1,720,974 research outputs found
Decoupling of Dynamic Processes in Surfactant-Based Liquid Mixtures: The Case of Lithium-Containing Bis(2- ethylhexyl)phosphoric Acid/Bis(2-ethylhexyl)amine Systems
No full textPure surfactant liquids and their binary mixtures, because of the
amphiphilic nature of the molecules involved, can exhibit nanosegregation and
peculiar transport properties. The idea that inspired this work is that the possibility
of including in such media salts currently used for technological applications should
lead to a synergy between the properties of the salt and those of the medium.
Therefore, the dynamic features of bis(2-ethylhexyl)amine (BEEA) and bis(2-
ethylhexyl)phosphoric acid (HDEHP) liquid mixtures were investigated as a
function of composition and temperature by 1H nuclear magnetic resonance (NMR)
spectroscopy and rheometry. Inclusion of litium trifluoromethanesulfonate (LiT)
has been investigated by infrared spectroscopy, pulsed field gradient NMR, and
conductimetry methods to highlight the solubilizing and confining properties of
these mixtures as well as the lithium conductivity. It was found that BEEA/HDEHP
binary liquid mixtures show zero-threshold percolating self-assembly with a
maximum in viscosity and a minimum in molecular diffusion at a 1:1 composition. Dissolution of LiT in such system can
occur via confinement in the locally self-assembled polar domains. Despite this confinement, Li+ conduction is scarcely
dependent on the medium composition because of the possibility of a field-induced hopping decoupled by the structural and
dynamical features of the medium
Novel gel-niosomes formulations as multicomponent systems for transdermal drug delivery
No full textThe percutaneous permeation profiles of sulfadiazine sodium salt, propranolol hydrochloride and tyrosol from novel liquid crystal-niosomes formulations as multicomponent systems, were investigated. The new carriers were prepared from mixture of water/surfactant, AOT or Pluronic L64 as anionic and nonionic surfactants, respectively, in order to obtain lamellar LLC phases. The same surfactants were used to prepare also the vesicular systems (niosomes) that were added to the corresponding gel. The obtained multicomponent drug carrier was characterized by deuterium nuclear magnetic resonance spectroscopy, in order to understand if the introduction of the drug or drug-loaded niosomal suspension, as third component in the formulations, could influence the microstructure of the system and then the drug delivery across the skin. Simple AOT and L64-based niosomal formulations and LLCs phases were then prepared and used as control. Different drugs percutaneous availability was achieved, and the results revealed that the obtained gel-niosomes carriers were affected by the chemical structure of the drugs and by their affinity for the components. As a consequence these systems could be proposed as novel transdermal drug delivery systems, since they were found able to control the percutaneous permeation of small drugs across the skin. (C) 2013 Elsevier B.V. All rights reserved
Dynamical Properties of Self-Assembled Surfactant-Based Mixtures: Triggering of One-Dimensional Anomalous Diffusion in Bis(2- ethylhexyl)phosphoric Acid/n‐Octylamine Systems
No full textFlow-induced structures observed in a viscoelastic reverse wormlike micellar system by magnetic resonance imaging and NMR velocimetry
No full textThe aim of the present work is to illustrate and discuss an application of rheo-NMR techniques in the investigation of the flow micro-morphology of a rheo-thinning fluid. The viscoelastic material is composed by weakly hydrated nonionic Wormlike Micelles (WM), stabilized by the biocompatible phospholipid in an organic solvent (lecithin organogel). By applying rheo-NMR techniques, such as micro-imaging and flow velocimetry in Couette flow, to lecithin organogels in the concentrated isotropic phase, a new phase nucleating inhomogeneously at the inner rotating cylinder showing periodic fluctuations in space in some cases, has been identified for applied shear rates within the isotropic-nematic stress plateau. On the other hand, evident slippage phenomena have been found in flow regimes consistent with a full shear-induced nematic state. Bulk rheometric investigations executed in oscillatory, steady state and transient mode have been finally carried out to bridge different flow micro-heterogeneities detected by rheo-NMR with a variety of mechanical responses manifested by lecithin WM
Rheological and rheo-SALS investigation of the multi-lamellar vesicle formation in the C12E3/D2O system
No full textUsually in nonionic surfactant aqueous systems of the CnEm type, a lamellar phase occurs over a wide temperature and concentration range. For some CnEm surfactants, multi-lamellar vesicle (MLV) formation has been observed when the lamellar phase is subjected to shear flow. This communication reports the shear flow behavior at different shear rate values of a CnEm (where "n" is 12 and "m" is 3) aqueous system at 34 degrees C. The typical transient viscosity behavior of the shear-induced MLV formation in C12E3/D2O at 50 wt% of surfactant has been observed. The MLV formation is confirmed by time-resolved rheo-small angle light scattering (SALS) experiments. The experimental data show an intermediate structure that has been attributed to a multi-lamellar cylinders (MLCs). (C) 2011 Elsevier Inc. All rights reserved
N,N’-hexadecanoyl-l-2-diaminomethyl-18-crown-6 Surfactant: Synthesis and Aggregation Properties in Aqueous Solutions.
