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showing 10 items of 1808 documents
On the origin of controlled anisotropic growth of monodisperse gold nanobipyramids
2021
We elucidate the crucial role of the cetyl trimethylammonium bromide (CTAB) surfactant in the anisotropic growth mechanism of gold nano-bipyramids, nano-objects with remarkable optical properties and high tunability. Atomistic molecular dynamics simulations predict different surface coverages of the CTAB (positively charged) heads and their (bromide) counterions as function of the gold exposed surfaces. High concentration of CTAB surfactant promotes formation of gold nanograins in solution that work as precursors for the smooth anisotropic growth of more elongated nano-bipyramidal objects. Nanobipyramids feature higher index facets with respect to nanorods, allowing higher CTAB coverages th…
Flow-through pore characteristics of monolithic silicas and their impact on column performance in high-performance liquid chromatography
2008
Abstract In order to elucidate the role of the flow-through characteristics with regard to the column performance in high-performance liquid chromatography (HPLC) native and n -octadecyl bonded monolithic silica rods and columns, respectively of 100 mm length and 4.6 mm ID with mesopores in the range between 10 and 25 nm and macropores in the range between 0.7 and 6.0 μm were examined by mercury intrusion/extrusion, scanning electron microscopy, image analysis and permeability. The obtained data of the flow-through pore sizes and porosity values as well as surface-to-volume ratio of the stationary phase skeleton enabled to predict their influence to the chromatographic separation efficiency…
Comprehensive pore structure characterization of silica monoliths with controlled mesopore size and macropore size by nitrogen sorption, mercury poro…
2005
The porosity of monolithic silica columns is measured by using different analytical methods. Two sets of monoliths were prepared with a given mesopore diameter of 10 and 25 nm, respectively and with gradated macropore diameters between 1.8 and 7.5 microm. After preparing the two sets of monolithic silica columns with different macro- and mesopores the internal, external and total porosity of these columns are determined by inverse size-exclusion chromatography (ISEC) using polystyrene samples of narrow molecular size distribution and known average molecular weight. The ISEC data from the 4.6 mm analytical monolithic silica columns are used to determine the structural properties of monolithi…
Organic salts and aromatic substrates in two-component gel phase formation: the study of properties and release processes
2015
To identify gel phases able to act as confined reaction media or materials for the removal of organic pollutants, we studied two-component gel phases formed by naphthalenedisulfonate diimidazolium salts in the presence of some organic guests, in 1-propanol solution. Guests differing in π-surface area, bulkiness and electronic properties were taken into account. Soft materials obtained were investigated for their thermal stability, self-repairing ability and morphology. Furthermore, two-component gel phase formation was studied using resonance light scattering (RLS) measurements. Guest release processes from the gel phase were also studied. These processes were monitored as a function of tim…
Effect of Hydrogen and Carbamide Peroxide in Bleaching, Enamel Morphology, and Mineral Composition: In vitro Study
2017
ABSTRACT Aim The aim of the study was to evaluate the bleaching effect, morphological changes, and variations in calcium (Ca) and phosphate (P) in the enamel with hydrogen peroxide (HP) and carbamide peroxide (CP) after the use of different application regimens. Materials and methods Four groups of five teeth were randomly assigned, according to the treatment protocol: HP 37.5% applied for 30 or 60 minutes (HP30, HP60), CP 16% applied for 14 or 28 hours (CP14, CP28). Changes in dental color were evaluated, according to the following formula: ΔE = [(La−Lb)2+(aa−ab)2 + (ba−bb)2]½. Enamel morphology and Ca and P compositions were evaluated by confocal laser scanning microscope and environmenta…
The influence of the raw material and production method on the morphology, microstructure, chemical and phase composition of tetrabasic lead sulfate …
1992
Abstract Tetrabasic lead sulfate (4BS) produced by two different methods (solution and paste) and from two different raw materials (tetragonal PbO and leady oxide) were charaterized by different analytical techniques. The techniques applied were wet-chemical methods, scanning electron microscopy, transmission electron microscopy and X-ray powder diffraction. The preparation method was observed to be the most decisive factor influencing the structure and the morphology of the 4BS pastes in this study.
Influence of resin viscosity and vacuum level on mechanical performance of sandwich structures manufactured by vacuum bagging
2010
The choice of process parameters is critical in optimizing the mechanical properties of sandwich structures produced using the vacuum bagging technique. The aim of this paper is to analyze how the viscosity of the resin/curing agent system and the vacuum level influence the morphology and the mechanical behavior of sandwich beams with composite faces (epoxy resin and glass fiber fabric named COMBI 900) and a PVC foam core. Four different sandwich structures were produced by varying the viscosity of the epoxy resin/curing agent at constant maximum vacuum pressure. Three further structures were manufactured by varying the strength of the vacuum with the resin viscosity maintained constant at …
Morphology and mechanical properties of extruded ribbons of LDPE/PA6 blends compatibilized with an ethylene-acrylic acid copolymer
2003
Two grades of low density polyethylene (LDPE) were blended with polyamide-6 (PA) in the 75/25 and 25/75 wt/wt ratios and shaped into ribbons with a Brabender single screw extruder. An ethylene-acrylic acid copolymer (EAA) was used in the 2 phr concentration as a compatibilizer precursor (CP). The morphology of the ribbons and its evolution during high temperature annealing were investigated by scanning electron microscopy (SEM). The results confirmed that EAA does actually behave as a reactive compatibilizer for the LDPE/PA blends. In fact, in the presence of EAA, the interfacial adhesion is improved, the dispersion of the minor phase particles is enhanced and their tendency toward fibrilla…
Effect of the nanotube aspect ratio and surface functionalization on the morphology and properties of multiwalled carbon nanotube polyamide-based fib…
2013
In this study, the effect of the carbon nanotube (CNT) aspect ratio and surface functionalization on the mechanical behavior and morphological changes of polyamide (PA)-based fibers was investigated. Composites were prepared by the melt blending of CNTs with PA, and at a later time, the fibers were prepared by melt spinning and cold drawing. A reinforcement effect was noticed for all of the CNTs samples, and the increase in the mechanical properties and dimensional stability was more pronounced for highly oriented filaments. When the elongational flow was increased, the orientation of CNTs along the fiber direction was observed, but the nanotube alignment was much more difficult for CNTs wi…
Synthesis and characterization of indium oxide at high pressures
2018
Introducción: La naturaleza es sorprendente pero a la vez limitada. A mi entender, nada tiene más potencial que aplicar el ingenio humano para modificar lo que nos rodea y crear algo completamente nuevo. La Física de la Materia Condensada es un campo que actualmente está ganando importancia en la Física moderna. En virtud de los éxitos logrados en Física de la Materia Condensada se han producido enormes avances en el campo de la electrónica cuántica, de los semiconductores y de la ciencia de materiales, teniendo como resultado numerosas aplicaciones tecnológicas que han cambiado nuestras vidas drásticamente en los últimos 50 años. Una de las ramas de la Física de la Materia Condensada es el…