Search results for "SILICA"
showing 10 items of 1092 documents
Structural properties of core and surface of silica nanoparticles investigated by Raman spectroscopy
2013
We studied the experimental Raman spectra of various commercial silica nanoparticles of average diameter from 7 to 40 nm and specific surface from 50 to 380 m2/g. We found that the peculiarities of the particles Raman spectra systematically depend on their specific surface. In detail, the peak position of the R band at about 440 cm−1 shifts towards high wavenumbers following an almost linear dependence on the specific surface. Similarly, the amplitudes of the D1 and D2 bands, at about 495 and 605 cm−1, respectively, increase linearly with the same quantity. Our results are interpreted in the frame of the shell model for the nanoparticles clarifying that the network of the core of the nanopa…
Luminescence of the surface nonbridging oxygen hole center in silica: Spectral and decay properties
2008
We investigated the red luminescence in a porous film of silica nanoparticles, originating from surface nonbridging oxygen hole centers. The excitation spectrum was measured from 1.8 to 8.0 eV by a tunable laser system and a synchrotron radiation source; this spectrum evidences a peak at 2.0 eV, nearly overlapping with the emission, and an ultraviolet broadband with peaks at 4.8 and 6.0 eV. The emission is characterized by a spectrum with two subbands split by 0.07 eV, its decay occurs with lifetime longer than 30 microsec and undergoes a thermal quenching by a factor aboout 2 with increasing temperature from 10 to 290 K. The optical characteristics of surface and bulk centers are discussed…
New insights into the surface functionalities and adsorption evolution of water molecules on silica gel surface: A study by second derivative near in…
2010
Accepted version of an article in the journal: Vibrational Spectroscopy. Published version available on Science Direct: http://dx.doi.org/10.1016/j.vibspec.2010.06.003 Surface functionalities and adsorption evolution of water molecules on silica gel samples were studied by second derivative near infrared spectroscopy. Four different silica gel samples with varying surface area were used in this experiment. Each of the dry samples was allowed to equilibrate with surrounding air and the near infrared spectra were accumulated at different time intervals using reflectance technique. The evolved spectra were analysed using second derivative technique to study the adsorption evolution of water mo…
Experimental and theoretical evidence of overcharging of calcium silicate hydrate
2007
International audience; Electrokinetic measurements such as electrophoresis may show an inversion of the effective surface charge of colloidal particle called overcharging. This phenomenon has been studied by various theoretical approaches but up to now very few attempts of confrontation between theory and experiment have been conducted. In this work we report electrophoretic measurements as well as Monte Carlo simulations of the electrokinetic potential for the surface of calcium silicate hydrate (Csingle bondSsingle bondH), which is the major constituent of hydrated cement. In the simulations, the surface charge of Csingle bondSsingle bondH nanoparticles in equilibrium with the ionic solu…
2D dynamical arrest transition in a mixed nanoparticle-phospholipid layer studied in real and momentum spaces
2015
AbstractWe investigate the interfacial dynamics of a 2D self-organized mixed layer made of silica nanoparticles interacting with phospholipid (DPPC) monolayers at the air/water interface. This system has biological relevance, allowing investigation of toxicological effects of nanoparticles on model membranes and lung surfactants. It might also provide bio-inspired technological solutions, exploiting the self-organization of DPPC to produce a non-trivial 2D structuration of nanoparticles. The characterization of interfacial dynamics yields information on the effects of NPs on the mechanical properties, important to improve performances of systems such as colloidosomes, foams, creams. For thi…
Toxicological assessment of mesoporous silica particles in the nematode Caenorhabditis elegans
2018
[EN] Here we report the toxicological evaluation of mesoporous silica particles (MSPs) in the nematode C. elegans. Specifically, we have investigated the effect of bare micro- (M0) and nano-sized (N0) MSPs, and their corresponding functionalized particles with a starch derivative (Glu-N) (M1 and N1, respectively) on C. elegans ageing parameters. The toxicity of MSPs, their impact on C. elegans lifespan, movement capacity, progeny and ability to survive upon exposure to acute oxidative stress were assessed. This study demonstrated that both size particles assayed (M0 and N0), labeled with rhodamine and monitored through fluorescence microscopy, are ingested by the nematode. Moreover, toxicit…
Azobenzene Polyesters Used as Gate-Like Scaffolds in Nanoscopic Hybrid Systems
2012
The synthesis and characterisation of new capped silica mesoporous nanoparticles for on-command delivery applications is reported. Functional capped hybrid systems consist of MCM-41 nanoparticles functionalised on the external surface with polyesters bearing azobenzene derivatives and rhodamine¿B inside the mesopores. Two solid materials, Rh-PAzo8-S and Rh-PAzo6-S, containing two closely related polymers, PAzo8 and PAzo6, in the pore outlets have been prepared. Materials Rh-PAzo8-S and Rh-PAzo6-S showed an almost zero release in water due to steric hindrance imposed by the presence of anchored bulky polyesters, whereas a large delivery of the cargo was observed in the presence of an esteras…
Intrinsic Point Defects in Silica for Fiber Optics Applications
2021
Due to its unique properties, amorphous silicon dioxide (a-SiO2) or silica is a key material in many technological fields, such as high-power laser systems, telecommunications, and fiber optics. In recent years, major efforts have been made in the development of highly transparent glasses, able to resist ionizing and non-ionizing radiation. However the widespread application of many silica-based technologies, particularly silica optical fibers, is still limited by the radiation-induced formation of point defects, which decrease their durability and transmission efficiency. Although this aspect has been widely investigated, the optical properties of certain defects and the correlation betwee…
Radiation tolerant fiber Bragg gratings for high temperature monitoring at MGy dose levels
2014
International audience; We report a method for fabricating fiber Bragg gratings (FBG) resistant to very severe environments mixing high radiation doses (up to 3 MGy) and high temperatures (up to 230 degrees C). Such FBGs have been written in two types of radiation resistant optical fibers (pure-silica and fluorine-doped cores) by exposures to a 800 nm femtosecond IR laser at power exceeding 500 mW and then subjected to a thermal annealing treatment of 15 min at 750 degrees C. Under radiation, our study reveals that the radiation induced Bragg wavelength shift (BWS) at a 3 MGy dose is strongly reduced compared to responses of FBGs written with nonoptimized conditions. The BWS remains lower t…
Heat capacities and volumes of suspensions in the presence of surfactants
2004
Abstract Density and heat capacity measurements of water–surfactant–silica ternary systems were carried out as functions of the silica and the surfactant concentrations at 298 K. From these properties, the apparent molar volume and heat capacity of the surfactant in a given water+silica mixture were evaluated. As well, the apparent specific volume and heat capacity of silica, at a given concentration, in the water+surfactant mixtures as functions of the surfactant concentration were calculated. Some surfactants (decyltrimethylammonium bromide, sodium octanoate, sodium decanoate, sodium dodecanoate, sodium decylsulfate, sodium perfluorooctanoate and N , N -dimethyldodecylamine- N -oxide) wer…