Search results for "surface"
showing 10 items of 9345 documents
Insights into grafting of (3-Mercaptopropyl) trimethoxy silane on halloysite nanotubes surface
2020
Abstract Functionalization of halloysite nanotubes surface by using organosilanes is sensitive to the reaction conditions. Halloysite nanotubes (HNTs) were modified using (3-Mercaptopropyl) trimethoxy silane (MPTMS). The experiments were performed under different reaction conditions including, various solvents [Toluene, Tetrahydrofuran (THF), Ethanol, n-Hexane, 1,4 Dioxane and Acetonitrile], water content in the reaction media, volume of solvent, number of moles of silane and catalysts (triethyl amine, ammonia solution and tetra-ethoxy titanium). The elemental analysis, FT-IR analysis were used to identify the samples, which attained the highest percent of functionalization. SEM image and t…
Interface Amorphization of Two‐Dimensional Black Phosphorus upon Treatment with Diazonium Salts
2021
Abstract Two‐dimensional (2D) black phosphorus (BP) represents one of the most appealing 2D materials due to its electronic, optical, and chemical properties. Many strategies have been pursued to face its environmental instability, covalent functionalization being one of the most promising. However, the extremely low functionalization degrees and the limitations in proving the nature of the covalent functionalization still represent challenges in many of these sheet architectures reported to date. Here we shine light on the structural evolution of 2D‐BP upon the addition of electrophilic diazonium salts. We demonstrated the absence of covalent functionalization in both the neutral and the r…
Halloysite nanotubes sandwiched between chitosan layers: novel bionanocomposites with multilayer structures
2018
This work is a contribution to the design of multilayer biocomposites based on halloysite nanotubes (HNTs) and chitosan. Both the polymer and nanotubular inorganic additive have been selected among easily available green materials. An innovative preparation procedure based on the sequential casting of chitosan and HNTs has been proposed in order to obtain multilayer composite biofilms. A physico-chemical investigation (contact angle measurements, differential scanning calorimetry, thermogravimetry) has been conducted to characterize the bionanocomposites. As evidenced by scanning electron microscopy, the nanocomposites possess an intermediate halloysite layer between the chitosan ones. The …
Gravimetric characterisation of the surface properties of a porous drug carrier
1995
The gas adsorption method is the most common means to characterise the topology of solid surfaces with regard to its use as an adsorbent. Adsorption isotherms are determined advanta-geously using a vacuum microbalance: Thermogravimetric techniques allow the observation of sample degassing and its optimization. The dry mass is determined in situ, the mass of gas adsorbed is measured directly and different gases can be used without calibration. From the isotherm the pore size distributions, specific surface area, fractal dimension and density can be derived. Commercially available gravimetric sorption apparata and vacuum balances as well as software for data evaluation are reviewed in tables.…
Middle to Upper Pleistocene morphostructural evolution of the NW-coast of Sicily: thermoluminescence dating and palaeontological-stratigraphical eval…
1997
Abstract Infralittoral and terrigenous Middle to Upper Pleistocene deposits outcropping at the NW-coast of Sicily (Gulf of Castellammare and peninsula of Capo San Vito) were investigated in order to recognise glacio-eustatically caused sea level highstands and the interference between tectonics, eustasy and local conditions of the coast. The results, originating from a stratigraphically important area, were obtained by palaeontological-stratigraphical analyses, physical age determination with the thermoluminescence method and by detailed morphostructural studies. The marine deposits, situated at 3–40 m a.s.l., mainly provide an oligotypic molluscan fauna referable to modern SGCF-, SFHN- and…
Nitrogen plasma pressure influence on the composition of TiNxOy sputtered films
2002
Thin films of TiNxOy were deposited by d.c. magnetron sputtering on glass substrates using an (Ar+,N2) plasma and Ti target. The N2 partial pressure was changed from 2.3 × 10−4 mbar to 4.6 × 10−3 mbar in order to obtain films with increasing nitrogen contents. X-ray photoelectron spectroscopy was used to determine the as-deposited composition. The presence of oxygen, which is probably due to contamination from the residual atmosphere in the vacuum chamber, is always detected, both in the surface layers and in the bulk of the films, confirming the formation of TiNxOy. When the nitrogen partial pressure was increased, a maximum for the nitrogen content in the films was reached, corresponding …
Thermally induced structural modifications and O2 trapping in highly porous silica nanoparticles
2014
Abstract In this work we investigate by Raman spectroscopy the effect of isochronal (2 h) thermal treatments in air in the temperature range 200–1000 °C of amorphous silicon dioxide porous nanoparticles with diameters ranging from 5 up to 15 nm and specific surface 590–690 m2/g. Our results indicate that the amorphous structure changes similarly to other porous systems previously investigated, in fact superficial SiOH groups are removed, Si–O–Si linkages are created and the ring statistic is modified, furthermore these data evidence that the three membered rings do not contribute significantly to the Raman signal detected at about 495 cm−1. In addition, after annealing at 900 and 1000 °C we…
Rapid Self-Healing and Thixotropic Organogelation of Amphiphilic Oleanolic Acid–Spermine Conjugates
2021
Natural and abundant plant triterpenoids are attractive starting materials for the synthesis of conformationally rigid and chiral building blocks for functional soft materials. Here, we report the rational design of three oleanolic acid-triazole-spermine conjugates, containing either one or two spermine units in the target molecules, using the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction. The resulting amphiphile-like molecules 2 and 3, bearing just one spermine unit in the respective molecules, self-assemble into highly entangled fibrous networks leading to gelation at a concentration as low as 0.5% in alcoholic solvents. Using step-strain rheological measurements, we show ra…
RHEOLOGICAL BEHAVIOUR OF MICROCRYSTALLINE CELLULOSE HYDROGELS
1992
ABSTRACT An extensive study was made of the rheological behaviour of microcrystal1ine cellulose-sodium carboxymethyl cellulose (MCC-NaCMC) gels at six different concentrations. The effect of agitation time, storage time, shear rate and temperature on the viscosity of these thixotropic gels was analysed, over 7200 resulting values of being available to this effect The pseudoplastic and thixotropic characteristics of the gels was established and a progressive decrease in gel viscosity with increasing storage time was observed, although retaining stability. On the other hand, constant agitation for five minutes was found to reduce gel viscosity by 40 to 50%, regardless of concentration.
An approach to rheological and electrokinetic behaviour of lipidic vesicles covered with chitosan biopolymer
2008
The rheological and electrokinetic properties of soybean lecithin vesicles prepared from concentrated soy lecithin dispersions (250 g/L) obtained by slow swelling under shear conditions and mixed with chitosan biopolymer solutions were studied. The rheological behaviour of lecithin-chitosan vesicles was determined by shear stress against shear rate measurements, as well as by the variation on the hysteresis loop area. The results were compared with the rheopectic behaviour of soy lecithin dispersions without chitosan. An important change on the rheological properties of the complex dispersion was observed, depicting in a thixotropic behaviour with a plastic character in the presence of chit…