1,720,973 research outputs found
Electro-Responsive Green Gels for Lower Environmental Impact Shale Gas Extraction
Full text linkIn this work, carbon black (CB) is added in small amounts (3-10% w/w) to green aqueous dispersions based on sodium oleate, guar gum, sodium hyaluronate, or hydroxypropyl cellulose gels to enhance their stability against mechanical and thermal stresses and to provide electric responsiveness to an external voltage. Rheology, optical microscopy, small angle X-ray scattering, and conductivity measurements are performed to compare the properties of CB-enriched formulations to those of pristine dispersions. Our results demonstrate that even small amounts of CB are able to confer interesting physicochemical properties to these formulations: a remarkable increase in the viscosity of at least 1 order of magnitude is observed for all systems even at high temperature (up to 60 °C) upon CB addition, indicating that carbonaceous particles play a structuring role for the polymeric network. Furthermore, the application of an external voltage of 30 V for 60 min to CB-containing formulations imparts a significant electric responsiveness to the systems, allowing the modification of their rheological behavior. The CB-loaded formulations can be recycled at least three times. All these results suggest that CB can be effectively used as an alternative green additive to enhance the mechanical and thermal stabilities of the formulations and that its addition can be a feasible way to easily tune the properties of viscoelastic materials, thereby avoiding the use of toxic or potentially dangerous chemicals. The possibility of achieving remote control of mechanical and thermal properties of viscoelastic formulations significantly expands the horizon of their potential applications, for example, in the field of shale gas extraction
Physicochemical characterization of green sodium oleate-based formulations. Part 2. Effect of anions
No full textHypothesis: In Part 1 of this work we reported the behavior of a moderately concentrated dispersion of sodium oleate (NaOL) in water that produces elongated wormlike micelles (WLMs). Prompted by the striking effect induced by adding potassium chloride to the original NaOL dispersion, here we investigate the effect of different anions (with fixed cation) on NaOL or KOL-based hydrogels upon addition of different strong electrolytes. The interest in these investigations relies on the fact that they are among the best candidates for the production of eco-friendly stimulus-responsive materials. Experimental: The thermal and rheological properties of a 0.43 M dispersion of NaOL or KOL in water were investigated by steady-state and oscillatory rheology, and DSC experiments in the presence of different potassium or sodium salts at the same concentration (0.54 m), respectively. Findings: This paper highlights the occurrence of a Hofmeister phenomenon in the case of oleate-based WLMs and illustrates the remarkable effect induced by kosmotropic and chaotropic anions in terms of rheology and hydration of the rod-like nanoassemblies, that reflect the different ion adsorption at the WLM interface. We also discuss the different ion condensation of sodium and potassium ions at the interface that can lead to a significant change in the curvature of the elongated rods
Specific ion effects in polysaccharide dispersions
No full textThe specific effects induced by some strong electrolytes or neutral co-solutes on aqueous mixtures of guar gum (GG), sodium alginate (SA) and sodium hyaluronate (SH) were studied through rheology and DSC experiments. The results are discussed in terms of changes in the polymer conformation, structure of the network and hydration properties. This study is also aimed at controlling the viscosity of the aqueous mixtures for application in green formulations to be used as fracturing fluids for shale gas extraction plants
Structuring effect of some salts on glycerol carbonate: A near-infrared spectroscopy, small- and wide-angle X-ray scattering study
No full textAlkylene carbonates such as ethylene, glycerol and propylene carbonates offer a valuable tool for the investigation of intermolecular interactions in polar non-aqueous liquids. Their physico-chemical properties suggest the presence of a strong structure that mainly depends on hydrogen bonds. The addition of salts bearing basic anions such as fluoride, carbonate and phosphate leads to the formation of free ions and ion pairs that are well accommodated in the solvent structure. In this work near infrared and attenuated total reflection Fourier-transform infrared spectroscopy, small- and wide-angle X-ray scattering were carried out on pure glycerol carbonate and on its solutions of saturated KF, K2CO3 and K3PO4 in order to probe the structure of the solvent. Linear and cyclic oligomeric clusters produced by the association of the liquid molecules are proposed. The different effectiveness of the studied anions in enhancing the internal arrangement of the liquid can be explained in terms of polarizability (i.e. of the delocalization of their charge), different basicity and hydrogen bonding (HB) accepting capacity and geometry of the anions