No full textbolaform-surfactant, self-diffusion, crown ethers, drug carrier
The efficiency of bitumen rejuvenator investigated through Powder X-ray Diffraction (PXRD) analysis and T 2 -NMR spectroscopy
No full textNowadays, many different materials are known to function, using different test methods, as rejuvenating agent when introduced into recycled asphalt pavements. However, it should be noticed that, an additive, which has a complete rejuvenating function, enables the chemical structure reorganization of the aged bitumen, otherwise not achieved by traditional methods. This rearrangement brings back the aged bitumen structure to the condition of the original one, restoring the elasticity and workability of the binder. In this study, two non-toxic and eco-friendly biocompatible additives have been tested to work as rejuvenators on an aged bitumen binder by means of Powder X-Ray Diffraction (PXRD) measurements and Nuclear Magnetic Spectroscopy (NMR). Powder X-ray diffraction (PXRD) analysis has been proved to be a very useful technique for assessing the structure of virgin, aged, and rejuvenating agent-added bitumen and for figuring out the chemical action of the additive in bitumen. All the test results were also supported by T2-NMR spectroscopy, which proves the validity of this method in chemical analysis
Advanced characterization of bituminous binders: Comparing industrial and paving-grade bituminous binders
Get PDFThis paper deals with the fundamental differences between industrial and paving-grade bituminous binders. The paper is presented in two main sections: 1) a review of the materials’ colloidal structure and the required properties for the industrial and paving applications; 2) a wide range of experimental tests with which the bituminous binders were studied and compared. In this research, a 160/220 industrial bitumen was studied and compared to a paving-grade bitumen with the same penetration and with a lower penetration, 70/100 one. The research consisted of physical, chemical, thermal, microstructural, and rheological analysis to provide a comprehensive understanding of these bituminous binders of diverse applications. Overall, the comparison of the tests’ results indicated that while the asphaltene content and its characteristics have a great influence on the bitumen’s properties, it is not the only fundamental factor. During the study of the chemical structures via Atomic Force Microscopy (AFM), it was found that the Peri phase (attributed to the resins) also plays an important role, defining the bitumen’s physical visco-elastic properties. In fact, from a microstructural point of view using AFM a significant difference was notified between the industrial bitumen and the paving-grade ones. These differences allow the paving-grade bitumens to be more elastic and ductile compared to the industrial bitumen
Gels of Pluronic F127 and nonionic surfactants from rheological characterization to controlled drug permeation
No full textThe role of nonionic vesicles on the theological behavior of Pluronic F127 is investigated above the dilute regime and below the cloud point of the nonionic surfactant. F127 is a copolymer possessing sol-gel transition by heating attributed to a phase transition from micellar to cubic. The presence of surfactant vesicles is expected to enhance the compartmentalization of a variety of drugs, independently of their affinity to the solvent. Such entrapment would be suitable for controlled release of the drugs in different applications.We address here a mixed Pluronic-nonionic surfactant system with particular emphasis to the effects of the surfactant on the rheological properties of the Pluronics, and the correlation between these properties and drug release control.The results show that the theological properties of the mixed system are mainly governed by the behavior of the polymer alone and that the mixed system can be useful to control the percutaneous permeation of a small drug, such as Diclofenac Sodium salt. (C) 2011 Elsevier B.V. All rights reserved
Quantitative evaluation of the restructuring effect of a warm mix additive on bitumen recycling production
No full textWarm mix asphalt (WMA) is a promising technique that allows the production of asphalt at a noticeably lower temperature. One of the methods in use is to add small quantities of specific organic compounds to the asphalt conglomerate. Although it is well established that this procedure leads to an effective reduction of the temperature of asphalt conglomerate production, there is still a lack in the comprehension and description of the real mechanism of the additive action on the colloidal structure. In this work 3D micro-scale atomic force microscopy (AFM) images of fresh, aged and doped bitumen were taken to characterise and study the interaction of a commercial WMA additive with bitumen. We also combined the AFM results with the inverse Laplace transform of the nuclear magnetic resonance relaxation times (T-2). Results revealed that the temperature lowering in the WMA recycling procedure is due to the restructuring action of the additive that leads to a re-organisation of the colloidal network of bitumen
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