres. Moreover, when
of the polymer was decreased from 7500 (PMSQ1) to 4300 (PMSQ2), with all other conditions kept constant, significant reduction in the AR of the as-spun fibres was observed. Short fibres with average AR of 15 were produced from PMSQ2 solution in 3:2
v
/
v
dimethylsulphoxide:2-nitropropane. The average AR of short fibres spun from PMSQ2 solution in 2:3
v
/
v
methanol:propanol was 31. Also PMSQ1 in both of the above-mentioned binary solvent systems produced long continuous fibres with AR >3000 under the same spinning conditions.
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•Layers of Tea Saponin, Escin and Berry saponins exhibit visco-elastic behavior.•These layers have very high viscosities and elasticities under dilatational and shear.•Visco-elastic ...behavior is due to the strong attraction between the saponin molecules.•These saponins form surface condensed phases in their adsorption layers.•Experimentally measured elasticities are close to the theoretically calculated ones.
Saponins are natural surfactants with non-trivial surface and aggregation properties which find numerous important applications in several areas (food, pharma, cosmetic and others). In the current paper we study the surface properties of ten saponin extracts, having different molecular structure with respect to the type of their hydrophobic fragment (triterpenoid or steroid aglycone) and the number of sugar chains (1 to 3). We found that the triterpenoid saponins Escin, Tea Saponin and Ginsenosides have area per molecule in the range between 0.5 and 0.7nm2, and the adsorbed molecules are orientated perpendicularly to the interface. The comparison of the experimentally measured surface elasticities with theoretically estimated ones shows that the saponins with very high dilatational and shear elasticities (up to 2000mN/m) have molecular interaction parameter in the adsorption layers which is above the threshold value for two-dimensional phase transition. In other words, the highly elastic layers are in surface condensed state, due to strong attraction between the adsorbed molecules. Furthermore, these adsorption layers have non-linear rheological response upon expansion and contraction, even at relatively small deformation. Layers from the other studied saponins (steroids and crude mixtures of triterpenoid saponins), which are unable to form strong intermolecular bonds within the adsorption layer, have zero shear elasticity and viscosity and low dilatational elasticity and viscosity, comparable in magnitude to those reported in literature for protein adsorption layers. The comparison of the results, obtained by several independent experimental methods, allowed us to formulate the conditions under which the results from different interfacial rheology tests could be compared, despite the complex non-linear response of the saponin adsorption layers.
Saponins are a wide class of natural surfactants, with molecules containing a rigid hydrophobic group (triterpenoid or steroid), connected via glycoside bonds to hydrophilic oligosaccharide chains. ...These surfactants are very good foam stabiliziers and emulsifiers, and show a range of nontrivial biological activities. The molecular mechanisms behind these unusual properties are unknown, and, therefore, the saponins have attracted significant research interest in recent years. In our previous study (Stanimirova et al. Langmuir 2011, 27, 12486-12498), we showed that the triterpenoid saponins extracted from Quillaja saponaria plant (Quillaja saponins) formed adsorption layers with unusually high surface dilatational elasticity, 280 ± 30 mN/m. In this Article, we study the shear rheological properties of the adsorption layers of Quillaja saponins. In addition, we study the surface shear rheological properties of Yucca saponins, which are of steroid type. The experimental results show that the adsorption layers of Yucca saponins exhibit purely viscous rheological response, even at the lowest shear stress applied, whereas the adsorption layers of Quillaja saponins behave like a viscoelastic two-dimensional body. For Quillaja saponins, a single master curve describes the data for the viscoelastic creep compliance versus deformation time, up to a certain critical value of the applied shear stress. Above this value, the layer compliance increases, and the adsorption layers eventually transform into viscous ones. The experimental creep-recovery curves for the viscoelastic layers are fitted very well by compound Voigt rheological model. The obtained results are discussed from the viewpoint of the layer structure and the possible molecular mechanisms, governing the rheological response of the saponin adsorption layers.
We present a genome assembly from an individual female Anopheles gambiae (the malaria mosquito; Arthropoda; Insecta; Diptera; Culicidae), Ifakara strain. The genome sequence is 264 megabases in span. ...Most of the assembly is scaffolded into three chromosomal pseudomolecules with the X sex chromosome assembled. The complete mitochondrial genome was also assembled and is 15.4 kilobases in length.
We present a genome assembly from an individual female Anopheles gambiae (the malaria mosquito; Arthropoda; Insecta; Diptera; Culicidae), Ifakara strain. The genome sequence is 264 megabases in span. ...Most of the assembly is scaffolded into three chromosomal pseudomolecules with the X sex chromosome assembled. The complete mitochondrial genome was also assembled and is 15.4 kilobases in length.
We report on the formation of tea cream of black tea infusions using turbidimetry and time-resolved (static and dynamic) light scattering. In all cases, the ‘equilibrium’ phase diagrams (which are to ...some extent kinetically determined) display similar trends to those of simple mixtures with solubility at high temperatures but separation into immiscible phases below an ‘upper critical solution temperature’. Especially in the more concentrated region of the miscibility gap (>2% w/w), demixing (spinodal decomposition) is the predominant mechanism of cream formation, reflecting the substantial insolubility of polyphenols. Time-resolved light scattering results demonstrate that the (narrow) metastable region of the miscibility gap is in general difficult to access even at low concentrations of tea and small temperature quench depths. Only in the case of a more water-soluble decaffeinated tea material did it prove possible to access such a region, with nucleation and growth then having been demonstrated as the important mechanism.