Ionochromism, solvatochromism and effect of dissolved gases on the spectral properties of bromothymol blue
Full text linkThe color of the pH indicator Bromothymol blue (BTB) changes from yellow to blue with increasing pH. The effect of some electrolytes (LiCl, NaCl, KCl, CsCl, KSCN and KClO3) and of D2O on the spectral properties of dilute solutions of BTB is explored. The results are interpreted in terms of dimerization of the dye molecules and of the different hydration that D2O induces. The effects of dissolved gases on the spectral properties of BTB is studied. Complete removal of dissolved gas is achieved. Surprising effects on the UV–vis spectra emerged. After degassing solutions, gases were re-admitted via bubbling. The gases He, Ar, N2, CO2 and CH4.were studied. The effects can be explained by presence or absence of nano- and microbubbles of gas in the solution. These allow formation of dimers and multiple association via adsorption and so affect the spectral properties of the dye molecules
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
Probing the structural organization of a low temperature transition mixture for CO2 capture through spectroscopic and theoretical studies
Full text linkWe investigated a low temperature transition mixture (LTTM) suitable for carbon capture through infrared spectroscopy, differential scanning calorimetry, absorption of CO2 and computational studies. The system, made up of a homogeneous mixture of ethylene glycol, potassium hydroxide and boric acid (3:1:1), is sensitive to temperature changes that affect the viscosity of the solvent and its capacity to exchange CO2 at the interface. The relationship between the LTTM's molecular structure and its ability to capture the gas were investigated in order to optimize the properties of the absorbing material for developing viable and reusable carbon capture systems. The results suggest that a large number of free OH groups is available to ensure an effective CO2 capture through the formation of the organic carbonate, leading to an average absorption of 22 ± 1 gCOjavax.xml.bind.JAXBElement@7fcbc253/kgsolv at room temperature. Boric acid acts as a catalyst for the carbonate decomposition and ensures the release of CO2 at 60 °C. ATR-FTIR measurements proved that the solvent is mostly regenerated after desorption and can thus continue to absorb further CO2 over a large number of cycles, making the system reusable
Pluronic/gelatin composites for controlled release of actives
No full textThis paper describes the preparation and the release properties of composite materials based on Pluronic F127 and gelatin hydrogels, which could be of interest in the field of enteral nutrition or drug administration. The composites were prepared by exploiting the opposite responsivity to temperature of a 20% w/w Pluronic F127 aqueous solution (critical gelation temperature around 23. °C) and gelatin (gel-sol temperature transition around 30. °C). Pluronic domains dispersed within a gelatin matrix were obtained by injecting cold Pluronic F127 solutions inside hot gelatin solutions, while homogenizing either with a magnetic stirrer or a high-energy mechanical disperser. Calorimetry indicates that the composites retain the individual gelling properties of Pluronic and gelatin. Different releasing properties were obtained as a function of the preparation protocol, the temperature and the pH. The release profiles have been studied by a Weibull analysis that clearly points out the dominating role of gelatin at 25. °C. At 37. °C the release accounts for a combined effect from both Pluronic F127 and gelatin, showing a more sustained profile with respect to gelatin hydrogels. This behavior, together with the ability of Pluronic F127 to upload both hydrophilic and hydrophobic drugs and flavors, makes these innovative composite materials very good candidates as FDA-approved carriers for enteral administration
Selenated and Sulfurated Analogues of Triacyl Glycerols: Selective Synthesis and Structural Characterization
No full textThe synthesis of sulfur- and selenium-containing isosters of triacyl glycerols is herein described. Regioselective fluoride-induced ring-opening reaction of suitable substituted thiiranes with bis(trimethyl)silyl selenide, followed by in situ S- and Se-acylation with fatty acid acyl chlorides, enables the one pot synthesis of mixed chalcogeno esters in good yield. The key step of this methodology is the functionalization of S−Si and Se−Si bonds of silyl chalcogenides, generated in situ under mild conditions. A related procedure for the synthesis of functionalized selenides, bearing two thiol ester and two ester moieties, was also developed through a fine tuning of the reaction conditions. The physico-chemical properties of these novel fatty acid chalcogeno esters have been investigated through DSC, SAXS, WAXS, FTIR and polarized optical microscopy, and compared to those of the common triglycerides in order to highlight the effect of the replacement of oxygen with other chalcogen elements in the polar head of the lipid
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